Integrated analysis of well logs for productivity prediction in sand-shale sequence reservoirs of the Niger Delta—a case study.

Work on fluid productivity prediction in the Niger Delta is sparse or even rare because of the need for expensive but limited information from core data, well test data, and nuclear magnetic resonance (NMR) data. Paucity of this information in the study area due to prohibitive cost makes justification of results of fluid productivity predictions very difficult to justify. However, an integrated well log analysis method is applied to three sand-shale sequence reservoirs of the Niger Delta for fluid productivity predictions in this work using basic log suites. This work utilizes irreducible saturation analysis calculated from the Buckles' method for three (3) reservoirs in Well "AW" and Well "T". Rock Physics estimates of Poisson's ratio values and V_p/V_s ratio values allow for fluid type designation from a cross plot of Poisson's ratio and V_p/V_s ratio; hence, it is possible to interpret gas saturation, brine saturation, and oil saturation for these reservoirs. The Buckle method yields numbers that are used to estimate irreducible water saturation values independently of Archie's and Archie's modified equations. In addition, Buckle's numbers allow for a pore size and grain size forecast for sandstone reservoirs being intercepted within the two wells. For each of these reservoirs, water saturation (S_w) is compared with the irreducible water saturation (S_wirr) with the logic that for a reservoir having S_wirr > S_w, no water production is expected. Conversely, for S_wirr < S_w, water production is expected. Difference in values of water saturation and irreducible water saturation is used as an index for predicting qualitatively reservoirs prone to high water cut production for these six reservoirs. Reservoir AW1 with S_w of 30.9% and S_wirr of 24.5% was predicted to have water production potential. While in reservoirs AW2 and AW3, where S_wirr > S_w, no water production should be expected. In well "T" reservoirs T1, T2, and T3, all had S_wirr > S_w. Hence, this work demonstrated the usefulness and effectiveness of the Buckle's method in estimating many useful petrophysical parameters to predict reservoir productivity in the studied area, Niger Delta for wells lacking core data, well test data, and NMR data. Field-wide deployment of this technique may help to improve the reduction in oil-related water production and the cost of managing the produced water at the initial stage of production in the Niger Delta in the reservoir. [ABSTRACT FROM AUTHOR]