Fracture Propagation and Productivity Prediction for Horizontal Wells in Shale Oil Reservoirs

Abstract

As a typical unconventional oil and gas resource, shale oil is characterized by tight reservoir matrices and low permeability; multi-stage horizontal well fracturing is the core technology for its effective development. The lack of a clear quantitative relationship between fracturing parameters, fracture geometry, and productivity response, as well as insufficient understanding of the laws governing production decline, are key scientific issues limiting the efficient development of shale oil reservoirs. Based on Petrel Kinetix fracture propagation simulation and INTERSECT reservoir numerical simulation, an integrated analysis workflow of fracture propagation–reservoir stimulation–productivity response was established in this paper. The controlling mechanisms of fracturing parameters on fracture geometry, the influence of fracture parameters on productivity, and the characteristics of production decline were systematically studied. The Arps and Duong decline models in the study area were evaluated and compared. The research results indicate that: (1) Pumping rate, cluster spacing, fracturing fluid volume, and stage spacing significantly influence fracture propagation patterns and the stimulated reservoir volume (SRV). When the displacement is increased from 8 m3/min to 16 m3/min, the stimulated reservoir volume (SRV) increases from 27.6 × 104 m3 to 35.3 × 104 m3; the simulation conditions used in this study, when the cluster spacing is about 10 m, the SRV is relatively large, if the spacing is too small, the stress interference will be enhanced, and if the spacing is too large, it will form an unstimulated zones may remain. (2) Cluster spacing, fracture half-length, and fracture conductivity jointly determine the reservoir drainage efficiency, and the contribution of fracture half-length to productivity exhibits diminishing marginal returns, and the production increment decreases significantly when the half-length increases from 200 m to 250 m; under the condition of different fracture spacings, cumulative production increases rapidly first and then tends to be stable with increasing fracture conductivity, and there is an obvious critical value of fracture conductivity. (3) The production decline in shale oil horizontal wells exhibits staged characteristics. The production decline in the study area under the open-flow conditions conforms to the Duong model and under the pump-installation conditions conforms to the Arps model. The average fitting accuracy of the Arps decline model (R2 = 0.818) is slightly higher than Duong model (R2 = 0.813). The integrated analysis workflow of fracture propagation–productivity response and the demand chart of fracture conductivity established in this paper can provide a reference for the optimization of fracturing parameters and scheme design of horizontal wells in shale oil reservoirs in the study area and similar geological conditions.