Delineation of Time-Stratigraphic Units on Open-Hole Geophysical Logs Acquired In Etsako Field, Onshore Niger Delta of Nigeria

Abstract

Etsako Field remains in appraisal phase since hydrocarbon is yet to be produced from it. Lithostratigraphic technique was earlier employed to subdivide and correlate sedimentary sequence penetrated within the field. The technique often results in exaggerated reservoir continuity and concomitant drilling of dry step- out and infill wells. ET2, ET4, and ET5 are dry step-out wells drilled in the field after ET1 (discovery well) and ET3 (successful or wet well). Parasequences and parasequence sets were employed in this study to generate a time stratigraphic framework for the field. Depth structure maps were produced from depth of sands’ top obtained within the time stratigraphic framework. Progradational and retrogradational parasequence sets were identified. Two unconformity and maximum flooding surfaces were delineated. Hydrocarbon reservoir sands in ET1 and ET3 are Sands I and M, while those in ET6 are sands B and F2. Sands B and M were found in lowstand systems tracts (LST), while sands F2 and I were found in highstand systems tracts (HST). Sand B’s depth structure map revealed infill wells will penetrate hydrocarbon bearing portion of the sand within longitudes 6.785օE to 6.786օE and latitudes 5.634օN to 5.638օN. Sand M’s depth structure map revealed opportunity for wet infill wells within longitudes 6.770օE to 6.7862օE and latitudes 5.632օN to 5.638օN. Infill wells should be drilled beyond present depth of 10000ft to test deeper LST and HST within the field.