3d Seismic Interpretation And Reservoir Characterization Of “Diba Field’’, Niger Delta, Nigeria

ABSTRACT

Interpretation of structures and reservoir characterization using 3D seismic cube and well data pose great challenges in mapping because of their complexities especially in structural deformations, and where identification of reservoir facies is a major challenge to plan delineation, field appraisal and development drilling. Thus, the project work takes a model approach. The ―DIBA‖ Field in the Niger Delta contains hydrocarbons that are largely trapped in sandstones and unconsolidated sands in the Agbada Formation – which comprised of multiple vertically-stacked reservoir sequences. The aim of the project work was to discover and delineate structural trends and traps with hydrocarbon accumulations and delineate petrophysical properties for field development and appraisals. The work took a multi-disciplinary style which saw seismic, well logging and petrophysical methods integrated to achieve these goals. Seismic data were integrated with well logs to define the subsurface structural geometry, stratigraphy and hydrocarbon trapping potential of ―DIBA‖ Field, Niger Delta. Lithologic units were identified on the logs and correlated across the wells. The stratigraphic trends show a general lateral continuity of the lithologic units across the field. Seismic-to-well ties were very good. High amplitude reflection events correspond to sand units while low amplitude reflection events correspond to shale units. Two horizons, H1 and H2 were mapped, and structure contour maps produced for each of the horizons. The study of faults showed a complex pattern of subsurface structures. The northern area has chiefly extensive simple rollover structures bounded by growth faults. Faulted rollover anticlines exist in the middle zone while the southern area is featured by collapsed crest structures. Structural closures considered as good hydrocarbon prospects were identified and delineated. The petrophysical result showed that the identified reservoir units are high quality sands with porosity values ranging from 27-31% for Sand A and 25-27% for Sand B respective, coupled with high net-to-gross values ranging from 76-100% (Sand A) and 75-91% (Sand B) and low water saturation values. The integration of seismic data with well logs proved to be a useful tool in structural and stratigraphic mapping and in predicting lateral and vertical variations in the lithologic units. Key exploration risk is that normal faults subdivided anticlinal traps that are growth-faulted; which may lead to trap failure and wrong interpretation as the true faulting is masked. Other risks associated with this prospect include lack of amplitude support in the reservoirs, possible fault seal failure and the lateral extent of some of the reservoirs.