Dip Azimuth Research Articles

Predict sandstone distribution by integrated study of deformed shale using borehole image and seismic data, a case study from northern Gulf of Mexico

Many Upper Tertiary reservoirs from the Gulf of Mexico (GoM) are sandstones deposited either in channel-levee systems or lobe systems in the intra-slope deepwater environment. One of the major uncertainties about those reservoirs is their distribution, which is likely controlled by salt tectonics. The current salt structure, however, does not represent the salt structure when the sands were deposited. It is difficult, if not impossible, to restore the salt history based on current salt structures. Salt movement resulted in a great amount of deformed shale in GoM. Borehole images on the other hand can be used to characterize the internal structure or texture of deformed shale; and the dips of deformed shale from borehole images may be used to define the paleo slope direction, which controls the movement of deformed shale. The internal structure or texture of deformed shale, therefore, may provide some information about the history of salt movement, which may also control the sand distribution. In this integrated study, all the available data, including borehole images, seismic volumes, and other petrophysical logs, were used to characterize the reservoir sands and shales. The reservoir sands are mainly composed of amalgamated sand, layered sand, and laminated sandstone. Based on dips from borehole images, paleo flow directions of reservoir sands were defined. The shales are categorized as hemipelagic shale and deformed shale. The hemipelagic shale has relatively lower and consistent dips; whereas deformed shale has relatively higher variable in both dip magnitude and dip azimuth. The integrated study suggests the main reservoir of the field is submarine lobe sands deposited above an allochthonous salt in the basin. The evacuation of the salt body below the basin created small geographic lower area for sand lobes to accumulate. The dips from the deformed shale provided information about the center of the small (or mini) basin, thus established a relationship between the dip pattern and sandstone distribution. If this relationship is valid for the other upper Tertiary deformed shale in the GoM area, a new method can be developed, which may enable us to predict the sandstone distribution using borehole images and provide guidance for petroleum evaluation and field development in the future.

Occurrence of wolfram, copper, cobalt and gold mineralization in the area of the Argentine Islands (West Antarctica)

Objective. The objective of our research was to search for manifestations of ore mineralization on the Roca and Cruls islands in the Argentine Islands, West Antarctica. Methods. Samples of rocks with the manifestation of ore mineralization were taken in the field routes. Silicate analysis of the rocks was carried out using the wet chemistry method in M.P. Semenenko Institute of Geochemistry, Mineralogy and Ore Formation of the National Academy of Sciences of Ukraine (IGMOF of NAS of Ukraine). The X-ray diffraction analysis of samples was carried out using a DRON-2 diffractometer, with copper radiation (СuКα = 1.54178A). The samples were surveyed in the 4—65° 2θ interval of angles, with a scan step of 0.1 degr. / min. For mineral diagnostics, the catalog of reference samples of the PDF-2 database (International Diffraction Data Center, ICDD) 2003. The chemical composition of minerals was examined using a JXA-733 X-ray microanalyzer (Jeol, Japan) using wave and energy-dispersion spectrometers. Contents of trace elements in the rocks were determined using the ICP-MS and quantitative spectral analysis methods. The validity of analyses was checked by means of determination of international and Russian reference samples GSP-2, VM, SGD-1А, ST-1.Concentration measuring errors were 3 to 5 wt. % for most elements. The quantitative spectrum analysis was carried out in IGMOF of NAS of Ukraine. Petrographic studies of rock sections were carried out using a MIN-8 polarized-light microscope. Results. Wolfram, copper, zinc, and lead were found in the minor intrusion of lamprophyres in the Andes complex granodiorites, on a small island of the Roca Islands. This semi-ring-shaped minor intrusion up to 0.5 m thick rooted in the not yet crystallized granodiorite intrusion. The dip angle of the minor intrusion is about 70°. It showed tungsten (28.7 g/t), copper (445 g/t), zinc (207 g/t), and lead (123 g/t) mineralization. In the eastern part of one of the Cruls Islands, a steep (dip azimuth NW 345°, angle 82°) tectonic zone up to 10 m wide was studied. Three metasomatic belts, one of which is up to 0.5 m thick, are associated with this zone. Metasomatites include pyrite-plagioclase rocks, epidosites and pyrite-epidote rocks, which have been formed due to hydrothermal and metasomatic changes of granodioritic tectonic breccia. The occurrence of cobalt (800 g/t), copper (200 g/t) and gold (up to 0.3 g/t) has beendiscovered. In these metasomatites, magnetite, pyrite, copper pyrite and pyrrhotite are available. Cobalt is present as magnetitic and pyritic impurities. Conclusions. During geological surveys in 2010 and 2012 the mineralization of wolfram, copper, lead, cobalt and gold was first discovered. The ore mineralization of such genesis was previously unknown in this area. The data obtained allow clarifying of perspectives of exploration activities in West Antarctica.

Precise Seismic Substructural Model of the Eocene Chorgali Limestone in the Turkwal Oil Field, Central Potwar, Pakistan

The precise seismic substructural interpretation of the Turkwal oil field in the Central Potwar region of district Chakwal of Pakistan has been carried out. The research work was confined to the large fore‐thrust that serves as an anticlinal structural trap through ten 2D seismic lines. A precise seismic substructural model of the Eocene Chorgali Limestone with precise orientation of thrust and oblique slip faults shows the presence of a huge fracture, which made this deposit a good reservoir. The abrupt surface changes in dip azimuth for the Eocene Chorgali Limestone verifies the structural trends and also the presence of structural traps in the Turkwal field. The logs of three wells (Turkwal deep X‐2, Turkwal‐01 and Fimkassar‐01) were analyzed for petrophysical studies, well synthetic results and generation of an Amplitude Versus Offset (AVO) model for the area. The AVO model of Turkwal deep X‐2 shows abrupt changes in amplitude, which depicts the presence of hydrocarbon content. Well correlation technique was used to define the overall stratigraphic setting and the thickness of the reservoir formation in two wells, Turkwal‐01 and Turkwal deep X‐2. The Eocene Chorgali Limestone in Turkwal‐01 is an upward thrusted anticlinal structure and because of the close position of both wells to the faulted anticlinal structure, its lesser thickness differs compared to Turkwal deep X‐2. The overall results confirm that the Turkwal field is comparable to several similar thrust‐bound oil‐bearing structures in the Potwar basin.

Characterization of mass transport deposits using seismic attributes: Upper Leonard Formation, Permian Basin

The Permian Basin is a structurally complex sedimentary basin with an extensive history of tectonic deformation. As the basin evolved through time, sediments dispersed into the basin floor from surrounding carbonate platforms leading to various mass movements. One such mass movement is observed on a 3D seismic survey in the Upper Leonard interval (Lower Permian) of the Midland Basin that is characteristic of a mass transport deposit (MTD). The 350 ft thick MTD mapped in the study area is 5 mi wide, extends up to 14 mi basinward, and covers only the translational and compressional regime of the mass movement. A unique sedimentary feature, unlike those observed previously, is mapped and interpreted as gravity spreading. MTDs have been extensively studied in the Delaware Basin of Permian-aged strata; however, only a few works have been published on the geomorphological expression of MTDs using seismic and seismic attributes to delineate the shape, size, and anatomy of this subsurface feature. The MTD in the study area exhibits an array of features including slide, slump, basal shear surface, and MTD grooves. In cross section, the MTD is characterized as chaotic with semitransparent reflectors terminating laterally against a coherent package of seismic facies, or the lateral wall. Sobel filter-based coherence, structural curvature, dip magnitude, and dip azimuth attributes are used to map thrust faults within the discontinuous MTD. Kinematic evidence provided by the Upper Spraberry isopach suggests that this MTD was sourced north of the Midland Basin and deposited on the basin floor fairway. Slope strata are interpreted from well-log analysis showing MTD as a mixture of carbonates and siliciclastics with a moderate to high resistivity response.

Fracture characteristics and stress directions in the quaternary sediments of the Ulleung Basin, East Sea: Based on resistivity image log data

Geophysical evidence indicating the presence of gas hydrate has been found in the Ulleung Basin, which lies off the east coast of the Korean Peninsula; however, hydrate distribution in the basin is not well understood. Logging-while-drilling data for 13 sites in the Ulleung Basin, East Sea, were obtained to investigate the distribution pattern of gas hydrate. Most of the sites yielded log data indicating the presence of gas hydrate. Prominent fractures (both resistive and conductive fractures) were clearly identified on the resistivity borehole images, particularly at seismic chimney sites. Resistive fractures, which contain large amounts of gas hydrate, are prominent in the seismic chimney sites. The strike and dip of each fracture was calculated and displayed on a stereographic plot and rosette diagram. From the fracture orientations on the stereographic plots, the maximum horizontal stress is NW–SE, reflecting the regional stress regime around the Ulleung Basin, although the fracture orientations are broadly distributed, indicating that the fracture pattern is not well-ordered on the rosette diagram. The fracture dips are between 36.46° and 63.66°; the range of dip azimuths is 0.94°–359°, and exhibit little change with depth. The dip azimuths are generally westerly to southwesterly.

Application of four-component dipole shear reflection imaging to interpret the geological structure around a deviated well

Acoustic reflection imaging in deep water wells is a new application scope for offshore hydrocarbon exploration. Two-dimensional (2D) geological structure images can be obtained away from a one-dimensional (1D) borehole using single-well acoustic reflection imaging. Based on the directivity of dipole source and four-component dipole data, one can achieve the azimuth detection and the three-dimensional (3D) structural information around the wellbore can be obtained. We first perform matrix rotation on the field four-component data. Then, a series of processing steps are applied to the rotated dipole data to obtain the reflector image. According to the above dipole shear-wave imaging principle, we used four-component cross-dipole logging data from a deviated well in the South China Sea to image geological structures within 50 m of a deviated well, which can delineate the structural configuration and determine its orientation. The configuration of near-borehole bedding boundaries and fault structures from shear-wave imaging results agrees with those from the Inline and Xline seismic profiles of the study area. In addition, the configuration and orientation of the fault structure images are consistent with regional stress maps and the results of the borehole stress anisotropy analysis. Furthermore, the dip azimuth of the bedding boundary images was determined using borehole wall resistivity data. Results of this study indicate that integrating borehole acoustic reflection with seismic imaging not only fi lls the gap between the two measurement scales but also accurately delineates geological structures in the borehole vicinity.

Geometrical dependence on the stress and slip tendency acting on the subduction megathrust of the Nankai seismogenic zone off Kumano

We assess the dependence of megathrust geometry near the updip edge of the Nankai seismogenic zone according to the slip tendency of the megathrust based on a reprocessed 3D PSDM seismic volume image and International Ocean Discovery Program (IODP) NanTroSEIZE drilling data off the coast of the Kii Peninsula, central Japan. The plate boundary fault surface is manually picked from the 3D seismic volume and is divided into three groups: low dip (10°–15°) trending NW to N in the NE region, intermediate dip (~ 25°) trending north in the western region, and high dip (30°–40°) trending NW in the SE corner. We then calculate the overburden (Sv) by converting the modeled 3D velocity to bulk density. Here, Sv ranges from 100 MPa near the SW edge to 160 MPa on the NE corner. In order to derive horizontal principal stresses (SH and Sh) and the pore fluid pressure (Pp), we assign the ratio of horizontal-to-vertical principal stresses, r (= SH/Sv), and the ratio of pore fluid pressure-to-vertical stress, λ (= Pp/Sv) based on IODP drilling data. The directions of SH and the slip on the fault are set parallel to the plate convergence vector (N55W). Assuming a triaxial condition (SH > Sh = Sv), the slip tendency (Ts) can be calculated from the dip angle and dip azimuth of the fault surface, r, and λ. We found that Ts is sensitive to the variation in fault geometry. For r = 1.2 and λ = 0.7 (normalized pore pressure ratio λ* = 0.25), Ts is low (~ 0.1) in the low-angle dip region and higher (> 0.2) in the high-angle dip region. This suggests that the high-angle fault is optimally oriented under this condition. Low Ts in the low-angle dip region would correspond to a weaker region due to a low frictional strength, assuming that the fault surface should slip simultaneously. Using the high pore pressure ratio (λ* ~ 0.85) beneath the fault zone, the fault beneath IODP Site C0002 is very close to failure if r > 1.2.

A reassessment of the stress and natural fracture orientations from analysis of image logs in the Chinese Continental Scientific Drilling Program borehole at Donghai county, Jiangsu province, China

The Chinese Continental Scientific Drilling (CCSD) project has drilled a 5100 m deep research borehole in the Sulu ultra-high pressure (UHP) metamorphic belt, eastern China. The UHP metamorphic belt is thought to be a product of continent-continent collision and has consequently experienced very intensive structural deformation. Based on a more complete well log data set of CCSD borehole, we can have a more detailed and reliable study on the structure features of borehole wall and other rock physical properties than a previous study published in 2009. Abundant data related to borehole breakouts (BOs), drilling induced tensile fractures (DITFs) and natural fractures were collected from the image logs. The BO and DITF data indicate that the average direction of the maximum horizontal principal stress (SH) of the CCSD borehole site is about 79.2° which is consistent with the convergent direction (E-W) of the Pacific Sea Plate with respect to the Eurasian Plate. Analysis of DITFs indicated that in the case of the CCSD borehole, axial drilling induced tensile fractures (ADITFs) occur occasionally in the upper section (0–2300 m) of the borehole with low dipping angle (0–10°), while transverse drilling induced tensile fractures (TDITFs) occur significantly in the lower section (3800–5000 m) with high dipping angle (10–30°). The natural fracture distribution at depth in the metamorphic rocks of the CCSD borehole indicates that (1) the failure strength of rocks and borehole depth are two factors that affects natural fracture frequency, (2) most of the dip azimuth of natural fractures is consistent with the dip azimuth of foliations observed in the core, (3) the development of most of the natural fractures probably was dominated by the development of foliations, and both the natural fractures and foliations developed in response to the subduction and exhumation of the Sulu terrene.

Complex bedding geometry in the upper portion of Aeolis Mons, Gale crater, Mars

The Upper formation of Aeolis Mons in Gale crater exhibits curvilinear bedding patterns on the surfaces of several erosional benches that have been interpreted as cross-bedding. We use High Resolution Imaging Science Experiment (HiRISE) stereo topography to test this hypothesis by measuring the bedding geometry within these benches. The bedding geometry is consistent with aeolian cross-beds: measured dips rarely exceed the angle of repose, and the distribution of dip azimuths is non-random, allowing dune morphology and paleo-transport directions to be inferred using computer models of bedforms. The inferred dune type and transport direction vary between the benches of the Upper formation, indicating that the benches are separated by sufficient time for the wind regime to change. The paleo-wind directions derived from bedding geometry measurements differ from modern wind modeling results, suggesting that the conditions during deposition of the Upper formation were unlike modern conditions. The concentric bedding patterns in some locations indicate that the rate of deposition approached the rate of bedform migration. The evidence for lithified hundred-meter-scale dunes in the Upper formation of Aeolis Mons indicates that the area was a sediment sink at the time of formation, and any hypothesis for the formation of Aeolis Mons must be compatible with these results. We present one possible sequence of events for the formation of Aeolis Mons.

Ancient Martian aeolian processes and palaeomorphology reconstructed from the Stimson formation on the lower slope of Aeolis Mons, Gale crater, Mars

AbstractReconstruction of the palaeoenvironmental context of Martian sedimentary rocks is central to studies of ancient Martian habitability and regional palaeoclimate history. This paper reports the analysis of a distinct aeolian deposit preserved in Gale crater, Mars, and evaluates its palaeomorphology, the processes responsible for its deposition, and its implications for Gale crater geological history and regional palaeoclimate. Whilst exploring the sedimentary succession cropping out on the northern flank of Aeolis Mons, Gale crater, the Mars Science Laboratory rover Curiosity encountered a decametre‐thick sandstone succession, named the Stimson formation, unconformably overlying lacustrine deposits of the Murray formation. The sandstone contains sand grains characterized by high roundness and sphericity, and cross‐bedding on the order of 1 m in thickness, separated by sub‐horizontal bounding surfaces traceable for tens of metres across outcrops. The cross‐beds are composed of uniform thickness cross‐laminations interpreted as wind‐ripple strata. Cross‐sets are separated by sub‐horizontal bounding surfaces traceable for tens of metres across outcrops that are interpreted as dune migration surfaces. Grain characteristics and presence of wind‐ripple strata indicate deposition of the Stimson formation by aeolian processes. The absence of features characteristic of damp or wet aeolian sediment accumulation indicate deposition in a dry aeolian system. Reconstruction of the palaeogeomorphology suggests that the Stimson dune field was composed largely of simple sinuous crescentic dunes with a height of ca 10 m, and wavelengths of ca 150 m, with local development of complex dunes. Analysis of cross‐strata dip azimuths indicates that the general dune migration direction and hence net sediment transport was towards the north‐east. The juxtaposition of a dry aeolian system unconformably above the lacustrine Murray formation represents starkly contrasting palaeoenvironmental and palaeoclimatic conditions. Stratigraphic relationships indicate that this transition records a significant break in time, with the Stimson formation being deposited after the Murray formation and stratigraphically higher Mount Sharp group rocks had been buried, lithified and subsequently eroded.

Evaluation of the impact of rock fracturing on the reservoir properties on the example of the hydrocarbon-bearing sandstones in the Polish part of the Western Carpathians - a case study

So far, the largest documented reserves of oil in the Skole unit are found in the Wańkowa-Łodyna-Brzegi fold, where the reservoir rock is composed of the sandstones belonging to layers of the menilite series. The oil inflow from Inoceramian, Hieroglyphic and Krosno layers was also obtained from this fold. These layers characterized by a low level of reservoir parameters, are associated with the presence of a system of fractures. The impact of fracturing on the permeability of these sandstones is of interest to the oil industry. The aim of the research was to carry out measurements of the basic geometric parameters of fractures, i.e: the length of the fracture trace, the assessment of the degree of mineral fill, the openness and the determination of the angle and azimuth of fracture dip. Then, linear densities, surface coefficients of fracture and the fracture permeability coefficient were calculated for each measuring field. Obtained research results in the form of diagrams, tables and diagrams showed that inoceramian sandstones belong to rocks of low-class reservoir capacity. The analyzed sandstones are characterized by low permeability and have a low effective porosity. The results of the analyzes carried out simultaneously confirmed the effect of the fracturing of inoceramian sandstones on their potential permeability.

A3Mark: Seismic attribute benchmarking

Seismic attribute computation is one of the most active research and engineering topics in the computational geophysics world. Although numerous algorithms for seismic attribute computation have been developed, relatively little work has been done on scientifically characterizing their quality and accuracy. Seismic attribute characterization effort is largely qualitative and subjective. We have developed a robust and reliable scientific process for functionally comparing similar attributes. Structural seismic attributes are addressed, including discontinuity, dip angle, dip azimuth, and curvature. To establish a common software platform, and collection of data sets for efficient fully automatic evaluation, a stand-alone flexible online web service is designed. It is based on a C#-MATLAB implementation, and it is called A3Mark. The publicly available web service enables the automatic evaluation of individual categories of seismic attributes using customized quality metrics. It can be easily extended to include new algorithms. Several new synthetic data sets covering various structural measurements are also created, including noise, with ground truth, and they are made publicly available through the web service. Finally, a comparative evaluation of some current seismic attribute algorithms is given with quantitative and qualitative results.

Research on the Mechanism and Control Method of Azimuth Drift in Shale Gas Horizontal Wells

Horizontal well has the technical superiority to improve recovery rate of unconventional reservoirs, which is widely used in shale oil and gas exploration. However, serious azimuth drift problems occurred commonly in shale gas horizontal wells in Weiyuan, Sichuan, China, which seriously affected the control of well trajectory, and the reason is not clear. At first, we measured the drillability anisotropy and acoustic travel time of rock sampled from field, and set up a model to evaluate rock drillability anisotropy by logging data. Then, combing the model with the previous study on formation force model, for a certain field instance, we analyzed and summarized the main factors influencing azimuth drift are:1) formation drillability indexes 2) the angle between the drilling azimuth and formation down dip azimuth. The main method to control the drift is to optimize angle between the drilling azimuth and formation down dip azimuth. Our research initially came up with the method to evaluate orthotropic rock drillability anisotropy by logging data and the main method to control the azimuth drift, so it`s significant for shale drilling.

Detection of potential methane gas pathways in deep South African gold mines

At a number of gold mines in South Africa, methane gas has been encountered when drilling into faults and/or dykes extending to depths beyond 7000 m. Methane gas has been reported to migrate up through structures from within the basin to the mine working environments (∼3000 m depth) and caused explosions. The Booysens Shale is one of the possible source rocks for hydrocarbons and it forms the footwall to the gold-bearing Ventersdorp Contact Reef (VCR, ∼1.5 m thick). The Booysens Shale lies at depths between 3500 and 4500 m below the surface and can be best described as a base of the divergent clastic wedge, hosting the quartzite and conglomerate units that sub-crop against the VCR towards the west of the gold mining areas. Geometric attributes (dip and dip azimuth) and instantaneous attributes (phase, frequency and envelope) computed for the Booysens Shale and VCR horizons provide insight into structures that extend from the Booysens Shale into the overlying mining level (i.e. VCR). These attributes successfully mapped the structures (faults and dykes) that have displaced both the VCR and Booysens Shale horizons. The edge-detection attributes were particularly useful in delineating faults with throws below the traditional seismic resolution criteria (e.g. a quarter of the dominant wavelength) that were not visible in the conventional seismic interpretation. The structural analysis using seismic attributes gives a new visual representation of geological structures that may be probable conduits for hydrocarbons, particularly methane, migrating from the Booysens Shale to the VCR mining levels.

Wind-pattern circulation as a palaeogeographic indicator: Case study of the 1.5–1.6 Ga Mangabeira Formation, São Francisco Craton, Northeast Brazil

The preserved deposits of dune-scale aeolian bedforms provide valuable palaeoenvironmental indicators of atmospheric circulation patterns and the latitudinal position and distribution of land masses. However, no attempts to use palaeowind directions and palaeogeographic reconstructions of ancient land mass distribution have been published to model Precambrian atmospheric circulation. The Mangabeira Formation is a large Mesoproterozoic aeolian erg succession (1.6–1.5Ga) composed of two aeolian units that accumulated in the São Francisco Craton, Brazil. The Lower Unit records multiple drying-upward depositional cycles, each of which represents an episode of erg expansion and contraction driven by climate changes. The Upper Unit is composed dominantly of stacked aeolian dune strata that lack intervening interdune deposits and which record extreme aridity. Palaeowind directions recorded from cross-strata of transverse, crescentic aeolian dunes of the Lower and Upper Units record dune migration under the influence of two dominant winds that blew to the southeast and northwest. Analysis of these palaeowind data in relation to assessment of regional palaeogeographic reconstructions for the period 1.6–1.5Ga reveals a correlation between atmospheric circulation and land mass distribution. At this time the São Francisco Craton was located between the mid-latitudes and the equatorial zone. The wind regime determined from analysis of dip azimuths of cross-strata of the Lower Unit (1.6–1.54Ga) are consistent with a palaeogeographic position between 25° and 35° S. Analysis of cross-strata dip azimuths of the Upper Unit indicate northwest-directed palaeowinds and a dominant monsoonal wind pattern from 1.54 to 1.5Ga. During this time the large land mass of the São-Francisco-Congo and Siberian cratons drifted northwards through the equatorial zone from palaeolatitude 30° S to 30° N.

Detection of sedimentary structural elements using formation micro imager technique, a case study from South Mansoura-1 well, Nile Delta, Egypt

A detailed structure and sedimentology interpretation was performed for the South Mansoura-1 well. The Formation Micro Imager (FMI) is recorded and interpreted over the interval 9100–8009ft. This interval belongs to Sidi Salem and Qawasim Formations. Based on azimuth trend of manually picked dips (bed boundaries), the interval can be divided into 4 structural dip zones (Zone 1 (9100–8800ft), variable azimuth direction with the major trends mainly to SW≠ Zone 2 (8800–8570ft), bedding dip azimuth is mainly to the NW; Zone 3 (8570–8250ft), bedding dip azimuth is mainly to the NE; and Zone 4 (8250–8009ft), bedding dip azimuth is mainly to the NW). Lamination identified over the interval shows a dominant dip azimuth trend toward North North-West direction. The interbedded shale units are highly laminated and show little evidence of bioturbation. Sand exhibits abundant cross bedding showing a dominant dip azimuth trends toward NNE and NE and more locally to the E. Sixteen truncations identified over the interval show variable azimuth trend with the major trend mainly to the North North-West.

Customized interpretation workflow for simultaneous assessment of unconventional shale-gas reservoirs and conventional reservoirs using seismic and log data

The same geophysical and geologic data have been interpreted for both unconventional shale-gas and conventional sandstone reservoirs simultaneously by framing and using a customized workflow. Customization was needed because of property differences between the two types of resources. Unconventional shale reservoirs differ significantly from conventional reservoirs in depositional environment, diagenesis, physical properties, and production techniques. Magnitudes and patterns of reservoir properties (e.g., velocity, resistivity, radioactivity, porosity, permeability, etc.) of shales differ significantly from those of sandstone/carbonate reservoirs. In a conventional play, we generally search for intervals with relatively low gamma, high resistivity, and low neutron porosity, whereas in shale gas we search for intervals with very high gamma, relatively higher resistivity than lean shales, low velocity, and very high neutron porosity. Production from shales is largely due to horizontal drilling, hydrofracturing, and stimulations. The shale-gas reservoir properties are governed mainly by organic richness and its thermal maturation. Organic material has significant impact on the elastic/petrophysical properties, which are manifested in log and seismic responses. Thus, identification and mapping of shale-gas reservoirs is based mainly on mapping of total organic carbon- (TOC) rich zones. The customized workflow was developed for identification of shale-dominant intervals and organic-rich-zones within them by integrating log and seismic data. Shales generally show low-amplitude signals, and internal reflection configurations are not easily identified. Seismic data conditioning and seismic attributes, e.g., phase and perigram, were applied for internal geometry mapping. Once shale-gas markers were identified, mapping of shale boundary, depth, thickness, and areal extent was done similarly to conventional plays. Sweet spots were identified by generating and analyzing log-property volumes like impedance, sonic, resistivity, and neutron porosity. Natural fractures, which are helpful in designing well trajectory, were mapped through geometric seismic attributes like curvature and dip azimuth. This study has enhanced geologic understanding and, hence, mappability of shale-gas plays along with conventional plays. The customized workflow is applicable in all stages of shale-gas-play exploration and development.

Enhanced real-time determination of resistivity anisotropy and dip using multifrequency and multicomponent induction logging

Multicomponent induction (MCI) logging is able to provide a wealth of measurements at multiple subarrays and frequencies that can be used to evaluate complex subsurface formations. Real-time and postprocessing inversion methods have been introduced by various researchers for determining formation resistivity anisotropy (horizontal and vertical resistivity or conductivity), dip, and dip azimuth/strike using MCI measurements. The majority of these methods are based on single-frequency information. We have developed an enhanced real-time method and relevant workflow for determining formation resistivity anisotropy, dip, and dip azimuth using multifrequency MCI information. This enhanced method can be used to improve accuracy in formation evaluation applications, such as reservoir identification, hydrocarbon/water saturation calculation, and geologic and structural interpretation. Enhancements over the present single-frequency data processing include: (1) optimal harmonization of multiple single-frequency inverted logs, (2) robust determination of dip and dip azimuth angle for low-resistivity anisotropy ratios, (3) practical data-quality evaluation that takes into account the effects of formation resistivity, anisotropy ratio, and dip parameters, and (4) a new integrated workflow that can be used to determine formation anisotropy, true dip, and dip azimuth by integrating processed relative dip and azimuth and borehole directional logging data. Finally, all of these data process enhancements have been validated with synthetic data and field log data.

Display and enhancement of volumetric fault images

Fault picking is a critical, but human-labor-intensive component of seismic interpretation. In a bid to improve fault imaging in seismic data, we have applied a directional Laplacian of a Gaussian operator to sharpen fault features within a coherence volume. We computed an [Formula: see text] matrix of the second moment tensor distance-weighted coherence values that fell within a 3D analysis window about each voxel. The eigenvectors of this matrix defined the orientation of planar discontinuities, whereas the corresponding eigenvalues determined whether these discontinuities were significant. The eigenvectors, which quantified the fault dip magnitude and dip azimuth, defined a natural coordinate system for smoothing of the planar discontinuity. We rotated the data to the new coordinate system and applied the sharpening operator. By comparing the vector dip of the discontinuity to the vector dip of the reflectors, we could apply a filter to either suppress or enhance discontinuities associated with unconformities or low-signal-to-noise-ratio shale-on-shale reflectors. We have revealed the value and robustness of the technique by application to two 3D data volumes from offshore New Zealand, which exhibited polygonal faulting, shale dewatering, and mass transport complexes.

Fault Interpretation Using Image Logs

In oil and gas reservoirs, having the faults attributes such as dip inclination degree, dip azimuth, strike, location of the faults and the type of the faults is essential due to their effect on production rate. Therefore, in this work a new method will be introduced to provide this geological information. By using the Formation Micro Imager (FMI) tool, the fault interpretation job will be done in one of the Iranian production wells, located in Gachsaran field.