The application of seismic-log sequence stratigraphy in mapping stratigraphic traps and reservoirs’ facies in Afam channel area, Niger Delta

Abstract

The concept of seismic-log sequence stratigraphy was used in mapping stratigraphic traps and reservoirs’ facies in Afam Channel area, Niger Delta, for the purpose of prospect re-evaluation and improving production. The data set consists of 3-D seismic data and conventional well logs, which were interpreted iteratively using workstation based interpretation technique. The well logs were converted from depth domain to time domain and subsequently superimposed on the seismic time sections at oil wells’ locations. Areal mapping of the delineated reservoirs’ facies based on composite well logs display, deduced trapping mechanisms and inferred depositional environments were then carried out on the seismic sections using consistency of the associated seismic reflection characters. The seismic sections and well logs were subsequently sub-divided into sequence units, systems tracts and facies units. The Afam Channel fill sequence is sub-divisible into lowstand, transgressive, and highstand system tracts with a major condensed section separating the transgressive from the highstand system tracts while a “type 1 sequence boundary separates it from the pre-channel sequence. Structural entrapments comprise one-way and two-way closures against faults that most often bound structural highs. Stratigraphic traps range from lithofacies thinning up dip, onlapping of pre-channel sequence, lateral facies change especially across channels edges and combination traps. The hydrocarbon reservoirs’ facies are interbedded within the paralic sequence of the lower transgressive through to the lowstand systems tracts and the pre-channel sequence within a depth range of about 6000ftss to 11800ftss (1829m to
3597m). Reservoirs geometries range from sheet, sheet drape, lenses, wedge and mounds. The hydrocarbon reservoirs’ facies are multi-stacked, thereby making the prolific level of each oil well being dependent on how many it intercepted optimally.

KEY WORDS: Declining Production Prospect Re-evaluation Seismic-Log-Sequence Stratigraphy Hydrocarbon Reservoirs’ Facies Exploitation Strategy