Temperature Distribution, Thermal Stress, and Thermal Displacements During In-Situ Heating of Oil Shales

Abstract

We have used a numerical simulation to study the temperature distribution, thermal stress, and thermal displacements during in-situ heating of shales. We have observed that the heater temperature and the temperature at the position of the casing do not change much, while the water temperature in the wellbore and in the region of the cement ring drops quickly. The temperature in layers below the wellbore reach the melting point of the shale after continuous heating for 10-100 hours, while it reaches the heater temperature after 1000 hours. The heating efficiency drops rapidly because of significant convection, which does not permit effective heating of the strata. At the same time, thermal expansion leads to a change in the displacement in the X direction and the equivalent stress. Both the indicated parameters reach a maximum on the well wall and remain unchanged as the distance from the borehole increases. Under these conditions, the casing – cement ring interface and the cement ring – stratum interface slip considerably, separating the two interfaces, and the equivalent stress leads to yield of the casing, the cement ring, and the stratum. The results obtained can be useful for cementing and completion of wells.