Finite element simulation of formation testing while drilling accounting for thermal-hydro-mechanical coupling

Abstract

Formation testing while drilling (FTWD) is useful for acquiring dynamic formation parameters in real time. However, the FTWD is inevitably affected by the thermal-hydro-mechanical (T-H-M) coupling effect as the current drilling depth and the formation temperature continue to increase. In order to clarify the mechanisms of the effect of T-H-M coupling on the pressure response of FTWD, a novel T-H-M coupling mathematical model of the pressure response of FTWD was proposed. The parametric studies of the pressure response of FTWD under T-H-M coupling condition were simulated using the finite element method (FEM). The influence of different borehole wall conditions and coupling conditions on the pressure response of FTWD were compared, and the effect of T-H-M coupling on the interpretation of formation parameters was also discussed. The results indicated that the stress perturbation of drilling has little effect on the FTWD, but the change in formation pressure and temperature around the wellbore will significantly affect the pressure response of FTWD. The T-H-M process can create the “coupling skin” effect in the formation, which further leads to the greater pressure drop in the pressure drawdown stage and the lower growth rate in the pressure recovery stage. Formation permeability and temperature differential have a large effect on the pressure response of FTWD, but in situ stress and probe orientation have almost no effect. When the inversion of the original formation parameters is performed using the formation rate analysis (FRA) method, the near-wellbore supercharging can lead to an overestimation of the original formation pressure and the T-H-M coupling can lead to an underestimation of the original formation mobility. The model established in this paper is more in line with the actual test conditions, and the results can provide theoretical support for parameter optimization and data interpretation of FTWD.