GEOPRESSURE PREDICTION AND INTENSITY CHARACTERIZATION BASED ON FUZZY INFERENCE SYSTEM IN BARBADOS FIELD OF THE NIGER DELTA, NIGERIA

In the paper we present a method of characterizing overpressure intensity in an oil field from wireline log with fuzzy inference system using well logs from Barbados field in the Niger Delta area of Nigeria. The method employs pressure coefficients obtained from the ratio of the pore pressure and the hydrostatic pressure as input into the fuzzy system. The lithostatic and hydrostatic pressures were derived from sonic and density log equations while the Hunt and Shi classifications were used to characterize the overpressure intensity, although with a slight modification. The plot of sonic log with depth in the wells followed a typical stepped-tiered configuration having a maximum of three episodes of abnormal pressure. The distribution of pressure coefficient (PC) increases from the left flank to the right flank of the field. Mild overpressure with PC values of 1.28, 1.35 and 1.53 were observed at shallowest depth and 1.33, 1.36 and 1.32 at intermediate depths. Strong overpressure with maximum PC values of 2.04, 2.46, 3.60 and 3.75 were observed in Barbados wells 1, 2, 3 and 4 respectively at greater depths. The result from this study has proven to be a dependable tool in the characterization of overpressure intensity as well as serve as a guide for predicting overpressure behavior in adjacent areas. Further work on pressure coefficient (PC) computation in the vicinity of well kicks, caving, loss of drilling mud, or possibly full blowout is welcomed from other workers.