Petrophysics and Flow Zone Indicator evaluation of reservoirs in OKX Field, offshore depobelt, Niger Delta

The evaluation of irreducible water saturation limits of reservoirs in the “OKX” Field was achieved using well log data from five wells, as well as core and analogue well data. It aimed to improve productivity by limiting unanticipated water production. A Flow Zone Indicator (FZI) was predicted using a regression model based on reservoir delineation and well log correlation. The net-to-gross ratio in the reservoirs is between 0.85 and 0.99. The net thickness of the reservoirs is between 14 m (45.9 ft) and 120 m (393.68 ft). The study observed that irreducible water saturation in the reservoirs decreased with increasing FZI or increasing permeability. Thus, variations in irreducible water saturation could be related to pore attributes. The magnitude and distribution of the FZIs (between 2.19 and 18.42) also influenced fluid saturations and their distributions: reservoirs with larger pore throats corresponded to higher average FZI values and lower irreducible water saturation. Similarly, Buckles plots revealed that reservoirs A and F in OKX 1, with BVW lines around 0.07 and 0.065, respectively, would produce hydrocarbons with a low water cut, whereas reservoir G, with sands plotting consistently around the BVW line of 0.03, which is suggestive of reservoirs with immobile water, may produce with a slight water cut. Channel sands (reservoirs A, F, and G) with large grain sizes, moderate to highly sorted, high permeability, average FZIs, and low irreducible water saturation are the best reservoirs in terms of rock quality. The core-log transformations used here are beneficial in locations with minimal core data.