The Interrelationships and Variations of the Resistivity, Porosity, and Permeability as Functions of Pressure in a Geopressured Reservoir

摘要

Fluid production from both normally and abnormally pressured reservoirs has long been recognized as a function of the formation fluid properties and the reservoir rock parameters. Fluid production itself, however, changes the stress state of the reservoir resulting in rock deformation which affects total fluid and, therefore, energy recovery. This study was undertaken as part of a project to determine and predict the effects of fluid production on the Pleasant Bayou geopressured, geothermal reservoir in Brazoria County, Texas. Data was collected from triaxial loading tests conducted on sandstone samples cored from the potential producing horizons of the reservoir. All tests were conducted at overburden and pore pressures which simulated insitu conditions. Empirical relations were developed which reflected changes in the resistivity, porosity, and permeability as functions of the effective stress. Relationships among the parameters were found to be of practical use in predicting formation changes as the reservoir stress state changed due to fluid withdrawal. Results showed that the resistivity, porosity, and permeability were dependent on the effective stresses in the reservoir. The cementation factor in Archie's equation was also found to be a pressure function.