Study on the design and forecast method of complex fracture in shale oil formation in at Da’anzhai Formation in the Sichuan Basin

Abstract

The exploration of lacustrine shale oil and gas located at Da’anzhai Formation in the Sichuan Basin has entered into the development stage, and the horizontal well volume fracturing is the main stimulating technology for shale oil and gas development. To solve the problems of the accurate description of induced stress, complex fracture design, and poor match in geological engineering, the complex fracture design model is developed by the extended finite element method and augmentation Lagrange multiplicator method in consideration of the contact problem of natural crack. And the induced stress distribution characters and mechanism of complex fracture propagation are analyzed. It is found that as for the stimulation measure for the formation developed a natural crack, the fracturing fluid with lower injection rate are smaller viscosity is suggested to generate complex fracture due to the strong stress interference. Moreover, applying the proposed design method of complex fracture to a well in Da’anzhai Formation, it is shown that the results were basically close to the on-site results.