Research on Production Improvement With Static and Dynamic Geomechanical Modelling For Hydraulic Fracture Optimization in Unconventional Resource-A Case Study from China
Authors: Qu Liming. , Zhou Wei. , Jiang Zhibin. , Xie Dan. , Zheng Sheng. , Qian Chuanchuan. , Lian Liming. , Wang Jie. , Qi Lisha , Li Zheng. , Huang Xingning. 
Published: February 2024

Unconventional oil and gas resources have extremely high reserves, and various countries have increasingly emphasized their development and utilization. Horizontal well fracturing with multiple clusters is one of the most critical technologies for economically and efficiently developing such reservoirs. At present, when studying the fracture extension law of horizontal well fracturing with multiple clusters, most of the injected fluids are pure fluids, and proppant is seldom considered. When optimizing the fracture parameters of horizontal wells, it is generally assumed that the fracture length, width, and height of each cluster of fractures are equal, without considering the fact that the fracture morphology is very complex during the actual multi-cluster fracturing process. The conventional fracture parameter optimization method only finds the block's most suitable and ideal fracture parameters without considering how the actual fracturing construction can produce the fracture. Therefore, there is an urgent need to master the multi-fracture expansion law of horizontal well fracturing, optimize the construction parameters, and predict the production capacity of fractured horizontal wells with the actual fractures formed by multi-fracturing clusters, so as to scientifically guide the construction design and production, and to provide technological support for the efficient development of China's unconventional oil and gas reservoirs. This paper's main results and understandings are as follows: (1) A mathematical model of multi-fracture extension is established by considering the fracture-induced stress field, fluid flow in the fracture and wellbore, fracture extension criterion, etc. The model is compared with the single-fracture extension analytical and the existing multi-fracture extension numerical models. The accuracy of the model in this paper is verified by comparing it with the analytical model of single-fracture extension and the existing numerical model of multi-fracture extension. (2) With low formation elastic modulus and high viscosity fracturing fluid, short and wide fractures are easily formed after fracturing; with high formation elastic modulus and low viscosity fracturing fluid, long and narrow fractures are easily formed after fracturing; and with high displacement fracturing fluid, long and wide fractures are easily formed after fracturing. With the increase of ground stress difference, the deflection angle of edge cracks decreases rapidly, and after the ground stress difference exceeds 5 MPa, the edge cracks hardly deflect. With the decrease of the elastic modulus of the formation, the increase of the ground stress difference, the decrease of the cluster spacing, and the increase of the diameter and the number of boreholes, the effective seam length, the average seam width, and the fluid injection volume of the edge cracks increase, and the effective seam height changes very little. The intermediate cracks’ effective seam length, average seam width, fluid injection volume, and effective seam height decreased. (3) The mechanism model of single-stage three-cluster fracturing in horizontal wells was established by combining the average physical property parameters of Block B in Xinjiang Oilfield. Conventional optimization methods were used to analyze the optimal number of fracture clusters, spacing of fracture clusters, fracture length, and fracture inflow capacity for single-stage fracturing of horizontal wells. The actual fracture parameters were simulated using the multi-fracture extension mathematical model in this paper, reasonably simplified and imported into the homogeneous model, and the optimal fracture placement and fracturing fluid parameters were selected with the goal of maximizing the cumulative oil production within ten years. The optimal number of fracturing clusters in this block is 3, the optimal cluster spacing is 40 m, the optimal fracturing fluid viscosity is ten mPa∙s, and the optimal fracturing fluid displacement is 12 m3/min. Finally, the fractured fractures under this fracturing construction method were reasonably simplified and arranged into the actual geological model of the block to predict the post-pressure production capacity of horizontal wells with segmented multi-cluster fracturing, and the cumulative oil production of this block is 45,190 m3 in 5 years using a single horizontal well development.