EVALUATION OF IN SITU STRESS DISTRIBUTION OF MARINE SHALE RESERVOIRS IN NORTHERN GUIZHOU PROVINCE USING 3D SEISMIC DATA AND GEOMECHANICAL MODELING

Many sets of marine shale rich in organic matter have developed in southern China, where shale gas resources are abundant. The Niutitang Formation of the Lower Cambrian is older than the Longmaxi formation of the Lower Silurian and is characterized by large structural fluctuations, complex structural deformation and a complex in situ stress state, which severely restricts the drilling trajectory design and fracturing location of horizontal wells in the study area. This problem is addressed in this paper by developing a 3D in situ stress prediction based on a combination of seismic inversion and 3D geomechanical heterogeneous modeling. (1) A detailed interpretation of seismic data and an analysis of tectonic evolution are used to establish a structural geometric model of the study area. (2) The well seismic method is used to invert the 3D distribution of the mechanical parameters of the shale reservoir, and the transformed dynamic and static rock mechanical parameters are used to construct a geomechanical heterogeneity model of the study area. (3) The direction of the maximum horizontal principal stress at the current well point is determined through hydraulic fracturing, wellbore collapse and drilling-induced fracture. Hydraulic fracturing and array acoustic logging are used to determine the vertical change in the in situ stress. The boundary load and displacement constraints on the model are determined, and the finite element method is used to calculate the 3D distribution of the in situ stress in the study area. The results show two stress transfer zones in the study area, which are located at 400 m and 900 m. However, the heterogeneity in the rock mechanical parameters and the occurrence and scale of faults affect the depth of the stress transfer zone. There are also different horizontal principal stress gradients in different parts of the structure. The principle stress gradient in the structurally gentle area is larger than those in the fault and fold areas.