Microanalysis of Fine Grained Rock for Reservoir Quality Analysis
1. A method of analyzing a rock sample, comprising:
- analyzing one or more large-area, low-resolution micrographs of the rock sample obtained with large-area, low-resolution microscopy and identifying and geo-locating areas requiring higher-resolution imaging;
selecting one or more analysis regions from the areas requiring higher-resolution imaging;
using multi-spectral imaging on the one or more analysis regions and thereby obtaining a corresponding one or more high-resolution, multi-spectral images; and
identifying one or more features of the rock sample from the corresponding one or more high-resolution, multi-spectral images.
A method of analyzing a rock sample includes analyzing one or more large-area, low-resolution micrographs to identify areas requiring higher-resolution imaging, and selecting one or more analysis regions from the areas requiring higher-resolution imaging. Multi-spectral imaging is used on the one or more analysis regions to obtain one or more high-resolution, multi-spectral images, and one or more features of the rock sample are identified from the corresponding one or more high-resolution, multi-spectral images. The method further includes upscaling the one or more high-resolution, multi-spectral images and thereby geo-locating the features of the rock sample to key regions of the rock sample.
- 1. A method of analyzing a rock sample, comprising:
analyzing one or more large-area, low-resolution micrographs of the rock sample obtained with large-area, low-resolution microscopy and identifying and geo-locating areas requiring higher-resolution imaging; selecting one or more analysis regions from the areas requiring higher-resolution imaging; using multi-spectral imaging on the one or more analysis regions and thereby obtaining a corresponding one or more high-resolution, multi-spectral images; and identifying one or more features of the rock sample from the corresponding one or more high-resolution, multi-spectral images.
- View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
- 13. An apparatus, comprising:
one or more processors; and a memory having embodied thereon processor executable instructions that, when executed by the one or more processors, cause the apparatus to; identify and select one or more key regions of a rock sample based on one or more attributes of the rock sample; analyze one or more optical thin sections of the rock sample with large-area, low resolution microscopy and thereby obtain one or more large-area, low-resolution micrographs; analyze the one or more large-area, low-resolution micrographs and identifying areas requiring higher-resolution imaging; select one or more analysis regions from the areas requiring higher-resolution imaging; use multi-spectral imaging on the one or more analysis regions and thereby obtain a corresponding one or more high-resolution, multi-spectral images; and identify one or more features of the rock sample from the corresponding one or more high-resolution, multi-spectral images.
- View Dependent Claims (14, 15, 16, 17, 18, 19, 20)
This application claims the benefit of U.S. Provisional Application No. 62/753,566 entitled “Microanalysis of Fine Grained Rock for Reservoir Quality Analysis” that was filed on Oct. 31, 2018, the disclosure of which is incorporated herein by reference.
The productivity of reservoir rocks is related to many rock properties, among them porosity, the composition of pore lining materials, and mineral fabric. These features are commonly examined by optical microscopy for conventional rocks, which provides a favorable alignment between high enough resolution to image the pore lining materials (e.g., few micrometers scale) as well as the laminae fabric variability (e.g., millimeter scale). As a result, optical microscopy of thin sections is a mainstay of geology.
Fine-grained rocks, such as mudstones, however, present a significant challenge. In mudstones, for instance, mineral grains and the intervening cements and associated pores are present in the micrometer to sub-micrometer range, which is well below optical resolution. Nonetheless, mudstone bedding and laminae scale variability are also important, and these features exist at millimeter scales that typically require large-area analysis. The fine-grained nature of the constituent phases of mudstones and their varying origin is crucial when they are being considered as targets for optimizing recovery engineering strategies and defining their performance as hydrocarbon source rocks and seals. Knowledge of the mineral type and distribution at various length scales, along with the spatial relationships between grains, is fundamental to developing these engineering strategies.
Imaging techniques can span many decades in size, but co-locating (e.g., geo-locating) high-resolution images within larger area, lower-resolution images can be difficult. To draw more accurate conclusions about reservoir quality, there is a need for large area, high-resolution (“fine-resolution”) rock imaging. There is also a need to account for rock structure at several scales.
Background references may include European Patent No. 1938281 B1, U.S. Pat. No. 8,967,249, and U.S. Patent Application Publication Nos. 2013/0257424 and 2015/0355158. Additional background references may also include Anders et al., “Microfractures: A Review”, Journal of Structural Geology, Vol. 69, Part B, pp. 377-394 (2014); Hiatt et al., “A Review of Applications for Understanding Diagenesiss, Reservoir Quality, and Pore System Evolution”, Cathodoluminescence Petrography of Carbonate Rocks, Mineralogical Association of Canada Short Course 45, pp. 75-96 (2014); and Lai et al., “Origin and Distribution of Carbonate Cement in Tight Sandstones: The Upper Triassic Yanchang Formation Chang 8 Oil Layer in West Ordos Basin, China”, Geofluids, Volume 2017, p. 1-13 (2017).
The following figures are included to illustrate certain aspects of the present disclosure, and should not be viewed as exclusive embodiments. The subject matter disclosed is capable of considerable modifications, alterations, combinations, and equivalents in form and function, without departing from the scope of this disclosure.
The present disclosure is related to petrography and, more particularly, to large-area microanalysis for fine-grained rocks.
Before the present methods and systems are disclosed and described, it is to be understood that the methods and systems are not limited to specific methods, specific components, or to particular implementations. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting.
Capturing the small-scale variability in a rock sample, while simultaneously determining and analyzing larger-scale variability can prove advantageous. The methods described herein help facilitate examination of large-scale texture components and structural and compositional trends of the rock simultaneously with very small features of the rock provided through high-resolution data. More specifically, embodiments of the present disclosure address the challenge of high-spatial resolution and extended area analysis in petrographic evaluation for fine-grained rocks, such as mudstones, which host abundant supplies of tight oil and shale gas reservoirs. For fine-grained rocks, it can be advantageous to determine the type and distribution (location) of grains and the location of pores present therein. Some grains are reactive and dissolve over time to cement adjacent grains together, but dissolution sometimes makes holes in the rock, thus resulting in intragranular porosity.
The presently disclosed methods help an analyst determine where the grains are, which grains are actual grains, which grains are instead cement, and what the porosity is located relative to grain and cement distribution. Understanding such features of a rock is important as porosity equates to hydrocarbon storage capacity, and once the characteristics and chemistry of the grains are determined, an informed determination of how the rock will respond to hydraulic fracturing may be made. As will be appreciated, this may lead to improved estimates of the quality of rock resources for oil and gas extraction.
With any petrographic imaging method, an analyst (e.g., a geologist) must define what rock features are important to image and what signal type can highlight those features. Additionally, the analyst must balance between information content, acquisition time, analysis time, and data file size. In analyzing fine-grained rocks, the methods described herein utilize various imaging methods including, but not limited to, optical microscopy imaging, backscattered electron imaging (“BSI”), elemental imaging via both energy dispersive x-ray spectroscopy (“EDS”) and wavelength dispersive x-ray spectroscopy (“WDS”), and spectrally-resolved cathodoluminescence (“CL”). Resulting data sets can be hyperspectral in nature, with full EDS and CL spectra obtained at each pixel, along with intensity information from electron detectors, optical microscopy, and WDS. Through spatial correlation (i.e., geo-locating) of these data, a rich description of the rock under study emerges. These data are particularly useful for elucidating porosity types and evolution through diagenesis.
Analysis of fine-grained rock tight reservoirs shows there is a significant compositional and grain origin variability visible at pore, lamina, and bed scales. These differences are controlled by varying starting compositions of the constituent as well as differences in the subsequent fluid flux through the different layers. This variability means that upscaling from small field of view (i.e., very high resolution), to optical thin section (i.e., large-area, low-resolution microscopy), to core, to well performance, without knowledge of the variability between the component elements, is almost impossible. In contrast, the presently described methods facilitate upscaling of high-resolution, multi-spectral images and relying on geolocation to place the high-resolution data into a broader context through linkage to larger-scale features of a rock sample.
According to methods described herein, a petrographic analyst (i.e., a geologist) may first identify and select key regions of a rock sample that have one or more attributes of interest. The rock sample may comprise a hand specimen sized sample of a fine-grained rock obtained from a geological region of interest. In some cases, the sample may originate from a downhole core sample obtained via a subsurface sampling operation. In other cases, the rock sample may alternatively comprise an exposure sample obtained from a surface location (e.g., an open quarry or the like). Example attributes of interest identifiable by the geologist in selecting key regions include the formation name, key mineral contents (e.g., quartz, carbonate, solid organic concentrations, etc.), spatial distribution of mineral phases and their composition within the sample (e.g., grans versus cement), fabrics visible (e.g., ripples, parallel bedding, etc.), grain origins, fossils present, organic carbon type, grain size of depositional components, depth in the well, porosity, and biostratigraphic context.
Once the key regions of the rock sample have been identified, one or more optical thin sections of the rock sample may be extracted at those key regions for further analysis. As used herein, the term “optical thin section” refers to a thin section (i.e., slice) of a rock sample suitable for performing light optical microscopy. The geologist may analyze the extracted optical thin sections of the rock sample using light optical large-area, low-resolution microscopy; high-resolution scanning on a computer scanner; confocal microscopy; fluorescence; and/or cathodoluminescence, and thereby obtain one or more large-area, low-resolution micrographs. These micrographs would typically show features that range from centimeters to micrometers in size. Example large-area, low-resolution microscopy technologies that may be used to obtain the large-area, low-resolution micrograph(s) include, but are not limited to, optical microscopy (also referred to as polarized light microscopy) and low magnitude (resolution) backscatter electron microscopy.
The large-area, low-resolution micrograph of each optical thin section may reveal particular mineralogical and fabric attributes of interest, or particular regions of the optical thin section where these attributes are (or might be) present. Some of the mineralogical and fabric attributes may comprise large-scale texture components identifiable by the geologist at the low-scale resolution. Since these features are identifiable, the petrographic analysis of these regions may be complete at this point and the data may be compiled for consideration. Other revealed texture components, however, may be present in the micrometer to sub-micrometer range, and thus may not be ascertainable at the large-area, low-resolution scale. Rather, such features may require higher-resolution imaging techniques to reveal their compositional and spatial distributions. Such texture components can include, for example, mineralogical and fabric attributes of the rock sample such as, but not limited to, mineral grains, presence of organic carbon, intervening cements, and associated pores (e.g., intragranular porosity, grain dissolution porosity, fracture porosity, and/or intercrystalline porosity).
At low magnification (i.e., thin section scale or lamina scale resolution), the two imaging methods of
According to embodiments of the present disclosure, one or more analysis regions may be identified and selected from a large-area, low-resolution micrograph of an optical thin section of the rock sample, and such regions may be analyzed using a multi-spectral imaging mode (technology) to enable more detailed characterization of such regions and thereby build an integrated picture of what cannot be observed with large-area, low-resolution microscopy. By geo-locating images derived from multiple techniques across scales, a geologist is able to maintain spatial context with information derived from a suite of analytical methods. This may prove advantageous in helping a geologist determine and understand how the reservoir from where the rock sample originated is constituted (put together).
In the depicted example, the size of the analysis regions 302 to 310 is indicative of the type of multi-spectral imaging used, the measurement time, and the computing power necessary to generate the corresponding high-scale micrograph (e.g., a quanta of data). The type of multi-spectral imaging may be selected, at least in part, by considering a desired image resolution, the time required to obtain the desired image resolution, and a maximum data set size. In some cases, there may be a trade-off between time and image quality, the longer the analysis (imaging) time, the higher the resulting resolution. In contrast, the shorter the analysis (imaging) time, the lower the resulting resolution. Moreover, another consideration may be potential damage to the sample that is caused by lengthening the analysis time as prolonged exposure of a sample to electron beams may physically damage the sample over time.
As the analysis regions 302 to 310 depicted in
It is noted that the data represented by the images of
Understanding the controls on the differences between the closely spaced laminae in the rock sample depicted in
In some embodiments, the CL image may be displayed with a variety of colors, where each color indicates a different grain origin, a different cement type, porosity, etc. Moreover, the data can be processed to look at the energy of a specific x-ray, which may be indicative of a particular atomic element, and thus ascertain chemistry of the rock sample. For example, the computer may be programmed to color-code various atomic elements, e.g., red=iron (Fe), green=calcium (Ca), blue=aluminum (Al), etc. In other embodiments, however, the CL image may be produced or otherwise displaced with gray scale intensities rather than color. In such embodiments, the intensity of the signal may be proportional to the brightness of the gray scale value.
The high-resolution, multi-spectral images at pore/grain scale essentially provide a chemical map that can be analyzed to identify important rock sample features including, but not limited to, grain shape, grain size, grain location (distribution), porosity, intervening cements, composition of constituent materials, chemistry, mineralogy, mineral fabric, etc. More specifically, in the resulting high-resolution, multi-spectral image, there are multiple pixels, and each pixel contains information (e.g., BSI, EDS, WDS, CL, etc.). In some embodiments, an expert (e.g., a geologist) may analyze the multi-spectral images to identify the important rock sample features and link these features together into a statement about their likelihood of being a grain (e.g., a fine grain, a coarse grain, grain shape, etc.), a cement, a pore, etc. If all the grains are cemented together, that rock will likely be very strong and brittle causing it to fracture (fail) during hydraulic fracturing. If the grains are generally not cemented together, however, they will tend to slide past one another during hydraulic fracturing and “bend” instead of fracture with the rock being ductile.
As will be appreciated, pixel scale registration of the high-resolution data may facilitate automation of the manual task undertaken by a geologist of identifying the important rock sample features mentioned above. More specifically, computer software may be programmed to simultaneously process the high-resolution data for image object identification, and elemental and mineralogical mapping. Moreover, it may be possible to train (program) a computer to recognize the results from cathodoluminescence, e.g., all the material in red is a specific grain, cement, pore space, etc. In some embodiments, the high-resolution data may be processed using a combination of machine learning and coded image analysis, or alternatively this may be done with hard software code. This additional step automates the analysis to reveal more about the rock.
The present methods and systems may further include upscaling the high-resolution, multi-spectral image(s) relying on geolocation to place the high resolution data into a broader context through linkage to larger-scale features of the rock sample. More specifically, relying on the fact that each multi-spectral image has the same location in the rock sample, the higher-resolution images can be geo-located on larger-scale (lower-resolution) optical micrographs (e.g.,
The present disclosure describes or otherwise discloses components that can be used to perform the disclosed methods and systems. These and other components are disclosed herein, and it is understood that when combinations, subsets, interactions, groups, etc. of these components are disclosed that while specific reference of each various individual and collective combinations and permutation of these may not be explicitly disclosed, each is specifically contemplated and described herein, for all methods and systems. This applies to all aspects of this application including, but not limited to, steps in disclosed methods. Thus, if there are a variety of additional steps that can be performed it is understood that each of these additional steps can be performed with any specific embodiment or combination of embodiments of the disclosed methods.
As will be appreciated by one skilled in the art, the methods and systems may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the methods and systems may take the form of a computer program product on a computer-readable storage medium having computer-readable program instructions (e.g., computer software) embodied in the storage medium. More particularly, the present methods and systems may take the form of web-implemented computer software. Any suitable computer-readable storage medium may be utilized including hard disks, CD-ROMs, optical storage devices, or magnetic storage devices.
Embodiments of the methods and systems are described herein with reference to block diagrams and flowchart illustrations of methods, systems, apparatuses and computer program products. It will be understood that each block of the block diagrams and flowchart illustrations, and combinations of blocks in the block diagrams and flowchart illustrations, respectively, can be implemented by computer program instructions. These computer program instructions may be loaded onto a general purpose computer, a special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions that are executed on the computer or other programmable data processing apparatus create a means for implementing the functions specified in the flowchart block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including computer-readable instructions for implementing the function specified in the flowchart block or blocks. The computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process such that the instructions that execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart block or blocks.
Accordingly, blocks of the block diagrams and flowchart illustrations support combinations of means for performing the specified functions, combinations of steps for performing the specified functions and program instruction means for performing the specified functions. It will also be understood that each block of the block diagrams and flowchart illustrations, and combinations of blocks in the block diagrams and flowchart illustrations, can be implemented by special purpose hardware-based computer systems that perform the specified functions or steps, or combinations of special purpose hardware and computer instructions.
Therefore, the disclosed systems and methods are well adapted to attain the ends and advantages mentioned as well as those that are inherent therein. The particular embodiments disclosed above are illustrative only, as the teachings of the present disclosure may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular illustrative embodiments disclosed above may be altered, combined, or modified and all such variations are considered within the scope of the present disclosure. The systems and methods illustratively disclosed herein may suitably be practiced in the absence of any element that is not specifically disclosed herein and/or any optional element disclosed herein. While compositions and methods are described in terms of “comprising,” “containing,” or “including” various components or steps, the compositions and methods can also “consist essentially of” or “consist of” the various components and steps. All numbers and ranges disclosed above may vary by some amount. Whenever a numerical range with a lower limit and an upper limit is disclosed, any number and any included range falling within the range is specifically disclosed. In particular, every range of values (of the form, “from about a to about b,” or, equivalently, “from approximately a to b,” or, equivalently, “from approximately a-b”) disclosed herein is to be understood to set forth every number and range encompassed within the broader range of values. Also, the terms in the claims have their plain, ordinary meaning unless otherwise explicitly and clearly defined by the patentee. Moreover, the indefinite articles “a” or “an,” as used in the claims, are defined herein to mean one or more than one of the elements that it introduces. If there is any conflict in the usages of a word or term in this specification and one or more patent or other documents that may be incorporated herein by reference, the definitions that are consistent with this specification should be adopted.
As used herein, the phrase “at least one of” preceding a series of items, with the terms “and” or “or” to separate any of the items, modifies the list as a whole, rather than each member of the list (i.e., each item). The phrase “at least one of” allows a meaning that includes at least one of any one of the items, and/or at least one of any combination of the items, and/or at least one of each of the items. By way of example, the phrases “at least one of A, B, and C” or “at least one of A, B, or C” each refer to only A, only B, or only C; any combination of A, B, and C; and/or at least one of each of A, B, and C.