Sequence Stratigraphic Analysis of ‘AB’ Field in the NIiger Delta, Nigeria, Using Well Logs and Seismic Data

Abstract

A study was carried out in the ‘AB’ field of the Niger Delta using well logs and seismic data so as to understand the local stratigraphy, identify and describe the sedimentation patterns in the field in order to identify the depositional environments likely to generate hydrocarbon accumulation in the study area. Sequence stratigraphic framework for ‘AB’ field was constructed by combining well log data and seismic volume from three wells in the field. Interpretation of the gamma, resistivity and density logs was done using the petrel software, in which sequences were identified on well logs from its trace and sequence boundaries. System tracts were used to foretell the reservoir location and quality in order to infer the depositional environment. Key bounding surfaces and depositional sequences were delineated from the seismic profiles through reflection termination patterns. Results were presented in form of well logs, seismic sections and tables for the 3 wells -A, B and C. 3 sequences were delineated with each of the sequences showing similarities in their log signatures to the others. Log patterns ranges from blocky to serrate, indicating intervals of abrupt decrease in gamma ray log response and intervals with increasing response. Log patterns conform to different environment of deposition in different system tracts, ranging from a basin floor fan in the Low stand to shore face sands and fluvial incisions in the High stand system tracts. Reflection packages observed from the seismic profiles showed different depositional geometries. Reflection patterns showed variable amplitude from high to low and high to low continuity. The prograding wedge complex is seen as high amplitude parallel reflections, high continuity of reflection patterns indicated uniform deposition of sediments while poor continuity showed non- uniform deposition. Structural analysis of the seismic profiles showed the presence of roll over structures which are good traps for hydrocarbon accumulation. Depth maps showed that the depth to the top of the prospects for the horizons mapped ranges from 4100-5500 feet .The alternation of high stand sands and transgressive shale was inferred to provide the desired combination of seal, source rock and reservoir necessary for hydrocarbon accumulation

AAPG Datapages/Search and Discovery Article #90332 © 2018 AAPG International Conference and Exhibition, Cape Town, South Africa, November 4-11, 2018