Microresistivity Images Research Articles

An efficient discontinuous Galerkin finite element method with nested domain decomposition for simulations of microresistivity imaging

A discontinuous Galerkin finite element method is employed to study the responses of microresistivity imaging tools used in the oil and gas exploration industry. The multiscale structure of an imaging problem is decomposed into several nested subdomains based on its geometric characteristics. Each subdomain is discretized independently, and numerical flux is used to couple all subdomains together. The nested domain decomposition scheme will lead to a block tridiagonal linear system, and the block Thomas algorithm is utilized here to eliminate the subdomain based iteration in the step of solving the linear system. Numerical results demonstrate the validity and efficiency of this method.

Integrated Fracture Delineation in Volcanics, Junggar Basin, China

Fracture effectiveness, extension and connectivity from borehole surface into deep formation are the key factors to control producibility of volcanic formations. A systematic and integrated fracture delineation approach was set up which integrated available measurements with multi-scale depth of investigation to cover borehole surface, near wellbore and deep formation. High resolution micro-resistivity image was used to identify fractures on the borehole surface; shear anisotropy enhanced by dispersion analysis was used to evaluate fractures away from the borehole; Borehole acoustic reflection survey technique was applied in vertical wells to assess probable fracture networks deep into formation up to maximal 10 meters. This multi-scale approach had been implemented in multiple wells drilled in volcanic formations in Junggar basin, which helped a lot on fracture evaluation and productivity estimation.

Borehole Imaging Technology Visualizes Photorealistically in Oil-Based Muds

Technology Update To estimate reserves, optimize well recovery, and place future development wells more accurately, operators require increasingly detailed understanding of complex oil and gas reservoirs. High-resolution geological data from the borehole— core samples and wireline microresistivity images—are essential to fully characterize reservoir architecture, guide and constrain reservoir models, and make timely decisions with precision and confidence. In unconventional resource plays, for example, geologists need to observe complex natural fracture systems, measure fracture density and direction, determine in-situ stresses, and calculate pressures required to initiate and propagate optimal hydraulic fracturing. In high-cost deepwater environments, exploration teams need to interpret a wide variety of sedimentary facies. Reservoirs often consist of thinly laminated sands or channels, which demand high-definition methods for visualization and interpretation. Typically, deepwater formations exhibit very low resistivities— from 1 ohm-m in shales to as low as 0.2 ohm-m in water-bearing sands. Operators often use whole cores to identify subtle sedimentary facies, but cores can be expensive and time-consuming to acquire. Thus, core samples are usually obtained only in select wells and in the most critical intervals. The resulting lack of geological detail can adversely affect reservoir analysis, interpretation, and modeling. On the other hand, microelectrical borehole images can be acquired continuously over the openhole interval at any depth or in any formation, with relative ease. Until recently, high-definition borehole imaging has been possible only in electrically conductive water-based muds (WBM). However, most deepwater wells and many unconventional shale wells today are drilled with high-performance, nonconductive oil-based muds (OBM). Legacy OBM borehole imaging tools, which were introduced in the last decade, are a significant technical advancement over the preceding dipmeter tools but still exhibit certain limitations. For example, spatial image resolution in OBM is nowhere near the quality obtained from WBM imagers. The lack of circumferential coverage of the borehole leaves large gaps that must be filled by inference.

Advanced aquifer characterization for optimization of managed aquifer recharge

Managed aquifer recharge (MAR) will play an increasingly important role in solving water scarcity. The performance of MAR systems depends primarily upon local hydrogeology. Greatest opportunities for improvement in the implementation of MAR systems lie in the targeted application of conventional and advanced technologies to improve aquifer characterization. Surface geophysics (e.g., VES, TDEM, and seismic reflection and refraction) generally provide low resolution, but areal extensive data on subsurface hydrogeology. Times series of relative microgravity measurements have been used to map changes in both vadose and phreatic zone storage and to augment monitoring well systems. Surface nuclear magnetic resonance (NMR) has the potential to provide quantitative data on water-filled porosity and pore size distribution and, in turn, an estimate of hydraulic conductivity. Standard borehole geophysical logging techniques can provide coarse-scale data on aquifer heterogeneity. Advanced borehole logging techniques, such as NMR, microresistivity imaging, and gamma ray spectroscopy, have been used in MAR projects in the USA and UAE to provide fine-scale petrophysical data (e.g., porosity, porosity-types, and pore-size distribution). Groundwater modeling is used in MAR investigations to evaluate system feasibility and to optimize system design and operation. Opportunities to improve groundwater modeling exist through the application of advanced reservoir simulation platforms that allow for the processing and integration of available lithological, geophysical, and aquifer testing data and their subsequent incorporation into groundwater flow models. Advanced groundwater modeling programs are available that allow for the simulation of complex aquifers such as dual-porosity systems and variable density.

Microresistivity borehole image inpainting

Images rendered from measurements made by wireline microresistivity imaging tools include longitudinal gaps whenever the well circumference exceeds the total width of the pad-mounted electrode arrays. The fraction of an image containing null data depends on tool design, and it is commonly approximately 30% for 261 mm (8.5 in.)-bit size wells increasing to approximately 50% in 311 mm (12.25 in.) wells. We use cues from the measured parts to infer information missing from the gaps; a method has been developed that simulates the process by decomposing the measured parts into their morphological components using sparse representations of multiscale multiorientation transforms, then recomposing the full-bore image assuming it to be efficiently represented by the transform’s elemental bases. The approach was evaluated using real data sets with a variety of geologic features, including full-coverage images from small diameter wells artificially obscured to simulate images from larger diameter wells. For borehole images dominated by curvilinear features, reconstructions from artificially obscured images were visually indistinguishable from the original unobscured images for a broad range of coverage loss and for all apparent dip angles below near-vertical, regardless of degree of parallelism (or lack thereof). Successful reconstruction of near-vertical features (including those with complex boundaries such as breakouts) was more dependent on coverage loss, but in these cases, the results were consistent with judgments made by interpreters. Therefore, we found that inpainting provides a consistent starting point for reproducible quantitative geologic analysis, and it is an enabler for automated feature recognition.

Automated detection of planar geologic features in borehole images

The interpretation of borehole images begins with the detection and classification of features—a time-consuming manual process subject to variations between interpreters. In seeking to automate the detection part for the most frequently picked features (which in circumferential images from clastic rock environments are sinusoids corresponding to planar or subplanar bedding surfaces and fractures), it is not necessary to pick all instances, but it is necessary to pick sufficient representative instances to satisfy the interpretation objective, accounting for a broad range of apparent dips, and allowing for the likelihood of fractures crossing bedding surfaces. A key challenge in this context is the minimization of false picks, as manual corrections would potentially negate the principal benefit of automation. A fast nonsubjective method is described for the detection of prominent discontinuities and the calculation of associated dip angles. It combines a gradient based approach for edge detection with a phase congruency method for validation, followed by a robust sinusoid detection technique. It has been evaluated on microresistivity images from wireline and logging-while-drilling tools, these images having a wide range of features with varying degrees of geologic complexity; the proportion of false positives in the case of noisy data is less than 5%, improving to better than 2% in the case of good-quality data. In contrast to manual picking, the method is fast and gives reproducible results. With potentially thousands of sinusoids in a single image, the method dramatically improves efficiency.

Using formation micro-imaging, wireline logs and onshore analogues to distinguish volcanic lithofacies in boreholes: examples from Palaeogene successions in the Faroe–Shetland Basin, NE Atlantic

Abstract Formation micro-imaging (FMI) is a tool that produces micro-resistivity images of the sidewall of the well bore. FMI logging used in conjunction with conventional well logging techniques (e.g. GR, Gamma Ray/RES, Resistivity/NPHI, Neutron Porosity/SONIC, Velocity tools) allows detailed analysis of volcanic lithofacies variation and informs a robust interpretation of volcanic sequences. This methodology is of particular use where rock core data are limited or not present. Examples are presented from the Rosebank Field in the Faroe–Shetland Basin (West of Shetland, UK continental shelf) where the re-establishment of fluvial activity between phases of effusive volcanism resulted in a complex sequence of siliciclastic sedimentary rocks and basaltic lavas. We demonstrate how high-resolution FMI images through this sequence can differentiate internal basalt lava flow features, such as vesicular zones, brecciated intervals, sediment–lava contact relationships and joint/fracture networks. If FMI data exist through volcanic packages and if assessed and calibrated properly via core, sidewall core and field analogue comparisons, it can provide additional constraints on the interpretation and classification of reservoir (siliciclastic) and non-reservoir (volcanic) rocks.

Numerical simulation and fracture evaluation method of dual laterolog in organic shale

Abstract Fracture identification and parameter evaluation are important for logging interpretation of organic shale, especially fracture evaluation from conventional logs in case the imaging log is not available. It is helpful to study dual laterolog responses of the fractured shale reservoir. First, a physical model is set up according to the property of organic shale, and three-dimensional finite element method (FEM) based on the principle of dual laterolog is introduced and applied to simulate dual laterolog responses in various shale models, which can help identify the fractures in shale formations. Then, through a number of numerical simulations of dual laterolog for various shale models with different base rock resistivities and fracture openings, the corresponding equations of various cases are constructed respectively, and the fracture porosity can be calculated consequently. Finally, we apply this methodology proposed above to a case study of organic shale, and the fracture porosity and fracture opening are calculated. The results are consistent with the fracture parameters processed from Full borehole Micro-resistivity Imaging (FMI). It indicates that the method is applicable for fracture evaluation of organic shale.

Present‐day principal horizontal stress orientations in the Kumano forearc basin of the southwest Japan subduction zone determined from IODP NanTroSEIZE drilling Site C0009

A 1.6 km riser borehole was drilled at site C0009 of the NanTroSEIZE, in the center of the Kumano forearc basin, as a landward extension of previous drilling in the southwest Japan Nankai subduction zone. We determined principal horizontal stress orientations from analyses of borehole breakouts and drilling‐induced tensile fractures by using wireline logging formation microresistivity images and caliper data. The maximum horizontal stress orientation at C0009 is approximately parallel to the convergence vector between the Philippine Sea plate and Japan, showing a slight difference with the stress orientation which is perpendicular to the plate boundary at previous NanTroSEIZE sites C0001, C0004 and C0006 but orthogonal to the stress orientation at site C0002, which is also in the Kumano forearc basin. These data show that horizontal stress orientations are not uniform in the forearc basin within the surveyed depth range and suggest that oblique plate motion is being partitioned into strike‐slip and thrusting. In addition, the stress orientations at site C0009 rotate clockwise from basin sediments into the underlying accretionary prism.

Optimum well trajectory design in a planned well in Blacktip field, Australia: a case study

A geomechanics study carried out in the Blacktip field, offshore Australia led to optimum wellbore deviation and azimuth to minimise drilling-associated instability problems near a major fault in the field. Elastic and strength properties of the formations and magnitude of principal stresses in the field were estimated from a mechanical earth model (MEM) based on offset well data. The direction of the minimum horizontal stresses was predicted from formation microresistivity image (FMI) logs available in offset wells. The MEM results were calibrated using results from laboratory experiments, well tests and drilling incidents from drilling reports. The MEM showed that formations at the lower section of the well are very competent and have high uniaxial strength; however, most of the failures in the form of breakouts observed from calliper and image logs were in this interval. Therefore, obtaining a good match between the model and observed failures required a large stress anisotropy to be considered for the lower section of the wellbore. Further investigations demonstrated that this is because the wellbore trajectory at deeper depth gets closer to the major fault plane, and this large stress anisotropy is due to the stress redistribution near the fault. The data from offset well was mapped into the planned trajectory, and the selection of the optimum trajectory and a stable mud weight window for the appropriate section led to successful drilling of the deviated well.

Application of advanced borehole geophysical logging to managed aquifer recharge investigations

Communities and water utilities are increasingly being forced to implement more hydrogeologically complex alternative water supply and storage options to meet increasing freshwater demands. The performance of managed aquifer recharge projects, including aquifer storage and recovery, is controlled by the movement and mixing of stored freshwater and native groundwater, and fluid–rock interactions, which, in turn, are strongly influenced by aquifer heterogeneity. Advanced borehole geophysical logging techniques developed for the oil and gas industry such as neutron-gamma ray spectroscopy, microresistivity imaging, and nuclear magnetic resonance, can provide hitherto unavailable fine-scale data on porosity (total and effective), hydraulic conductivity, salinity, and the mineralogical composition of aquifers. Data on aquifer heterogeneity obtained from advanced borehole geophysics logs, combined with information on larger-scale aquifer hydraulics obtained from pumping tests, have the potential for improving aquifer characterization and modeling needed for feasibility assessments and the design and optimization of the operation of managed aquifer recharge systems.

Microresistivity Imaging Technology Adapted for Wells Drilled With Nonconductive Muds

Technology Update - No abstract available.

Distribution of Upper Cenozoic Carbonate-Cemented Sandstones, Kuche Depression, Northwest China: Insights from High-Resolution Borehole Micro-Resistivity Imaging

ABSTRACT High-resolution micro-resistivity images are used to study the distribution of neoformed carbonate concretions in Upper Cenozoic shallowly buried fluvial sandstones in the Kuche Depression, northwest China. The carbonate concretions are high-resistivity white facies on borehole images. Most of them occur as patches 1-40 cm thick and in shapes ranging from equant, oblate, to elongate. These concretions contrast markedly with the poorly cemented or uncemented host sandstones, which appear as dark to immediate grayscale facies on the images. Three patterns of occurrence of carbonate concretions are identified: isolated concretions, discontinuously cemented layers, and continuously cemented layers. Most concretions occur in fine-grained, low-permeability laminae, suggesting that their growth was controlled more probably by diffusion transport rather than advective transport. Grain size, lamination, and distribution of intergranular clay all potentially influenced the selective distribution of carbonate cement in the sandstones. Shale interbeds and terrigenous carbonate rock fragments in the sandstones are potential sources of carbonate cement.

A Simple Method for Orienting Conventional Core Using Microresistivity (FMS) Images and a Mechanical Goniometer to Measure Directional Structures on Cores

Orienting core and gathering downhole orientation data, such as paleocurrents or fractures, has always been a challenge in the petroleum industry and academia. Downhole core orientation while drilling is expensive, time consuming, and not always accurate. Nowadays, microresistivity logs are run in many boreholes and can easily be used for orienting conventional core of all sizes and many shapes (whole, slabbed, or plugged). The only requirement is a facies or lithologic change with a sharp contact visible in both core and microresistivity log. Downhole logging tools can thus provide a quick and inexpensive way to orient conventional core. A simple mechanical goniometer can then be used to measure foresets of cross-stratification for paleocurrent analysis. Mechanical goniometers have the advantage of being more robust than their electronic counterparts, and measurement errors are within a reasonable margin. Using this setup, paleocurrents from core were commonly found to be more precise than those generated digitally from microresistivity logs.

A Simple Method for Orienting Conventional Core Using Microresistivity (Fms) Images and a Mechanical Goniometer to Measure Directional Structures on Cores: RESEARCH METHODS PAPERS

ABSTRACT Orienting core and gathering downhole orientation data, such as paleocurrents or fractures, has always been a challenge in the petroleum industry and academia. Downhole core orientation while drilling is expensive, time consuming, and not always accurate. Nowadays, microresistivity logs are run in many boreholes and can easily be used for orienting conventional core of all sizes and many shapes (whole, slabbed, or plugged). The only requirement is a facies or lithologic change with a sharp contact visible in both core and microresistivity log. Downhole logging tools can thus provide a quick and inexpensive way to orient conventional core. A simple mechanical goniometer can then be used to measure foresets of cross-stratification for paleocurrent analysis. Mechanical goniometers have the advantage of being more robust than their electronic counterparts, and measurement errors are within a reasonable margin. Using this setup, paleocurrents from core were commonly found to be more precise than those generated digitally from microresistivity logs.

The recognition of artefacts from acoustic and resistivity borehole imaging devices

Abstract Image artefacts, that is, non-geological features present on acoustic or micro-resistivity borehole image logs are a fact of life. In poor quality image logs, they can constitute the bulk of the data-set although fortunately, such features generally constitute the minority of a data-set. The recognition of artefact features must form part of the log quality control process and should also form part of the interpretation process. By applying sound log quality control principles, these artefacts can be identified systematically and the remaining image data will be geologically related. This paper provides an up-to-date summary of borehole image artefacts, their cause and recognition. It also, for the first time, considers artefacts arising from acoustic (ultrasonic) as well as micro-resistivity images. Four main artefact image categories related to data acquisition, borehole wall condition, post processing of data and measurement physics form the basis for the systematic identification procedure. These are discussed and developed herein.

Advances in borehole imaging technology and applications

Abstract Borehole imaging devices are currently available for both wireline and logging-while-drilling (LWD) environments for use in both openhole and cased wells. Most wireline, and all LWD devices provide indirect images that are derived from a high-density grid of electrical or ultrasonic acoustic measurements. Optical techniques, such as television and photography, provide direct images of the borehole. Imaging devices consist of (1) a rotating sensor (acoustic or electrical) that scans the borehole with each revolution, (2) multiple, azimuthally placed sensors, or (3) a downhole television or photographic camera. Advances in digital acquisition and processing permit real-time display and evaluation of images of the open borehole or the inside of casing. The resolution and borehole coverage of microelectrode devices has increased with newer designs that allow additional measurement sensors per pad, additional pad segments on a four-arm tool, and the introduction of six-arm imaging tools. In nonconductive borehole fluids, a four-arm microinduction device can provide crude images. Macroelectrode imaging tools (laterolog-type; wireline) provide lower-resolution electrical images from either an azimuthal arrangement of sensors around a mandrel (wireline), or from azimuthally sensitive sensors (logging-while-drilling), that scan the borehole during rotation of the bottomhole assembly. In acoustic imaging, recent devices incorporate design changes that provide improved image resolution and operate in a wider range of borehole conditions. Ultrasonic transducers now use lower transmitting frequencies and spherical focusing and these tools also offer surface-selectable acquisition parameters. Acoustic and microresistivity imaging techniques measure different physical properties and these data are complementary. One recently introduced wireline service combines microresistivity and acoustic imaging devices in a single tool for simultaneous, single-pass acquisition. Recent advances in cable and sonde design permit downhole video in a wider range of petroleum environments, in flowing wells, and in tubing. Openhole image interpretation involves qualitative (visual) identification and quantitative characterization of strike and dip on planar features, lithology, bedding, fractures, and vugs. When core is available, features identified on log-derived images can be correlated or calibrated to it, or when core is absent, images may serve as a substitute. Borehole images are useful in formation evaluation (when calibrated), sedimentology, stratigraphy, and structural analysis. Current applications include core orientation, ‘reconstructing’ missing core, identification and characterization of fractures and depositional features (e.g. bedforms), reservoir architecture, bedding, grain size, porosity, permeability, net sand and net pay counts, faults, folds, and fractures (hydrocarbon, water, geothermal wells, and in rock engineering), evaluation of borehole stress (borehole stability), directional placement of wellbore for optimal drainage (fractured reservoirs), evaluation of fracture stimulations, and perforation control. Cased hole applications include cement evaluation, casing inspection, detection of fluid entry, identifying production blockages, and assisting in fishing operations.

Two-dimensional variability in porosity, density, and electrical resistivity of Eckernförde Bay sediment

Image-based analysis techniques are employed to compare sediment density heterogeneity as interpreted from X-radiography and electrical resistivity measurements. Assessments of sediment heterogeneity in two dimensions through the use of the two methods, with some exceptions, yield similar results. Autocorrelation functions estimated from density fluctuations reveal an anisotropy between vertical and horizontal sediment structure indicated by horizontal correlation lengths being greater than vertical correlation lengths. In addition to the anisotropy, discrepancies between values of correlation lengths calculated from two statistical methods are indicative of the scale-dependent nature of the sediment structure. This scale dependence is also exemplified by the differences between the images of X-radiography and electrical resistivity. The unequal volume of sediment over which the respective methods are integrated produces results differing by the amount and type of information included in each image. Electrical microresistivity is more sensitive than X-radiography to many smaller-scale variations in sediment density. Combining the results from X-radiography and microresistivity imaging allows the calculation of Archie’s m parameter, an extremely sensitive indicator of sediment microstructure. In addition, electrical microresistivity gives a measurement of sediment tortuosity coincident with sediment porosity and density.

High-resolution core-log integration techniques: examples from the Ocean Drilling Program

Abstract Cores offer the ability to describe lithological, physical, and chemical properties of rocks at the millimetre and smaller scale. However, continuous coring is expensive and only occasionally recovers 100% of the drilled interval. Microresistivity images of the borehole wall depict features down to the centimetre and smaller scale and can complement, or in some cases substitute for, core description as a means of geologic interpretation. This paper describes two techniques of integrating core data with borehole image and log data. Two case studies in carbonate rocks recovered during Ocean Drilling Program Legs 160 and 166 are presented. Microresistivity log images, grey-scale reflectivity from core photographs, and gamma ray logs are correlated at the centimetre scale over up to 300-metre cored intervals. Direct visual correlation of core photographs with borehole images and correlation of gamma ray measurements on core with downhole logs are shown to be complementary techniques. High-resolution core-log depth matching may be best achieved by correlating multiple datasets to reduce the error inherent in each and more precisely constrain depth matching. Depth matching of individual features allows a more accurate and consistent depth scale for use in quantitative stratigraphic analysis.

Resistivity Calibration Technique for Micro-Resistivity Image Logs: Applications for Thin-Bedded, Shaly Sand Reservoirs, Gulf of Mexico : ABSTRACTS

Resistivity Calibration Technique for Micro-Resistivity Image Logs: Applications for Thin-Bedded, Shaly Sand Reservoirs, Gulf of Mexico : ABSTRACTS