CALCULATION OF THERMODYNAMIC PARAMETERS OF THE HEAT TRANSFER AGENT DOWNWARD FLOW IN A WELL, TAKING INTO ACCOUNT PERMAFROST MELTING

The relevance of the research is caused by the necessity of calculating the parameters of a heat-transfer agent pumped into an oil-containing reservoir throughout its movement from the exit from a heater or steam generator to the porous collector. The main method used today for developing the deposits of highly viscous and bituminous oils is the injection of thermal agent (hot water or steam) into such deposits. With thermal method of enhanced oil recovery, oil viscosity decreases and oil recovery factor increases. Increased oil recovery factor can lead to the profitability of the development of fields with highly viscous oils. Since the production of a hot steam-water mixture requires sufficiently high energy costs and for effective thermal effects on the oil reservoir a considerable amount of heat-transfer agent is required at sufficiently high injection rates, for the successful implementation of this development method, preliminary calculations are needed, which are based on an adequate mathematical model that takes into account various aspects the studied process. The main aim of the research is to analyze the influence of various factors on the nature of the distribution of heat-transfer agent parameters along the well depth, as well as the permafrost melting intensity. Objects: hydrodynamic and thermophysical processes occurring during heat-transfer agent movement in an injection well, taking into account thermal interaction with the surrounding rock. Methods. This theoretical study was performed on the basis of the methods of the mechanics of multiphase systems and computational mathematics. The task of finding the parameters of the downward two-phase flow in an injection well is divided into two parts. In the first part, the thermodynamic parameters of steady-state downward flow of a hot steam-water mixture in a well are determined taking into account heat losses to the surrounding rocks. In the second part, non-stationary propagation of heat, coming from the well product, in the surrounding rock is investigated, taking into account possible thawing of permafrost. The surrounding rocks temperature distribution found in the second part then used in the first part. Results. The paper introduces the mathematical model of the downward flow of a heat-transfer agent in an injection well, taking into account the external heat exchange of the well product with surrounding rocks (including permafrost). Using this mathematical model, the influence of various factors (mass flow rate, dryness of injected steam, different thickness of heat insulating material on the outer surface of the well lifting column, etc.) on the change in thermodynamic parameters of the two-phase flow along the well depth and on the melting of permafrost was numerically studied. The authors have obtained the dependences of the thawed zone radius in permafrost on the mass flow rate, as well as on the different filling of the well annular space.