Study on thermal decomposition of oil shale: Two-phase fluid simulation in wellbore

The world is rich in oil shale resources, but exploration and development are difficult. Increasing oil shale reservoir temperature has been proved to be one of the effective technologies to improve oil shale recovery. This paper takes the concentric dual pipe saturated steam injection of oil shale reservoir as the research object, and carries out the following three research works: firstly, a mathematical model of concentric twin tubes filled with saturated steam is proposed. Then, the coupling mode of the vertical and horizontal sections of the concentric double pipe is studied. Thirdly, the internal and external characteristics of wellbore in the process of saturated steam cycle are systematically modeled. Results show that: (a) Since the steam absorption index method is used to calculate the steam absorption along the way, the saturated steam mass flow rate in the horizontal annular space is in a uniform decline mode. (b) The slope of saturated steam dryness near the oil shale reservoir is about 1.3 times of that in the vertical wellbore. (c) In the annular space of horizontal wellbore, the pressure of saturated steam is flat U-shaped. (d) With the increase of the steam absorption capacity of oil shale reservoir, the mass flow rate of saturated steam in the annular space of the horizontal section wellbore decreases continuously. (e) The higher the steam absorption capacity of oil shale reservoir is, the lower the saturated steam dryness in annular space is. •A wellbore thermal model for recovery of oil shale reservoirs is proposed.•The full length pipe flow model of the concentric double pipe is established.•The distribution characteristics of thermodynamic parameters are revealed.