Fracturing and Production Observations from the First Two Horizontal Wells for Shale Oil Exploration in Ordos Basin

Abstract

Abstract The continental depositional environment poses unique challenges for the exploration of unconventional resources. The tight reservoir nature requires horizontal drilling and multistage completion. However, the geologic discontinuity and the geomechanical heterogeneity complicate lateral completion design, fracturing treatment execution, and production analysis. The experience of developing the first two horizontal wells for shale oil exploration in the Ordos basin resulted in observations that link the geology, reservoir, geomechanics, and production behaviors, which can be used for future appraisal and development in similar environments. In 2014, one exploration well in the south Ordos basin demonstrated that the source rock from the Chang-7-3 formation could produce good light oil, but the tight reservoir needed horizontal drilling and multistage fracturing completion to achieve the production potential. In 2019, two horizontal wells were placed adjacent to each other for appraisal purposes. Due to the unique lacustrine deposition environment of the Chang-7-3 formation, landing the laterals in the target formation proved to be very challenging even with special geosteering tools. For both wells, the net-to-gross ratio is less than expected (51% and 38%), creating significant challenges for the ensuing completion phase. The multistage completion and fracturing were designed with full consideration of the horizontal lateral conditions. Reservoir quality (RQ), completion quality (CQ), and geology quality (GQ) were considered to optimize the completion staging strategy and fracturing plans. Besides the pressure response during fracturing, two additional monitoring and evaluation systems were deployed during the completion phase: microseismic interpretation and chemical tracers. Observations from these three measurements provided valuable information of how the formation responded to the staging strategy, fracturing initiation and diversion, and flowback and production. Post-fracturing production from both wells met expectations in the testing phase. Additionally, the observations during fracturing and flowback of those two wells provide unique value for better understanding the Chang-7-3 formation. Fracture initiation proved to be feasible only in the lateral sections with proper sand facies where good RQ and CQ were found. Microseismic monitoring showed fracture orientation and planar extension in space. Tracer results revealed where the formation hydrocarbons came from and how the two wells interacted. This case study will have significant influence for future drilling and completion in the Chang-7-3 formation and provide a useful case history for continental shale oil scenarios.