A new method of forecasting initial formation temperature during the whole drilling process based on proportional-integral control principle

Abstract

A strategy based on proportional-integral feedback control was applied to gradually feedback the error between simulation of transient heat transfer model and logged date to forecast initial formation temperature. In this study, based on the each control unit of mass, momentum and energy conservation principles in a wellbore, the transient heat transfer model was developed between circulation and shut-in stages under real casing program and drilling string assembly condition, which were solved by full implicit finite difference method. Meanwhile, the proportional-integral control principle was introduced to compare the error range between measured temperature and prediction temperature, which can precisely and quickly obtain initial formation temperature. Combined with a deep well basic data, the results show that the heat exchange efficiency of wellbore and formation was changed by the casing pipe depth, thus affecting formation temperature distribution of the near-well zone. What’s more, the initial and boundary conditions of each control unit in the down-hole was also changed by circulation and shut-in operating time during the drilling process, leading to the variation of distribution distance of the initial formation temperature of the near-well zone. Development of the numerical models and the research methods can provide accurately, economically and quickly to obtain theoretical basis for oil drilling, geothermal well exploiting and the initial formation temperature information.