An integrated pore-pressure model and its application to hydrocarbon exploration: A case study from the Mahanadi Basin, east coast of India

摘要

An integrated pore-pressure modeling approach was adopted to understand the basin architecture from a pressure perspective and its inference toward possible hydrocarbon occurrence. Kriging-based 3D pore-pressure modeling was used with offset well data and seismic velocities to establish the pressure stratigraphy of the northeast coast (NEC) field (southern part) in the Mahanadi Basin. Late Pliocene sediment is moderately pressured (10.4-11.8 MPa/km), whereas early Pliocene sediment is normally pressured (9.6 MPa/km) and compacted, representing a regional seal for this part of the basin. Miocene represents the onset window for major undercompaction and associated high pressures (12.7-15.7 MPa/km) in conformance with the regional pressure trend. Overpressure distribution and its mechanisms in the late Miocene level across the NEC field shows distinct patterns with highly elevated pressures (>19.7 MPa/km) in the northern part resulting from a hybrid unloading mechanism, whereas moderate to high pressure (<15.7 MPa/km) toward the southern part is associated with undercompaction. Regional pressure correlation across the study area suggests a pressure dependent habitat of hydrocarbons in the Miocene and late Pliocene levels. Pressure distribution and an excess pressure pattern within the Miocene stratigraphy shows a regression trend from north to south, possibly indicating a preferred subsurface fluid flow direction, which is supported by high-quality gas reservoirs discovered in the southern part of the study area. A similar but reverse pressure regression trend is observed within the late Pliocene stratigraphy, which is also validated by the presence of gas reservoirs in the northern part of the study area. Major hydrocarbon reservoirs in the Miocene and Pliocene stratigraphy from the southern part of study area exhibit a strong correlation with effective stress distribution. High-quality gas reservoirs are mostly associated with high effective stress (>7.9 MPa/km), whereas a high probability for reservoirs to be water wet are observed below this threshold value.