The mechanism of faulting regimes change over depths in the sedimentary layers in an intracratonic basin

Abstract

It has long been found that faulting regimes can change over depths at a similar location in a sedimentary basin. Such knowledge is very important for the estimation of the magnitude and orientation of the in situ stress, which are generally very difficult to estimate because of many uncertain factors, such as tectonic movement, rock heterogeneities, discontinuities, pore pressures, heat flow, etc. In comparison with many other geological settings, a stable intracratonic basin has a relatively flat structure that allows for a tractable numerical conceptualization to be made to help understand the faulting regime conditions. Some intracratonic basins such as the Williston Basin (USA), the Tarim Basin (China), and the Siberia Basin (Russia) are important sites to host oil reservoirs and may also provide the spaces for CO2 sequestration. In this paper, numerical simulation is used to characterize the Illinois Basin in North America. This paper presents the methodology for estimating the in situ stress conditions of an intracratonic basin using a poroelastic model. The numerical simulation results show that a thrust-faulting regime is expected at shallow depths, while the three principal stresses are close in magnitude at intermediate depths. A strike-faulting regime dominates at great depths, which corresponds to the continental stress pattern. Such an in situ stress pattern is shared by another intracratonic basin in the North America—the Williston Basin. This methodology is also applicable to estimate in situ stress for other intracratonic basins worldwidely.