Abstract:

Evaluation of fracture-network systems along fractured horizontal wells is vital to an efficient development of tight-oil reservoirs.Given the lack of efficient evaluation means, we propose a method based on the dynamic inversion theory for the evaluation of fracture networks along fractured horizontal wells in tight-oil reservoirs.To begin with, a mathematical model of well testing that takes into consideration the nonhomogeneous and insufficient fluid supply of the networks is developed based on seepage activities and fracture network geometry.The bottom pressure of wells is obtained through an analytical method from the mathematical model and then used to establish a method for evaluating the fracture-networks.Subsequently, a field application in Jimusar tight oil reservoirs in the Junggar Basin is performed to prove the reliability of the method.The results show that the flow stages in the fracture networks of horizontal wells in the reservoirs involve the wellbore storage and skin effects, fracture bilinear flow, formation linear flow as well as fluid channeling, linear and quasi-stable flow in stimulated areas.It is also found that after fracturing, networks composed of major hydraulic fractures with a half-length of 135 m and a conductivity of 118.87×10^-3 μm² are generated near wellbores.The storability of the minor fracture networks ranges between 6.30% and 17.99%, and the permeability of the stimulated areas is 100.8×10^-3 μm².This study provides a theoretical basis for research works or operations such as reservoir parameter inversion, fracturing evaluation and dynamic monitoring of tight oil reservoirs in the Junggar Basin.

Key words: well test model, dynamic inversion, fractured network system, fractured horizontal well, tight oil, Jimusar area, Junggar Basin