Major Growth Faults Research Articles

The Messinian reservoir in El-Tamad oil field, Nile Delta, Egypt: Seismic interpretation and 3D modeling

El-Tamad Field, the first oil discovery in the onshore Nile Delta, is one of the promising areas in the Nile Delta for oil and gas. Therefore, thirty seismic lines, core data, and real-time flowline resistivity measurements of the Messinian Qawasim Formation were analyzed to characterize and model the reservoir in El-Tamad Field. The structure model shows that there are three main faults in the investigated area; F1 fault is a major growth fault trending E-W with a downthrown to the north, F2 trending NW-SE with a downthrown northeast, and the NE-SW trending F3 fault with a downthrown southeast. The depth-structure contour map on the reservoir's top shows that there is a rollover anticline fold formed at the downthrown side of the major growth fault. The petrophysical model illustrates that effective porosity increases towards both of southeastern and southwestern parts, while water saturation decreases in the southeastern part of the field, and the net-to-gross increase towards the center. Penetrating more vertical and sidetrack wells along the line connecting wells 1, 3, and 4 in El-Tamad Field, especially in the crest of the anticline fold that was recorded in the area is highly recomended. The spatial variation of the reservoir quality was attributed to the depositional setting, where many branches of larger distributary channels (sand facies) accumulated within a muddy estuary (shale facies) on the front of a bay-head delta.

Rectangular drainage pattern of a submarine canyon controlled by extensional tectonic structures: Case study of the Afam Incision Surface (Tortonian, Niger Delta, Nigeria)

Submarine canyons are a key element of the growth of continental margin depocentres such as the Niger Delta, the progradation of which is commonly influenced by syn-sedimentary processes of gravity-driven tectonism. In such setting, canyons commonly constitute combined stratigraphic-structural traps because of: (i) their clayey infilling and, (ii) the incision of marine reservoirs. Nevertheless, most of the time, their drainage network and/or the external factors leading to their formation are poorly characterized, which is also the case in other settings when the resolution of geophysical dataset is less accurate. Here we use 3D seismic reflection data from the onshore eastern Niger Delta to study the morphology of a buried canyon system in relation to extensional tectonic structures, which are E-W trending growth-faults and roll-over anticlines. We map the Afam Incision Surface (AIS), which cuts up to 1000 m into subjacent Eocene-Miocene deltaic and continental series. In planform, the AIS is organized in 6 stream orders. The Afam Canyon which has the highest stream order is globally NNW-SSE oriented and is locally controlled by E-W oriented grabens, which give it right-angle changes of direction. It perpendicularly captures 5th and 4th order tributaries, each of which has an asymmetric cross-sectional profile controlled by one major growth-fault. In the southern area, the western tributaries all include an upstream part that drains in the opposite direction to the regional slope, leading to bayonet-shaped paths in planform. Whatever the stream order of the tributary considered; its increase is controlled by growth-faults. Therefore, the AIS planform network has the characteristics of a rectangular pattern. Erosion of the AIS as a submarine canyon system is consistent with its more than one-kilometer depth, preserved knickpoints within the thalweg of the main canyon; and the many erosional terraces boarded by arcuate scarps located along the main canyon and its tributaries. The formation of the AIS is correlated to the 50 m Tor2 sea-level fall at 9.5–9.2 my, and may have been initiated by by-pass currents that acted in tandem with retrogressive erosion. The latter greatly contributed to deepening and widening of the canyon and its tributaries whatever the orientation of the local slope. Erosion of the AIS was favored by the high-density of growth-faults. During the final excavation phases, the channelization of longshore drift currents by the canyon and its tributaries probably contributed to the destabilization of their upper margins.

The Application of Seismic Attributes in Fault Detection and Direct Hydrocarbon Indicator in Tomboy Field, Western-Offshore Niger Delta Basin

Seismic attribute analysis is important in subsurface data interpretation, such as seismic interpretation, which could involve seismic stratigraphic and structural interpretation. This interpretation is often hampered by seismic resolution and, sometimes, human inability to identify a subtle feature on the seismic. These factors have frequently led to the poor seismic interpretation of geologic features. Thus, an integral approach to studying structural patterns and hydrocarbon bearing zones using seismic attributes was carried out on the Tomboy field using 3D seismic data covering approximately 56 km2 of the western belt of the Niger Delta. The seismic volume underwent post-stack processing, which enhanced seismic discontinuities. A deep steering volume was first created, and several dip filters were applied to enhance faults in the study area. After that, curvature and similarity attributes were calculated on the dip-steered and fault-enhanced volume. These calculations show detailed geometry of the faults and zones of subtle lineaments. Six faults (F1, F2, F3, F4, F5 and F6) were identified and mapped. These faults range from antithetic to crest growth faults. Two major growth faults (F5 and F6) were revealed to dip in the northeast to southwest directions. A near-extensive crest fault (F4) appeared beneath the major faults. Although several minor fractures were displayed in the southern and central portions of the crest fault of the dipping seismic data, the southwest (F4) and growth fault, F6, are responsible for holding the hydrocarbon found within the identified closures. Using attributes on the seismic data increased confidence in mapping and interpreting structural features. Furthermore, energy attributes were used as Direct Hydrocarbon Indicators (DHI) to visualize viable areas within the study, which allows a more robust interpretation. Time slices were taken in regions of flat and bright spots. The spectral decomposition attribute was run on these slices to display areas of high amplitude reflection typical of hydrocarbon-bearing regions trapped mainly by regional to sub-regional growth faults. The surface attribute calculated on the generated surface shows that the field is predominantly controlled by faults serving as traps for hydrocarbon.

INTEGRATION OF LOGS AND SEISMIC DATA FOR DELINEATION OF DEPOSITIONAL ENVIRONMENT OF CLASTIC SEDIMENTS IN TOMBOY FIELD, NIGER DELTA

The depositional environment of Clastic sediments in Tomboy Field Onshore Niger Delta were delineated using 3D Seismic and lithological logs. Well log suites from 5 wells comprising Spontaneous potential, Gamma ray, Sonic, Resistivity, Density, and Neutron logs were obtained and analyzed. Reverse estimation was done for the Neutron log and Bulk Density log using volumetric method. Gamma-ray log were used to calibrate Log motifs and correlate sand bodies TMB-01, TMB-02, TMB-03, TMB-04, and TMB-06. Prediction of depositional environment was made through the usage of wireline log shapes of facies combined with result from seismic data. Results of correlation across the five wells showed that. there was continuity at depth interval of 4000-5000ft across the wells as well 3 did not have any gamma information to correlate accros it. The seismic section showed two major growth faults and a channel fill on seismic (inline 5940, crossline1660) between 3.3-3.6ms. According to the paleo-reconstruction from the correlated wells within the tomboy field, the reservoir is made up of sands from fluvial and tidal channels, barrier, and barrier bar. These sand bodies are likely to contain hydrocarbons because of the rollover anticline, which is found at the fault’s downthrown block. This study has revealed that the Clastic sediments in Tomboy Field Onshore Niger Delta were deposited within a predominantly deltaic environment (transitional).

3-D Seismic Structural Interpretation of High Field Offshore Western Niger Delta

Seismic Structural interpretation of subsurface system is a vital tool in mapping source rocks and good trapping system which enhances good understanding of the subsurface system for productive drilling operation. This study is geared towards mapping the structural traps available within the hydrocarbon bearing zones of the “High field” with the use of well log and 3D seismic data. Seven horizons (H1, H2, H3, H4, H5, H6 and H7) were identified on well logs using gamma ray log and resistivity logs. Nine (9) faults were mapped on seismic sections across the field, two (2) of which are major growth faults (F1 and F2), two (2) synthetic faults (F3 and F7) and five (5) antithetic faults (F4, F5, F6, F8 and F9). Rollover anticlines which are structural closure and displayed on the depth structural maps suggest probable hydrocarbon accumulation at the down throw side of the fault F1. Structural interpretation of high field has revealed a highly fault assisted reservoir which depicts the tectonic setting of Niger Delta basin.

Seismic amplitudes and spectral attribute analysis in reservoir characterisation, \u2018MUN\u2019 onshore Niger delta field

Integrating seismic amplitudes and spectral attribute analysis has successfully mapped, validated and characterised hydrocarbon-saturated channel sands by high-amplitude low-frequency anomaly. The aim of the study was targeted at using these novel geophysical tools to improve characterisation of tertiary clastic reservoir in the field. These attributes were extracted along H4 seismic horizon and analysed independently for structure, lithology and hydrocarbon saturation. The result of the analysis shows that both attributes complimented each other in mapping the hydrocarbon-saturated reservoir channel sands. However, the spectral attributes in combination with spectral-based Red, Blue and Green (RGB) colour blending attribute map reveal finer and subtle details of the channel structure and stratigraphy which hitherto were not apparent in the seismic amplitude maps. The channel sands trend NE–SW, broadening towards the southwest and bounded by major growth faults to the northeast and southwest, respectively. It is thick to the southwest and thins to the northeast. By-passed hydrocarbon prospect was delineated to the northeast of the existing wells, and as such, infill wells can be drilled in these areas to recover hydrocarbons.

Transition zones analysis using empirical capillary pressure model from well logs and 3D seismic data on \u2018Stephs\u2019 field, onshore, Niger Delta, Nigeria

Capillary pressure is an important characteristic that indicates the zones of interaction between two-phase fluids or fluid and rock occurring in the subsurface. The analysis of transition zones (TZs) using Goda (Sam) et al.’s empirical capillary pressure from well logs and 3D seismic data in ‘Stephs’ field, Niger Delta, was carried out to remove the effect of mobile water above the oil–water contact in reservoirs in the absence of core data/information. Two reservoirs (RES B and C) were utilized for this study with net thicknesses (NTG) ranging from 194.14 to 209.08 m. Petrophysical parameters computed from well logs indicate that the reservoirs’ effective porosity ranges from 10 to 30% and the permeability ranges from 100 to > 1000 mD, which are important characteristics of good hydrocarbon bearing zone. Checkshot data were used to tie the well to the seismic section. Faults and horizons were mapped on the seismic section. Time structure maps were generated, and a velocity model was used to convert the time structure maps to its depth equivalent. A total of six faults were mapped, three of which are major growth faults (F1, F4 and F5) and cut across the study area. Reservoir properties were modelled using SIS and SGS. The capillary pressure log, curves and models generated were useful in identifying the impact of mobile water in the reservoir as they show the trend of saturating and interacting fluids. The volume of oil estimated from reservoirs B and C without taking TZ into consideration was 273 × 106 and 406 × 106 mmbbls, respectively, and was found to be higher than the volume of oil estimated from the two reservoirs while taking TZ into consideration which was 242 × 106 and 256 × 106 mmbbls, respectively. The results have indicated the presence of mobile water, which have further established that conventionally recoverable hydrocarbon (RHC) is usually overestimated; hence, TZ analysis has to be performed for enhancing RHC for cost-effective extraction and profit maximization.

3D Spatial Distribution of Reservoir Parameters for Prospect Identification in ''Bizzy'' Field, Niger Delta

This study focuses on the use of some geostatistical tools to spatially distribute reservoir parameters in order to identify the bypassed prospects from the earlier seismic interpretation that was carried out in the field using 3D seismic data. Four wells and seismic data were used to generate the interpreted input horizon grids, fault polygons and to carry out detailed petrophysical analysis. Structural and property modeling which include; facies, net to gross, porosity and water saturation were distributed stochastically within the constructed 3D grid using Sequential Gaussian Simulation (SGS) algorithm. The reservoir structural model show system of different oriented growth faults F1 to F9. Faults F1, F2, F3 and F4 were the major growth faults, dipping towards south-west and are quite extensive almost across all the seismic section. A rollover anticline formed as a result of deformation of the sediments deposited on the downthrown block of fault F1. The other faults were minor fault (synthetic and antithetic). The trapping mechanism is a fault assisted anticlinal closure. Results from well log analysis and petrophysical models shows Godwin reservoir to be a moderate to good reservoir in terms of facies, with good net to gross, porosity, permeability and low water saturation. This study has also demonstrated the effectiveness of 3D geostatical modeling technique as a tool for better understanding the distribution with respect to space of continuous reservoir properties. It will also provide a framework for the future prediction of reservoir qualities and yield rate of the reservoirs.

Sequence stratigraphy, structural framework and hydrocarbon migration of Ariki Field, Nigeria

Abstract The structural framework and stratigraphy of the Ariki Field in the Western Shallow Offshore Depobelt, Niger Delta Basin, Nigeria are interpreted using well logs and 3-D seismic data, and the control of rift on hydrocarbon accumulation is analyzed. Five maximum flooding surfaces and five sequence boundaries are identified in the major reservoir succession of Agbada Formation in the field; and the structural framework of the field is controlled by the major growth faults, minor faults and rollover anticlines formed by synsedimentary tectonic movements. There are a total of seven faults identified across the field, including three major faults and four minor faults. On the western flank of the field, graben and horst-like structures were bounded by minor faults. Fault throw analysis shows that below 1800 ms, the major faults with large fault throws act as hydrocarbon migration pathways, while above 1 800 ms, faults with small throws act as seals of hydrocarbon traps. There are four-way dip rollover anticlines and three-way downdip traps created by the minor faults. Six other prospective traps (drilling targets) were identified, which have promising oil accumulation potential.

High-frequency stacking pattern and stages of canyon/gully evolution across a forced regressive shelf-edge delta-front

The succession of varying facies tracts filling within a canyon, or a deep incised gully, cutting across the delta-front lobes at the shelf-edge requires to be explained by high-frequency allocyclic and/or autocyclic events. A ‘fifth- and sixth-order’ sequence-stratigraphic model for the shelf-edge canyon-fill or gully-fill is here proposed for the first time. The first Gelasian cold phase and the renewal of transpressional uplift of basin-margin occurring at the same time enforced regressive transit of the inner-shelf paleo-Orinoco delta onto the paleo-shelf-edge. Its delta-front developed along the shoulders of the major successive basin-bounding growth faults. The delivery of clastic sediments into the deeper slope and beyond in the Columbus Basin was through the gullies and canyons that incised and cannibalized across the shelf-edge delta. The Mayaro Formation of southeast Trinidad furnishes the role of growth faulting during the first phase of delta-front development at the paleo-shelf-edge. Thereby, it serves as an example of several ‘fifth-order sequences’, within a ‘fourth-order’ equivalent episode, which is contemporaneous to both the glacio-eustatic episode, the Pretiglian, and the renewal of transpressional uplift after a pause during the Pliocene. Thus, large incision and subsequent filling within the Mayaro Formation cover a passage of time (‘fifth-order’ equivalent) that is unequivocally shorter than the span of the falling Pretiglian eustatic sea-level and second renewed phase of transpression tectonism. The categorization of sedimentary facies of the canyon-fill or gully-fill and the encasing delta-front outside the canyon/gully cut into a series of ‘sixth-order’ genetic facies tracts shows variations of geomorphic stages of the canyon/gully evolution – from accommodation creation to the stages of filling. These stages, therefore, should be attributed to the ‘sixth-order’ equivalent autogenic changes influenced by high-frequency growth-tectonics, instead of assuming the stages to be related to the relatively lower-frequency glacio-eustatic allocyclicity of the earliest Gelasian.

Static Reservoir Modeling Using Well Log and 3-D Seismic Data in a KN Field, Offshore Niger Delta, Nigeria

This study focuses on the application of 3D static model using 3-D seismic and well log data for proper optimization and development of hydrocarbon potential in KN field of Niger Delta Province. 3D Seismic data were used to generate the input interpreted horizon grids and fault polygons. The horizon which cut across the six wells was used for the analysis and detailed petrophysical analysis was carried out. Structural and property modeling (net to gross, porosity, permeability, water saturation and facies) were distributed stochastically within the constructed 3D grid using Sequential Gaussian Simulation and Sequential Indicator Simulation algorithms. The reservoir structural model show system of different oriented growth faults F1 to F6. Faults 1 and Fault 4 are the major growth faults, dipping towards south-west and are quite extensive. A rollover anticline formed as a result of deformation of the sediments deposited on the downthrown block of fault F1. The other faults (2, 3, 5 and 6) are minor fault (synthetic and antithetic). The trapping mechanism is a fault assisted anticlinal closure. Results from well log analysis and petrophysical models classified sand 9 reservoir as a moderate to good reservoir in terms of facies, with good porosity, permeability, moderate net to gross and low water saturation. The volumetric calculation of modeled sand 9 horizon reveals that the (STOIIP) value at the Downthrown and Ramp segment are 15.7 MMbbl and 3.8 MMbbl respectively. This implies that the mapped horizon indicates hydrocarbon accumulation in economic quantity. This study has also demonstrated the effectiveness of 3-D static modeling technique as a tool for better understanding of spatial distribution of discrete and continuous reservoir properties, hence, has provided a framework for future prediction of reservoir performance and production behavior of sand 9 reservoir. However, more horizontal wells should be drilled to enhance optimization of the reservoir.

The Use of Seismic Attributes to Enhance Fault Interpretation of OT Field, Niger Delta

An integrated approach to the study of the fault patterns and seismic attributes was carried out on the OT field using a 3D swamp seismic data covering approximately 420 Km2 of western belt of the Niger Delta. This study aimed at improving the visualization of faults in the study area using different seismic attributes. Three major growth faults dipping south with few antithetic faults dipping in opposite direction to the growth faults and other minor faults were identified manually on the original and steered seismic cube in the inline 11669, while in the cross line only one major fault was identified manually. The seismic volume was subjected to several stages of post-stack processing to enhance discontinuities. First, a dip-steering volume was created. Several dip-steered filters were then applied to enhance faults and fractures visualization. Finally, similarity and curvature attributes were calculated on the dip-steered and fault enhanced volume. These final attributes show detailed geometry of the fault system and the numerous subtle lineaments in the study area. The integration of the attributes has increased confidence in the seismic mapping of the faults and the other numerous subtle lineaments which were difficult to identify on the input data. Similarity and curvature attributes of the seismic volume preserve subtle structural details and permit a more robust interpretation of the structures.

The Use of Seismic Attributes to Enhance Structural Interpretation of Z-Field, Onshore Niger Delta

An integrated approach to the study of the structural patterns and seismic attributes was carried out on the Z-field using a 3D seismic data covering approximately 56 Km2 of western belt of the Niger Delta, checkshot data for well to seismic tie and log information for six wells from the field. This study aimed at investigating the available prospects, the responses of the basic seismic attributes to structural and stratigraphic elements within the study area. In all, six hydrocarbon bearing levels were delineated from well logs and correlated across the field. These horizons were analysed and petrophysical parameters estimated. An integration of well and seismic data was done by applying a time-depth relationship to identify where the hydrocarbon bearing sands from well posts on the seismic lines. These studies revealed two major regional growth faults (F1 and F5) dipping in the NE-SW directions and crestal faults (F4) dipping in the northern direction. The north dipping crestal fault F4 is responsible for holding the hydrocarbon in the proven closure A. The northernmost regional growth fault F1 is responsible for trapping the hydrocarbon in the prospect closure B in the north eastern part of the field. The closure C prospect is a four way dip closure to the spill point but becomes fault assisted on regional growth faults F1 and F5 at deeper levels. The trapping mechanism identified from our interpretation indicates that the field is characterized mostly by fault assisted closures and a few four way closures. The fault zones are identified by distinct displacement of walls and amplitude distortions towards the fault zones identified on the seismic sections and the extracted amplitude maps. At the south-western part of the field, using only seismic Stratigraphic approach, a part of fault F5 was too subtle to be identified, and this may lead to missing out on the potentials of the identified closure C prospect. Thus, where conventional seismic interpretation has failed, seismic attribute analysis complements.

The Use of Seismic Attributes to Enhance Structural Interpretation of Z-Field, Onshore Niger Delta

An integrated approach to the study of the structural patterns and seismic attributes was carried out on the Z-field using a 3D seismic data covering approximately 56 Km2 of western belt of the Niger Delta, check shot data for well to seismic tie and log information for six wells from the field. This study aimed at investigating the available prospects, the responses of the basic seismic attributes to structural and stratigraphic elements within the study area. In all, six hydrocarbon bearing levels were delineated from well logs and correlated across the field. These horizons were analysed and petro physical parameters estimated. An integration of well and seismic data was done by applying a time-depth relationship to identify where the hydrocarbon bearing sands from well posts on the seismic lines. These studies revealed two major regional growth faults (F1 and F5) dipping in the NE-SW directions and crestal faults (F4) dipping in the northern direction. The north dipping crestal fault F4 is responsible for holding the hydrocarbon in the proven closure A. The northernmost regional growth fault F1 is responsible for trapping the hydrocarbon in the prospect closure B in the north eastern part of the field. The closure C prospect is a four way dip closure to the spill point but becomes fault assisted on regional growth faults F1 and F5 at deeper levels. The trapping mechanism identified from our interpretation indicates that the field is characterized mostly by fault assisted closures and a few four way closures. The fault zones are identified by distinct displacement of walls and amplitude distortions towards the fault zones identified on the seismic sections and the extracted amplitude maps. At the south-western part of the field, using only seismic Stratigraphic approach , a part of fault F5 was too subtle to be identified, and this may lead to missing out on the potentials of the identified closure C prospect. Thus, where conventional seismic interpretation has failed, seismic attribute analysis complements.

Structural controls and timing of fault-hosted manganese at Woodie Woodie, East Pilbara, Western Australia

High-grade fault-hosted manganese deposits at the Woodie Woodie Mine, East Pilbara, are predominantly hydrothermal in origin with a late supergene overprint. The dominant manganese minerals are pyrolusite, braunite, and cryptomelane. The ore bodies are located on, or near the unconformities between the Neoarchean Carawine Dolomite and the Paleoproterozoic Pinjian Chert breccia (weathering product of Carawine Dolomite), and sedimentary units of the overlying ca 1300–1100Ma Manganese Group. Stratabound manganese is typically located above or adjacent to steep fault-hosted manganese. The ore bodies range in size from 0.2 to 5.5Mt with an average of 0.5Mt. Historically, over 35Mt of manganese has been mined at Woodie Woodie, and current ore resources are 29.94Mt at 39.94% Mn, 6.96% Fe (resource and reserves statement, June 2011, Consolidated Minerals Pty Ltd).Manganese mineralization at Woodie Woodie is related to northwest–southeast directed extension and basin formation during the Mesoproterozoic. Basin architecture is generally well preserved and major manganese occurrences are localised along growth faults which down-throw the Pinjian Chert Breccia into local extensional basins. Manganese ore bodies are typically located on steep 2nd and 3rd order structures that extend off the major growth faults. Mineralized structures display a dominant northeast-trend reflecting the direction of maximum dilation during northwest–southeast extension.A paragenetic sequence is identified for the manganese ore at Woodie Woodie, with early hydrothermal braunite–pyrolusite–cryptomelane–todorokite–hausmannite, overprinted by late supergene oxides. Preliminary fluid inclusion studies in quartz crystals intergrown with pyrolusite and cryptomelane indicate that primary and pseudosecondary inclusions display a range of salinities from 1 to 18eq. wt.% NaCl and trapping temperatures estimated to be from 220º to 290º at 1kbar pressure.A lead–manganese oxide (coronadite) is common in manganese ores at Woodie Woodie, and Pb-isotope studies of 40 lead-rich ore samples from 16 pits indicate mineralization occurred within an age range of 955–1100Ma. A mixed source is suggested for the lead, but was predominantly basalts and/or volcanogenic sedimentary units (e.g., Jeerinah Formation) of the ca 2700Ma Fortescue Group. The typically high Mn:Fe ratios and enrichment in elements such as Pb, As, Cu, Mo, Zn are consistent with a dominantly hydrothermal origin for the manganese at Woodie Woodie. Supergene manganese is distinguished from hypogene manganese by a marked enrichment in REE in the supergene manganese.An early structural framework, established during Neoarchean rifting, provides a major structural control on manganese ore distribution. The Woodie Woodie mine corridor is located in a zone of oblique strike-slip extension on major northwest-trending transform faults and north-trending oblique normal faults. A major transform structure at the southern end of the Woodie Woodie mine corridor (Jewel-Southwest Fault Zone) likely acted as a major fluid conduit for manganese-bearing hydrothermal fluids and this would account for the concentration of significant manganese ore occurrences to the north and south of this structure.

GEOPHYSICAL INTERPRETATION OF SEISMIC REFLECTION DATA OBTAINED FROM UMUREUTE AND AMIYNAIBO AREA OF DELTA STATE, NIGERIA

Geophysical interpretation of seismic reflection data was carried out around Umureute and Amiynaibo to determine the hydrocarbon capabilities of the area under study. The data were collected using the seismic reflection technique of geophysical prospecting for hydrocarbon. A total of fourteen seismic reflection data were collected and interpreted using the principles of picking, timing, posting and contouring. This study revealed the presence of two major growth faults and two minor faults. The contour maps shows that the horizons deepen from north east to south west which is an indication that the migration path for fluid is from south west to north east. Results indicated further the presence of two closures against the major faults which acts as migration seal to the prospect. The study has shown that hydrocarbon capability exist in Umureute at a depth of 1822 meters while the capability of Amiynaibo exist at a depth of 2130 meters below ground level.

FAULT SLICING IN THE INTERPRETATION OF FAULTS IN SEISMIC DATA PROCESSING IN ATALA PROSPECT OF RIVER STATE, NIGERIA

Faults are of high interest in petroleum development and production because they segment a reservoir. As a result of the role faults play in the entrapment of hydrocarbons, the techniques for finding and mapping them have considerable practical importance. A fault slice is a section sliced from a 3 – D data volume parallel to the interpreted position of a fault plane and can be used in several ways for the study of faults. The tracking of horizons on fault slices provides a map of fault thrown. Since a fault slice is found within one fault block, it becomes necessary in the study of growth in that block. There exist splinter faults that cause a lot of difficulty in horizon tracking because the data under study experiences small throw faults of limited laterial extent spawned by the major growth faults or parent fault. These splinter faults are secondary faults caused by movement on parent fault. A lot of Splinter faults were identified in the area of study and the azimuths of the Splinter faults relative to the parent fault are fairly constant.

Temporal and lateral variation in the development of growth faults and growth strata in western Niger Delta, Nigeria

This study examines eight syndepositional faults and syntectonic sediments in five major fault blocks in western Niger Delta, offshore Nigeria, on three-dimensional seismic data. The initiation, lateral growth and retreat, periods of activity and quiescence, and decay of faulting around these blocks can be ascertained by analyzing a series of time-structure and isopach maps. The study area can be subdivided into three structural zones. The first structural zone is a northwestern zone characterized by a major counterregional growth fault in the deep subsurface. This deep-seated structure is superposed by an array of younger regional growth faults displacing a kilometer-thick sedimentary overburden that accumulated on the former footwall. The second structural zone is a central to eastern zone that seems mostly unaffected by young deltaic faulting. This zone is characterized by the thinnest sedimentary record of the study area. The third structural zone is a southeastern zone that is dominated by a large, listric, backstepping master fault zone associated with a kilometer-scale rollover system. Regional structural and stratigraphic analyses document an apparently strong relationship between syntectonic sedimentation and syndepositional fault activity in that phases of significant fault activity, lateral fault growth, and fault migration concur with major depositional phases; in turn, areas and intervals characterized by the least sediment accumulation also record the lowest fault activity. However, one particularity of the studied system is that it underwent at least one period of seaward fault progression that coincided with a backstepping of faulting on the landward side. Although the forward stepping of faulting near the delta front can be interpreted as the consequence of the progressive loading during delta progradation, the contemporaneous backstepping of faulting further inboard likely reflects the sustained lateral growth of mature deltaic faults into previously undeformed proximal parts of the depocenter. The results of this study, thus, document that although an apparent correlation with the superimposed depositional system exists on a regional scale, inboard deltaic faults may persist to grow irrespective of sedimentary loading. The recognition of such fault trends is particularly important for estimating the influence of late-stage fault movement on hydrocarbon migration or the discovery of subtle fault-controlled hanging-wall reservoirs.

Sequence stratigraphy and syndepositional deformation of the Agbada Formation, Robertkiri field, Niger Delta, Nigeria

The Agbada Formation in Robertkiri field is a 2.7-km (9000-ft)-thick succession of Miocene shallow-marine and nonmarine deposits formed as the continental margin of the Niger Delta structurally collapsed under accumulating sediments. A high-resolution sequence-stratigraphic framework for these strata was constructed by combining data from 20 well logs and a 1400-km2 (550-mi2) seismic volume. Syndepositional structural collapse occurred along a succession of major, cuspate, offshore-dipping normal faults and associated antithetic faults and rollover anticlines within downdropped blocks. Six fourth-order sequences, each hundreds of meters thick, formed during episodic progradation and retrogradation of deltaic shorelines. Their development was complicated by the thickening of deposits across major growth faults and away from the crests of adjacent rollover anticlines. Successively younger sequences became thinner, more laterally uniform in thickness, and less structurally deformed and contain less growth strata above downdropped fault blocks. Erosion along successively younger sequence boundaries became shallower and broader as accommodation declined and more sediment was bypassed basinward. Areas of deepest sequence boundary incision and most rapid structural deformation shifted basinward over time with regional delta progradation. Stratigraphic patterns across successive downdropped fault blocks suggest that collapse of this continental margin occurred under prograding deltaic deposits on the shelf instead of within lowstand intraslope basins. Differences in the development of successive sequences reflect gradually slowing rates of structural collapse as underlying mobile shale is depleted, allowing deltaic deposition to shift farther basinward.

Are there Middle Jurassic contourites in the Tarnovo depression (Southern Moesian platform margin)?

Abstract The first boreholes in the Tarnovo depression, located in the central Southern Moesian platform margin zone (Bulgaria), drilled at the end of the 1970s, display intervals of unusually thin, irregular and lens-like interbedding of shales and siltstones in the Middle Jurassic succession. Their specific lithological, log and seismic features, which resemble or distinguish them from contourites, have been studied and described in detail. The depositional setting in the Tarnovo depression during the Late Aalenian-Early Bajocian was favourable for the accumulation of deeper-water sediments, influenced by bottom currents. These were deposited along the hanging walls of major growth faults, which have a decisive geodynamic importance for Early-Middle Jurassic basin evolution throughout the Southern Moesian platform margin zone. Some lithological characteristics of the studied sediments correspond to diagnostic criteria for contourites. However, some other features, such as tractive indications, thin fine-grained laminae and wavy facies alternation, are also indicative of fine-grained turbidites and/or reworked bottom-current deposits.