Abstract:
A study was carried out in the ‘AB’ field of the Niger Delta, Nigeria 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. Three sequences were delineated with each of the sequences showing
similarities in their log signatures to the others. Log patterns range 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 lowstand to shoreface sands and fluvial incisions in the
highstand system tracts. Reflection packages observed from the seismic profiles showed different
depositional geometries. Reflection patterns showed variable amplitudes from high to low and
high to low continuity. The prograding wegde 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. The alternation of highstand sands and
transgressive shale was inferred to provide the desired combination of seal, source rock and
reservoir necessary for hydrocarbon accumulation.
