Pressure Regime, Pressure Regression Detection and Implications in the SMK Field, Onshore, Western Niger Delta, Nigeria

摘要

Background and Objective: Pore pressure evaluations are crucial in assessing exploration risk factors and enabling reserve development models for well production and management, concepts affected by the presence of pressure regressions/reversals. The study aimed at quantifying encountered overpressures, understanding pressure regimes/distribution and suggesting possible implications in SMK field. Materials and Methods: Eight wells and two well reports were subjected to qualitative (log analysis) and quantitative analysis (pressure models). Results: Quantitative pressure analysis carried out using Wireline/MWD logs revealed that compaction disequilibrium was the dominant overpressure mechanism in the field with deviations from normal compaction trend around 9000 ft (2727 m) on the sonic logs. Shale pressures determined using standard Eaton and Equivalent depth methods revealed three pressure regimes, the normally pressured ( 0.495 psi/ft) (SMK 1, 8, 11, 12 and 13). An important phenomenon observed from the pressure-depth plots was pressure regression/reversal typified by the presence of “shoulder effects”, a consequence of dewatering of higher overpressured shale’s above and below lower overpressured reservoir sand stones. These effects were very distinct in the overpressured wells (SMK 1, 8, 11, 12 and 13) with imprints in the normally (SMK 6) and transitionally pressured wells (SMKs 10 and 14). Conclusion: An overpressure implication was the suggested/probable occurrence of lateral reservoir drainage using pressure-depth plots and log analysis.