1. Field of the Invention
The present invention relates to rock material characterization, and in particular to characterization of mechanical properties of formation rock from hydrocarbon reservoirs for geological and engineering purposes such as design and planning of well completion, well testing and formation stimulation.
2. Description of the Related Art
Characterization of the mechanical properties of formation rocks in subsurface hydrocarbon reservoirs has become an important feature for exploration and development of oil and gas. The data obtained from characterization has been used in a variety of ways. Characterization data has been used in well planning and completion and for numerous other purposes. Examples include assessing wellbore stability, hydraulic fracture design, mud weight design, geosteering, reservoir characterization, static and dynamic modeling, and reservoir simulation.
The study of geological strata involved on-site collection of geological samples from rock formations of the strata in the well bore while drilling. Characterization data about the mechanical properties of subsurface rock have been obtained by subjecting rock samples (obtained from geological strata at depths of interest in well bores through formations of interest in the reservoir) to special tests in the laboratory.
The collected geological sample material has been in the form of an elongated cylindrical body of rock known as a core sample. The samples once retrieved to the surface through the well were then transported to laboratories for analysis. The laboratories were by definition at some distance from the well and the samples had to be transferred to the lab for testing.
So far as is known, the rock mechanical properties, including strength of the rock sample have been determined from the core sample by testing what were known as core plugs (small cylindrical plugs) taken from the larger original core sample. The smaller plugs from the reservoir core sample are illustrated for example in U.S. Pat. No. 7,126,340, of which applicant is a named inventor. The core plugs taken would then be tested in various types of specialized rock testing equipment according to data requirements and mechanical properties of interest.
After the plugs were extracted, the larger original core sample was then cut or split along its longitudinal axis to expose the interior stratigraphic profile of the core material in a process which is commonly referred to as “slabbing”. The longitudinal section split off from the core sample comprising the core material was often referred to as a “slab”. After slabbing, a rock hardness test could then be conducted using what was known as a scratch test to measure another feature of the formation rock, its hardness. A measure of the hardness of formation rock has served as an indication of the resistance of the formation rock to fracture.
The existing methods to assess rock mechanical properties were thus conducted separately before or after the slabbing procedure. This has been time consuming and costly in terms of time and equipment. Further, existing rock characterization testing frequently did not meet short term or urgent operational needs for data necessary for well completion, well testing and stimulation.
Briefly, the present provides a new and improved computer implemented method of characterizing a mechanical property of formation rock from a subsurface reservoir from a core sample of the rock while the core sample is being cut by a slabbing machine. Data concerning forces applied to the core sample as the sample is being cut are obtained, and a ratio measure of the applied forces to an area measure of the cut sample is formed. An indication of the strength of the formation rock in the core sample is obtained from the formed ratio measure.
Data concerning forces applied in directions normal and tangential to a transverse core sample surface parallel to a longitudinal axis of the core sample are also obtained as the sample is being cut. A ratio measure of the tangential forces to the normal forces applied to the transverse core sample surface is then formed. An indication of the angle of internal friction of the formation rock in the core sample is then obtained from the formed ratio measure of the tangential forces to the normal forces.
The present invention also provides a new and improved data processing system for characterizing a mechanical property of formation rock from a subsurface reservoir from a core sample of the rock while the core sample is being cut by a slabbing machine. The data processing system includes a processor which obtains data concerning forces applied to the core sample as the sample is being cut, forms a ratio measure of the applied forces to an area measure of the cut sample, and obtains from the formed ratio measure an indication of the strength of the formation rock in the core sample. The data processing system also includes a memory storing a record of the obtained indication of the strength of the formation rock in the core sample, and an output device providing an output record of the obtained indication of the strength of the formation rock in the core sample.
The processor of the data processing system according to the present also obtains data concerning forces applied in directions normal and tangential to a transverse core sample surface parallel to a longitudinal axis of the core sample as the sample is being cut, then forms a ratio measure of the tangential forces to the normal forces applied to the transverse core sample surface, and obtains from the formed ratio measure an indication of the angle of internal friction of the formation rock in the core sample. The data processing system also includes a memory storing a record of the obtained indication of the angle of internal friction of the formation rock in the core sample, and an output device providing an output record of the obtained indication of the angle of internal friction of the formation rock in the core sample.
The present invention further provides a data storage device which has stored in a non-transitory computer readable medium therein computer operable instructions causing a data processor to characterize a mechanical property of formation rock from a subsurface reservoir from a core sample of the rock while the core sample is being cut by a slabbing machine. The stored instructions in the data storage device cause the processor to obtain data concerning forces applied to the core sample as the sample is being cut, form a ratio measure of the applied forces to an area measure of the cut sample, and obtain from the formed ratio measure an indication of the strength of the formation rock in the core sample.
The present invention further provides a data storage device which has stored in a non-transitory computer readable medium therein computer operable instructions to cause the processor to obtain data concerning forces applied in directions normal and tangential to a transverse core sample surface parallel to a longitudinal axis of the core sample as the sample is being cut, form a ratio measure of the tangential forces to the normal forces applied to the transverse core sample surface, and obtain from the formed ratio measure of the tangential forces to the normal forces an indication of the angle of internal friction of the formation rock in the core sample.
In the drawings, the letter B designates generally a core slabbing machine in which a core sample S is cut or split along its longitudinal axis to expose the interior stratigraphic profile of the core material. The core sample S is a cylindrical plug or body of formation rock obtained from a subterranean formation of interest and is, for example, usually ≦1 meter or so in length and ≦10 centimeters in diameter. The core sample or plug S is fixedly held in place with machine B while a motor driven saw blade 10 is moved along a longitudinal axis of the core sample S as indicated by an arrow 8. The saw blade 10 is provided with cutting surface of a material with adequate hardness, cutting strength and durability, such as a polycrystalline diamond material. The saw blade 10 is preferably a rotating cutting blade as shown by arrows 9 in
The saw blade 10 is mounted and driven by its associated motor for rotational cutting movement as it is advanced with respect to the core sample S for cutting purposes. The cutting procedure performed in the machine B is commonly referred to as “slabbing”, and the longitudinal section split off from the core sample is referred to as a “slab”.
The cutting machine B is preferably a machine-controlled one which controlled in its speed of movement based on controls provided as indicated schematically at 12, along with other input information, such as dimensions of the sample S, including its diameter and depth. The cutting machine is controlled to move at a constant rate of speed as it moves along the longitudinal axis of the sample S during cutting.
The core sample S is placed and secured such as by brackets of the conventional type in the machine B and the machine B serves as a rigid tool framework holding the sample in position as the cutting blade 10 advances through the sample during cutting. A conventional force-sensing dynamometer 14 is fixedly mounted with the frame of the machine B to sense forces imparted to the sample by the cutting blade 10 during cutting. The dynamometer is one capable of sensing forces along three mutually perpendicular axes, such as a Kistler 9251A three-dimensional piezoelectric force transducer or dynamometer from Kistler Instrument Corp.
The dynamometer 14 is located at a suitable position on the frame of the machine B and provides as outputs electrical signals corresponding to the magnitude of forces exerted between the saw blade 10 and the core sample S in three vector force measurements. Force measurements are thus obtained for processing according to the present invention as follows: the total force Ftotal exerted to cut the sample core at a constant rate of movement; measurement of the force Fn normal or perpendicular to the direction of such constant movement of the blade 10 to the longitudinal axis of the sample during cutting; and Ft the force parallel to the direction of constant speed cutting movement of the blade 10 to longitudinal axis of the sample S. The transformation of the measured vector forces along the three-dimensional axes into the required force measurements Ftotal, Fn and Ft for processing may be performed in the dynamometer/transducer 14 or during subsequent processing.
The electrical signals formed by the dynamometer 14 indicative of forces sensed are transferred to an amplifier bank or circuit 16 composed of separate charge amplifiers for each of the sensed forces. The amplifiers in circuit 16 amplify the force signals and convert them to voltage levels indicative of the sensed forces. The voltage level signals from the charge amplifiers 16 are provided to a data acquisition board 18 where computer compatible digital signals are formed corresponding in digital computer compatible form to the magnitude of forces sensed by the dynamometer 14. The digital signals so formed are transferred to a data processing system D (
As will be set forth, the data processing system D characterizes a mechanical property or properties of formation rock from a subsurface reservoir from the core sample S of the rock while the core sample is being cut by the slab cutting or slabbing machine B. The mechanical properties obtained according to the present invention include hardness or rock strength and angle of internal friction. Hardness of the core sample (strength) determined according to the present invention is an indication of the resistance of the formation rock to fracture. The angle of internal friction φ or friction angle of the core sample S is a measure of the ability of the formation rock to withstand a shear stress.
As illustrated in
The user interface 36 of computer 30 also includes a suitable user input device or input/output control unit 42 to provide a user access to control or access information and database records and operate the computer 30. Data processing system D further includes a database 44 stored in memory, which may be internal memory 34, or an external, networked, or non-networked memory as indicated at 46 in an associated database server 48. The database 44 can contain various data including: core sample dimensions, such as depth and diameter; movement speed of the saw blade 10; blade movement distance; cutting time measurements; forces as well as conventional data and records used in characterizing mechanical properties of formation rock.
The data processing system D includes program code 50 stored in memory 34 of the computer 30. The program code 50, according to the present invention system 30, is in the form of non-transitory computer operable instructions causing the data processor 32 to characterize mechanical properties of the formation rock of the core sample S while the sample is being cut by a slabbing machine B, as will be set forth.
It should be noted that rock characterization program code 50 may be in the form of microcode, programs, routines, or symbolic computer operable languages that provide a specific set of ordered operations that control the functioning of the data processing system D and direct its operation. The instructions of program code 50 may be may be stored in memory 34 of the computer 30, or on computer diskette, magnetic tape, conventional hard disk drive, electronic read-only memory, optical storage device, or other appropriate data storage device having a computer usable medium stored thereon. Program code 50 may also be contained on a data storage device such as server 48 as a non-transitory computer readable medium, as shown.
The computer 30 may also in some cases, if desired, be a mainframe computer of any conventional type of suitable processing capacity such as those available from International Business Machines (IBM) of Armonk, N.Y. or other source. As noted above other digital processors, however, may be used, as well.
In any case, the processor 32 of the computer 30 accesses the cutting data measurements from the slab cutting machine B to perform the logic of the present invention, which may be executed by the processor 32 as a series of computer-executable instructions. The instructions may also be contained on other forms of data storage device, as described above, with a computer readable medium, such as a computer diskette having a computer usable medium stored thereon containing computer operable instructions. The instructions are computer operable instructions causing the data processor computer 30 to characterize a mechanical property of the core sample S of the rock while the core sample is being cut by the slabbing machine B. The stored instructions are thus a computer program product causing the processor to perform a sequence of steps for this purpose:
The processor 32 of the computer 30 thus receives the data of interest from the slab cutting machine B during slabbing to perform the processing logic of the present invention, which is executed as a series of computer-executable instructions. The results of such processing are then available on output display 38.
A flow chart F (
It is important to note that, while the present invention has been, and will continue to be, described in the context of a fully functional computer system, those skilled in the art will appreciate that the present invention is capable of being distributed as a program product in a variety of forms, and that the present invention applies equally regardless of the particular type of non-transitory signal-bearing media utilized to actually carry out the distribution. Examples of non-transitory signal-bearing media include: recordable-type media, such as diskettes, hard disk drives, CD ROMs, floppy disks, and tangible media capable of storing the computer operable instructions.
As indicated at step 64, a ratio Ft/Fn of parallel force Ft to the normal force Fn is determined in real time by the processor 30, as well as a measure of the angle of internal friction φ, again as a function of cutting time or longitudinal distance of movement of the blade 10 through the sample S. During step 66, the results determined in real time during steps 62 and 64 are stored in the database 44 of formation rock characterization records. The results of completed processing, as well as other data and records, are available in real time during slabbing of core sample S, and are also subsequently available for review and analysis as also indicated in step 66. The angle of internal friction φ as a mechanical property of the core sample S is thus also characterized in real time as the sample is being slabbed in the machine B.
The processing results obtained as disclosed above are thus accomplished in real time during slabbing and the data results are readily and quickly available while the core sample is being cut in the slabbing machine B to characterize mechanical properties of formation rock.
The present invention thus measures mechanical properties of rock samples expediently and promptly. The present invention permits data to be obtained during the conventional process of slabbing the core sample. Thus mechanical properties of the core can be available concurrently while the sample is slabbed for other types of analysis and study.
The present thus saves time and money by simultaneously assessing mechanical properties of the formation rock while performing core slabbing. This enables support of operational needs at short turnaround times and low costs. It optimizes core usage and conserves the core sample for future needs.
The invention has been sufficiently described so that a person with average knowledge in the matter may reproduce and obtain the results mentioned in the invention herein Nonetheless, any skilled person in the field of technique, subject of the invention herein, may carry out modifications not described in the request herein, to apply these modifications to a determined structure, or in the manufacturing process of the same, requires the claimed matter in the following claims; such structures shall be covered within the scope of the invention.
It should be noted and understood that there can be improvements and modifications made of the present invention described in detail above without departing from the spirit or scope of the invention as set forth in the accompanying claims.
The present application is a divisional of, and claims priority to, co-pending, commonly owned U.S. patent application Ser. No. 12/876,634, filed Sep. 7, 2010.
Number | Date | Country | |
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Parent | 12876634 | Sep 2010 | US |
Child | 13949648 | US |