The Niger Delta basin is dominated by shoreface deposits although tidal and estuarine channel deposits are typical. While reservoir modelling, HCIIP assessment, development strategy and placement of wells are commonly understood to be underpinned by sand distribution, there might have been a common tendency to apply a shoreface mindset in the channel reservoir settings. A methodologicalgeological understanding of channelized sand-bodies, their distribution and development underpinned by the integration of seismic and well data is therefore critical to optimal hydrocarbon maturation and development. The Eureka X7000 reservoir interpreted as channel sands from well logs of REKA-001 and mapped consistently on reflectivity data, suggested good sand development across the structure. Subsequent REKA-002 and REKA-003 flank wells results, resulted in a suprise in sand development, and a resultant reduction in HCIIP and reserves, highlighting blindspots that could have beenmitigated by the integration of acoustic impedance seismic volume, log data and realistic conceptual model scenarios of the reservoir. REKA-001 penetrated a channel complex 94 ft thick within the Eureka X7000 reservoir comprising three individual channel units~ 30 ft thick. Therefore, the reservoir was thought to be a channel complex with a maximum width of 2km comprising of series of individual channels with a width/thickness ratio of 66:1 based on REKA-001 results and existing analogues. This model would imply very good sand development with high NTG in the reservoir. REKA-002 was planned (1.6km away from REKA-001)as an appraisal/development well as part of the initial field development plan on the eastern flank of the structure. Post-drill assessment of the well results showed that the REKA-002 well penetrated the channel sand deposit sub-optimally and poorly developed which translated to a reduction in hydrocarbon volumes and in general well promise for the reservoir. The current estimated GIIP for X7000 reservoir is 169 Bscf some55% less than the pre-drill volumes of 376 Bscf. The REKA-002 well result on the X7000 is discussed to highlight the pre-drill geological evaluation pit-falls based on available well data and post-drill integration of quantitative seismic data, facies/property and sequence stratigrahic modelling approach to provide lessons for future field development plans.

The importance of multi-discipline integration in the various phases of hydrocarbon exploitation cannot be over-emphasized. In the past, the various subsurface disciplines, within the oil and gas industry, worked in silo-like organizations which often results in a sub-optimal understanding/evaluation of the subsurface data. However, in recent times, much has been done and written on multi-disciplinary integration and its benefits particularly with respect to subsurface studies. The Zed field, which is the subject of this paper, is a predominantly gas bearing partially appraised field. The field is composed of a series of stacked sandstone reservoirs located in the Niger-Delta Region of Nigeria. Given the limited subsurface data available within the hydrocarbon-bearing areas of the field (only 2 of the 6 wells in the field penetrated the hydrocarbon-bearing sections), one of the biggest challenges of developing this field remain the high level of subsurface uncertainties coupled with the potentially low economic value of further appraisal and development of the field. In order to adequately assess these uncertainties and the economic feasibility of developing the Zed field, a detailed subsurface study involving a full re-evaluation of all potential hydrocarbon bearing sands penetrated by the wells was required. The study, which kicked off with a comprehensive integrated multi-discipline data review and quicklook evaluation, resulted in the identification of two additional reservoirs previously considered too marginal to contain substantial hydrocarbon. This paper details how the systematic, multi-discipline data integration and review of these two reservoirs helped in the identification and determination of higher hydrocarbon volumes in these reservoirs; and how this has helped in improving the economic value of the Zed field development project.

Faults are subsurface entities in clastic fields that can influence the economic viability of a field at various stages. In Exploration, fault-seal behavior impacts prospect analyses, whilst in the Development stage, compartmentalization and fault transmissibility analyses impact Well placement, recovery and reserves estimation (Brem Et al; 2019). Accurate representation of structures -major and Intra-reservoir faults is a key requirement in any fault analysis and resulting impact. Hence, fault modeling-a key part of the structural modeling workflow in field development work cannot be over emphasized. The Eureka field is a high-pressure gas discovery asset in Shell 's operated acreage in onshore Niger delta. The field, which is currently in the mid development stage, comprises of stacked reservoirs with series of anticlinal dip assisted/fault bounded structure with minor faults. The potential compartmentalization of target reservoirs for development by intra-reservoir faults is the major uncertainty in the development of the Eureka field. This work aims to define the fault sealing properties of the intra reservoir faults and their impact on Eureka green field gas development. The current development plan requires two or more Wells to be drilled to optimally develop the resource volumes in one reservoir (X2000) in the field. Mapping of each of the intra-reservoir faults from seismic and available log data were used to determine how well connected the segments separated by the faults are. Fault zone properties studied include fault throw/thickness, shale gauge ratio (SGR), fault zone permeability and transmissibility multiplier. The intra reservoir fault uncertainties were mitigated by building different realisations during the modeling process. The intra-reservoir faults which are normal faults on the crest of the anticline in the study area have low SGRs and high permeabilities which indicates partial sealing capabilities. Also, the majority of the intra-reservoir faults have transmissibilities <1 which indicates partial fluid flow to partial seal. Partially sealed faults give rise to hydrocarbon movement through and along fault planes (Fagelnour Et al; 2018). Results of the fault zone properties were incorporated with fault transmissibility multiplier in a dynamic simulator and showed that one development Well can drain the gas bearing reservoir.