Key Technologies and Practices of Geosteering in Horizontal Wells for Jimsar Shale Oil

The LuCaoGou Formation in the Jimsar Sag of the Junggar Basin, Xinjiang, represents a typical terrestrial mixed sedimentary shale oil reservoir. Distinct from North American marine shale oils, interbedded shale oils in the Changqing Oilfield, and laminated shale oils in the Daqing Oilfield, this reservoir exhibits three defining characteristics: triple-source mixing, source-reservoir symbiosis, and dispersed sweet spots. These features manifest as complex lithology and pore-throat structures, significant lateral burial depth variations, well-developed interlayers and barriers, thin oil layers, and pronounced heterogeneity. Consequently, the reservoir presents substantial geosteering challenges for horizontal wells, with precise targeting of thin sweet spots requiring advanced technological solutions to address compounded geological uncertainties. To enhance sweet spot penetration rates and ensure robust productivity and sustainability of horizontal wells, a comprehensive geosteering workflow was implemented through three operational phases, Pre-drilling: A high-precision 3D structural modeling technique integrating seismic and well data was developed, enabling 1.5-m-scale delineation of the gold target zone. Trajectory optimization was achieved through multi-target control, ensuring geometric alignment with heterogeneous reservoirs. During drilling: A precision entry technology guided by stable cyclic marker beds reduced targeting errors to <1 m. Real-time logging-while-drilling (LWD) data combined with diagnostic mineralogical analysis established identification criteria for key reservoir parameters, achieving an average gold target zone drilling ratio exceeding 85%. Post-drilling: Local 3D geological models were iteratively refined using drilled-well constraints, enhancing structural and sweet spot predictability further improved gold target zone drilling ratio in subsequent wells. These integrated geosteering technologies in the Jimsar shale oil play have significantly contributed to establishing a national terrestrial shale oil demonstration zone, providing a replicable template for economically viable development of heterogeneous unconventional reservoirs in China.