Distribution Patterns of Deep Shale Reservoirs and Longitudinal Utilization Degree of Horizontal Wells

To explore and evaluate the longitudinal utilization degree of marine shale gas horizontal wells in southern Sichuan Basin (hereinafter referred to as “southern Sichuan”), focusing on the shale of Wufeng formation-Longyi1 sub-member in the deep Z block. By using the data from core experiments, well logging, and fracture height detection, a systematic analysis from the perspectives of reservoir distribution, longitudinal utilization height of hydraulic fractures, and longitudinal utilization degree of horizontal wells was conducted. The research results show that: (1) The overall reservoir conditions of the Wufeng formation-Longyi1 sub-member in the study area are relatively favorable, although the quality of Type I reservoir varies significantly among different well blocks; (2) The proppant tracer fracture height detection results show that fractures tend to extend upwards, the average total fracture height of fracture extend is 12.7 m, with the average upward extension height is 2.5 times the downward extension height; (3) The combination of fracture height and gas well productivity analysis suggests that targeting sub-layer ① as the horizontal well target can achieve full production of the continuous thickness of Type I reservoir in Z2 well block, whereas in Z1 well block, due to the significant proportion of the Wufeng formation in the continuous thickness of Type I reservoir, in the areas where the continuous thickness of Type I reservoir in Wufeng formation to middle sub-layer ① is greater than 4 m, horizontal wells cannot achieve full longitudinal utilization of the continuous thickness in top-quality Type I reservoir. The conclusion is that due to the limitations of longitudinal utilization height by artificial fracture networks and the variability in the distribution of continuous thickness of Type I reservoir, Z1 well block can continue to conduct horizontal well target tests and differentiated fracturing designs to further enhance the longitudinal utilization degree of the top-quality Type I reservoir.