A New Comprehensive, Mechanistic Model for Underbalanced Drilling Improves Wellbore Pressure Predictions

Abstract

A new comprehensive, mechanistic model that allows more precise predictions of wellbore pressure and two-phase flow parameters for underbalanced drilling (UBD) is proposed. The model incorporates the effects of fluid properties and pipe sizes and, thus, is largely free of the limitations of empirically based correlations.The model is validated against actual UBD field data and fullscale experiments in which the gas and liquid injection flow rates as well as drilling fluid properties were similar to those used in common UBD operations. Additionally, a comparison against two different commercial, empirically based UBD simulators shows better performance with the mechanistic model. IntroductionIt is generally accepted that the success of UBD operations is dependent on maintaining the wellbore pressure between the boundaries determined by formation pressure, wellbore stability, and the surface equipment's flow capacity. Therefore, the ability to accurately predict wellbore pressure is critically important for both designing the UBD operation and predicting the effect of changes in the actual operation.Because of the complex nature of the hydraulic system of UBD operations in which two or more phases (liquid, gas, and solids) commonly flow, the prediction of pressure drop and flow parameters, such as liquid holdup and in-situ liquid and gas velocities, are performed mainly with empirical, two-phase flow methods. The Beggs and Brill 1 correlation is the most popular among the current, commercial UBD simulators. However, it is recognized by the petroleum industry that most of these empirical correlations were developed from experimental databases, thereby making extrapolation hazardous. 2 Moreover, the Beggs and Brill 1 correlation has been shown to overpredict or fail to predict bottomhole pressures for both vertical and horizontal UBD operations. 3,4 Since the mid-1970s, significant progress has been made in understanding the physics of two-phase flow in pipes and production systems. This progress has resulted in several two-phase flow mechanistic models to simulate pipelines and wells under steadystate as well as transient conditions. Consequently, mechanistic models, rather than empirical correlations, are being used with increasing frequency for designing multiphase production systems. Based on this trend of improvement, the application of mechanistic models to predict wellbore pressure and two-phase flow parameters seems to be the solution to increasing the success of UBD operations by improving such predictions.Literature Review. Bijleveld et al. 5 developed a steady-state UBD program to assist well engineers in planning and executing underbalanced operations. This in-house computer program uses the mechanistic two-phase flow approach. However, there is almost no technical information in the literature about implementing the mechanistic models in UBD operations.Hasan and Kabir 6 developed a mechanistic model to estimate the void fraction during upward concurrent two-phase flow in

Transient flow in wellbores and phase transition of CO2 during formation supercritical CO2 invasion

“…Except for the partial differential term of time variables, the annular multiphase flow pressure drop includes hydrostatic pressure gradient, friction pressure gradient and acceleration pressure gradient. Perez model for gas‐liquid two phase flow pressure drop gradient calculation is adopted in the paper.…”

Review of two-phase flow models for control and estimation

“…The more complicated approach, sometimes referred to as mechanistic models, predicts local flow regimes and then uses different correlations depending on the regime predicted, see e.g. Fjelde et al (2003); Perez-Tellez et al (2003). This typically entails solving implicit relations using an iterative numerical procedure.…”

“…A mechanistic approach for finding correlations, which considers the annular geometry and upward flow encountered in drilling, was developed by ; ; Lage and Time (2002), which uses 5 different flow patterns Bubble, Slug, Churn, Annular and dispersed bubble. This approach was further studied by Perez-Tellez (2003); Perez-Tellez et al (2003) and employed on Iranian field data by Ashena and Moghadasi (2010).…”

Real-Time Interpretation Model of Reservoir Characteristics While Underbalanced Drilling Based on UKF

“…Fjelde et al [10] established a new multiphase flow model of UBD, which used the MUSCL format to modify the classical upwind format, and could better describe the pressure fluctuation law during pipe connection. Perez-Tellez et al [11] proposed a mechanical model for predicting the pressure of two-phase flow in an annulus and a drill pipe, in which a drift flux model is coupled. Khezrian et al [12] developed a two-fluid model in the Eulerian frame of reference for simulation of gas-liquid two-phase flow in the UBD operation.…”