Pitfalls in Channel Reservoirs Development: Implications for HCIIP Assessment and Development

Abstract

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.