Publications

Reservoir rocks of the Kasim and Walio fields consist of reefal carbonates of the Miocene Kais Formation. Walio field covers 3460 acres with 297 wells of which 238 currently produce 10,160 BOPD with a 98.5% water cut. JSasii field is smaller with an areal extent of 550 acres and with 57 wells, of which 40 currently produce 1,870 BOPD witha 99.4% water cut. The reservoirs are stratigraphic with faults providing the closure for the western extremity of both fields.Walio field is located on the northern rim of an extensive carbonate bank or shelf and KaSi field is part of an elongate p'hacle reef complex. Reservoir rocks consist mainly of skeletalkoral wackestones and packstones with occasional coral grainstones and boundstones. Dolomite commonly replaced the original argillaceous mud matrix, but on the flanks of the reefs the process is more advanced and much of the original texture has been destroyed. Porosity is derived mainly from leaching of aragonitic coral and skeletal fragments. Where this type of porosity is well developed, reservoir quality is moderate to excellent with very high flow rates. Matrix porosity became important in maintaining continued oil production as water encroachment increased.The Walio and Kasim reservoirs are highly stratified and were divided into five units (I to V) based on reservoir characteristics. Core data was compared to wireline logs, with excellent correlations achieved in all cases. This has enabled reliable interpretations to be made of the lithologies where no core data exist, both within the wells studied and adjacent wells.