| Abstrakt: |
The work is aimed at predicting shale pore pressures in order to identify the different pressure zones and estimate fracture pressures in some wells in COBALT Field, Niger Delta. To achieve this, geoscientific software was used to analyze the well log data. The data was quality checked and true vertical depth computation was carried out to facilitate overburden stress estimation. The extrapolation method was used to compute the overburden stress, through the merging of the bulk density log and the synthetic bulk density that was generated. Using a gamma ray log, mechanical stratigraphy for lithology delineation was carried out to delineate shales from sands. Normal compaction trendline was applied to sonic and resistivity logs using Eaton's method together with Bower's sonic method to predict pore pressures. The Mathews and Kelly's empirical method was applied to vertical stress and pore pressures obtained to estimate fracture pressures. Also, Petrel software was used for seismic interpretation, after which time and depth maps were generated. The tops of overpressure ells were incorporated into structural maps to show the distribution of the tops of overpressure wells. It was observed that Wells Cobalt-01 and 06 are normal pressure wells with the highest-pressure values of 8.61 and 8.67 ppg, respectively; while Wells Cobalt-02, 03, 04, and 05 were over-pressured with values of 10.9, 9.5, 10.5, and 10.01 ppg respectively, with corresponding depths of 1288, 12057, 9674, and 1019 FTTVD, respectively. The fracture pressure for each well was also estimated from the pore pressures. The main mechanisms responsible for overpressure in the COBALT field were identified as loading and unloading, with a small contribution from fault-related lateral pressure transfer. The results observed from the depth map show that the top of overpressure wells is distributed or compartmentalized into different fault blocks. The outcome of this work could facilitate proper planning and drilling of future wells in the field. [ABSTRACT FROM AUTHOR] |
