A Mathematical Model Accounting for Pore Pressure Generation in Sedimentary Basins

The abnormal pore pressure is possibly generated through a comprehensive process including geological, physical, geochemical, or hydrodynamic factors. Generally, all mechanisms are abstracted as four typical categories, namely skeleton deformation, pore fluid mass increase, temperature change, and other mechanisms. Traditional methods for evaluating reservoir overpressure often only consider the influence of a single factor and lack mathematical methods for a comprehensive explanation of reservoir overpressure. Therefore, this article is dedicated to proposing a comprehensive mathematical model, incorporating effective mean stress, shear stress, temperature, pore collapse-induced plastic deformation, time-dependent skeleton deformation, and pore fluid mass increase, to account for pore pressure generation in sedimentary basins. The effects of various factors on pore pressure generation are analyzed, and case studies are conducted. Main conclusions are drawn that both the compressibility of sediments and the porosity at the surface control the pore pressure generation rate and vertical gradient. The pore pressure generation rate and vertical gradient in deep formation are larger than those in shallow formation. The higher compressibility and lower porosity at the surface lead to a greater pore pressure generation rate and vertical gradient during the skeleton deformation. The lower compressibility and a lower porosity at the surface can cause a higher pore pressure change rate and vertical gradient during the pore pressure mass increase and temperature change. By comparison, mechanical loading plays a more important role in pore pressure generation rate and vertical gradient than aquathermal pressuring.