Analytical modeling on the geo-stress and casing damage prevention with the thermo-hydro-mechanical (THM) coupling of multi-field physics

Abstract

Understanding the rule of squeezing force on casing changing with the working parameters of wells, such as steam injection pressure, steam injection temperature and bottom hole pressure, is very important to prevent casing damage in the complex thermal recovery process involving the interaction of temperature, stress and seepage field. According to the theory of heat transferring, seepage mechanics and elastic–plastic mechanics, the mathematical model considering seepage-stress-heat transferring coupling of thermal recovery was established. The numerical model of the thermal recovery for a block in GuTong oil field was built, and the stress sensitivity of the rock was tested. The research work indicates that the permeability is more sensible to the stress when the maximum stress is less than 35 MPa. The calculation results of the temperature, pressure and vertical displacement fit well with the monitoring data, and the error is less than 20%. The stress and displacement of well wall achieve peak value in the 7th–9th cycles. In the ninth cycle, the maximum horizontal displacement of the well wall occurs and reaches about 13 cm, and the casing damage is most likely to happen in the 7th–9th production cycles. The equivalent element method was used to calculate the extrusion force on the casing pipe. The pressure on casing under different steam injection rate, temperature of steam and bottom hole pressure was obtained and used for prevention of casing damage during the thermal recovery of heavy oil.