Microscopy offers scientists and engineers a way to gain a better understanding of the materials with which they work. Under high magnification, it becomes evident that many materials (including rock and bone) have a porous microstructure that permits fluid flows. Such fluid flows are often of great interest, e.g., in subterranean hydrocarbon reservoirs. Accordingly, significant efforts have been expended to characterize materials in terms of their flow-related properties including porosity, permeability, and the relation between the two.
Scientists typically characterize materials in the laboratory by applying selected fluids with a range of pressure differentials across the sample. Such injection tests often require weeks and are fraught with difficulties, including requirements for high temperatures, pressures, and fluid volumes, risks of leakage and equipment failure, and imprecise initial conditions. (Flow-related measurements are generally dependent not only on the applied fluids and pressures, but also on the history of the sample. Experiments should begin with the sample in a native state, but this state is difficult to achieve once the sample has been removed from its original environment.)
Accordingly, industry has turned to digital rock analysis to characterize the flow-related properties of materials in a fast, safe, and repeatable fashion. Efforts to increase the amount of information that can be derived from digital rock analysis are ongoing.
Accordingly, there are disclosed herein computed tomography (CT) systems and methods that determine rock property changes resulting from a treatment. In the drawings:
It should be understood, however, that the specific embodiments given in the drawings and detailed description below do not limit the disclosure. On the contrary, they provide the foundation for one of ordinary skill to discern the alternative forms, equivalents, and other modifications that are encompassed in the scope of the appended claims.
Disclosed herein are methods and systems for applying computed tomography (CT) analysis to improve understanding of the effects of treatment on rock core samples (plugs) or sub-samples. The rock core samples or sub-samples described herein may vary in size and may be obtained using known drilling techniques. The size of the rock core samples or sub-samples should be adequate to facilitate treatment as well as physical tests for determining properties of the rock samples or sub-samples such as porosity, permeability, and seismic velocity. Before and after a rock sample or sub-sample is treated, CT scanning of the rock core sample or sub-sample is performed. Without limitation to other examples, a suitable rock core sample may be approximately cylindrical with a radius of 10-20 mm and a length of 50-60 mm. Meanwhile, without limitation to other examples, sub-samples may be approximately cylindrical with a radius of 2-4 mm and a length of 5-10 mm.
As disclosed herein, image capture and digital rock physics (DRP) analysis may be applied to rock samples and sub-subsamples to determine rock properties such as porosity, permeability, and seismic velocity. However, if the porosity of a rock sample is not detectable by whole plug scanning, then one or more sub-samples are then extracted from the rock sample and scanned at a higher resolution to reveal a detectable porosity structure. Accordingly, extracting a sub-sample from a rock sample and capturing pre-treatment and post-treatment CT images of the sub-sample may be in response to determining that detectable porosity in at least one CT image of the rock sample is less than a threshold level (i.e., a higher resolution is needed to determine rock properties such as porosity, permeability, and seismic velocity).
In at least some embodiments, a sub-sample may subsequently be restored to its parent sample to enable standard physical tests and treatment on the parent sample and any related sub-samples. Alternatively, treatments and physical tests may be applied to a sub-sample while separated from its parent sample. After completion of a treatment, physical tests may be performed on rock samples (or sub-samples) to ascertain the effect of the treatments. Further, CT scanning of a parent sample and any sub-samples are performed again (the sub-samples may be removed again as needed) to enable an image-based comparison of a rock sample or sub-sample before and after the treatments. When analyzing the pre-treatment and post-treatment CT scans, image normalization operations (to normalize orientation, scaling, or color) may be performed. The results of comparing pre-treatment and post-treatment CT images may be recorded as a report that describes the effects of a treatment on a rock core sample (including any sub-samples). The report may include charts, histograms, joint histograms, distribution of changes between pre-treatment 2D/3D images and post-treatment 2D/3D images, segmented images, or other analysis comparison of pre-treatment and post-treatment CT images. Further, the report may relate pre-treatment CT image features or post-treatment CT image features with physical test parameters (pre-treatment or post-treatment) and/or with DRP parameters (pre-treatment or post-treatment). The report may include pre-treatment information or post-treatment information in various forms as described herein.
It should be understood that the treatments described herein may vary. Some treatments may be intended to increase permeability or porosity of a rock sample, while others are intended to decrease permeability or porosity of a rock sample. Further, some treatments may be carried out to test a particular treatment application technique. Further, some treatments are requested or performed by entities that do not know what the effect of the treatment on the rock sample will be.
Various operations are described herein such as pre-treatment CT scanning, pre-treatment physical tests, treatment, post-treatment physical tests, post-treatment CT scanning, and analysis of pre-treatment and post-treatment CT images. These various operations may be performed by the same entity or different entities. As an example and without limitation to other scenarios, CT scanning/analysis of samples and sub-samples may be performed by one entity as a service to at least one other entity interested in collecting information regarding the effect of treatments on a rock sample.
Without limitation to other drilling arrangements,
In addition to producing cuttings, the drill bit 32 also may collect a rock core sample 14 for later analysis as described herein. In various embodiments, downhole cutting tools such as drill bit 32 may collect rock core samples from any of the formations 18 along borehole 16 for later analysis. Additionally, cutting tools such as the drill bit 32 (or supplemental cutting tools along drill string 8) may extend in different directions (e.g., angled or horizontal) along the borehole 16 to collect sidewall core rock samples. The process of drilling for rock core samples may occur while the borehole 16 is being drilled or afterwards. More generally speaking, the rock core sample 14 may correspond to sidewall cores, whole cores, drill cuttings, outcrop quarrying samples, or other sample sources which can provide suitable samples for analysis using methods of the present disclosure.
X-ray signals captured by the CT scanner 100 may be stored and processed by the computer 60 to generate CT images (e.g., of rock sample 14 or sub-sample 15). The computer 60 also may provide one or more control signals (automatically or by user request) to initiate CT scanning operations. The illustrated computer 60 includes a chassis 62, an output device 64 (e.g., a monitor as shown in
As previously mentioned, the information storage media 68 may store a software program for execution by computer 60. For example, instructions of a software program may cause the computer 60 to collect data/images from CT scanner operations. Further, instructions of a software program may cause the computer 60 to normalize pre-treatment and post-treatment CT images. Further, instructions of a software program may cause the computer 60 to analyze/compare pre-treatment and post-treatment CT images as described herein. Further, instructions of a software program may cause the computer 60 to correlate variations in pre-treatment and post-treatment permeability, porosity, or seismic velocity of a rock sample with pre-treatment and post-treatment CT images. Various types of analysis are possible based on pre-treatment and post-treatment CT images, pre-treatment and post-treatment physical test data, and DRP data. The analysis of the data available from CT scanning, physical tests, and DRP analysis may result in generating charts to display information regarding a rock sample or sub-sample such as: pre-treatment porosity versus post-treatment porosity; pre-treatment permeability versus post-treatment permeability; formation factor versus porosity; pre-treatment porosity/permeability versus post-treatment porosity/permeability; pre-treatment velocity/porosity versus post-treatment velocity/porosity; pre-treatment compressional velocity versus post-treatment compressional velocity; pre-treatment shear velocity versus post-treatment shear velocity; correlation studies of pre-treatment/post-treatment porosity, pre-treatment/post-treatment permeability, or pre-treatment/post-treatment velocity; histograms based on pre-treatment/post-treatment porosity, pre-treatment/post-treatment permeability, or pre-treatment/post-treatment velocity; and profiles of average CT values as a function of depth for pre-treatment CT images and post-treatment CT images. Select pre-treatment CT images and post-treatment CT images as well as select charts may be included in a report. The report may be generated, for example, according to customer specifications for information and/or to highlight notable changes in a rock sample or sub-sample that has undergone a treatment. Further, the report may include joint histograms, distribution of changes between pre-treatment 2D/3D images and post-treatment 2D/3D images, segmented images. The report may include pre-treatment information or post-treatment information in various forms as described herein.
Typically, a user would employ a personal workstation 202 (such as a desktop or laptop computer) to interact with the larger system 200. Software in the memory of the personal workstation 202 causes its one or more processors to interact with the user via a user interface, enabling the user to, e.g., craft and execute software for processing the images acquired by the CT scanner 100. For tasks having small computational demands, the software may be executed on the personal workstation 202, whereas computationally demanding tasks may be preferentially run on the high performance computing platform 206.
Additionally or alternatively, other alignment marks that do not interfere (or minimally interfere) with treatment or physical tests may be added to rock sample 14 or sub-sample 15. For example, a material visible in CT scans may be added to rock sample 14 or sub-sample 15 to provide alignment marks. Further, pattern recognition software may be used to identify unique pattern characteristics of rock sample 14 or sub-sample 15 that enable alignment. As an example, the pattern recognition software may identify shapes, lines, or other unique marks in CT images. To align CT images (e.g., pre-treatment and post-treatment images), unique marks, patterns, or templates are compared to determine whether a match occurs. The orientation/size of unique marks, patterns, marker materials, or cuts in rock sample 14 or sub-sample 15 can also be used as input parameters for CT image rotation/scaling operations. The alignment and comparison of CT images using natural or man-made markers enables a treatment's effect on porosity or other rock attributes to be analyzed, charted, and reported as described herein.
At block 404, a pre-treatment CT scan of the rock sample 14 or sub-sample 15 is performed by a CT scanner. At block 406, pre-treatment physical rock property and fabric test parameters such as permeability (“K”), porosity (“P”), and seismic velocity (“V”) are determined for the rock sample. At block 408, treatment is applied to the rock sample 14 or sub-sample 15. At block 410, various post-treatment physical test parameters such as changes in distribution of properties and changes in rock fabric, K, P, or V are determined for the rock sample 14 or sub-sample 15. Post-treatment CT scanning is performed on the rock sample 14 or sub-sample 15 at block 412. At block 414, a comparison is performed to compare pre-treatment CT images with post-treatment CT images and/or to correlate CT images with pre-treatment K/P/V parameters or post-treatment K/P/V parameters. At block 416, a report is generated. Without limitation to other examples, the report of block 416 may report on: pre-treatment rock properties/fabric vs post-treatment rock properties/fabric; pre-treatment porosity versus post-treatment porosity; pre-treatment permeability versus post-treatment permeability; formation factor versus porosity; pre-treatment porosity/permeability versus post-treatment porosity/permeability; pre-treatment velocity/porosity versus post-treatment velocity/porosity; pre-treatment compressional velocity versus post-treatment compressional velocity; pre-treatment shear velocity versus post-treatment shear velocity; correlation studies of pre/post porosity, pre/post permeability, or pre/post velocity; histograms based on pre/post porosity, pre/post permeability, or pre/post velocity; and profiles of average CT values as a function of depth for pre-treatment CT images and post-treatment CT images. Further, the report of block 416 may include select pre-treatment CT images and post-treatment CT images. The information in the report of block 416 may be based on customer-specified criteria and/or notable changes identified by comparison of pre-treatment CT images with post-treatment CT images.
In some embodiments, CT scanning or other imaging technology may be employed to verify that the restoration of a sub-sample to its parent sample is successful. To be successful, the restoration should enable physical tests and/or treatment of the parent sample and its sub-sample(s). CT scanning may reveal, for example, the accumulation of adhesive material between a sub-sample and its parent sample in the direction of fluid flow for treatment. In such case, a sub-sample may be extracted and restored again until the restoration process is determined to be successful.
At block 510, CT scanning of the rock sample 14 with the restored sub-sample 15 is performed. Subsequently, treatment of the rock sample 14 with the restored sub-sample 15 is performed at block 512. At block 514, post-treatment CT scanning of the rock sample 14 with the restored sub-sample 15 is performed. At block 516, the sub-sample 15 is again extracted from the rock sample 14, after which the extracted sub-sample 15 is subjected to post-treatment CT scanning at block 518. At block 520, the pre-treatment and post-treatment CT scans of the rock sample 14 with the restored sub-sample 15 are compared. Further, the pre-treatment and post-treatment CT scans of the sub-sample 15 may be compared at block 520. Further, pre-treatment and post-treatment DRP-based parameters (e.g., K, P, V) for the sub-sample 15 may be compared at block 520. The comparisons of block 520 may be based on previous alignment operations, previous extraction operations to produce pre-treatment and post-treatment digital volumes that correspond to a physical volume, previous scaling operations, or previous color calibration operations. At the comparison step of block 520, CT images are correlated with each other, and may be correlated with physical test parameters or DRP-based parameters.
The pre-treatment and post-treatment DRP-based parameters for the sub-sample 15 may be determined at block 522. The comparisons of block 520 may be based on various computer programs that operate to align, scale, or color calibrate CT images, to correlate CT images with each other, and to correlate CT images with physical test parameters or DRP-based parameters.
The result of the comparisons of block 520 is a report 524, which may include the same or similar information as was described for the report 416 of
In some embodiments, processes 400 and 500 are combined. In other words, pre-treatment and post-treatment CT scans may be obtained for rock sample 14, sub-sample 15, or a combination sample (rock sample 14 with restored sub-sample 15) as described herein. Further, pre-treatment and post-treatment physical tests as described for steps 406 and 410 of process 400 as well as DRP analysis as described for step 522 may be employed to gather information that is correlated with pre-treatment and post-treatment CT images to generate a report regarding the effect of treatment on rock sample 14, sub-sample 15, or a combination sample (rock sample 14 with restored sub-sample 15).
For explanatory purposes, the operations of the foregoing processes and method have been described as occurring in an ordered, sequential manner, but it should be understood that at least some of the operations can occur in a different order, in parallel, and/or in an asynchronous manner.
Numerous variations and modifications will become apparent to those skilled in the art once the above disclosure is fully appreciated. In some embodiments, pre-treatment CT scanning operations, treatment operations, post-treatment CT scanning operations, and CT image analysis are performed by a single entity. Alternatively, one of more of the pre-treatment CT scanning operations, treatment operations, post-treatment CT scanning operations, and CT image analysis operations described herein may be performed by different entities.
It is intended that the following claims be interpreted to embrace all such variations and modifications.
This application claims priority to Provisional U.S. Application Ser. No. 61/706,505, titled “Computed Tomography (CT) Systems and Methods Analyzing Rock Property Changes Resulting from a Treatment” and filed Sep. 27, 2012 by Avrami Grader, Chuck Baldwin, and Carl Sisk, which is incorporated herein by reference.
Number | Date | Country | |
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61706505 | Sep 2012 | US |