Patent Grant
8296114
This application is a non-provisional of and claims priority to and the benefit of U.S. Provisional Patent Application No. 61/080,594, filed Jul. 14, 2008, and is related to PCT Patent Application No. PCT/US09/50479, filed Jul. 14, 2009, each incorporated herein by reference in its entirety.
1. Field of Invention
This invention relates in general to drilling bit design optimization and selection for use by the oil and gas industry, and in particular to systems, program product, and related methods for selecting and designing a drilling bit tailored for a target section of the earth.
2. Description of the Related Art
Drilling is essential in civil, mining, and petroleum industries. It is also a pre-requisite in exploration and exploitation of oil, gas, and other energy resources. With the depletion of shallow energy resources, however, the cost of drilling is getting increasingly higher; especially, when harder rock formations are encountered and where higher rate of penetration is desired. Therefore, in order to minimize the cost of drilling, it is important that the conditions for optimum performance of drilling are identified.
The optimum performance of drilling depends on large number of factors; most importantly rock type, bit type, rock-bit interactions, hydraulics, stability, and the type of drilling system employed. Over the years, a significant advancement has taken place in understanding of these subjects.
Knowledge of rock and rock-bit interations, however, remains a weak link in drilling. The poor understanding of rock and its interaction with drilling bits primarily stems from the fact that it is an interdisciplinary subject. It requires at least some expertise in the field of geology of rock formations, chemistry of minerals and its bond structures, physics of force or energy application, rock mechanics aspects of the deformation process, and fracture mechanics aspects of the failure process. Moreover, it is difficult, if not sometimes impossible, to mimic the actual drilling process in rocks taking place in the original environments of boreholes. Thus, recognized by the inventors is the need for additional work on rock and its interactions with the drill bit to further enhance the understanding of optimum performance of the bit and drilling system.
In any drilling or cutting process, energy is applied through the cutting tool to generate stresses in the working surface. The stresses may be classified as compressive, shear or tensile or some combination of these. If the stresses are sufficiently high, some type of cutting action occurs, such as crushing, scraping, chipping or indenting. In the drilling industry, the ease at which a given rock can be crushed, scraped, chipped or indented is known as its drillability. Drillability depends on elastic and strength properties of the material. In particular, the unconfined compressive strength (UCS) of rock is recognized in the industry as an important if not sole factor to be used in determining its drillability. Realistically, however, drillability involves a large number of factors, including physical, mechanical, and micro-structural properties. The micro-structure of rock becomes particularly important when the size of the chips generated are near the grain size level. The macro-structure (e.g. bedding planes, interbeddedness, rattiness characterized using log data) is often times absent in relatively small diameter drilling holes, but if present it can significantly influence the drilling process. These and other factors affecting drillability, however, are often overlooked such that drillability of rock is often inaccurately expressed solely in terms of its UCS. There is, therefore, a need in the art for an efficient and systematic way to express the drillability of rocks comprehensively. This can be particularly important with respect to carbonate rocks.
The microstructure of rock is defined by its mineral components, grain shapes, sizes and their interlocking or packing (a.k.a. texture). Minerals are naturally occurring inorganic compounds and are present in the grains, grain-boundaries and as cementing material between two or more grains. Contrary to the fixed proportions of atoms, molecules or ions, as dealt with in chemistry, rocks are mainly solid solutions of silicates, carbonates, oxides, etc. Some of the inorganic elements get replaced in course of rock formations, and thus, the elements are typically represented in parenthesis to represent rock, as nearly as possible. The exact portion, however, is difficult to present. The individual minerals get crystallized and get crowded until they make a rigid mass of shapeless lumps called grains. Most of the minerals constituting rocks are silicates, e.g., quartz, feldspar, mica, clay, calcite, dolomite, olivine, garnet, pyroxenes, and amphiboles. The basic building block of silicate is Silicon-oxygen tetrahedron being linked in a single- or double-chain, sheets, a three-dimensional network, or not linked at all. Their bond structure, in combination with the characteristic cleavage property, makes a rock strong or weak. Minerals in sedimentary rocks are typically carbonates in addition to quartz and clay. Sulphate minerals are typical in gypsum and anhydrite.
About 99 percent of the sedimentary rocks consist of quartz, clay and carbonates resulting from sedimentary processes, such as weathering, transportation, sorting, and deposition, compaction and its typical diagenesis, up to the present age. The dominance of these individual minerals depends on the location where they were formed. For example, sandstone mainly consists of broken pieces, well sorted, un-weathered quartz. The fine sand and clay are transported more in suspension as they travel down the stream, thus forming shale. The dissolved portion of the lime and carbonate travels much further with the water. The calcite is deposited because plants and animals extract it from sea water and use it to build their skeleton. The other common rocks associated with shale sandstone and carbonates include coal, salt, gypsum, phosphate, chert and conglomerate. A large body of knowledge exists in the literature dealing with clastic rocks such as sandstones. As a result there are several models which can be used to predict the behavior or rocks from one basin to other, albeit with limited success. In contrast, relatively few works have been accomplished dealing with carbonate rocks.
Carbonate rocks, in general, are significantly different than other sedimentary rocks of sandstone or shale, due to their typical diagenesis processes including compaction, cementation, precipitation, dissolution, re-crystallization, dolomitization, or replacement of some constitutive minerals or fluids by other elements in the space available including in and around grains. Due to these typical diagenesis processes, porosity may be either reduced (dolomitization causes shrinkage by ˜12.5%), or enhanced (moldic porosity, fracturing, vug or cavity formation), and/or a discontinuity may be formed as in stylolytes, like the horizontal layers seen in Carthage marble, or extended as in caverns or vugs. For example, in the Jurassic Arab limestone of Ghawar field in Saudi Arabia, replacement has caused a reduction in primary porosity. In the Jurassic Smackover Formation of Alabama and the Leduc reef carbonates in Alberta, porosity and permeability were preserved due to the existence of a rigid framework formed during early dolomitization. In general, however, dolomitization enhances porosity because dolomites are denser, and consequently, take up less volume than the original calcite. Accordingly, recognized by the Applicants is that lessons learned in one carbonate rock does not apply to others, and that such lessons are case specific, in contrast to lessons learned with respect to the majority of sandstone and shale rocks. There is, therefore, a need for an efficient and systematic way to ascertain drillability of each significant rock formation for a specific target hole section.
Conventionally, carbonate rocks have been characterized by providing qualitative rather than quantitative information. That is, typical carbonate rock characterization consists of communicating as much information as possible with respect to the depositional environments of carbonates and its evolutions, together with its constitutive mud, cement and grain network. These are gathered from testing the rock with dilute hydrochloric acids, and observing the rock under binocular microscopes, or hand lenses. Traditionally, Folk (1959) and Dunham (1962) are the only two classification systems for characterizing carbonates. Some of the recent work by Akbar et. al. (2001) and Embry and Klovan (1971), however, enhance and clarify the classification systems with more details of grain sizes and pore systems in albeit a qualitative way. Further, the work of Choquette and Pray (1970) and Lucia (1983) adds to the aspects of porosity and grain sizes, but with limited success due to complex nature of carbonates. Further, some of the recent works on above classifications have added grain sizes, pore types and porosity which altogether clarify and characterize carbonates in a much better way; albeit still in a descriptive way. Accordingly, unlike sandstones which are characterized by grain sizes only, there is no general procedure to characterize carbonate rocks (in general), as the carbonate rocks of one place may be completely different than that found at other places, and as the lessons learned on one carbonate rock would not be able to be readily used for other carbonates. There is, therefore, a need for an efficient and systematic way to quantitatively characterize and evaluate rocks (including carbonate rocks) on a case-by-case basis in order to objectively evaluate drillability.
In the oil and gas industry, drilling bits such as, for example, polycrystalline diamond compact (PDC) drilling bits, are generally selected based on design features. These design features can include, for example, blade count, cutter count, cutter size, gauge design (length, geometry), nozzle count, face volume, and junk slot area. Performance characteristics and not design features, however, directly determine the success of a design in a given application. Examples of performance characteristics can include the level of dynamic stability (e.g. torsional stability, lateral stability), axial and lateral aggressiveness, mechanical efficiency, cleaning efficiency, cooling efficiency, erosion resistance, impact resistance, and abrasion resistance. As a result of the focus on design features rather than performance characteristics, bit selection has involved a trial-and-error approach. There is, therefore, a need in the art for an efficient and systematic way to capture and compare performance characteristics for drilling bits to performance requirements associated with a target hole section of rock to facilitate bit design optimization and selection.
In view of the foregoing, various embodiments of the present invention provide a system, program product, and method for bit design optimization and selection considering detailed characterizations of the formations being drilled. Various embodiments of the present invention include a computer model and image expressing the drillability of a target section in terms of physical, mechanical, and micro-structural properties determined from component subterranean formation data. Various embodiments of the present invention further include a computer model and image of the critical drilling bit performance characteristics responsive to the physical, mechanical, and micro-structural properties of the target section. This model and image employ a bit design space approach, in which each of plurality of performance characteristics is normalized and then plotted on its own axis forming, for example, a spider graph, allowing for easy comparison by human or computer. Various embodiments of the present invention include selection of a drilling bit from an assembled library of computer models and spider graphs of drilling bit characteristics for a suite of drilling bit designs having various features/configurations. Various embodiments of the present invention further allow modification to the drilling bit design features to optimize the critical drilling bit performance characteristics.
Specifically, various embodiments of the present invention provide methods of selecting a drilling bit for drilling an identified target hole section of earth containing one or more formations. According to an embodiment of the method, the method can include the steps of determining a formation property value for each member of a set of a plurality of formation properties for each of the plurality of formations forming the target hole section to thereby define a plurality of sets of formation properties, and determining a drillability parameter value of each member of a set of individual formation drillability parameters for each separate one of the plurality of formations forming the target hole section responsive to the plurality of sets of formation properties to thereby define a plurality of sets of individual formation drillability parameters. The method can also include the steps of combining each of the plurality of sets of individual formation drillability parameters to thereby represent the target hole section with a set of combined drillability parameters, determining a performance attribute value for each of a plurality of performance attributes describing target hole section performance requirements of the target hole section for drilling the target hole section responsive to the set of combined drillability parameters to thereby define a set of target hole section performance requirements, and generating a multidimensional performance attribute map of the target hole section performance requirements responsive to the step of determining the target hole section performance requirements.
The method could also include the steps of determining a performance attribute value of each of a plurality of performance attributes describing drilling system performance characteristics associated with a preselected drilling system for drilling the target hole section to thereby define a set of drilling system performance characteristics, and generating a multidimensional performance characteristics map of the drilling system performance characteristics responsive to the step of determining the drilling system performance characteristics.
The method can further include the steps of combining the set of target hole section performance requirements and the set of drilling system performance characteristics to determine a performance attribute value for each of a plurality of performance attributes describing performance characteristics of an ideal or optimal drilling bit for drilling the target hole section with the preselected drilling system to thereby define a set of drilling application performance requirements, and generating a multidimensional performance requirements map of the drilling application performance requirements responsive to the step of combining the set of target hole section performance requirements and the set of drilling system performance characteristics.
The method could also include the steps of determining a performance attribute value of each of a plurality of performance attributes describing drilling bit performance characteristics associated with a preselected drilling bit for each of a plurality of candidate drilling bits responsive to a plurality of drilling bit features to thereby define a plurality of sets of drilling bit performance characteristics, and generating a performance characteristics map of the drilling bit performance characteristics for each separate one of the plurality of candidate drilling bits to thereby define a plurality of drilling bit performance characteristics maps.
The method can still further include performing a multi-objective optimization between the set of drilling application performance requirements and each set of drilling bit performance characteristics to identify one or more of the plurality of candidate drilling bits having a substantial alignment between the set of drilling application performance requirements and the respective set of drilling bit performance characteristics to thereby select a best match drilling bit for drilling the target hole section, providing a rank ordered list of candidate drilling bits responsive to performing the multi-objective optimization, and generating a multidimensional map comprising a drilling application performance requirements map of the drilling application performance requirements overlaid with at least one of a plurality of drilling bit performance characteristics maps of the drilling bit performance characteristics to thereby provide a multidimensional visual comparison between the drilling application performance requirements and drilling bit performance characteristics for at least one of the plurality of candidate drilling bits.
The method can also or alternatively include the steps of generating at least one virtual drilling bit model having a plurality of adjustable (selectable) virtual drilling bit features responsive to a virtual library including the plurality of adjustable virtual drilling bit features, and performing a multi-objective optimization between the set of drilling application performance requirements and each of the plurality of adjustable virtual drilling bit features to thereby determine feature attributes of the plurality of drilling bit features that when combined to form a candidate virtual drilling bit provide the candidate virtual drilling bit with drilling bit performance characteristics substantially coinciding with the determined drilling application performance requirements to thereby provide a virtual design for an optimal drilling bit defining a candidate optimal drilling bit for drilling the target hole section.
The method can further include determining drilling bit performance characteristics of the candidate optimal drilling bit, and generating a multidimensional map comprising a drilling application performance requirements map of the drilling application performance requirements overlaid with a drilling bit performance characteristics map of the drilling bit performance characteristics of the candidate optimal drilling bit to thereby provide a multidimensional visual comparison between the drilling application performance requirements and drilling bit performance characteristics for the candidate optimal drilling bit.
Various embodiments of the present invention also provide bit selection and design program product stored in a tangible computer medium to select a drilling bit for drilling an identified target hole section of earth containing one or more formations. According to an embodiment of the bit selection and design program product, the program product can include instructions that when executed by a computer, cause the computer to perform the operations of determining a performance attribute value for each of a plurality of performance attributes describing target hole section performance requirements of the target hole section for drilling the target hole section responsive to a set of drillability parameters to define a set of target hole section performance requirements to thereby define a set of drilling application performance requirements, determining a performance attribute value of each of a plurality of performance attributes describing drilling bit performance characteristics associated with a preselected drilling bit for each of a plurality of candidate drilling bits responsive to a plurality of drilling bit features to thereby define a plurality of sets of drilling bit performance characteristics, and performing a multi-objective optimization between the set of drilling application performance requirements and each set of drilling bit performance characteristics to identify one or more of the plurality of candidate drilling bits having a substantial alignment between the set of drilling application performance requirements and the respective set of drilling bit performance characteristics to thereby select a best match drilling bit for drilling the target hole section.
The operations can also include providing data to display a rank ordered list of candidate drilling bits responsive to performing the multi-objective optimization, and generating a multidimensional map comprising a drilling application performance requirements map of the drilling application performance requirements overlaid with at least one of a plurality of drilling bit performance characteristics maps of the drilling bit performance characteristics to thereby provide a multidimensional visual comparison between the drilling application performance requirements and drilling bit performance characteristics for at least one of the plurality of candidate drilling bits.
According to another embodiment of the program product, the operations can include determining a performance attribute value for each of a plurality of performance attributes describing performance requirements of the target hole section for drilling the target hole section responsive to a set of drillability parameters, to define a set of target hole section performance requirements to thereby define a set of drilling application performance requirements, and receiving at least one virtual drilling bit model having a plurality of adjustable virtual drilling bit features responsive to a virtual library including the plurality of adjustable virtual drilling bit features. At least one of the plurality of adjustable drilling bit features can include a plurality of selectable virtual versions having a different size, shape, or quantity selectable within a continuum of values. The operations can also include performing a multi-objective optimization between the set of drilling application performance requirements and each of the plurality of adjustable virtual drilling bit features to thereby determine feature attributes of the plurality of drilling bit features that when combined to form a candidate virtual drilling bit provide the candidate virtual drilling bit with drilling bit performance characteristics substantially coinciding with the determined drilling application performance requirements. That is, the candidate virtual drilling bit providing a virtual drilling bit design for an optimal drilling bit defining a candidate optimal drilling bit for drilling the target hole section.
The operations can further include determining drilling bit performance characteristics of the candidate optimal drilling bit, and generating a multidimensional map comprising a drilling application performance requirements map of the drilling application performance requirements overlaid with a performance characteristics map of the drilling bit performance characteristics for the candidate optimal drilling bit to thereby provide a multidimensional visual comparison between the drilling application performance requirements and drilling bit performance characteristics for the candidate optimal drilling bit.
According to another embodiment of the program product, the operations can include determining a formation property value for each member of a set of a plurality of formation properties for each formation forming the target hole section to thereby define at least one set of formation properties, determining a drillability parameter value of each member of a set of individual formation drillability parameters for each separate one of the plurality of formations forming the target hole section responsive to the plurality of sets of formation properties to thereby define a plurality of sets of individual formation drillability parameters, and combining each of the plurality of sets of individual formation drillability parameters to thereby represent the target hole section with a set of combined drillability parameters. The operations also include determining a performance attribute value for each of a plurality of performance attributes describing target hole section performance requirements of the target hole section for drilling the target hole section responsive to the set of combined drillability parameters to thereby define a set of target hole section performance requirements, determining a performance attribute value of each of a plurality of performance attributes describing drilling system performance characteristics associated with a preselected drilling system for drilling the target hole section to thereby define a set of drilling system performance characteristics, and combining the set of target hole section performance requirements and the set of drilling system performance characteristics. The operations also include, responsive to the operation of combining the set of target hole section performance requirements and the set of drilling system performance characteristics, determining a performance attribute value for each of a plurality of performance attributes describing performance characteristics of an optimal drilling bit for drilling the target hole section with the preselected drilling system to thereby define a set of drilling application performance requirements.
Various embodiments of the present invention also provide systems for selecting and optimizing a drilling bit for drilling an identified target hole section of earth containing at least one formation. An example of an embodiment of such a system can include a computer having a processor, memory coupled to the processor, and various embodiments of the drilling bit selection and optimization program product stored in the memory of the computer including instructions that when executed by the computer, cause the computer to perform the foregoing selecting and optimizing functions.
So that the manner in which the features and advantages of the invention, as well as others which will become apparent, may be understood in more detail, a more particular description of the invention briefly summarized above may be had by reference to the embodiments thereof which are illustrated in the appended drawings, which form a part of this specification. It is to be noted, however, that the drawings illustrate only various embodiments of the invention and are therefore not to be considered limiting of the invention's scope as it may include other effective embodiments as well.
The present invention will now be described more fully hereinafter with reference to the accompanying drawings, which illustrate embodiments of the invention. This invention may, however, be embodied in many different forms and should not be construed as limited to the illustrated embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout.
As shown in
Referring again to
The system 30 can also include drilling bit selection and optimization program product 51 stored in memory 35 of the computer 31 and adapted to assign values to a set of dimensions that define a “design and application space,” where each of these dimensions is a quantifiable performance attribute; to quantify both drilling bits and hole sections, preferably considering drilling systems and well profiles, in terms of these dimensions/attributes; and to seek and find a drilling bit that has characteristics that map as closely as possible to the application requirements (either an existing drilling bit, or feature sets that are desirable in a new design), as will be described in more detail below.
Note, the drilling bit selection and optimization program product 51 can be in the form of microcode, programs, routines, and symbolic languages that provide a specific set or sets of ordered operations that control the functioning of the hardware and direct its operation, as known and understood by those skilled in the art. Note also, the drilling bit selection and optimization program product 51, according to an embodiment of the present invention, need not reside in its entirety in volatile memory, but can be selectively loaded, as necessary, according to various methodologies as known and understood by those skilled in the art.
The physical properties data can include porosity, density, compressional sonic wave (P-wave) velocity or Dtc slowness, and shear sonic wave (S-wave) velocity or Dts slowness, which can be obtained through physical testing and/or log data. These properties represent the behavior of a rock in absence of load or under low level of load application. The mechanical properties can include, for example, unconfined compressed strength (UCS) and borehole pressure strengthening Mohr's friction angle (which can be indicated as a strengthening coefficient (“m”)), which can be measured directly from core samples in the laboratory or calculated indirectly from log data using software (like “ROCKY”) disclosed in U.S. Pat. No. 6,386,297, incorporated by reference in its entirety. The micro-structural properties considered are hard and abrasive minerals and grain sizes or block sizes. For simplicity, only quartz minerals are considered as an indicator of hardness (illustrated in
Density: Density is a bulk property which represents mass per unit volume. Since density of an individual mineral matrix is fixed (e.g., quartz 2.65 g/cc, calcite 2.71 g/cc, dolomite 2.89 g/cc etc.), a decrease in density of rocks can be indicated of the porosity of the rock type. Further, this formation property is unaffected due to presence of cracks or fracture, especially in a closed condition. The interpretation of it, however, is not as simple as it appears. A complication arises when the rock matrix is not pure and is mixed with other mineral types. Another source of discrepancy is whether the pore space is filled with gas or one or more different kinds of fluids. Accordingly, another variation of density representing porosity and fluid saturations, e.g. bulk density, dry density, nominal saturated density, vacuum saturated density, water saturated or KCl saturated density etc., can be used. If the pore volume, water volume, and matrix volume are known, all of the interrelated parameters can be readily calculated. Therefore, density can be used to estimate UCS, and thus CCS, accordingly, with a substantial correlation therebetween. It can be assumed that the same correlation exists between log measured data of density and UCS of the formation. Due care, however, should be taken as even the log data needs some expert interpretation as presence of gas and fluids of different type may complicate the true density. As such, according to an embodiment of the present invention, density alone should not be the only parameter used to estimate UCS and or CCS. Accordingly, an embodiment of the method can include developing and referencing correlation curves between UCS and the density, and between CCS and the density along with returning a respective correlation coefficient to allow the user to assess the strength of the estimate based on the individual parameter, or altogether with other formation parameters.
Porosity: Porosity is sometimes considered one of the most usable parameters in the petroleum industry, whether for drilling, reservoir engineering, completion, or production purposes. Data for such formation parameter, however, is often difficult to obtain, as it may be confidential to operators. A proper estimate of porosity, however, may be vital for the drilling process. Fundamentally, porosity is void space or pore volume, which causes stress concentration in the deformation or failure process. Porosity also causes a decrease in modulii of elasticity, and thus wave velocity, as well. The presence of a compliant crack or fracture contributes little to porosity, but decreases the modulii of elasticity to a great extent, and can make the rock type anisotropic. The anisotropy is reflected in the S wave being horizontally and vertically polarized. The pore volume and its shapes, and even the compliant crack, can be vital for determination of strength of rock if it favors a suitable stress concentration, e.g., depending upon sharpness of pore edges and alignment of crack or fractures. In any case, porosity can be characterized in various parameters such as primary porosity, secondary porosity, fracture porosity, vuggy or channel porosity, effective porosity, etc. Approximately 17 variations of porosity related terms have been used in the literature to characterize texture, grain sorting and shape, deposition environments, high or low energy, evolution to present state, etc, which makes precise interpretation difficult. Further, the presence of gas and fluids of different types may complicate the bulk porosity values. Accordingly, an embodiment of the method can include developing and referencing correlation curves between UCS and the porosity, and between CCS and the porosity along with returning a respective correlation coefficient to allow the user to assess the strength of the estimate based on the individual parameter, or altogether with other parameters.
Compressional Sonic. Dtc: The compressional wave (P wave velocity or Dtc slowness) is the fastest wave that can travel in a rock type. This feature is easy and economic to measure and needs the least expertise in its interpretation. For this reason, it has been used to characterize rock material in other branches of engineering (rippability in civil engineering, percussion and diamond drilling in mining and estimating triaxial strength and stiffness in petroleum engineering). This feature can also be used to characterize the extent of brokenness in rock mass by taking the ratio of log derived sonic data to that of its matrix velocity. Although, the P wave is largely dependent on stiffness values, it does not remain fixed in a given rock type due to compliant cracks, fractures and pore types due to refraction, reflection and attenuation of traveling wave. As the P wave speed is very low in pore spaces (˜330 m/s in air and ˜1450 m/s in water) as compared to the rock matrix (˜7000 m/s), the P wave gets drastically reduced in the presence of pores or voids. Some stiff rocks, however, give fixed velocity even at low confining pressure (e.g. Kingstone limestone, Solenhofen limestone and Bonne Terre dolomite). Accordingly, an embodiment of the method can include developing and referencing correlation curves between UCS and the P wave velocity, and between CCS and the P wave velocity along with returning a respective correlation coefficient to allow the user to assess the strength of the estimate based on the individual parameter, or altogether with other parameters.
Shear sonic, Dts: The shear sonic wave (S wave or Dts) is much slower than the P wave. In an isotropic material, the S wave is largely influenced by Poisson's ratio, which is affected by the micro- and macro-structure, and fluid saturation. In anisotropic material it may be vertically and horizontally polarized. Further, measurement of S wave is more complicated and costly and may require the use of costly transducers to filter the accompanying surface and stonely waves, which, together with the reflected and refracted P waves, form at joint or bedding planes. Therefore, due care should be taken in its interpretation. S waves have been found through testing, according to an embodiment of the method, to indicate complicated behavior at low confining pressure, which is largely due to compliant crack closure, grain adjustments or possible reflection, refraction and attenuation at various sites. Further, such testing has shown that stiff rocks show almost no change in velocity, but at the same time, fail to show isotropic behavior (two S waves merging) even at high confining pressure. Accordingly, an embodiment of the method can include developing and referencing correlation curves between UCS and the S wave velocity, and between CCS and the S wave velocity along with returning a respective correlation coefficient to allow the user to assess the strength of the estimate based on the individual parameter, or altogether with other parameters.
Mineralogy: Mineralogy plays a significant role in wear and balling characteristics in drilling. For example, quartz, being the hardest mineral in common rock types, causes extensive wear, where clay, due to its affinity to moisture and swelling characteristics, causes balling. Due recognition and quantification of these minerals, already determined via core samples and log measurements, provides a much better characterization of the rock type. For example, gamma-ray analysis can indicate the presence of clay or shale. Furthermore, log data of uranium, thorium and potassium can be used to indicate type of clay, such as kaolinite, illite, smectite, montmorillonite, etc. According to an embodiment of the method, however, individual minerals are quantified from thin section or X-Ray Diffraction analysis. It should be noted that both quartz, as well as clay, are absent in carbonate rocks. In such cases, other common but vital minerals can be quantified (e.g. dolomite, pyrite, ankerite, etc). With respect to UCS, particularly in carbonic rocks, a higher UCS has been found to correspond with a higher value of Vickers Hardness Rock Number (VHRN) formed from the respective Vickers hardness number and a cumulative average thereof for each type of rock. Accordingly, an embodiment of the method can include developing and referencing correlation curves between UCS and the mineralogy (VHRN), and between CCS and the mineralogy (VHRN) along with returning a respective correlation coefficient to allow the user to assess the strength of the estimate based on the individual parameter, or altogether with other parameters. Notably, the resulting correlation coefficient improves very much when combined with porosity.
Grain or Block size: Grain sizes and block sizes are among the most important features of the microstructure having relevance in drilling, but are analyzed the least. One factor is the difficulty in collecting and measuring such features both in core sample as well as in log measurements. Block size can be even more important when rocks are highly interbedded, as it shows brokenness of the rock formation. Grain size can be more important in absence of block or joint sizes. In either case, both grain size and block size are reflected in bulk properties such as wave velocity, density, porosity, etc. Notably, as carbonate rocks are generally not crystalline in nature, grain size tends to vary widely, making it difficult to ascertain a representative value. Accordingly, an embodiment of the method can include developing and referencing correlation curves between UCS and the grain size or block size, and between CCS and the grain size or block size along with returning a respective correlation coefficient to allow the user to assess the strength of the estimate based on the individual parameter, or altogether with other parameters.
Unconfined compressive strength, UCS: UCS is considered to be a fundamental property, and is widely used in the drilling industry. UCS represents the maximum stress sustained in a uniaxial loading condition beyond which load carrying capacity decreases drastically until physical disconnection between broken pieces occurs. Further, since the amount of strain sustained in compressive loading is about 0.2-0.5% only, the slope of the line in stress-stress space (Young's modulus of elasticity) is also proportional to UCS. This direct correlation of the Young's modulus with UCS also indicates that sonic velocity is proportional to UCS. Further, as the area (of a plot) between stress and strain is the energy consumed in the destruction process, for a given strain value at failure, the UCS reflects deformation and destruction energy. If the compressive strength is measured under confinement, as noted previously, it is termed as CCS. Several additional characteristics can be obtained in a full suit of CCS “strength” testing. Accordingly, an embodiment of the method can include developing and referencing correlation curves between USC and deformation, axial strain, or other characteristics, and between CCS and deformation, axial strain, or other characteristics along with returning a respective correlation coefficient to allow the user to assess the strength of the estimate based on the individual parameter, or altogether with other parameters. Such correlative analysis has shown that the effect of pore pressure and confining pressure oppose each other. Thus, CCS can be considered to depend upon a net differential pressure.
Mohr Friction Angle: The Mohr-Coulomb diagram is one of the effective ways to graphically visualize normal stress and shear stress along a failure plane. Very limited works exists in the literature, however, on the Mohr's Friction Angle and its correlation with other rock properties. Particularly, there is no consensus on definition of “friction angle.” Some call it an internal friction angle, some call it coefficient of friction angle. Further, some calculate it using a simple moving block on a horizontal table and by measuring the ratio of tangential load to normal load. Further, some use a standard “shear-box” system, and some calculate it as the slope of the line on a Mohr-Failure envelope, etc. An embodiment of the method considers the latter as a true reflection of that which it embodies for calculating confined compressive strength. The slope of the line is called “Mohr-Friction Angle-Ø.” The same plot can also be visualized in a maximum and minimum principal stress plot. In the former the Y-intercept is cohesion or shear stress at zero confining pressure, and slope is the Mohr-Friction Angle; whereas in the latter, the Y-intercept is UCS and the slope is equivalent to the Mohr-friction angle. Although, the slope of the line in the latter condition can be different than that of the former, it can, nevertheless, be used directly to calculate the Mohr-Friction Angle. This friction angle is highest at low confining pressure and it decreases continually at high confining pressure. For all practical purposes, i.e., in the borehole pressure environment where drillability is investigated, however, it can be assumed to be a straight line. Accordingly, an embodiment of the method can include developing and referencing correlation curves between USC and Mohr-Friction Angle, and between CCS and Mohr-Friction Angle along with returning a respective correlation coefficient to allow the user to assess the strength of the estimate based on the individual parameter, or altogether with other parameters. Note, such correlation curves have indicated an inverse relationship between the Mohr-Friction Angle and porosity in a wide variety of sandstones and carbonate rock types.
According to embodiments of the present invention, for each component subterranean formation 21-26, these values can be compiled and normalized into a computer model of the properties of the respective subterranean formation 21-26. As illustrated in
Referring again to
UCS, strengthening coefficient, and abrasive minerals values can be obtained from the previously calibrated log data as above or lab-core-testing. Required bit-cutter force per unit contact area is proportional to the Mechanical Specific Energy of drilling. The Mechanical Specific Energy is proportional to CCS×Strain-at-Failure. CCS can be calculated from the UCS and a Strengthening coefficient. The UCS and the Strengthening coefficient can be calculated from density, porosity, P and S, as shown, for example, in
Strain-at-failure can be calculated from borehole pressure environment, porosity, calculated Poisson's ratio and mineralogy. Expected strain at failure, under hard and brittle, semi-brittle and ductile conditions is shown in
The values of the drillability parameters can be based on objectives such as, for example, constraints and requirements of ROP (e.g., aggressiveness, efficiency), durability (e.g., wear, impact, erosion, heat), stability, and stearability, which can depend or be based upon the results of a pre-drill analysis and environmental constraints. The predrill analysis can include the analysis of offset bit records (drilling practice), offset dull characteristics, well prognosis (pore pressure (Pp), drilling fluid desity (MW), hole curvature (DLS), etc.) and equipment (rig, pumps, bottom hole assembly (BHA) design). The environmental constraints can include, for example, rock mechanical properties, rig/pump, hydraulic horsepower per square inch (HSI), flow rate capacity (GPM), in situ stress, operating practices, people, etc.
Referring to
Still referring to
Mechanical efficiency represents the desirability of cutting efficiency, which is inversely proportional to specific energy, which in turn is related to compressive strength (UCS or CCS). Thus, mechanical efficiency can be quantified using “combined” UCS or CCS for the hole section. High UCS and/or friction imply strong rock and slow drilling, which in turn implies a greater need for mechanical efficiency. Correspondingly low UCS and/or friction lead suggest a lesser need for mechanical efficiency.
Axial aggressiveness represents the desirability of bits that are axially aggressive, where aggressiveness is defined as the amount of torque generated for a given amount of weight-on-bit. High attribute values would be appropriate for continuous sections of homogenous rock. Interbedded intervals, especially with high interfacial severity (a parameter which can be computed, for example, in the Rocky software) would require lower attribute values. Low UCS and/or friction lead to high axial aggressiveness. Correspondingly high UCS and/or friction lead to low axial aggressiveness.
Lateral aggressiveness represents the desirability of bits that are laterally aggressive, where aggressiveness is defined as the ability to deviate laterally under a given amount of side load. Most hole sections call for low, but non-zero values based on directional response and vibration tendencies. Low UCS and/or friction lead to high lateral aggressiveness. High UCS or friction lead to low lateral aggressiveness. Drilling system considerations are addressed later.
Lateral stability indicates the importance of lateral vibration control. High attribute values would be required for hole sections with significant amounts of hard rock (high acoustic impedance, high modulii of elasticity, lower Poisson's ratio). In such sections, vibrations are more likely, and impact damage is probable. Likewise, high attribute values would be required by hole sections with high interfacial severity. Correspondingly, lower values would be suitable for hole sections where soft rock is prevalent.
Torsional stability, having similar considerations as that of lateral stability, indicates the importance of torsional vibration control. Formations with high acoustic impedance, high modulii of elasticity and lower Poisson's ratio are more prone to vibration, and require bits with greater torsional stability. Further, hole sections at greater measured depth require greater torsional stability due to the increase in drill string compliance, and corresponding proclivity for tosional vibration, with total length.
Cooling efficiency is the ability to dissipate heat associated with rock cutting in the downhole environment. Cutter wear is affected by heat, which in turn is related to cutting efficiency. Target hole sections/formations with high confined compressive strength, and possibly abrasiveness, would demand high attribute values (i.e., demand a higher cooling efficiency). Similarly, hole sections/formations with high shale content (possibly reflected through bit balling and/or bottom balling indices per Rocky algorithms) would require high attribute values for cleaning efficiency. High carbonate content and/or S-wave velocity require high cooling efficiency. Correspondingly, low carbonate and/or S-wave velocity require lesser cooling efficiency. High Mohr-Friction Angle (Ø) and/or low amounts of clay reduce the need for cleaning efficiency. Conversely, low Mohr-Friction Angle and/or high amounts of clay make bit cleaning difficult and require high cleaning efficiency.
Erosion resistance, abrasion resistance, and impact resistance are related to robustness. Hole sections with high sand content, even if formations are not particularly strong, would call for higher erosion and abrasion resistance values. Similarly, hole sections with high values of combined rock strength and abrasiveness would demand high attribute values for both abrasion resistance and impact resistance. Also similarly, hole sections with high significance of lateral and/or torsional vibration would demand high attribute values for impact resistance. High grain size, density, and/or Mohr-Friction Angle (Ø) require high abrasion and erosion resistance. Correspondingly, low grain size, density, and/or Mohr-Friction Angle allow lower abrasion and erosion resistance to be tolerated. High CCS×Mohr-Friction Angle requires high abrasion resistance. Correspondingly, low CCS×Mohr-Friction Angle allows lower abrasion resistance. High acoustic impedance requires high impact resistance. Correspondingly, low acoustic impedance leads to low impact resistance requirements.
Referring to
Mechanical efficiency can be considered a neutral attribute for drilling systems.
Axial aggressiveness, on the other hand, would not be neutral. Steerable motor systems would tend to require or favor lower attribute values for toolface control. Some vertical drilling systems would also require or favor lower attribute values, for similar reasons. Rotary steerable systems can tolerate higher attribute values. With respect to lateral aggressiveness, low (but nonzero) values are typically desired for rotary applications to minimize lateral vibration and maintain verticality. Directional intervals requiring low to moderate doglegs would call for similar values as vertical sections. Very low values would be called for when point-the-bit rotary steerable systems are employed. Embodiments of the present invention include algorithms that allow desired side cutting efficiency to be specified given dogleg requirements and bottom hole assembly design.
With respect to lateral stability, most, if not all, systems generally would favor high values, but rotary steerable systems would be expected to require the highest levels of stability to ensure directional control and maximize mean time between failures (MTBF). High speed motors, which tend to lead to low depths of cut, would demand high levels of lateral stability.
With respect to torsional stability, similar to the above, torsional stability becomes more significant when high depths of cut are expected (low speed motors) and at greater depth.
With respect to cooling efficiency, applications where pump pressure and flow rate are limited would require high efficiencies. Similar to the above with respect to cleaning efficiency, applications where pump pressure and flow rate are limited would require high efficiencies.
With respect to erosion resistance, applications where high bit pressure drops are used would require high erosion resistance.
With respect to abrasion resistance, applications where high rotary speeds are expected (medium to high speed motors, turbines) would require high abrasion resistance.
With respect to impact resistance, applications where low depths of cut are expected (high rotary speeds, motor applications) would call for high levels of impact resistance. Applications featuring steerable (i.e. bent housing) motors would call for high values.
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In alignment with the set of target hole section performance requirements (see, e.g.,
Mechanical efficiency can be measured or computed, for example, from calibrated models based on the Mechanical Specific Energy (MSE) required to drill a given rock at a given depth of cut. The baseline conditions can vary. For illustrative purposes, the baseline conditions can be Carthage limestone, 3 kpsi confinement (or atmospheric), 120 RPM, 30 ft/hr. In this example, the depth of cut would equal 0.050 in. per revolution, (e.g., depth of cut=0.2*30/120=0.050 inch/revolution). The evaluation methods can include, for example, use of a high pressure simulator, single point cutter test, or surface rig.
Axial aggressiveness can be measured or computed, for example, as the bit specific friction coefficient while drilling a given rock at a given depth of cut (e.g. same conditions as above). Lateral aggressiveness can be measured or computed, for example, as the lateral rate of penetration using a given side load and rotary speed in a given rock (e.g. Carthage limestone with 1,000 lb side load at 120 RPM). Evaluation methods can include, for example, use of a surface rig, or computer models as described in “Dynamics Modeling of PDC Bits,” SPE/IADC 29401, H. Hanson and W. Hansen.
Lateral stability can be measured or computed, for example, as “Whirl Traction” or “μ Variation” (coefficient of variation of the axial aggressiveness) in a given rock at a given depth of cut, e.g., Carthage limestone at 0.050 in/rev, as above. Evaluation methods can include, for example, use of a surface rig or the software described in SPE/IADC 29401.
Torsional stability can be measured or computed, for example, as a function of the change in aggressiveness at two depths of cut (0.010 versus 0.050 in/rev), or alternately the change in torque with weight-on-bit held constant at two different rotary speeds in a given rock, e.g., 30 RPM versus 180 RPM with 10,000 lb of weight-on-bit in Carthage limestone. Evaluation methods can include, for example, use of a surface rig or the above referenced software.
Cooling efficiency can be measured or computed, for example, as a function of the maximum cutter temperature on the bit profile at 30% wear under reference conditions (e.g., 50 gal/min per inch of bit diameter, nozzle area required to generate four hydraulic horsepower per square inch). Alternately, the temperature adjacent to a reference cutter (e.g., the last cutter on the profile) under these conditions can be used as a measure. Evaluation methods can include, for example, use of computational fluid dynamics (CFD) software such as FLUENT or bit performance prediction software (e.g. PDC Wear).
Cleaning efficiency can be measured or computed, for example, as the rate of penetration (ROP) at which balling occurs tinder baseline conditions, the percentage of particles that escape the bit face in a fixed amount of time, or the minimum “Pinch Point Ratio” (cross sectional area of flow versus volume of cuttings passing through) along the profile computed using CAD and PDC Wear software. Evaluation methods can include, for example, use of a high pressure simulator, flow visualization experiments, CFD software, and/or PDC Wear software.
Erosion resistance can be measured or computed, for example, as a function of maximum fluid velocity adjacent to any cutter on the profile of the bit under reference conditions, e.g., 50 gal/min per inch of bit diameter, and nozzle area required to generate four hydraulic horsepower per square inch. Evaluation methods can include, for example, use of CFD software.
Abrasion resistance can be measured or computed, for example, as a function of the combined result of cutter properties and bit design (i.e. number of cutters). Cutter properties can be quantified (evaluated), for example, via measuring the volume of reference rock (e.g. Sierra White granite) machined on a vertical boring mill versus volume of diamond table removed at a given number of round trips (e.g. 150) at a given depth of cut (e.g. 0.010 in). Bit design effects can be quantified using software such as the PDC Wear program as predicted footage drilled at a specified weight-on-bit in a specified rock at a specified rotary speed, at which point a minimum rate of penetration is reached (e.g. 10 ft/hr).
Impact resistance can be measured or computed as a function of both cutter properties and bit design. High cutter counts, high stability levels, and impact resistant cutters would yield high values. Cutter toughness can be quantified, for example, by measuring the total impact energy required to cause cutter spalling/fracture in drop impact tests.
Note, as with the target hole section performance requirements and the drilling system performance characteristics, a person having ordinary skill in the art will recognize that the list of exemplary characteristics/requirements (e.g., drilling bit performance characteristics) are representative and are neither a minimal nor exhaustive list.
Referring again to
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The optimization/selection process can be based upon selecting candidate drilling bits which maximize an alignment between the identified drilling application performance requirements and the drilling bit performance characteristics of each candidate drilling bit. Note,
ā·
The higher the sum of the products of the various dimensional values, the better the quality of the match between bit and application. Further, according to various other schemes, one or more of the vectors (dimensions) are weighted. Using this approach, a quick series of computations can be accomplished such that the drilling application performance requirements/map is compared to every bit in the size of interest with predefined drilling bit performance characteristics/maps, and those that match the best could be identified and ranked, as described above. Beneficially, this can be accomplished manually by the user responsive to viewing the drilling bit performance characteristics maps in comparison with the drilling application performance requirements map, or automatically by computer 31 as part of the optimization process. Further, if no suitable match is found, the drilling application performance requirements/map can be used as the basis for specifying drilling bit performance characteristics in a new design. That is, if the readymade “out of box” bit having sufficiently matching features is available, the bit is generally selected. Otherwise, a custom design can be created by a design engineer or design team using analytical, numerical and experimental techniques including cost benefit analysis.
Accordingly, as perhaps best shown in
The method can also include performing a multi-objective optimization between the set of drilling application performance requirements and each of the plurality of adjustable virtual drilling bit features (block 135) to thereby determine feature attributes of the plurality of drilling bit features that when combined to form a candidate virtual drilling bit (see, e.g.,
In order to evaluate the candidate virtual design (
According to another embodiment of a method of, or program product for, selecting a drilling bit for drilling an identified target hole section 20 of earth, rather than generating a multidimensional map displaying the relative importance/values of the target hole section performance requirements, generating a multidimensional map displaying the relative importance/values of the drilling system performance characteristics, generating a multidimensional map displaying the relative importance/values of the drilling application performance requirements, and/or generating a multidimensional map displaying the relative importance/values of the drilling bit characteristics for each candidate drilling bit, the user is provided the end product: one or more of the various multidimensional maps. In such embodiments of the present invention, pattern recognition technology (e.g., software), known to those skilled in the art, can be used to extract the base data contained within the map or maps, and/or to directly perform the bit selection through graphical acquisition and comparison of the predefined multidimensional maps. For example, given the drilling application performance requirements multidimensional map and a plurality of drilling bit performance characteristics maps, the pattern recognition software can be utilized to return an identification of a candidate drilling bit having the closest match between the associated drilling bit performance characteristics and the drilling application performance requirements. Other such variations are, of course, within the scope of the present invention.
It is important to note that while the foregoing embodiments of the present invention have been described in the context of a fully functional system and process, those skilled in the art will appreciate that the mechanism of at least portions of the present invention and/or aspects thereof are capable of being distributed in the form of a computer readable medium in a variety of forms storing a set of instructions for execution on a processor, processors, or the like, and that embodiments of the present invention apply equally regardless of the particular type of signal bearing media used to actually carry out the distribution. Examples of computer readable media include, but are not limited to: nonvolatile, hard-coded type media such as read only memories (ROMs), CD-ROMs, and DVD-ROMs, or erasable, electrically programmable read only memories (EEPROMs), recordable type media such as floppy disks, hard disk drives, CD-R/RWs, DVD-RAMs, DVD-R/RWs, DVD+R/RWs, HD-DVDs, memory sticks, mini disks, laser disks, Blu-ray disks, flash drives, and other newer types of memories, and certain types of transmission type media such as, for example, digital and analog communication links capable of storing the set of instructions. Such media can contain, for example, both operating instructions and operations instructions described with respect to program product 51, the program products 51, itself, and the computer executable portions of the method steps according to the various embodiments of the present invention related to selecting or optimizing a drill/drilling bit for drilling an identified target hole section of earth, described above.
The various embodiments of the present invention have several advantages. For example, the system, program product, and methods of the present invention, described herein, advantageously provide for an efficient and systematic way to capture and compare performance characteristics for drilling bits to facilitate bit design optimization and selection. Furthermore, the embodiments of the present invention conveniently provide a novel, efficient and systematic way to express the drillability of a rock in terms of its physical, mechanical, and micro-structural properties. Embodiments of the present invention advantageously employ multiple measured parameters, some of which could be considered redundant, to characterize, in a quantitative sense, a given rock, along with application of a similar approach to characterize, in a quantitative sense, a given drilling bit design (and drilling application), which when used together, can provide a means for selecting suitable, or alternatively optimal, bits for a given application. For example, where Folk (1959) and Dunham (1962), and its progeny (which have enhanced and clarified the two classification systems with more details of grain sizes, pore systems and porosity), still only provide such data in a qualitative way, various embodiments of the present invention, in contrast, characterize various rock formations (e.g., carbonate rocks) in terms of its porosity, density, compressional sonic (P wave or Dtc slowness), and shear sonic (S wave or Dts slowness), grain or block sizes and mineralogy data for estimating UCS and friction angle which together indicates the in-situ strength. These rock properties can be readily obtained either from core samples obtained from borehole, or captured while logging. Further, if there is prior calibration work, the drillability can be inferred directly. Further, these eight rock properties are simple enough to understand and use in the drilling industry, but detailed enough to describe drillability to a great extent. Embodiments of the present invention advantageously assign values to a set of dimensions that define a “design and application space,” where each of these dimensions is a quantifiable performance attribute; quantify both drilling bits and hole sections, preferably considering drilling systems and well profiles, in terms of these dimensions/attributes; and seeks and finds a drilling bit that has characteristics that map as closely as possible to the application requirements (either an existing drilling bit, or feature sets that are desirable in a new design). Further, embodiments of the present invention provide for selection and optimization of a complete array of types of drilling bits including the polycrystalline diamond compact (PDC) drilling bit, and the roller cone drilling bit.
This application is related to U.S. Provisional Patent Application No. 61/080,594, filed Jul. 14, 2008, and is related to PCT Patent Application No. PCT/US09/50479, filed Jul. 14, 2009, each incorporated herein by reference in its entirety.
In the drawings and specification, there have been disclosed a typical preferred embodiment of the invention, and although specific terms are employed, the terms are used in a descriptive sense only and not for purposes of limitation. The invention has been described in considerable detail with specific reference to these illustrated embodiments. It will be apparent, however, that various modifications and changes can be made within the spirit and scope of the invention as described in the foregoing specification.
| Number | Name | Date | Kind |
|---|---|---|---|
| 5787022 | Tibbitts | Jul 1998 | A |
| 6349595 | Civolani et al. | Feb 2002 | B1 |
| 6386297 | Cooley | May 2002 | B1 |
| 6424919 | Moran et al. | Jul 2002 | B1 |
| Number | Date | Country | |
|---|---|---|---|
| 20100030527 A1 | Feb 2010 | US |
| Number | Date | Country | |
|---|---|---|---|
| 61080594 | Jul 2008 | US |
