Patent Application
20140191762
The present invention relates to techniques for performing wellbore operations. More particularly, the present invention relates to techniques for determining characteristics of subterranean formations.
Oil rigs are positioned at wellsites for performing a variety of oilfield operations, such as drilling a wellbore, performing downhole testing and producing located hydrocarbons. Downhole drilling tools are advanced into the earth from a surface rig to form a wellbore. Drilling muds are often pumped into the wellbore as the drilling tool advances into the earth. The drilling muds may be used, for example, to remove cuttings, to cool a drill bit at the end of the drilling tool and/or to provide a protective lining along a wall of the wellbore. During or after drilling, casing is typically cemented into place to line at least a portion of the wellbore. Once the wellbore is formed, production tools may be positioned about the wellbore to draw fluids to the surface.
During drilling, measurements are often taken to determine downhole conditions. In some cases, the drilling tool may be removed so that a wireline testing tool may be lowered into the wellbore to take additional measurements and/or to sample downhole fluids. Once the drilling operation is complete, production equipment may be lowered into the wellbore to assist in drawing the hydrocarbons from a subsurface reservoir to the surface.
The downhole measurements taken by the drilling, testing, production and/or other wellsite tools may be used to determine downhole conditions and/or to assist in locating subsurface reservoirs containing valuable hydrocarbons. Such wellsite tools may be used to measure downhole parameters, such as temperature, pressure, viscosity, resistivity, etc. Such measurements may be useful in directing the oilfield operations and/or for analyzing downhole conditions.
Attempts have been made to measure certain characteristics of a wellbore. Various techniques have been developed for measuring downhole parameters as described, for example, in US Patent/Application Nos. 20090204346, 20090153155, 20090072833, 20090090176, 20080288171, U.S. Pat. Nos. 7,689,363, 7,394,258, 7,397,250, 7,258,005, 5,457,396, 6,527,923, 7,066,282, 6,801,039, 5,677,631, 5,574,371, 5,345,179, 6,191,588, 3,879,644, 3,816,811, 4,608,983, 4,567,759, and 7,689,363. Techniques have also been developed for scanning as stated in publications “Formation Imaging with Microelectrical Scanning Arrays”, and “A General Framework for Constraint Minimization for the Inversion of Electromagnetic Measurements.”
More specifically, European Patent Application Nos. 102900084.2 and 10290083.4, filed by Applicant and incorporated herein by reference, relate to techniques for determining electrical parameters of downhole fluids.
In addition, International Patent Application No. PCT/EP2009/007637, filed by Applicant and incorporated herein by reference, relates to a tool and method for imaging a formation through a substantially non-conductive medium. The tool comprises a first circuitry for injecting a current into the formation, wherein a complex impedance to the current is measured. A second circuitry for determining a phase angle of an impedance of the nonconductive medium and a third circuitry for determining a component of the complex impedance that is orthogonal to the phase angle.
Despite the development of techniques for measuring downhole parameters, there remains a need to provide advanced techniques for determining parameters of downhole formations and/or wellbore fluids. It may be desirable to provide techniques that enhance downhole fluid and/or downhole formation measurements. It may be further desirable to provide techniques that correct for the effects of mud on downhole imaging and/or measurement. Preferably, such techniques involve one or more of the following, among others: accuracy of measurements, optimized measurement processes, operability in a variety of downhole fluids such as conductive and non-conductive muds, flexible measurement and/or analysis, operability in downhole conditions (e.g., at high temperatures and/or pressures), etc.
The present invention relates to a formation imaging unit for imaging properties of at least one subterranean formation in a wellbore at a wellsite. The formation imaging unit comprises a current management unit for collecting data from at least two currents injected into the at least one subterranean formation, the at least two currents having at least two different frequencies, and a drilling mud data unit for determining at least one drilling mud parameter. The formation imaging unit comprises a formation data unit for determining at least one formation parameter from the collected data, and an inversion unit for determining at least one formation property by inverting the at least one formation parameter.
The present invention relates to a system for imaging properties of at least one subterranean formation in a wellbore at a wellsite. The system comprises a formation sensor for collecting at least two currents injected into the at least one subterranean formation, the formation sensor positionable on a downhole tool deployable into the wellbore, a controller for controlling the formation sensor, and a formation imaging unit. The formation imaging unit comprises a current management unit for collecting data from the at least two currents injected into the at least one subterranean formation, the at least two currents having at least two different frequencies. The formation imaging unit comprises a drilling mud data unit for determining at least one drilling mud parameter, a formation data unit for determining at least one formation parameter from the collected data, and an inversion unit for determining at least one formation property by inverting the at least one formation parameter.
The present invention relates to a method for imaging properties of at least one subterranean formation in a wellbore at a wellsite. The method comprises deploying a downhole tool into the wellbore, the downhole tool having a formation sensor thereon and collecting at least two currents sent through the at least one subterranean formation from the formation sensor. The method comprises sending formation data from the at least two currents to a formation imaging unit. The formation imaging unit comprises a current management unit for collecting data from the at least two currents injected into the at least one subterranean formation, the at least two currents having at least two different frequencies, a drilling mud data unit for determining at least one drilling mud parameter, a formation data unit for determining at least one formation parameter from the collected data, and an inversion unit for determining at least one formation property by inverting the at least one formation parameter. The method comprises determining at least one formation property with the formation imaging unit.
The present embodiments may be better understood, and numerous objects, features, and advantages made apparent to those skilled in the art by referencing the accompanying drawings. These drawings are used to illustrate only typical embodiments of this invention, and are not to be considered limiting of its scope, as the invention may admit to other equally effective embodiments. The figures are not necessarily to scale and certain features and certain views of the figures may be shown exaggerated in scale or in schematic in the interest of clarity and conciseness.
The description that follows includes exemplary apparatus, methods, techniques, and instruction sequences that embody techniques of the present inventive subject matter. However, it is understood that the described embodiments may be practiced without these specific details. Presently preferred embodiments of the invention are shown in the above-identified Figures and described in detail below.
The downhole tool 104 is shown as a wireline logging tool lowered into the wellbore 106 to take various measurements. The downhole tool 104 may include a conventional logging device 119, one or more sensor pads 120, one or more telemetry devices 122, and an electronics package 124. The conventional logging device 119 may be provided with various sensors, measurement devices, communication devices, sampling devices and/or other devices for performing wellbore operations. For example, as the downhole tool 104 is lowered, it may use devices, such as resistivity or other logging devices, to measure formation parameters and/or downhole fluid parameters. The formation parameters and/or the downhole fluid parameters may be the collected data regarding the formation and/or the downhole fluid. The formation imaging unit 118 may manipulate the formation parameters and optionally the downhole fluid parameters to determine formation properties and/or downhole fluid properties for example resistivity.
As shown, the downhole tool 104 may be conveyed into the wellbore 106 on a wireline 126. Although the downhole tool 104 is shown as being conveyed into the wellbore 106 on a wireline 126, it should be appreciated that any suitable conveyance may be used, such as a slick line, a coiled tubing, a drill string, a casing string and the like. The downhole tool 104 may be operatively connected to the controller 112 for communication therebetween. The downhole tool 104 may be wired via the wireline 126, as shown, and/or wirelessly linked via the one or more telemetry devices 122. The one or more telemetry devices 122 may include any telemetry devices, such as electromagnetic devices, for passing signals to the controller 112 as indicated by communication links 128. Further, it should be appreciated that any communication device or system may be used to communicate between the downhole tool 104 and the controller 112. Signals may be passed between the downhole tool 104, the controller 112, the communication network 114, and/or the offsite computer(s) 116 and/or other locations for communication therebetween.
While the downhole tool 104 is depicted as the wireline tool having the one or more sensor pads 120 thereon, it will be appreciated that the one or more sensor pads 120 may be positioned downhole on a variety of one or more tools. For example, the one or more sensor pads 120 may be placed on any downhole system and/or tool for example, on a drilling string, a logging while drilling tool (LWD), a measurement while drilling tool (MWD), a coiled tubing, a drill stem tester, a production tubing, a casing, a pipe, or any other suitable downhole tool. Although only one of the one or more sensor pads 120 is shown, it should be appreciated that one or more sensor pads 120 and/or portions of the one or more sensor pads 120 may be located at several locations in the wellbore 106. The one or more sensor pads 120 are preferably positioned about an outer surface of the downhole tool 104 so that the wellbore fluid 108 may pass therealong for measurement thereof. However, it will be appreciated that the one or more sensor pads 120 may be positioned at various locations about the wellsite 100 as desired for performing fluid and/or formation measurements.
The electronics package 124 may include any components and/or devices suitable for operating, monitoring, powering, calculating, calibrating, and analyzing components of the downhole tool 104. Thus, the electronics package 124 may include a power source, a processor, a storage device, a signal conversion (digitizer, mixer, amplifier, etc.), a signal switching device (switch, multiplexer, etc.), a receiver device and/or a transmission device, and the like. The electronics package 124 may be operatively coupled to the one or more sensor pads 120 and/or the formation imaging unit 118. The power source may be supplied by the wireline 126. Further, the power source may be in the electronics package 124. The power source may apply multiple currents to the one or more sensor pads 120. The power source may be provided by a battery power supply or other conventional means of providing power. In some cases, the power source may be an existing power source used in the downhole tool 104. The power source may be positioned, for example, in the downhole tool 104 and wired to the one or more sensor pads 120 for providing power thereto as shown. Optionally, the power source may be provided for use with the one or more sensor pads 120 and/or other downhole devices. Although the electronics package 124 is shown as one separate unit from the one or more sensor pads 120 and/or the formation imaging unit 118, it should be appreciated that any portion of the electronics package 124 may be included within the one or more sensor pads 120 and/or the formation imaging unit 118. Further, the components of the electronics package 124 may be located at various locations about the downhole tool 104, the controller 112 and/or the wellsite 100. The one or more sensor pads 120 may also be wired or wirelessly connected to any of the features of the downhole tool 104, the formation imaging unit 118, the communication network 114, and/or the controller 112, such as communication links, processors, power sources or other features thereof.
The downhole fluid 108, or wellbore fluid, or borehole mud fluid, used at the wellsite 100 may be an oil-based drilling mud. The downhole fluid 108 may be pumped into the wellbore 106 during drilling and/or other downhole operations. The downhole fluid 108 may coat a wellbore wall 130 as it encounters the wellbore wall 130. The downhole fluid 108 coated on the wellbore wall 130 may form a mud cake 132, or mud standoff. The mud cake 132 may create a gap 134, or standoff, or mud standoff, or sensor standoff, between the one or more sensor pads 120 and a subterranean formation 136. Further roughness of the wellbore wall 130 may cause the gap 134, or standoff, or sensor standoff, between the one or more sensor pads 120 and the subterranean formation 136. The oil-based drilling mud may have a high resistivity. For example, the resistivity of a water-based drilling mud may be between 0.01-20 Ohm and the resistivity for the oil-based drilling mud may be 10,000 to 10,000,000 times higher than the water-based drilling mud. Due to the high resistivity of the oil-based drilling mud, the properties of the oil-based drilling mud must be accounted for when determining formation properties, as will be discussed in more detail below. Because the same downhole fluid 108, or drilling mud, is typically used during wellsite operation, the properties of the downhole fluid 108 may remain relatively constant along the length of the wellbore 106.
The one or more sensor pads 120 may be capable of determining one or more downhole fluid parameters and/or one or more formation parameters. The one or more sensor pads 120 may determine the downhole parameters of the downhole fluids 108 and/or the subterranean formations 136 as the downhole tool 104 passes through the wellbore 106. As shown, the one or more sensor pads 120 may be positioned on an outer surface 138 of the downhole tool 104. A portion of the one or more sensor pads 120 may be recessed a distance below the outer surface 138 to provide additional protection thereto, or protruded a distance therefrom to access fluid and/or subterranean formation 136. The one or more sensor pads 120 may also be positioned at various angles and locations as desired.
The formation sensor 200 may be any sensor configured to determine one or more formation parameters. The formation sensor 200 may send, or inject, a plurality of currents through a portion of the subterranean formation 136 between two electrodes. The plurality of currents may have two or more frequencies, as will be discussed in more detail below. The plurality of currents may pass through the downhole fluid 108 and the subterranean formation 136. The injected current may include information regarding formation and/or fluid parameters. The current detected by the formation sensor 200 may be sent to the formation imaging unit 118. The formation and/or fluid parameters may be manipulated by the formation imaging unit 118 to determine one or more formation properties, as will be discussed in more detail below. When the downhole fluid 108 is the oil-based drilling mud, the impedance contribution from the mud cake 132 may be significantly larger than the impedance contribution from the formation 136.
The mud sensor 202 may be an optional sensor configured to determine one or more downhole fluid parameters. The mud sensor 202 may be configured to send, or inject, current through the downhole fluid 108 and/or the mud cake 132. The current injected and detected by the mud sensor 202 may have the same frequencies as the plurality of currents injected by the formation sensor 200. The current detected by the mud sensor 202 may be sent to the formation imaging unit 118.
The sensor pad 120 may optionally have the mud sensor 202. The mud sensor 202 may be configured to send a plurality of currents 304B through the mud cake 132 and/or the downhole fluid 108 (as shown in
The plurality of currents 304A and/or 304B may be high frequency current in order to penetrate the highly resistive oil-based drilling mud. Due to the high frequency of the plurality of currents 304A and/or 304B, the source electrodes 300 and the return electrode 302 and/or the mud return electrode 306 may be located in close proximity to one another, as shown in
The source electrodes 300, the return electrodes 302, and the mud return electrode 306 may be any conventional electrode capable of generating the plurality of currents 304A and/or 304B across the oil-based drilling mud, or downhole fluid 108. A power source (e.g., included in the electronics package 124 of
The current from the electrodes may be used to determine various parameters. In an example involving a fluid passing between a pair of electrodes, an AC voltage V is applied between two electrodes to generate a resultant current I that can be measured at the sensor electrode, for example the return electrode 302 or the mud return electrode 306. The complex impedance Z may be determined from the measured current I based on the following:
z=|z|exp(iφz) Equation (1)
where its magnitude |z| based on Ohms law and phase φz are defined as follows:
|z|=|V/I| Equation (2)
φz=phase of I relative V Equation (3)
and where exp (iφz) based on Euler's formula is defined as follows:
exp(iφz)=cos αz+i sin φz Equation (4)
The magnitude and phase of the impedivity (sometimes referred to as the complex impedivity) of a fluid ζ is defined as follows:
ζ=|ζ|exp(iφζ) Equation (5)
Equation (5) may be derived from z when the fluid is measured by the mud sensor 202 by the relations as follows:
|ζ|=k|z| Equation (6)
Equation (6) may also be written as follows:
|ζ|=k|V|/|I| Equation (7)
The phase (or dielectric angle) of the fluid ζ is derived as follows:
φζ=φz Equation (8)
where:
The constant k may be measured empirically, for example, by measuring the impedance V/I between electrodes as a fluid of known impedivity. The constant k may also be calculated from the geometry of the electrodes using conventional methods.
Data concerning the measured current may be used to determine fluid parameters, such as impedivity, resistivity, impedance, conductivity, complex conductivity, complex permittivity, tangent delta, and combinations thereof, as well as other parameters of the downhole fluid 108. The data may be analyzed to determine characteristics, or properties, of the wellbore fluid 108, such as the type of fluid (e.g., hydrocarbon, mud, contaminants, etc.) The formation imaging unit 118 may be used to analyze the data, as will be discussed in more detail below. Such analysis may be performed with other inputs, such as historical or measured data about this or other wellsites. Reports and/or other outputs may be generated from the data. The data may be used to make decisions and/or adjust operations at the wellsite. In some cases, the data may be fed back to the wellsite 100 for real-time decision making and/or operation.
The formation imaging unit 118 may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.), or an embodiment combining software and hardware aspects. Embodiments may take the form of a computer program embodied in any medium having computer usable program code embodied in the medium. The embodiments may be provided as a computer program product, or software, that may include a machine-readable medium having stored thereon instructions, which may be used to program a computer system (or other electronic device(s)) to perform a process. A machine readable medium includes any mechanism for storing or transmitting information in a form (such as, software, processing application) readable by a machine (such as a computer). The machine-readable medium may include, but is not limited to, magnetic storage medium (e.g., floppy diskette); optical storage medium (e.g., CD-ROM); magneto-optical storage medium; read only memory (ROM); random access memory (RAM); erasable programmable memory (e.g., EPROM and EEPROM); flash memory; or other types of medium suitable for storing electronic instructions. Embodiments may further be embodied in an electrical, optical, acoustical or other form of propagated signal (e.g., carrier waves, infrared signals, digital signals, etc.), or wireline, wireless, or other communications medium. Further, it should be appreciated that the embodiments may take the form of hand calculations, and/or operator comparisons. To this end, the operator and/or engineer(s) may receive, manipulate, catalog and store the data from the downhole tool 104 in order to perform tasks depicted in the formation imaging unit 118.
The formation imaging unit 118 may include a storage device 502, a current management unit 504, a drilling mud data unit 506, a formation data unit 508, an inversion unit 510, a formation model unit 512, a wellbore optimizer unit 514, an analyzer unit 516, and a transceiver unit 518. The storage device 502 may be any conventional database or other storage device capable of storing data associated with the wellsite 100, shown in
The current management unit 504 may be configured to generate and collect the appropriate number and frequency of the plurality of currents 304A and/or 304B, depending on the wellbore 106 conditions and/or the type of sensor pad 120 used. The number of frequencies used may depend on the number of formation parameters and/or downhole fluid parameters to be calculated using the inversion unit 510. The number of currents and frequencies used may be dependent on the downhole fluid 108 (as shown in
The current management unit 504 may send the determined number of multiple logging frequencies into the formation at substantially the same time at multiple locations along the formation. The plurality of currents 304B for measuring the downhole fluid properties may have the same logging frequencies, or a portion of the logging frequencies, as those sent into the subterranean formation 136 (as shown in
The drilling mud data unit 506 may be used to collect, catalog, store, manipulate and/or supply mud data. The mud data may be the measured data from the mud sensor 202 (as shown in
The formation data unit 508 may be used to collect, catalog, store, manipulate and/or supply formation data. The formation data may be the measured data from the formation sensor 200 (as shown in
The inversion unit 510 may obtain the formation data and mud data from the drilling mud data unit 506 and/or the formation data unit 508. To determine formation resistivity, or an inverted formation resistivity, the inversion unit 510 may invert, or parametrically invert, the multiple current measurements made at several frequencies, as will be described in more detail below. The number of frequencies used may depend on the number of parameters to be inverted. The inversion unit 510 may invert the mud data and/or the formation data in order to determine formation properties and/or downhole fluid properties. The inverted formation data, and optionally, the mud data, obtained at the plurality of frequencies may be used to obtain formation properties for borehole imaging. The parameters to be inverted may be the formation resistivity, the formation permittivity, and/or the mud standoff (if the mud data is collected independently of the formation data). If the mud parameters are not measured, for example, by the mud sensor 202 (as shown in
The plurality of currents 304A (as shown in
Where Δ is the mud standoff, Kmud and Krock are tool related coefficients, and ω is the operating frequency, or logging frequency for each of the plurality of currents 304A. ∈mud and ∈rock may be the relative permittivity of the mud and the formation respectively. Rmud and Rrock may be the resistivity of the mud and the formation respectively. The term ∈0 represents the permittivity of free space (a constant=8.85419×10−12) and j represents √{square root over (−1)}. The terms subscripted by “mud” represent the contribution to Z from the mud or mudcake occupying the space between the padface and the formation, depending of the electrical properties of the formation, the properties ∈rock and Rrock the contribution from the mud or mud cake 132 may be significantly larger than the contribution from the formation.
In equation 9, the formation sensor 200 (as shown in
real(V/I)=ΔKmudRmud/[1+(ω∈o∈mudRmud)2]+KrockRrock/[1+(ω∈o∈rockRrock)2] (Equation 10)
and
imag(V/I)=−ω∈o{ΔKmud∈mudRmud2/[1+(ω∈o∈mudRmud)2]+Krock∈rockRrock2/[1+(ω∈o∈rockRrock)2]} (Equation 11)
There may be five unknowns in these two equations Rrock, ∈rock, Rmud, ∈mud, and Δ. Rrock may be the property of interest that is used to create a formation model. Therefore, if three of these unknowns may be accounted for then Rrock may be calculated.
The measured impedance Z, the formation resistivity Rrock and the mud standoff Δ may be frequency independent parameters. Therefore, these frequency independent parameters may correspond to two unknown parameters that are fixed at a particular logging point irrespective of the number of frequencies used. The formation permittivity ∈rock may also be an unknown parameter. The unknown formation permittivity ∈rock may be included in the inversion. The formation permittivity ∈rock may be frequency dependent. Thus, the number of formation permittivities ∈rock to be inverted may be equal to the number of operating frequencies, or logging frequencies used. Alternatively, the inversion unit 510 may model the formation permittivity ∈rock as a polynomial function of frequency or in terms of any other functional form. Ideally we would like to have a minimum number of coefficients to describe this frequency dependence. We can then invert for these coefficients instead of the formation permittivity ∈rock. One example of an inversion may be given as follows:
∈rock=a1+a2ωn
where a1, a2, n1, n2 may be unknown coeffiecients which may be found by performing an inversion with the inversion unit 510. The number of coefficients may be fixed and therefore does not change with the number of logging frequencies used. Therefore, the number of unknowns due to the formation permittivity ∈rock may not increase with the number of frequencies if the coefficients are determined by inversion. Alternatively, we may also consider that Rrock is frequency dependent and ∈rock is frequency dependent, or that both are frequency dependent. The coefficients introduced to represent the frequency dependence can be inverted for by increasing the number of logging frequencies to make available a sufficiently large number of equations.
The downhole fluid properties, or mud properties, such as permittivity and conductivity, may also be frequency dependent, or function of the frequencies. The mud properties may be directly inverted for at each logging frequency. Alternatively, the mud properties may be expressed as a polynomial function of frequency or in any other functional form with a minimum number of coefficients. These coefficients may be determined by inversion using the inversion unit 510.
To determine the unknown parameters, or formation and/or downhole fluid properties Rrock, ∈rock, Rmud, ∈mud, and Δ, the inversion unit 510 may perform an inversion of the formation data and/or the mud data. The inversion may be an iterative process where guesses for the unknown properties Rrock, ∈rock, Rmud, ∈mud, and Δ are successively refined to reduce to a minimum the difference between the measured current values and corresponding values computed from a forward model, using as input the guessed values of the unknown parameters. In one example, equation 9 is the forward model. The functions Kmud and Krock may be specific to a particular downhole tool 104 (as shown in
The inversion unit 510 may perform forward modeling techniques to increase efficiency in representing tool responses. As an imaging tool may acquire large amounts of data, employing a full scale numerical model to calculate impedance or other tool responses may not be practical or time-efficient. A forward model may involve using a polynomial fitting of finite-element generated responses. For example, in one embodiment, a high order polynomial may be constructed with inputs of formation impedivity ξf=1/(jω∈0∈f+σf), mud impedivity ξm=1/(jω∈0∈m+σm), and mud standoff. The residuals of a polynomial fitting may be in relatively low range, for example, less than approximately 10%, and in some embodiments, less than 5%. Further, in some embodiments, more than one forward model may be used for increased accuracy, and the mismatch between more than one forward model may also be relatively low, for example, less than 5%.
In some embodiments, inversion techniques and/or forward modeling may also be used in combination with other calculations or estimations or models, such as analytic Jacobian calculations. For example, the sensitivities for model parameters (e.g., elements of a Jacobian matrix) may be derived by polynomial differentiation. Furthermore, forward modeling may be used in conjunction with interpolation from a look-up table.
Any suitable method of representing the behavior of the downhole tool 104 may be used. For example, a finite element (FE) modeling may be used to compute the formation sensor current, and/or the mud sensor current, for a particular downhole tool 104. The FE model may take into account the geometry and frequency of the downhole tool, and the materials used in its construction. It may also take into account the position of the downhole tool relative to the wellbore wall 130 and/or the mud cake 132, the size of the wellbore 106 and the materials inside and surrounding it. A large number of such FE simulations may be made to populate a representative volume of (Rrock, ∈rock, Rmud, ∈mud, and Δ) space, for the logging frequencies concerned. These numerical data may then be represented in an analytic form, such as equation 9 with the analytic functions Kmud and Krock. Using this inversion process, the formation resistivity Rrock, or inverted formation resistivity, may be determined.
The downhole tool 104 electronics may be difficult to calibrate at a high operating frequency. Therefore impedance measurements might have a systematic drift in the in-phase or out-of-phase components. The systematic drifts may be part of the unknowns to be inverted by the inversion unit 510.
If the mud parameters are not directly measured, for example by the mud sensor 202 (as shown in
The formation model unit 512 may construct a formation model from the formation properties obtained by the inversion unit 510. The formation model may be any suitable model for determining formation properties and/or the location of valuable downhole fluids such as hydrocarbons. The formation model may be constructed based on the formation resistivity Rrock. The formation model unit 512 may store, manipulate, and organize one or more formation models. The formation model may be an approximate model, or may be replaced by a tool model derived using 3D modeling. The 3D model may be constructed using the data from the inversion unit 510, for example the multi-frequency parametric inversion, to obtain the formation resistivity from the measured impedance.
The formation model may be constructed with one or more layer boundaries using inverted formation properties from measurements taken at multiple logging points in the wellbore 106 (as shown in
While each individual log point may have its own formation properties, the mud properties of an individual log point may be used for multiple log points in each inversion. Since mud properties may change with depth, the mud properties may be inverted periodically after initial segmentation. In one embodiment, the mud properties may be inverted for a relatively short interval (e.g., approximately less than 10 ft long). The mud properties may then be used to invert the sensor standoff and formation properties for longer log sections (e.g., approximately 200 ft or longer). The inversion may be run in multiple passes, iteratively refining the mud properties. In some embodiments, multiple inversions may be run for the same inversion outputs, and the accuracy of inversion outputs may be determined based on a comparison of the outputs from the multiple inversions.
Mud properties may also compensate for imperfect measurement calibration. In some embodiments, different mud properties may be assumed for each button. An inversion of multiple buttons may be conducted simultaneously, using common mud properties for a pad or group of pads. The calibration amplitude and phase may be solved. After mud properties are calibrated, a more accurate mud angle may be used in a suitable processing scheme. In some embodiments, the mud angle variation may also be taken into account based on changes observed in conventional mud angle logs.
The inversion unit 510 may also be used for inversion workflows which increase the efficiency of the inversion process. For example, in one embodiment, periodic inversions may be conducted after an initial segmentation. The inversion unit 510 may perform inversion on relatively smaller portions of the wellbore to reconstruct mud data from the formation. The mud data may be interpolated between these smaller portions of the wellbore to make assumptions on a larger zone of the wellbore. A full inversion may be conducted at a later time.
The wellbore optimizer unit 514 may use the formation model and/or any of the data stored in the formation imaging unit 118 to construct, optimize, change and/or create a well plan. The well plan may allow an operator, controller and/or driller to optimize the production of hydrocarbons from the wellsite. For example, the well plan may determine drilling trajectories, location of multiple wellbores, drilling methods, completion methods, production methods, and the like. The wellbore optimizer unit 514 may be an optional unit. Further, the wellbore optimizer unit 514 may be located offsite.
In the example as shown in
In phase signal=Re{Z}+∥Z∥*ran*δ% (Equation 13)
Out of phase signal=Im{Z}+∥Z∥*ran*δ% (Equation 14)
where ∥Z∥=√{square root over ([(Re{Z})2+(Im{Z})2]/2)}{square root over ([(Re{Z})2+(Im{Z})2]/2)} and ran is a random number. −1<ran<1. As shown in
The inversion unit 510 (as shown in
For the outputs shown in
Comparing all the outputs shown in
While the embodiments are described with reference to various implementations and exploitations, it will be understood that these embodiments are illustrative and that the scope of the inventive subject matter is not limited to them. Many variations, modifications, additions and improvements are possible. For example, additional sources and/or receivers may be located about the wellbore to perform seismic operations.
Plural instances may be provided for components, operations or structures described herein as a single instance. In general, structures and functionality presented as separate components in the exemplary configurations may be implemented as a combined structure or component. Similarly, structures and functionality presented as a single component may be implemented as separate components. These and other variations, modifications, additions, and improvements may fall within the scope of the inventive subject matter.
This application is a continuation-in-part of and claims the benefit of priority to co-pending U.S. Ser. No. 12/945,928, filed on Nov. 15, 2010, published as U.S. Patent Application No. 2012/0119744, the entire contents of which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12945928 | Nov 2010 | US |
| Child | 14210385 | US |
