Pore Pressure Prediction From Basin Simulation of Heat and Fluid Flow: Application to a Realistic Earth Model in the Gulf of Mexico

Abstract

Pore pressure prediction in the Gulf of Mexico remains critical for exploration and development of hydrocarbon resources locked in deep and variably pressured reservoirs. This is especially true in areas dominated by salt tectonics, facies heterogeneity in terms of low permeability versus porous and permeable rock, and connectivity of porous and permeable rocks both laterally and vertically; Society of Exploration Geophysicists Advance Modelling consortium has developed a compelling and realistic earth model to understand in detail critical mechanisms that drive the pore pressure distribution in the Gulf of Mexico. Structural restoration of complex allochthonous and autochthonous salt bodies has proved to have an impact on the overall mechanisms that affect pore pressure, such as disequilibrium compaction and lateral fluid transfer as well as secondary modification of shales properties. Heat flow and thermal conductivity through time and in the presence of salt not only impacts smectite to illite transformation depth, resulting from natural distortion of temperature isolines but also affects the timing of the transformation. The objective of the study was to sample the solution space for a number of uncertain parameters affecting a simulated pore pressure. Analyzed parameters are: simulated grid size, constitutive laws for compaction and fluid flow, illitization and fault permeability. The geological history, salt geometry evolution trough time and differential sedimentation rates are additional drivers for the pore pressure. Comparison of a scenario with no clay diagenesis and proposed salt geometry reconstruction simulation shows overpressure variation of up to 30% at the units away from the salt canopy and less than 5% below the salt, which is explained by the thermal conductivity of the salt and its impact on the illitization process. As a consequence of thermal cooling generated by salt emplacement, water replacement during the illitization process is not as aggressive in the salt surroundings. On the other hand, it is substantial away from the salt body. This phenomenon combined with the hydraulic connectivity of the facies, generates unique overpressure trends controlled by a rather large number of variables that can be fully investigated by a 3D full-physics forward basin modelling. The results of the modeling were blind-checked with the overpressure profile from the well Poseidon-1, proving outstanding calibration on similar geological settings.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018