As Nigerian operations expand into more challenging and costly operating environments of deepfrontiers, there is need for critical access to sound stratigraphic, depositional and reservoir facies models. The extraction of facies types from geometric insights and pattern recognition using predominantly 3D seismic data is a rapidly evolving discipline that facilitates the development of reservoir prediction models linked to significant plays. Play based exploration approach such as this provides the critical link between regional observations and prospect generation. In this study a regional dataset which comprised of a merged 3D seismic volume, well logs, biostratigraphic, biofacies, paleobathymetry and core data from Eastern Niger Delta was interpreted. Results clearly show the overall structural, stratigraphic and architectural styles within the region to ensure that successes achieved in the past can be repeated and also significant advances made to ensure future exploration success. An added outcome is a low-risk exploration workflow that is capable of correctly predicting reservoir rocks to be encountered in a new play and prospect. Three plays have been identified from this study: (1) shelf edge deltas, (2) pinch-out play and (3) hanging wall play. Each play displays a unique morphology, seismic expression, structural configuration, migration pathway, seal integrity and reservoir dispersal pattern. These prediction models provide play based exploration targets for areas with similar depositional settings. The successful application of this technique serve to encourage exploration in the Niger Delta Basin by adopting strategies where seismic stratigraphy will be the most likely means to provide drilling targets to more independent operators.

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This study integrated lithofacies, foraminifera and seismic data to develop a sequence stratigraphic approach to hydrocarbon exploration for Chiadu field. The application of lithostratigraphic approach led to correlation of diachronous lithofacies and wrongly defined an approximately accurate extent of the reservoirs. This study necessitated the use of sequence stratigraphic framework for the purpose of establishing chronostratigraphic concept and facies prediction. The genetic sequence model of Galloway was adopted for sequence stratigraphic interpretation of the field. The structural style is dominated by closely spaced simple rollover anticline bounded by growth faults, and this includes down-to-basin listric faults, collapsed crest structures, antithetic and synthetic faults. Result of foraminifera analysis showed that the analyzed interval is very rich in calcareous benthic but decreased in planktic and arenaceous benthic foraminifera. Lithofacies analysis shows that the continental lithofacies is made up of dominantly sand with thin bands of shales, while Agbada lithofacies is made up of alternating intervals of sandstones and shales to very thick shale unit in the lower section. The facies identified using log motifs and their stacking patterns include braided fluvial, crevasse splay, fluvial point bar, distributary/tidal channels, intertidal, subtidal and storm-dominated shelf facies. The presence of water depth indicator fossils confirmed the water depths of coastal deltaic, shallow inner neritic, inner neritic, middle neritic and outer neritic were based largely on the presence of environmentally restricted benthic foraminifera species.Integration of lithofacies and biofacies data suggests depositional environments ranging from coastal deltaic to outer neritic environment. Sequence stratigraphic analysis identified three complete sequences with accompanying system tracts over the interval 7922.3-14,856.34 ft. The transgressive system tracts (TSTs) within these sequences are dominated by marine shales and thin sands. Reservoir quality sands are found in highstand system tract and shelfal lowstand system tract, while the shales of TSTs and HSTs form potential source and seal units. The delineation and correlation of sequence stratigraphic surfaces enable us to build an approximate chronostratigraphic framework, which is essential for determining facies relationships. Reacquisition and/or processing should be done to improve seismic data quality for better imaging and interpretation/ mapping, especially hydrocarbon prospect at deeper horizon.

In the drive for excellent reservoir management practices and optimizing oil and gas production through efficient reservoir performance, the role of conventional coring cannot be overemphasized. Core data provides most representative and relevant data for the interpretation and understanding of the subsurface. Continuous coring techniques were deployed in the study area to obtain high quality cores for analysis and reservoir characterization of the productive intervals and development of appropriate enhanced oil recovery strategy. The reservoir cored is characterized as poorly consolidated sandstone reservoir comprising of a calcite roof, moderately sorted and very fine-grained, friable and laminated with shale. A thick column of shale intercalation separates the reservoir into upper and lower lobes. Generally, the formations were characterized as weak with the sand minimum stress of 7.5ppg to 11.0ppg and shale collapse pressure of 8.5ppg to 11.5ppg. Some of the challenges encountered in coring this reservoir includes but not limited to the following: Well collision issues, wellbore instability, depleted reservoirs, selection of effective coring bottom hole assembly and drilling fluid as well as rig space constraints. This paper presents how innovative techniques aided in mitigating the challenging drilling conditions. The systematic approach deployed comprises the use of gyro survey while drilling (GWD), anti-collision analysis, utilization of well-designed drilling fluid with low invasion properties that still maintain wellbore integrity and stability. A close monitoring of equivalent circulating density (ECD), use of fiberglass inner core barrel and low fluid invasion system that comprises core heads with special fluid pass ports to deviate flow away from already cut cores, and full core catcher system was employed. A detailed stratigraphic correlation with the offset wells to identify vital stratigraphic markers was carried out prior to coring. A 15 feet hole was drilled into the calcite roof of the reservoir with PDC bit and the hole cleaned prior to pulling out of hole with the drilling bottom hole assembly (BHA) to minimize the risk of core jamming. Cores were cut with special selected coring BHA using controlled coring parameters while plotting inverse rate of penetration (i-ROP). In addition, controlled trip out speed based on field experience, and proper core handling/ on-site core preservation was employed. The innovative approach resulted in achieving a recovery factor of more than 93 percent of high quality cores.

An integrated structural and stratigraphic analysis of a regional dataset from Eastern Niger Delta was undertaken with the objective of improving the present understanding of the structural development, seismic reflection geometries and implication on sand transportation and deposition within the shelf-edge and farther into the basin floor. Well log correlations were carried out using third-order sequence stratigraphy. Fault dynamics and evolution was interpreted with the aid of seismic transect sections, growth fault indexes and dip-extracted semblance slices. Lithofacies and paleobathymetric data were utilized to create gross depositional environment maps for the various sequences from inner-shelf to upper slope environment. The fault dynamics and evolution analysis of co-planar faults shows that older co-planar faults are associated with more accommodation space and depocentres than relatively younger faults. Conceptual subsurface models from this study shows that there is an increase in sand thickness in the proximal part of the sequence associated with precursor (older) faults, while towards the distal part, it reduces. There is also a relative decrease in sand thickness in the proximal part of the sequence associated with younger initiated faults, while towards the distal part, it increases in sand thickness. This study shows that at the shelf-edge, the thickest sand is of the lowstand system tract and the possibility of transporting sands into the basin is more associated with younger co-planar faults with small accommodation space at the shelf-edge, while the precursor older faults retain majority of sand deposits within its subsidence/depocentre axis.