Anticlinal Structure Research Articles

Fold geometry and kinematics of inversion tectonics for Kosrat anticline, northeastern Iraq

The Kosrat anticline structure in the northeastern part of Iraq has been studied from structural and tectonic points of view. The anticline was described and classified according to the field measurements. The southwestern limb is steeper and shorter than the northeastern one which makes it an asymmetrical double-plunged anticline verging towards the southwest. The folding kinematics model was based on the changing of the competency of the formations to have a flexural slip fold that is controlled by the compositions of the layers and the primary response of each rock unit to the deformation. Structural and tectonic history of the anticline was interpreted according to the study of faults that have been reactivated. The deduction of the reactivation was through the comparison between the thicknesses of the geologic formations in both limbs of the anticline. Parts that differ in lithology and show deformation or crushing zones in different levels were observed as a footwall shortcut and used to indicate inversion. Thin sections analysis for rock samples in extension fractures showed evidence of a faulting mechanism represented by the deformed crystals to give a clue of being inverted faults in the Kosrat anticline.

Structural controls on coalbed methane accumulation and high production models in the eastern margin of Ordos Basin, China

Significant progress has been made in coalbed methane (CBM) exploration and development in the eastern margin of the Ordos Basin where nearly 2000 CBM wells have been drilled, achieving a maximum gas production rate of 16000 m3/d by 2013. The geological evolution of the eastern Ordos Basin plays an important role in the CBM formation. This study is focused on the interrelationship between structural geology, gas accumulation and production characteristics of the No. 4 + 5 coal in the Permian Shanxi Formation as well as the No. 8 + 9 coal in the Carboniferous Taiyuan Formation. This research is based on the data collected from CBM production wells and coal samples from coalmines and exploration wells. The results show that thermogenic gas is the dominant CBM source in the study area and there are two significant generation periods, the coalification in the Triassic and the magmatic thermometamorphism during the Yanshan movement. Combining the structure background and hydrogeological conditions, the monoclinic-hydraulic sealing model was proposed as the representative CBM enrichment model. Different types of structures are also classified, and their influence on the CBM accumulation is discussed. Compressional structures formed during the Yanshan movement are conducive to CBM enrichment and retention; however, the tensional structures formed during the Himalaya movement may have led to CBM dissipation. Combining the structural effect on the CBM production with CBM exploration and development practices in the study area, the following three types of high gas production models are summarized: updip of the monocline, the axial part of the anticline or nose structure, and the structural high far from the normal fault.

Geologic evolution of the Iraqi Zagros, and its influence on the distribution of hydrocarbons in the Kurdistan region

Whereas the vast majority of discovered hydrocarbon reserves in Iraq reside in Cretaceous and Cenozoic reservoirs, numerous oil and gas fields have been discovered recently in deeper Jurassic and Triassic reservoirs in the Kurdistan region of Iraq. This study presents a Middle–Upper Jurassic thermal maturity map for the Kurdistan region of Iraq and demonstrates that regional first-order trends in Jurassic source rock maturity show a close correlation to the spatial distribution of oil gravities within the overlying Jurassic (and Cretaceous) reservoirs. This distribution is consistent with compartmentalization of the active source rock kitchens due to Zagros folding, resulting in relatively short-distance migration and charge of the anticlinal structures from the adjacent synclinal lows. The thermal maturity map confirms relatively low maturity over the Mosul high, where the Cretaceous and Cenozoic section overlying the source rock interval is relatively thin, and increasing maturity to the southeast as the thickness of the Cenozoic foredeep sediments increases toward the depocenter located in the southeastern Iraqi Zagros and the adjacent Iranian Zagros. The correlative trend in oil gravities is exemplified by the recent Jurassic discoveries: low to medium gravity oils (14–27° API) in Shaikan and Atrush to the northwest, light oil (39–47° API) in Mirawa and Bina Bawi, and gas condensate (55° API) in Miran West to the southeast. Understanding thermal maturity patterns and hydrocarbon fluid-type distributions will help to guide risk assessment for remaining prospectivity and future exploration drilling within the Kurdistan region of Iraq.

Pitfalls in the seismic interpretation of fault shadow events — Vicksburg formation of south Texas

Reliance on prestack time-migrated seismic data to define structural highs without incorporating all subsurface data and without taking into account the regional and local lateral depositional trends may result in dry holes or poorly positioned production wells due to local velocity changes, which are usually caused by some depositional or structural phenomenon. Tying check-shot control to depositional units may reveal those phenomena and permit assumptions to be made about velocities in areas beyond check-shot control points. We discovered a significant gas accumulation in an area surrounded by dry holes and marginal wells in the Vicksburg Formation in McAllen Ranch Field, Hidalgo County, Texas, by treating a seismic velocity anomaly as a geologic problem and by simple application of arithmetic and geometry to a 3D velocity model. Due to the effects of the anomaly, seismic data displayed in time gave no indication of the existence of a 325 ha (800 ac), 150 BCFG anticlinal structure. A subsurface model that accounted for the velocity anomaly was able to predict its extent and severity by readily identifiable thickness changes in the anomalous units. The resulting discovery yielded a sevenfold increase in field production within a two-year time span.

Hydrocarbon reservoir volume estimation using 3-D seismic and well log data over an X-field, Niger Delta Nigeria

This study delineates and maps the hydrocarbon-bearing reservoir HD2000 from surface seismic sections and well logs within the depth interval of 5,700 ft (1,737 m) and 6,200 ft (1,890 m). The objective is to establish the geometry, reservoir distribution, delineate hydrocarbon-bearing reservoirs from surface seismic sections and well logs. In this process, a 3-D structural interpretation and estimation of the volume of hydrocarbon in place of the reservoirs was carried out. Well-to-seismic tie revealed that hydrocarbon-bearing reservoirs were associated with direct hydrocarbon indicators (bright spots and dim spots) on the seismic sections. Two horizons were studied (HD2 and HD2_version2) and several faults mapped for the purpose of carrying out 3-D subsurface structural interpretation. This was used in generating the time structure maps. From the maps, it was observed that the principal structure responsible for hydrocarbon entrapment in the field was the anticlinal structure at the center of the field which tied to the crest of the rollover structure seen on the seismic sections. Check shots from the control well were used to create a velocity model from which the time to depth conversion was made. Horizon slice taken shows the reservoir spans a thickness of 400 ft. Direct hydrocarbon indicators were used to map the reservoir boundary. They were seen on the reflection amplitude maps as high amplitude zones (bright spots) and low amplitude zones (dim spots). Reservoir area extent estimated by square grid template method revealed that reservoir HD2000 had an area estimate of 5.29 km2. The results show the effectiveness of the estimation techniques in the lateral prediction of reservoir properties, discriminating litho-fluid and determining the porosity, saturation, net-to-gross ratio, and moreover the reserve volume. Hydrocarbon saturation varied between 0.64 and 0.65, while effective porosity varied between 0.31 and 0.32. Estimation of the volume of hydrocarbon in place revealed that the delineated reservoir HD2000 contained an estimate of 776,545,418.22 barrels (123,460,855.4 cm3) of hydrocarbon which shows great potential of considerable size.

Plume Migration of Different Carbon Dioxide Phases During Geological Storage in Deep Saline Aquifers

This study estimates the plume migration of mobile supercritical phase (flowing), aqueous phase (dissolved), and ionic phase CO_2 (bicarbonate), and evaluates the spatial distribution of immobile supercritical phase (residual) and mineral phase CO_2 (carbonates) when CO_2 was sequestered. This utilized a simulation, in an anticline structure of a deep saline aquifer in the Tiechenshan (TCS) field, Taiwan. All of the trapping mechanisms and different CO_2 phases were studied using the fully coupled geochemical equation-of-state GEM compositional simulator. The mobile supercritical phase CO_2 moved upward and then accumulated in the up-dip of the structure because of buoyancy. A large amount of immobile supercritical phase CO_2 was formed at the rear of the moving plume where the imbibition process prevailed. Both the aqueous and ionic phase CO_2 finally accumulated in the down-dip of the structure because of convection. The plume volume of aqueous phase CO_2 was larger than that of the supercritical phase CO_2, because the convection process increased vertical sweep efficiency. The up-dip of the structure was not the major location for mineralization, which is different from mobile supercritical phase CO_2 accumulation.

An integrated approach to defining well placement strategies for heterogeneous CSG reservoirs

Operators developing the vast CSG resources held in the Surat and Bowen basins of Queensland, Australia, face significant challenges. Given the heterogeneous nature of CSG reservoirs, and often sparse data from wells and 2D seismic, there are significant uncertainties regarding reservoir quality and productivity. The prolific number of wells required to extract the economic reserves (more than 30,000) requires workflows that can efficiently integrate information for rapid development planning. Traditionally, most of the efforts dedicated to assessing uncertainties in CSG reservoirs focus on the estimation of the gas-in-place (GIP), and how it varies laterally. Variations in productivity (mainly dependent on permeability) are usually more abrupt, have a larger impact on project economics, and are far less understood than the GIP. Authors such as Chopra and Marfurt (2012) have recently developed analytical methods using 3D seismic attributes to identify fractured areas with higher permeability. As well as permeability, other factors influencing productivity, such as GIP, thickness, depth and saturation, must be combined to define a complete well placement strategy. In this study, the authors propose a holistic approach for the assessment and integration of the uncertainties in CSG reservoirs, using the Baralaba Coal Measures in the Bowen Basin as a case study to demonstrate the workflow. Various seismic attributes are used to identify fracture drivers associated with faulting and folding around the Burunga Anticline structure, and map areas predicted to have higher permeability, calibrated against well production. Chance-of-success mapping is used to integrate the permeability heterogeneities with traditional well-derived maps of coal properties, such as gas content, to isolate sweet spots in the CSG reservoir. The integrated model is transformed into geological pseudo-cost and combined with surface development costs and restraints to automatically generate potential well placement scenarios.

Detachment Surface Morphology and Shortening Distribution in the Foreland Folds of Iraq

Determinations of detachment surface depth and amount of local shortening were carried out in the more specific location foreland folds of Iraq. Twenty one traverses of anticlinal structures which are normally distributed on the study area were used for this application. Two types of deformation styles were found in the study area. They are thin-skinned and thick-skinned tectonics. Depth of the detachment surface generally increases towards east with as abnormal case appeared in Aqra Anticline. Westerlythe depth becomes shallower depth from the south towards Dohuk Anticline and it returns to increase toward the north. In Ain Zala, Butma West, Dohuk and Dahqan Anticlines and some parts of Bekhair Anticline, thin-skinned style was indicated. The shortening generally increases towards the north and northeast, with specific anomaly at Permam Dagh. It increases in the area after Permam Dagh to the north and northeast. However southeast of this area has low amount of shortening and the lowest appears in Qara chauq Anticline.

The A-to-Z of faulting in the offshore Arabian Gulf: Arabian trend structures overprinted by a Zagros wrench-fault assemblage

Abstract.Most major fields in the northeastern area of Saudi Arabia and Kuwait are anticlinal structures developed above north-northeast–south-southwest-trending basement lineaments. Based on structural interpretation of 3D seismic data sets, the fault pattern over one such field in the offshore Arabian Gulf of Kuwait and Saudi Arabia was analyzed in detail and integrated into the regional tectonic framework. Two discrete fault sets were identified. First, a system of Cretaceous extensional block faulting was observed that is parallel to and associated with folding over the basement structure. Second, a complex wrench-fault assemblage was identified associated with a Palaeogene dextral couple across the Zagros suture, which overprinted the inherited structural fabric. Convex-upward, Zagros-parallel flower structures were interpreted along with coeval synthetic and antithetic strike-slip fault systems. The interpretation of two discrete faults sets was then applied to an adjacent field that proved to have experienced a more complex tectonic history. Integration of the seismic fault interpretation into the regional tectonic history provided a robust framework that enhanced the understanding of the fault pattern and the structural interpretation of a nearby more complex field.

3-D gravity modeling of basement reliefs an offshore case study in the Persian gulf, Iran

In this paper we have proposed a three-dimensional approach to determine depth of basement in which the density contrast varies parabolically with depth. This program based on Newtons forward difference formula that with optimization of gravity anomalies calculate depths of basement reliefs indeed are anticlinal and synclinal structures has been buried under sediments. This structures are the causes of the positive and negative gravity anomalies. We assume the measured gravity fields have been distributed on a horizontal plane and also sedimentary basin is combined of juxtaposition 3-D cubic prisms. The measurement stations of the gravity field (grid nodes) coincide with center blocks. The initial depth is computed using gravity data and the estimated depths are adjusted with iteration. The advantage of the method is utilization of positive and negative gravity anomalies together as two inputs for written algorithm as well as application of a coded non-linear filter. The efficiency of the code is illustrated with a set of synthetic gravity anomalies. Further, the code is exemplified with the gravity anomalies of an offshore case study in the Persian Gulf, Iran. The purpose of exploratory project in this area will include the development of Hydrocarbon Fields. Keywords: Basement, Gravity Anomalies, Newtons Forward Difference Formula, Non-Linear Filter, Persian Gulf.

Formation history of large anticlinal trap structures for unique gas pools in northern West Siberia (by the example of the Medvezh’e field)

We consider the formation history of high-amplitude anticlinal trap structures for unique Cenomanian gas pools using the example of the Medvezh’e field. Analysis shows that the Turonian-Cenozoic was the most crucial stage of formation of the world’s largest gas-bearing province in northern West Siberia. This stage was marked by (1) the formation of large anticlinal traps—petroleum-promising objects; (2) the highest intensity of gas formation, which caused the filling of these traps; and (3) the formation of the Kuznetsov seal, which shields the giant Cenomanian gas pools.

Seismic attributes add a new dimension to prospect evaluation and geomorphology offshore Malaysia

The Malay Basin is a mature Tertiary extensional basin with a later inversion regime in the Late Miocene. The general geology is simple “layer cake” seismically, with some compressive anticlinal inversion structures. The Borneo Basin, on the other hand, is tectonically complex, with steep dips, overthrust, and complex faulting. The rocks are unconsolidated, and geophysical techniques such as amplitude and other attributes should work well. In early years, seismic interpretation was based mostly on mapping structures. The advent of AVO and inversion technologies and pioneering geophysical work brought about increased usage of seismic attributes, solving various problems of geologic interpretation. In Southeast Asia, concentrated efforts since 2000 in seismic data acquisition and processing have resulted in significant improvement in data quality and hence success of attribute application. Seismic imaging and attributes meet challenges such as (1) inversion structural plays in the Malay Basin, (2) stratigraphic channels, (3) fractured basement, (4) deep high-pressure (HP) and high-temperature (HT) plays, (5) steep-dip/overthrust plays, (6) deepwater turbidite plays, (7) carbonate plays of Luconia Province, and (8) thin pay beds, often below seismic resolution, using spectral attributes. Various attributes can be applied to a widespread problem in prospect-maturation evaluation and reservoir characterization.

Structural and Stratigraphical Interpretation of Seismic Profiles along Safed Koh Trend (Eastern Part of Sulaiman Fold Belt), Pakistan

Safed-koh Trend is located in D.G.Khan district, Punjab province, Pakistan. It is a north south trending fold belt that lies in Eastern Part of Sulaiman Fold Belt. Seismic data correlation is done with the help of well data, Formations' tops, Synthetics and general stratigraphy of the area. The Structural and Stratigraphical interpretation shows subsurface variations. Depth model shows Dhodak, Rodho, Afiband and Zindapir anticlines, the four culminations of Safed-Koh Trend without marking the faults. Dhodak is a northern lower most culmination. Zindapir is the most uplifted one and broader structure comparatively that lies at southern edge. 3D subsurface Time & Depth models of Rubbly Limestone, Dunghan Formation, Pab Sandstone, Lower Goru Formation and Chiltan Limestone map Dhodak anticlinal structure with reverse faults at its flanks. Dunghan, Ranikot, Pab and Chiltan Formations in this area have already proved to be good quality reservoirs for gas. Pab Sandstone and sands of Lower Goru Formation of Cretaceous and Chilton Limestone of Jurassic age could also be the important reservoirs in unexplored area. Rock Physics analysis of Chilton Formation confirms the hydrocarbon potential.

Compaction and Migration of Hydrocarbons in East Baghdad Oil Field

An attempt is done to present a simple concept to combine the geochemical results with the concept of compaction- abnormality, reflecting a high variation in the porosity and internal pore pressure. The different compaction levels and the variation of the bulk volume may lead to the expulsion of fluids both hydrocarbon and interstitial H2O from high potential zones towards low potential zones, or in other words from low porosity towards high porosity areas. Furthermore, the both formations (Ratawi and Zubair) of lower Cretaceous age showing compaction trend as well as fluid expulsion current with a NW-SE trend of the primary hydrocarbon migration, while the sedimentary basin revealing a deepening towards the southern eastern part of the anticline structure. A change in thickness and the facieses of the rock packages is manifested. The horizontal porosity distribution of shales in Ratawi formation particularly in the upper part (15m thick) reveal differential compaction and such a mechanism is responsible for the kinetic of fluid and gas.

SUPERPOSE-An excel visual basic program for fracture modeling based on the stress superposition method

AbstractAn Excel Visual Basic program, SUPERPOSE, is presented to predict the distribution, relative size and strike of tensile and shear fractures on anticlinal structures. The program is based on...

The Mishrif, Yamama, and Nahr Umr reservoirs petroleum system analysis, Nasiriya oilfield, Southern Iraq

Forty rock samples were taken from cores and cuttings, and five oil samples were taken from Mishrif, Nahr Umr, and Yamama formations in the Nasiriya oilfield wells, of longitudinal, asymmetrical anticline structure, of about 34 km length and 13 km width located at the unstable plat form, Mesopotamian basin zone. Three major oil reservoirs in the Nasiriya oilfield: (1) Late Cenomanian–Early Turonian Mishrif Formation with reserved oil approximately 1,009 million tons show measured porosities up to 40 % and the oils are aromatic, medium gravity, high sulfur content, and interpreted as being sourced from: type II/III carbonate rocks interbedded and deposited in a reducing marine environment with high salinity based on biomarkers and isotopic analysis; Middle–Upper Jurassic age is based on sterane ratios analysis of isoprenoids and isotopes, and thermally mature source rocks. (2) The reservoirs of the Albian Nahr Umr of approximately 68 million tons reserved oil show measured porosities up to 23 %. (3) Late Berriasian–Early Valanginian Yamama formations of 275 million tons reserved oil measured porosities up to 28.8 %. The Nahr Umr and Yamama reservoirs oils are saturated, light to medium API gravity, low to medium sulfur content which are usually derived from marine shale and carbonate source rocks (containing type II kerogen). The upper seal is the Middle Miocene anhydrites of the Lower Fars Formation and the lower regional seal is Upper Jurassic Gotnia anhydrites. Source rock geochemical analysis suggests for all Cretaceous source rocks samples, immature to mature, and shows that the Sulaiy and Yamama formations to be of good quality source rock with high total organic carbon (up to 8 wt% TOC). The Lower Cretaceous source rocks were deposited in a suboxic–anoxic basin and show good hydrogen indices, and are likely to have charged the reservoirs with low amounts of hydrocarbons, during the Miocene. The most likely source rock for the Mishrif-, Yamama-, and Nahr Umr-reservoired oils are the Middle–Upper Jurassic source rock. The migration from the source rock is likely to be largely vertical and possibly along faults before reaching highly permeable reservoirs of the reservoir formations. Structural traps in the Mishrif, Nahr Umr, and Yamama formation reservoirs are likely to have formed in the Late Cretaceous.

Simultaneous measurements of radon and thoron, and their progeny levels in dwellings on anticlinal structures of Assam, India

Radon and thoron, and their progeny concentrations along with equilibrium factors for gas progeny and radiological risks to the residents have been measured in dwellings of Digboi and Mashimpur areas located on anticlines during the winter season. In this present investigation, twin-cup dosemeters fitted with LR-115 (II) nuclear detectors have been employed. The present work has shown that there exist considerable house-to-house variations in values with maximum values in mud houses and minimum values in assam type (AT) houses. It has been found that mean (and geometric standard deviations (GSD)) radon concentrations are 83.8 (1.3), 113.5 (1.1) and 157.2 (1.2) Bq m(-3) in AT, reinforced cement concrete (RCC) and mud houses in Digboi area and 63.0 (1.1), 87.1 (1.4) and 182.1 (1.2) Bq m(-3) in AT, RCC and mud houses in Mashimpur area, respectively. The overall mean radon concentrations in Digboi and Mashimpur are estimated to be 114.4 (1.4) and 100.0 (1.7) Bq m(-3). The mean radon concentrations are found to be less than the lower reference level of 200 Bq m(-3) of the International Commission on Radiological Protection (ICRP 2007). The thoron concentrations in Digboi area are estimated to be 31.1 (1.3), 50.8 (1.4) and 67.0 (1.6) Bq m(-3) in AT, RCC and mud houses, respectively, whereas in Mashimpur area, the thoron concentrations are estimated to be 26.4 (1.3), 44.4 (1.3) and 77.7 (1.3) Bq m(-3) in AT, RCC and mud houses, respectively. The mean annual effective doses in Digboi area are found to be 1.9 (1.3), 2.7 (1.2) and 4.1 (1.4) mSv y(-1) in AT, RCC and mud houses, respectively, while in the case of Mashimpur area, the mean annual effective doses are found to be 1.5 (1.4), 2.2 (1.2) and 4.9 (1.3) mSv y(-1) in AT, RCC and mud houses, respectively. Nevertheless, the obtained results are much lower than the upper reference level of 10 mSv (ICRP 2007).

Cenozoic deformation in the Otway Basin, southern Australian margin: implications for the origin and nature of post‐breakup compression at rifted margins

AbstractThere is growing recognition that pulses of compressive tectonic structuring punctuate the post‐breakup subsidence histories of many ‘passive’ rifted continental margins. To obtain new insights into the nature and origin of compression at passive margins, we have conducted a comprehensive analysis of the post‐breakup (<43 Ma) deformation history of the offshore Otway Basin, southern Australian margin, using a regional seismic database tied to multiple wells. Through mapping of a number of regional intra‐Cenozoic unconformities we have determined growth chronologies for a number of major anticlinal structures, most of which are ˜NE–SW‐trending folds that developed during mild inversion of syn‐rift normal faults or through buckling of the post‐rift succession. These chronologies are supplemented by onshore structural evidence and by thermochronological data from key wells. Whilst our analysis confirms the occurrence of a well‐documented pulse of late Miocene–early Pliocene compression, post‐breakup deformation is not restricted to this time interval. We highlight the growth of a number of structures during the mid‐late Eocene and the Oligocene‐early Miocene, with evidence for considerable temporal and spatial migration of strain within the basin. Our results indicate a long‐lived ˜NW–SE maximum horizontal stress orientation since the mid‐late Eocene, consistent with contemporary stress observations but at variance with previous suggestions that this stress orientation was initiated in the late Miocene by increased coupling of the Australian‐Pacific plate boundary. We attribute the observed record of deformation to a compressional intraplate stress field, coupled to the progressive evolution of the boundaries of the Indo‐Australian Plate, ensuring that this margin has been subject to ongoing compressional forcing since mid‐Eocene breakup. Our results indicate that compressional deformation at passive margins may be more common than is generally assumed, and that passive margin basins with evidence for protracted post‐breakup deformation histories can provide useful natural laboratories for obtaining improved understanding of the evolution of intraplate stress fields over geological timescales.

Subsurface Characterisation of a Saline Aquifer Cited for Commercial Scale CO2 Disposal

The Yorkshire & Humber area contains some of the biggest CO2 emitters in the UK. The UK Southern North Sea (SNS) contains a number of gas fields and saline aquifers which could provide storage for some of that CO2. National Grid Carbon (NGC) has plans to connect these sources and sinks via a shared 24” pipeline in a hub & spoke arrangement called “The Humber Cluster Project”. After several years of high level study using multi-client seismic surveys and a database of released well data, an anticlinal structure of around 25 km length and 8 km width with a 275 m thick Bunter sandstone formation (saline aquifer) was selected for detailed analysis. Two crestal wells in the structure called 5/42 were drilled in 1970 and 1990 looking for hydrocarbons but only brine was found. Basic formation evaluation logs were acquired in both wells. Limited core and pressure data were acquired in the 1990 well. No record of any water analysis is available and the core and log coverage was limited. As of mid-2012 some uncertainties remained with respect to the suitability of 5/42 for CO2 disposal. Little was known about the strength & permeability of the cap rock which consists of 10-12 m of shale overlain by about 80 m of halites and mudstones. Although the structure seems well defined and no major faulting was seen in the Bunter sandstone there was little reservoir permeability data, especially vertical permeability. In addition no flow test, production or injection, had been undertaken in 5/42. To address these issues, the company applied for and was awarded the UK's first Carbon Storage licence from the UK Government in November 2012 which permitted the drilling of appraisal well 42/25d-3 in the summer of 2013 with generous financial support from the European Commission (through their EEPR scheme) and the UK Energy Technologies Institute (ETI).

SUPERPOSE—An excel visual basic program for fracture modeling based on the stress superposition method

AbstractAn Excel Visual Basic program, SUPERPOSE, is presented to predict the distribution, relative size and strike of tensile and shear fractures on anticlinal structures. The program is based on the concept of stress superposition; addition of curvature-related local tensile stress and regional far-field stress. The method accurately predicts fractures on many Middle East Oil Fields that were formed under a strike slip regime as duplexes, flower structures or inverted structures.The program operates on the Excel platform. The program reads the parameters and structural grid data from an Excel template and writes the results to the same template. The program has two routines to import structural grid data in the Eclipse and Zmap formats.The platform of SUPERPOSE is a single layer structural grid of a given cell size (e.g. 50×50m). In the final output, a single tensile or two conjugate shear fractures are placed in each cell if fracturing criteria are satisfied; otherwise the cell is left blank. Strike of the representative fracture(s) is calculated and exact, but the length is an index of fracture porosity (fracture density×length×aperture) within that cell.