Fracture Swarms Research Articles

Logging-While-Drilling Laterolog vs. Electromagnetic Propagation Measurements: Which Is Telling the True Resistivity?

Summary The electromagnetic propagation (EMP) measurement frequently acquired with logging-while-drilling (LWD) tools in high-angle wells is sensitive to geometrical effects that can mask the true formation resistivity. Less commonly used, the LWD laterolog measurement is sometimes perceived as providing data too shallow to give a true formation resistivity (Rt). In this paper, we presents modeling and actual examples to demonstrate that the laterolog can often provide a superior resistivity measurement for formation evaluation to that of the LWD EMP tool. We examine the laterolog and EMP resistivities in several high-angle wells crossing carbonate formations in 8.5-in. and 6.125-in. hole sizes. In the 8.5-in. sections, producers and water injectors (high- and low-resistivity ranges) were evaluated. In the 6.125-in. sections, one reservoir sandwiched between two very high-resistivity layers and another borehole in a highly fractured reservoir were examined. The laterolog data were corrected for invasion using a 1D inversion of the memory data. Structure-based forward modeling was used to examine and explain the differences between the laterolog and EMP resistivity measurements. In the first example in a thick low-resistivity water reservoir, laterolog resistivity and EMP resistivity agree, showing that the two tools provide the same measurement when no geometrical effects are present. In the first part of the second example, a reservoir zone was initially drilled only with the LWD EMP resistivity measurement. The LWD laterolog was run several days later, and the resistivity data read much lower in the relogged section compared with the EMP resistivity. The laterolog 1D inversion was unable to resolve Rt because of the excessively deep invasion that occurred over the course of several days. In the second part of the second example, the laterolog resistivity showed a clear conductive invasion profile. While the deepest laterolog real-time resistivity data indicated lower resistivity than the EMP resistivity, the true resistivity, Rt (invasion-corrected 1D-inverted laterolog resistivity), matched the EMP Rt resistivity. This result validated both measurements and emphasized that the differences were due to invasion. The first two examples demonstrated that when acquired in normal drilling conditions (within 1–2 hours of drilling the section), the laterolog measurements can provide uninvaded formation resistivity even in the presence of invasion. A reservoir in another example was sandwiched between resistive layers that caused difficult-to-explain elevated EMP resistivity readings. Structural modeling reproduced the elevated behavior of the EMP data and explained the differences between resistivity measurements. This result showed that the laterolog is better suited to evaluate resistivity in thin reservoirs where there is a high-resistivity contrast to the adjacent layer. Finally, fractured reservoir examples are presented, which show that both the laterolog and EMP can be affected by the presence of fracture swarms. The examples presented in this paper demonstrate that in high-angle wells, when acquired under normal drilling conditions, invasion-corrected laterolog resistivity is often nearer to Rt than EMP resistivity. In those cases, the laterolog measurement provides data that are better inputs to water saturation calculations. Multiple examples from high-angle wells illustrate the findings.

Distributed Fiber Optic Monitoring of Asymmetric Fracture Swarm Propagation in Laminated Continental Shale Oil Reservoirs

Distributed Fiber Optic Monitoring of Asymmetric Fracture Swarm Propagation in Laminated Continental Shale Oil Reservoirs

Origin of Fracture-Controlled Conduits in Calcite-Rich Highly Productive Aquifers Impregnated with Diagenetic Silica

The origin of highly permeable flow paths in carbonate-siliciclastic rocks, such as large-aperture fractures in aquifers in the Eastern Bohemian Cretaceous Basin (EBCB), is poorly understood. The karst potential was assessed from the rock carbonate content and the degree of disintegration after leaching in HCl. Surprisingly, dissolution of calcite in EBCB usually did not lead to rock disintegration until calcite > 78%. Instead, porosity increased significantly. High-porosity rock is held together by microns-thick secondary silica cement with a foam-like structure and considerable tensile strength. Three types of conduits occur in the EBCB: (i) bedding-parallel conduits associated with calcite-rich layers, (ii) subvertical fracture swarm conduits that develop on damaged zones of fracture swarms, and (iii) conduits formed by dissolution of calcite veins by groundwater flow. These are ghost-rock karst features where calcite is leached from the rock in the first phase and the residue is washed out by conduits under steep hydraulic gradients in the second phase. Very similar features have been described in Minnesota and Wisconsin, USA. Research has shown that fractures with sharp-edged walls that give the impression of an extensional tectonics origin may actually be ghost-rock karst features in which dissolution and piping have played an important role in their enlargement.

Variations and causes of in-situ stress orientations in the Dibei-Tuziluoke Gas Field in the Kuqa Foreland Basin, western China

The Kuqa Foreland Basin, adjacent to the southern Tianshan Mountains, is an important gas-producing basin in northwestern China. The development of the basin is dominated by a regional stress field with orientations of the maximum horizontal stress (SHmax) in the north-south direction, as a result of the collision between the Indian and Eurasian Plates. Previous studies have noted variations in the stress state in the Kuqa Foreland Basin; however, little attention has been paid to understanding the mechanisms causing such variations. In this study, a systematic analysis of in-situ SHmax orientations and fractures has been carried out using image logs from eight wells and XMAC/DSI logs from five wells. These wells are located in an East-West (E-W) trending fold-thrust in the foreland basin. The SHmax orientations (having quality ranked between A and D) obtained from borehole breakouts and drilling-induced fractures are highly variable and occur as two evidently different stress patterns on a scale of less than 10 km. The first stress pattern with SHmax orientations between NNW and NNE (165.08 and 188.59 °N) is broadly comparable to the regional stress field inferred from earthquake focal mechanism solutions in northwestern China from the World Stress Map (WSM). The stress pattern is interpreted to be controlled by plate boundary forces related to the collision between the Indian and Eurasian Plates. The SHmax orientations for the second stress pattern, however, ranging from NNE to ENE (26.65–57.77 °N), are clearly inconsistent with the regional stress filed and have been influenced by local geological factors. Faults and hinge-parallel fractures (trending in an approximately W-E direction) formed during the syn-folding stage probably resulted in heterogeneity of elastic properties and thus deflected SHmax orientations, both laterally and vertically, to generate the second stress pattern. The NE-striking hinge-oblique fractures are interpreted to have formed in response to the stress reorientation. Observations in this study suggest that there may exist a close relationship between fracturing (faulting) and stress variations, and pre-existing faults and fractures can influence subsequent fracturing by regulating local stress fields on a scale of several kilometers. The coupling between fracturing or faulting and stress produced fracture swarms, which can significantly enhance fluid flow and hence petroleum production.

Fracture Characteristics and Distribution in Slant Core from Conglomerate Hydraulic Fracturing Test Site (CHFTS) in Junggar Basin, Northwest China

Hydraulic fracture networks, especially fracture geometry, height growth, and proppant transport within the networks, present a critical influence on productivity evaluation and optimization of fracturing parameters. However, information about hydraulic fracture networks in post-fractured formations is seldom available. In this study, the characteristics (density and orientation) of hydraulic fractures were obtained from field observations of cores taken from conglomerate hydraulic fracturing test site (CHFTS). A large number of fractures were observed in the cores, and systematic fracture description was carried out. The fracture analysis data obtained includes fracture density, fracture depth, fracture orientation, morphology, fracture surface features, apertures, fill, fracture mechanical origin (type), etc. Our results show that 228 hydraulic fractures were intersected in a span of 293.71 m of slant core and composed of irregularly spaced single fractures and fracture swarms. One of the potential sources of the observed fracture swarms is near-wellbore tortuosity. Moreover, for regions far away from the wellbore, reservoir heterogeneity can promote complex hydraulic fracture trajectories. The hydraulic fractures were mainly cross-gravel and high-angle fractures and align with maximum horizontal stress (SHmax) ± 15°. The fracture density, orientations, and types obtained from the core fracture description provided valuable information regarding fracture growth behavior. For the near-wellbore area with a transverse distance of less than 25 m from the hydraulically-fractured wellbore, tensile fractures were dominant. While for the area far away from the wellbore, shear fractures were dominant. Our results provide improved understanding of the spatial hydraulic fracture dimensions, proppant distribution, and mechanism of hydraulic fracture formation. The dataset acquired can also be used to calibrate numerical models and characterize hydraulic fracture geometry and proppant distribution.

Fault zone fluid pathways in the carbonate Irecê basin, NE Brazil

AbstractWe applied field structural data and isotope geochemical (δ13C, δ18O and 87Sr/86Sr) analyses to understand the relationship among calcite veins, fault damage zones and carbonate host rocks in a thrust fault damage zone in the Achado quarry, Irecê Basin in the São Francisco Craton, NE Brazil. Our results reveal three hydrological packages with different rheological behaviours in a stratified carbonate succession. The upper package includes the Achado fault damage zone that is characterised by interlayered dolomitised grainstones and mudstones. These rocks display high positive δ13C values (10‰–13‰), negative δ18O values (mean −6.34‰) and radiogenic (87Sr/86Sr) isotope values (0.70885–0.71519). A second package is marked by a cataclastic brittle shear zone lateral parallel to dolograinstones bedding. These rocks show low to positive δ13C values (−3.41‰ to +8.85‰), more positive δ18O values (mean −3.73‰) and radiogenic (87Sr/86Sr) isotope values (0.71039–0.71373). The lower package is characterised by well‐preserved pristine limestone succession that shows δ13C values ranging between −0.46‰ and +3.17‰, mean δ18O = −5.41‰ and less radiogenic 87Sr/86Sr values (0.70762–0.70818). In contrast to the upper and intermediate packages, rocks from the lower one exhibit very low permeability and behaved as a seal for fluid migration. Fluid flow occurred several times during basin evolution, for example along syn‐rift fault damage zones, bedding‐parallel carbonate breccia, thrust faults, cataclastic shear zones, synorogenic conjugate shear fractures or joints and opening mode I fracture‐fill calcite veins. These fractures allowed pervasive fluid flow in the porous intermediate cataclastic shear zone where fluids flowed and formed veins, as diffuse fluid flow in randomly oriented fracture swarms, or channelised fluid flow in aligned fracture corridors. They record significant centimetre‐scale to km‐scale hydrological behaviour within carbonate layers. Most carbonates that are associated with veins, fault damage zones and hydraulic breccia were formed by fluids of the same origin with low δ13C (−6.0 to −2.0‰) and δ18O (−6.0 to −8.5‰) values, and more radiogenic 87Sr/86Sr values compared to the carbonate host rocks.

Intraplate Strike-Slip Corridor within South America (NE Border of the Paraná Basin) Unveiled by Structural Analysis of Faults and Fracture Swarms

We present the effect of neotectonics in intracratonic settings as revealed by the surface, brittle deformation associated to a regionally-sized shear corridor, which affects Southeastern Brazil. The deformation zone is characterized by the presence of nearly orthogonal fracture sets, interpreted as systematic and non-systematic joints often cutting Quaternary deposits. An original methodology of fault and joint inversion by the Monte Carlo converging approach is used to infer multiple paleostress fields. The method provides the best orientation of the principal paleo-stresses responsible for the observed fracturing. At each step of the inversion process, structures are uniquely associated to the stress tensor that provides the lowest error. The results showed the poly-phased tectonic history of the shear corridor studied and paleostresses compatible with a regional strike-slip motion. Specifically, an E-W, left-lateral shear was followed by an E-W, right-lateral kinematics related to the post-Paleogene drifting of South American Plate and its clockwise rotation. The latter tectonic event is presently responsible for brittle deformation observed in Quaternary deposits. The proposed deformation corridor may represent the Cenozoic reactivation of an ancient weakness zone. We speculate that the described intraplate strike-slip deformation belt represents the continental prosecution of the Rio de Janeiro fracture zone.

Microseepage through evaporite sequences — A Gulf of Suez example

Salt is one of the most effective agents for trapping oil and gas. As a ductile material, it can move and deform surrounding sediments and create traps. However, effective sealing of reservoirs for movement of hydrocarbons along breaching faults or fracture swarms (i.e., macroseepage) is a different mechanism than the movement of hydrocarbons on a molecular scale along grain boundaries and microfractures as happens with microseepage. To address salt seal integrity, Forum Exploration has chosen to evaluate the applicability of passive surface geochemical surveys for mapping hydrocarbons in their onshore West Gebel El Zeit lease in part due to difficulties in seismic imaging through salt and anhydrite sequences. Two economic producing wells have been drilled in the lease, but due to compartmentalization and complexity in the area, three dry wells also have been drilled. Target formations include the Kareem Formation at approximately 2700 m and the Rudeis Formation at approximately 3000 m. The geochemical survey encompasses 100 passive geochemical modules. Passive samplers also have been deployed around two producing wells and one dry well for geochemical calibration. Calibration data indicate positive thermogenic signatures around the two producing wells in contrast to the background or baseline signature from around the dry well. The Kareem Formation calibration signature ranges from approximately C6 to C12 with the Rudeis Formation calibration signature ranging from C5 to C9. This suggests that the Rudeis calibration signature is lighter than the Kareem, in agreement with independent measurement of American Petroleum Institute (API) gravity on produced oil samples (API gravity 41° oil for the Rudeis and 35° oil for the Kareem). A postsurvey well, Fh85-8, has been drilled based on combined geochemical and seismic data results. The well is a Kareem oil discovery, with an initial production of approximately 800 barrels of oil per day. We have developed evidence in this Gulf of Suez example to show that microseepage occurs through substantial salt sequences. Consequently, ultrasensitive passive surface geochemical surveys provide a powerful tool for derisking salt plays.

Fault-related fracture modeling in a pre-salt lacustrine carbonate reservoir from Santos Basin, offshore Brazil: Predicting preferential fluid flow paths using 3D geological and flow simulation models

The authors propose an integrated workflow from seismic to flow simulation to predict sub seismic and inter-well fracture distribution. This methodology provides insights in order to fulfill a knowledge gap in reservoir 3D modeling of naturally fractured carbonates applied in the industry. The workflow includes interpretation of borehole image logs, 3D seismic, geophysical and geomechanical attributes, and calibration with dynamic data. The main natural fracture parameters analyzed for the case study are direction, dip, and fracture intensity. The studied area is a naturally fractured Aptian lacustrine carbonate reservoir within the Santos Basin, offshore Brazil. The isolated platform developed over a series of elongated NE-SW horsts structures. The main seismic scale structures in the reservoir are NE-SW trending faults that show normal displacement, defining en échelon relay ramps that contain NW-SE sub seismic faults and diffuse fracture swarms. The damage zones that surround these main faults define continuous fracture corridors intercepted by oblique sub-seismic faults in relay-ramp zones. Structural analysis showed that fracture intensities are higher at the north domain in the Barra Velha Formation. The fractures were simulated stochastically using a discrete fracture network (DFN), generating a dual porosity and dual permeability model (DPDK) for the flow simulation resulting in a suitable model configuration for the history match.

Development of 3‐D Curved Fracture Swarms in Shale Rock Driven by Rapid Fluid Pressure Buildup: Insights From Numerical Modeling

AbstractDespite the variety of studies that have investigated the development of fracture networks during kerogen maturation in organic‐rich shale, the fracture interaction modes and generation mechanisms in three‐dimensions are not yet fully understood. In this study, we introduce a novel numerical approach to model the evolution of fracture swarms with three‐dimensional nonplanar geometries. This model enables precise simulation of the propagation, interplay, and coalescence of the fracture swarms with variable apertures and geometries via solving fluid flow, fracture growth, and stress interference. Our results suggest five basic fracture interaction modes between neighboring fractures. The evolving fracture swarms exhibit simultaneous, alternant, and differential growth characteristics at different development phases. We also elucidate the mechanical mechanisms that determine the evolution of three‐dimensional curved fracture swarms. This work yields an improved understanding of fluid‐driven fracture swarms' development in organic‐rich shale due to rapid fluid generation.

Developing Upscaling Approach for Swarming Hydraulic Fractures Observed at Hydraulic Fracturing Test Site through Multiscale Simulations

Summary This work aims to address a challenge posed by recent observations of tightly spaced hydraulic fractures in core samples from the hydraulic fracturing test site (HFTS) in the Middle Wolfcamp Formation. Many fractures in retrieved cores have subfoot spacing, which is at odds with conventional models in which usually one hydraulic fracture is initiated per cluster. Models assuming a single fracture at each cluster, although a common practice, often predict excessive fracture propagation that is inconsistent with microseismic observation. Here, we aim to develop a numerical approach to effectively account for densely spaced hydraulic fractures in field-scale simulations. Because it is impractical to explicitly model all aforementioned fractures, we develop a new upscaling law that enables existing simulation tools to predict reservoir response to fracture swarms. The upscaling law is derived based on an energy equivalence argument and validated through multiscale simulations using a high-fidelity code, GEOS. The swarming fractures are first modeled with a spacing that is much smaller than the cluster spacing; these fractures are then approximated by an upscaled, single fracture based on the proposed upscaling law. The upscaled fracture is shown to successfully match the energy input rate and produce the total fracture aperture and average propagation length of the explicitly simulated swarm. Afterward, the upscaling approach is further implemented in 3D field-scale simulations and validated against the HFTS microseismic data of a horizontal well. Our results show that hydraulic fracture swarming can significantly affect fracture propagation behaviors compared with the propagation of single fractures as assumed by conventional modeling approaches. Under the considered situations, the conventional treatment yields fast propagation speed that far exceeds that indicated by the microseismic data. We also illustrate that this discrepancy can be reduced readily through the implementation of the upscaling law. Our results demonstrate the importance of accounting for the fracture swarming effect in field-scale simulations and the efficacy of this approach to enable realistic predictions of reservoir responses to fracture swarms, without the need to model tightly spaced fractures individually.

Development of 3-D Curved Fracture Swarms in Shale Rock Driven by Rapid Fluid Pressure Buildup: Insights from Numerical Modeling

Development of 3-D Curved Fracture Swarms in Shale Rock Driven by Rapid Fluid Pressure Buildup: Insights from Numerical Modeling

Development of 3-D Curved Fracture Swarms in Shale Rock Driven by Rapid Fluid Pressure Buildup: Insights from Numerical Modeling

Development of 3-D Curved Fracture Swarms in Shale Rock Driven by Rapid Fluid Pressure Buildup: Insights from Numerical Modeling

Petrophysical analysis of the unconventional reservoirs of the Lennard Shelf and Fitzroy Trough in Canning Basin, Australia

A US operator with a commitment to future drilling, stimulation and testing of unconventional wells has initiated a new evaluation to better define and understand the hydrocarbon plays along the northern margin of the Canning Basin’s Lennard Shelf and Fitzroy Trough. The goal of the evaluation is to determine the commercial viability of the region. In this paper, an integrated petrophysical hybrid model that has been calibrated to core data is highlighted. From this model, multiple play types were identified, including an unconventional siltstone-shale play, a conventional basin-centred tight gas play and a fractured tight gas play with potential analogs to North American unconventional plays. Six primary lithofacies were identified through the integration of thin section analyses, core descriptions, logs and petrophysical models. The results were calibrated to high-resolution formation image data to better understand the thin-bedded nature of these plays. The lithofacies were also utilised for defining core poro/perm transforms. Furthermore, an integrated descriptive mud log algorithm was utilised to define the types of hydrocarbons, including wetness, balance and ratios as the hydrocarbons’ fingerprints. Significant gas influxes were noted at the intervals with highly permeable beds, at swarms of fractures and faults, as well as within the organic rich layers. In this study, a pressure top seal for the Laurel Formation was defined as well as the highlights of one well, which includes 11 zones and over 389m of net pay behind pipe. The significance of this work is that it highlights a path forward for unconventional development that, if economically viable, would provide increased energy independence for Australia.

Fracture inference and optimal well placement using a multiscale history matching in a HPHT tight gas reservoir, Tarim Basin, China

Fractures play an important role in well placement by influencing the well productivity and dominating the fluid flow underground. Though seismic data is often used to identify fracture swarms, the conductivities of fractures can be hard to evaluate, and data quality of seismic surveys typically decreases as the reservoir becomes deeper. In terms of inferring complex fracture patterns, dynamic production data integration can play a vital role. This paper presents a hierarchical multi-scale history matching approach that combines evolutionary algorithm and streamline method to calibrate fracture permeabilities in a HPHT tight gas reservoir using dual porosity models. The reservoir is located in the Tarim basin, China, and has a depth of more than 7500 m with high pressure (18000 psi) and high temperature (340 °F). The fracture properties of the dual porosity model are initially derived from seismic attributes and further calibrated with dynamic data using the proposed multi-scale history matching. The calibrated fracture model can detect the fracture swarm locations underground. The streamlines generated from the history matched model in conjunction with reservoir properties are used to define a ‘depletion capacity map’ which is then used for optimal infill well placement. Most of the previous streamline-based field applications are limited to incompressible or slightly compressible flow. In this paper streamline-based analytical sensitivities are extended to highly compressible flow. To our knowledge, this is the first-time streamlines have been used to facilitate history matching and optimal well placement for gas reservoirs.

A case study of azimuthal fracture characterization in Cambay Basin, India

Shale gas, shale oil, tight-sand, heavy oil, gas hydrates and CBM are most important unconventional hydrocarbon resources of the 21st century. Tight-sand and shale plays are of low permeability, to exploit hydrocarbon economically, their permeability are increased artificially by creating fractures, which is termed as fracking. Ever widening gap between import and domestic hydrocarbon production in India mandates efficient exploitation of unconventional hydrocarbons. Prevailing hydrocarbon market does not support acquisition of specialized seismic data and specialist software for unconventional hydrocarbon exploitation. It is imperative to devise cost effective way of exploiting tight sand, shale oil and gas. Natural fractures in tight sand and shale plays are helpful in production, its characterization is important. Since seismic amplitude varies along and across swarms of fractures, Multi-Azimuth seismic data can be analyzed for fracture characterization. Onshore seismic data, which are acquired and processed for conventional seismic exploration, can be used in unconventional exploration/exploitation after 5d interpolation of the seismic data in inline, crossline, offset, azimuth and frequency. We analyze seismic amplitude variation with offset and azimuth using conventional seismic data from Cambay Basin, in India for fracture characterization by making the data rich in azimuth by 5d interpolation.

Least-squares path-summation diffraction imaging using sparsity constraints

Diffraction imaging aims to emphasize small-scale subsurface heterogeneities, such as faults, pinch-outs, fracture swarms, channels, etc. and can help seismic reservoir characterization. The key step in diffraction imaging workflows is based on the separation procedure suppressing higher energy reflections and emphasizing diffractions, after which diffractions can be imaged independently. Separation results often contain crosstalk between reflections and diffractions and are prone to noise. We have developed an inversion scheme to reduce the crosstalk and denoise diffractions. The scheme decomposes an input full wavefield into three components: reflections, diffractions, and noise. We construct the inverted forward modeling operator as the chain of three operators: Kirchhoff modeling, plane-wave destruction, and path-summation integral filter. Reflections and diffractions have the same modeling operator. Separation of the components is done by shaping regularization. We impose sparsity constraints to extract diffractions, enforce smoothing along dominant local event slopes to restore reflections, and suppress the crosstalk between the components by local signal-and-noise orthogonalization. Synthetic- and field-data examples confirm the effectiveness of the proposed method.

Line sampling of fracture swarms and corridors

Scanlines across a range of fracture networks are analysed using cumulative frequency plots, spacing distribution and correlation integral plots. Synthetic samples from known distributions are used to distinguish uniform and random positioning of fractures from various types of clustering and the results used to interpret fracture corridors from the Bergen area, Norway. The Kuiper test provides a means of establishing the statistical significance of clustering, and the correlation integral allows assessment of clustering at different scales. A simple workflow is proposed that uses quantitative measures for the definition and characterisation of the spatial organisation of fractures. The form of fracture networks is shown to vary from uniform or random distributions, through the development of simple corridors, to clustering at various scales.

Unconventional-Reservoir Characterization With Azimuthal Seismic Diffraction Imaging

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper URTeC 2695232, “Unconventional-Reservoir Characterization With Azimuthal Seismic Diffraction Imaging,” by Dmitrii Merzlikin, Sergey Fomel, Xinming Wu, and Mason Phillips, The University of Texas at Austin, prepared for the 2017 Unconventional Resources Technology Conference, Austin, Texas, USA, 24–26 July. The paper has not been peer reviewed. The complete paper proposes an azimuthal plane-wave-destruction (AzPWD) seismic-diffraction-imaging work flow to efficiently emphasize small-scale features associated with subsurface discontinuities such as faults, channel edges, and fracture swarms and to determine their orientation by properly accounting for edge-diffraction phenomena. The work flow is applied to characterize an unconventional tight-gas-sand reservoir in the Cooper Basin in Western Australia. Extracted orientations of edges provide valuable additional information, which can be used by the interpreter to locate finer-scale features and distinguish them from noise. Introduction Unconventional reservoirs may exhibit high structural variability, which is difficult to characterize with a discrete wells network. 3D reflection seismology allows the extraction of additional information about the subsurface with significantly denser spatial sampling intervals. However, conventional images of the subsurface have low spatial resolution and are dominated by continuous and smooth reflections, which carry the information associated with only large-scale heterogeneities. Diffraction images are more capable than conventional reflection images in emphasizing small-scale features associated with subsurface discontinuities. Many studies employ diffraction images as a source of additional information for interpretation. Past work has proposed an AzPWD work flow, which extends a plane-wave destruction diffraction imaging framework to account for edge-diffraction orientation and allows efficient extraction of these orientations on the basis of scanning of different azimuths. Two modifications to the previously proposed AzPWD work flow are considered in this paper. Edge-diffraction-orientation determination is performed through a structure-tensor estimation based on PWD. A PWD-based structure tensor allows determination of edge-diffraction orientation from two volumes corresponding with PWDs applied in inline and crossline directions. Thus, no scanning over the PWD azimuth is required. Because reflection/diffraction separation is performed on the basis of the PWD filter in the data domain, the approach pertains to a diffraction imaging framework. The structure-tensor estimation approach has been applied previously in the image space on the basis of image gradients, the highest contribution to which is connected with strong and coherent reflection events masking diffractions. The second improvement presented by the AzPWD work flow is based on additional smoothing along the edge orientation, which makes the diffraction/ reflection-separation operator equivalent to the structure-oriented Sobel filter.

Structural Analysis: Folds Classification of metasedimentary rock in the Peninsular Malaysia

Understanding shear zone characteristics of deformation are a crucial part in the oil and gas industry as it might increase the knowledge of the fracture characteristics and lead to the prediction of the location of fracture zones or fracture swarms. This zone might give high influence on reservoir performance. There are four general types of shear zones which are brittle, ductile, semibrittle and brittle-ductile transition zones. The objective of this study is to study and observe the structural geometry of the shear zones and its implication as there is a lack of understanding, especially in the subsurface area because of the limitation of seismic resolution. A field study was conducted on the metasedimentary rocks (shear zone) which are exposed along the coastal part of the Peninsular Malaysia as this type of rock resembles the types of rock in the subsurface. The analysis in this area shows three main types of rock which are non-foliated metaquartzite and foliated rock which can be divided into slate and phyllite. Two different fold classification can be determined in this study. Layer 1 with phyllite as the main type of rock can be classified in class 1C and layer 2 with slate as the main type of rock can be classified in class 1A. This study will benefit in predicting the characteristics of the fracture and fracture zones.