In-situ stress, pore pressure, and hydrocarbon migration and accumulation in sedimentary basins.

摘要

An important concept for understanding fluid flow in hydrocarbon fields is that dynamic mechanisms governed by the stress state present drive oil and gas migration and accumulation. The principal goals in this dissertation are to constrain the full in-situ stress tensor and reservoir pore pressure conditions, identify hydrocarbon migration pathways, and test dynamic processes controlling fluid flow and rock deformation. For this purpose I analyze various types of downhole measurements from two hydrocarbon producing sedimentary basins.; In the Santa Maria Basin, on- and offshore California, stress orientations derived from borehole breakouts and inversion of earthquake focal plane mechanisms indicate a rather uniform stress field consistent with the regional trend. Analysis of borehole wall images reveal ubiquitous fractures and faults that exhibit great variations in orientation and occurrence. These variations can be correlated with changes of lithology and physical properties. Permeability appears to be enhanced in the vicinity of fractures and faults that are active and optimally oriented for failure in the current stress field.; In the South Eugene Island 330 field, Gulf of Mexico, drilling induced borehole breakouts, reveal least principal horizontal stress orientations, that are predominantly perpendicular to active normal faults. Minimum principal stress magnitudes show significant scatter revealing fracture gradients that cannot be correlated with previously published models from this area. Reservoir pore pressures are highly variable and range from hydrostatic to severely overpressured indicating compartmentalization and production induced depletion.; Reservoir depletion, pore pressures, and hydrocarbon column heights in individual reservoirs appear to be a function of stratigraphy. Shallow sands are hydrostatically pressured, well drained, and normally compacted. Oil and gas columns are long and controlled by a spill point. At intermediate stratigraphic levels, reservoir sands are undercompacted, moderately overpressured, and depletion induces stress changes that follow a stress path along which differential stresses strongly increase. Hydrocarbon columns are either small and dynamically constrained by reservoir bounding faults or long and controlled by a spill point. Deep sands exhibit small hydrocarbon columns and severe overpressured conditions near hydraulic fracturing or active faulting. The sand is extremely undercompacted and production appears to be accompanied by plastic and viscous deformation.