Forward modeling of evolution of shale properties in geological time

The overburden is an essential part of the petroleum system. It provides the reservoir seal and host a significant part of the production facilities, and reservoir depletion might trigger severe deformations in the overburden compromising both seal and infrastructure integrity. In addition, the initial in-situ conditions in the reservoir (geo-stresses, pore pressure, fractures etc.) are result of the weight of the overlaying sediments. However, since the dawn of the O&G Industry, the main focus of the predictive, modelling and data acquisition efforts was the reservoir, thus, there is a massive lack of data (core samples, logs etc.) and significant gaps in our understanding of the medium and its reaction to our E&P activities. Large part of the overburden is composed by mudrocks/shales, since mudrocks account for 60% of all sedimentary formations (Nichols, 2009). In recent years, the advent of shale-gas and shale-oil production put shales/mudstones in focus and both industry and academia intensified their efforts to understand these much neglected formations. Both present day rock properties (porosity, permeability, stiffness etc.), pore pressure and the current stress state (magnitude and orientation of vertical and horizontal stresses) of the subsurface formations are the result of the geological evolution. Due to burial, clays consolidate and compact under the weight of the overburden. The sedimentation rate changes during geological times due to to the interplay between climate, tectonics and other planetary processes. Important oil provinces such as the North Sea in Europe and the Gulf of Mexico (GoM) in North America consist of basins where a thick shale overburden was deposited very quickly during the Cenozoic. Both regions are characterized by significant overpressure (pore pressure above the hydrostatic) in the thick Cenozoic shale formations (Vejbaek, 2008; Dickinson, 1953). In our study, we use 2D forward finite element modelling to simulate the deposition of a shale column during the Cenozoic. The scope is to study the evolution in time of shale properties with respect to changes in sedimentation rate.