Efficient development technology slope-type strongly heterogeneous shale gas reservoirs: A case study on the Longmaxi Formation shale gas reservoir in the Weiyuan area of the southern Sichuan Basin

The efficient development of the slope-type strongly heterogeneous shale gas reservoir of Lower Silurian Longmaxi Formation in the Weiyuan area of the southern Sichuan Basin faces several difficulties, such as long drilling cycle, difficult formation of complex fracture network, and low single well production. In view of this, one theory and four key technologies are developed after years of technological innovation, technological research and production practice, which provide effective support for the efficient construction of the Weiyuan National Shale Gas Demonstration Area. And the following research results were obtained. First, the differential enrichment theory of slope-type shale gas reservoir in the setting of paleouplift is put forward, namely "sedimentation area selection, tectonic zonation and preservation controlling reservoir". The multi-stage structure superimposed marine shale gas zone evaluation and sweet spot selection technology is developed. The organic-rich siliceous shale in the middle and lower parts of S1l1 layer is determined to be the optimal target in the vertical direction. The core productivity construction area covers 165 km2, where the deployed wells have an average daily gas production of 27×104 m3 during the testing and the EUR is more than 1.1×108 m3. Second, the efficient navigational drilling technology with geology-engineering integration guided technology and efficient long horizontal section drilling technology as the core for the horizontal well with a narrow target is developed, and the rate of penetration (ROP) improvement model of shale gas well is established. The drilling cycle is shortened by 33.1%, the drilling rate of quality shale reservoir is increased to 97.2%, and the extension capacity of horizontal section exceeds 3 000 m. Third, based on the dynamic propagation model of hydraulic fracture network, the volume fracturing optimization technology for strongly heterogeneous shale reservoir is developed, and the key evaluation indexes can be predicted quantitatively, including net fracturing stimulation area dimension, stimulated reservoir volume, effective stimulation volume and propped fracture area. The sanding intensity is increased from 1.3 t/m to 2.7 t/m, and the stimulation effect is improved. Fourth, the main factors controlling the productivity of shale gas wells in the Weiyuan area include Long111 reservoir thickness, pressure coefficient, total gas content, perforation cluster quantity, sanding intensity and fracturing horizontal section length. Thanks to the application of the shale gas well production performance prediction method based on general regression neural network and modified embedded discrete fracture model, the coincidence rate of shale gas well production performance prediction result is close to and even higher than 95%. © 2021, Natural Gas Industry Journal Agency. All right reserved.