Investigation of multiple hydraulic fractures evolution and well performance in lacustrine shale oil reservoirs considering stress heterogeneity

摘要

Giant Ordos basin, which locating in the northern China, consists of Palaeozoic lacustrine stacked sandstone and shale deposits with characteristics of low-permeability matrix rock and less-developed natural fractures (NFs). Recognizing the successful exploration of shale gas reservoirs in United States, Changqing oilfield uses advanced fracturing technology to create multiple straight hydraulic fractures (HFs) in shale oil zones with large differential horizontal stress. This paper firstly describes a hydraulic fracture propagation model (HFPM) that couples fracture deformation and fluid flow to simulate the growth of multiple HFs in the horizontal wellbore. We then integrated an embedded discrete fracture model (EDFM) and commercial reservoir simulator to analyze well performance based on the provided data from Changqing oilfield. We calibrated the fracture propagation model with reservoir performance data. Shale oil deposits in the Changqing oilfield have a relatively high brittleness index (BI) and large differential horizontal stress. This is the reason why reservoir with less-developed NFs system in the Ordos basin has less opportunity of generating complex fracture networks. Large-scale physical simulation experiments were conducted to validate the possibility of fracture networks generation. Our model considers the stress heterogeneity and offers the capability to address HF propagation in the presence of less-developed NFs and adjusts dimensions and spacing of NFs to achieve a history match with production data. This paper emphasizes the extensive application of an integrated model for lacustrine shale oil deposits. Considering features of Ordos basin, our model can provide a guideline for HF treatment design and optimization of well performance.