Prediction of the maximum compressive horizontal principal stress directions of medium to deep shale gas in the Nanchuan region, China

 Abstract

The Nanchuan region is located on the southeastern margin of the Sichuan Basin, South China. Silurian Wufeng-Longmaxi Formation, buried between 2000-4500m deep in this area, is an important shale gas-producing formation. Influenced by multi-phase tectonic action during Mesozoic- Cenozoic ^[1], the maximum compressive horizontal principal stress (σ_Hmax) directions are complex and the orientation changes rapidly (55°-135°). Therefore, effectively predicting the maximum compressive horizontal principal stress (σ_Hmax) is important for improving the shale gas production capacity and optimizing the fracturing scheme development.

In this paper, the SHELLS finite element stress field modeling ^[2] was introduced and used to understand the above problems. Based on the increased and improved resolution of its program, and faults topography, heat flow, petrophysical parameters, and boundary conditions in the shale gas target layer, the σ_Hmax directions in the study area were modeled and calculated. The prediction results show that σ_Hmax directions in the Nanchuan region vary multi-directionally (0-180°), and are consistent with 11 of the 13 drilled wells, with only two drilled wells having minor differences (Figure 1). 85% of the predicted wells are consistent with the measured wells, achieving significant geological results and laying the foundation for the effective development of shale gas production capacity and optimized fracturing schemes in the area.

Keywords: Stress field modeling, maximum compressive horizontal principal stress directions, shale gas, mid-deep, the Nanchuan region

Figure 1 σ_Hmax directions in the Nanchuan region compared to actual drilling

References:

[1] Tang J G., Wang K M., Qin D C., Zhang Y., Feng T., 2021. Tectonic deformation and its constraints to shale gas accumulation in the Nanchuan area, southeastern Sichuan. Bulletin of Geological Science and Technology. 40(5), 11-21. ( in Chinese version).

[2] Bird, P., 1999. Thin-plate and thin-shell finite-element programs for forward dynamic modeling of plate deformation and faulting 1. Comput. Geosci. 25, 383–394.