Abstract
Identifying and controlling a kicking well hinge on quickly obtaining reliable and accurate formation pore pressure. In this study, we derive an analytical model for estimating formation pore pressure when a gas kick occurs during tight reservoir drilling. The model considers the variations in gas volume and pressures in the annulus affected by mutual coupling between the wellbore and formation, as well as bubble migration and expansion in the annulus. Additionally, a numerical computation method that reduces the effect of measurement noise using the Hooke-Jeeves algorithm is proposed. The method is capable of estimating pore pressure during the early stage of a kick in real time, is robust to the inherit noise of the measurements, and can be applied in scenarios when a well shut-in process cannot be performed. The simulation results demonstrate that both kick simulation and formation pore pressure inversion can be conducted via the proposed methodology. The errors of the pore pressure estimating results are less than 2.03% compared to the field data of seven wells. The method is tested and validated to be robust to noise and maintain good convergence performance, thereby providing drilling engineers with a simple and quick way to estimate pore pressure during a kick.
Highlights
A well kick occurs when the formation pressure is higher than the wellbore pressure, causing fluid to flow from the formation into the wellbore
Once a gas kick occurs, appropriate operations, which are designed based on specific pore pressures, should be performed as quickly as possible to stop the influx and circulate out the formation fluid; quick estimation of the formation pore pressure is needed to effectively respond to a change in the drilling environment
We propose an analytical model for estimating the pore pressure on a kicking well
Summary
A well kick occurs when the formation pressure is higher than the wellbore pressure, causing fluid to flow from the formation into the wellbore. The pore pressure can be evaluated from the evolution process of gas influx, similar to pressure transient analysis during well testing [5,6,7,8] To combat this problem, Samuel [9] and Miska et al [10] proposed a method to estimate formation pore pressure and permeability based on buildup data collected upon shutting in a kicking well. A genetic algorithm in conjunction with a transient two-phase reservoir simulator was developed by Biswas et al [17] to analyse the variation of formation permeability along the wellbore These models commonly rely on a complicated wellbore multiphase flow model, which is difficult to be incorporated into the numerical parameter inversion algorithm. Applied to the drilled gas-kick scenarios, the simulated results indicate that the model is in good quantitative agreement compared to commercial software and field data
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