CHARACTERISTICS OF THE FAULTS AND FOLDS AND ITS INSIGHTS ON SHALE GAS EXPLORATION: AN EXAMPLE FROM THE LUZHOU AREA, SOUTHERN SICHUAN BASIN, CHINA

The southern Sichuan Basin, a shale gas bearing area, presents great potential for increasing storage and production in the future. However, the structure characteristics and their control on shale reservoir quality have not been documented. Here the Luzhou area was selected as an example to study the structure characteristics and its insights on shale gas exploration in the southern Sichuan Basin.

In this study, multiple methodologies, including 3D seismic interpretation, strain simulation, seismic attributes analysis, and fault system topology, were employed to investigate the fault characteristics, fault-fold system distribution and fault connectivity in the southern Sichuan Basin. The quality and potentials of shale reservoirs were then evaluated.

In section view, the fore-thrust and back-thrust faults were identified in the study area. Accordingly, the folds developed in the study area were classified into the anticlines of pop-up zones and the synclines and slopes of imbricate zones. The strain simulation indicates that the fold of different types results in different level of reservoir damages, with high level of damage in the anticlines of pop-up zones, low level of damage in the synclines of imbricate zones, and intermediate level of damage in the slopes of imbricate zones. In plan view, two primary sets of faults, trending NNE and W-E, were interpreted based on 3D seismic attribute analysis. However, the two sets of faults present different distributions, with the NNE trending faults distributed throughout the study area and the W-E trending faults distributed primarily in the southwest portion. Based on fault topological analysis, the fault connectivity was quantitatively evaluated, demonstrating high level of variation in the study area. The anticlines of pop-up zones present high level of fault connectivity, whereas the synclines of imbricate zones present low level of fault connectivity. The slopes of imbricate zones present fault connectivity is in between. By integrating the production data of shale gas wells in the study area, it is believed the high productive shale gas wells are primarily distributed within the slopes of imbricate zones with intermediate fault connectivity, which may provide important hints for the shale gas exploration in the Luzhou area in the future.