INTEGRATION OF SEISMIC AND WELL LOG DATA USING ACOUSTIC IMPEDANCE FOR LITHOLOGY AND HYDROCARBON EVALUATION OF “OVI” FIELD, NIGER DELTA.

Abstract

One of the critical challenges in hydrocarbon exploration is the assessment of reservoir quality beyond areas covered by well. This research work is aimed at using acoustic impedance as a means of predicting lithology and hydrocarbon away from well control of “Ovi” Field hence providing a detailed evaluation of the hydrocarbon potential of the area. The methodology used involved identification of hydrocarbon bearing reservoirs from well logs using Gamma ray and resistivity logs, wells correlation, petrophysical analysis, well to seismic tie, horizon and fault mapping, generation of structural maps, acoustic impedance crossplot analysis and seismic inversion using model based approach on Hampson RussellTM software. Three reservoir sands (A, B and C) were mapped within the Agbada Formation. From the reservoir parameters determined the Net/Gross ranges from 0.60-0.93, porosity,  ranges from 26%-43%, permeability, K ranges from 2300mD- 3500mD and hydrocarbon saturation, Sh ranges from 52%-73%. Eleven faults (F1, F2, F3, F4, F5, F6, F7, F8, F9, F10 and F11) were mapped. F7 and F8 are the only growth faults. From the crossplot analysis of acoustic impedance against gamma ray, porosity and water saturation the acoustic impedance ranges from 24500-27500(ft/s)*(g/cc) for shale and 17500-24500(ft/s)*(g/cc) for sand based on the saturating fluids, its results also shows that acoustic impedance have a linear relationship with water saturation, while porosity have an inverse relationship with acoustic impedance for the study area. Average acoustic impedance maps for reservoir tops (i.e. sand A, B and C) generated from the inverted seismic data indicated areas of low acoustic impedance corresponding to hydrocarbon bearing zones (i.e. A, B, X, Y, Z, R and Q) that were not detected on the time maps. The study has been able to provide better information about the subsurface lithology, porosity, and Sh away from well control, locate new prospect and provide Information needed for accurate well placement to enhance the productivity