More Insight into Kick Tolerance Calculations, and Effect of Kick Classification, Frictional Losses, Pore Pressure Profile and Influx Temperature

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Abstract Kick Tolerance (KT) calculation is essential for a cost-effective well design and safe drilling operation. While most E&P operators have a similar definition of KT, the calculation is not consistent because of making different assumptions and/or computational power of KT calculators. A dynamic drilling simulator usually gives the most realistic KT value but the simulation services may not be always available unless for critical wells that marginal KT imposes an additional casing string and/or major operational risks. Thus, companies widely use simplistic steady-state models through their own KT calculation worksheets or commercial software. In order to prepare a standard procedure for KT calculation and to generate a reliable KT worksheet for Company P, we reviewed relevant academic literature, common practices, and assessed several off-the-shelf software programs. Development of the company new worksheet, QA/QC and subsequent investigations found that there are some important criteria and parameters that affect the calculation but in most cases, they are missing in simplistic models or ignored by engineers because of unawareness or lack of adequate references. To address KT sensitivity to different parameters, we generated a new computer program based on a gas bubble model that applies the effect of annular frictional pressure losses, influx/mud temperature, gas compressibility factor, well trajectory and BHA. The program, however, provides different KT models for swabbing kick and underbalanced kick scenarios which are two different categories on the basis of their cause, this kick classification concept that usually ignored by many engineers as well as in many kick tolerance models prevents the risk of swabbing kick overestimation. Besides kick classification as a main criterion for KT model, we also discuss how frictional losses, mud weight and temperature profile affect KT and may add to operational risks. Annular Pressure Loss (APL) parameter is sometimes missing in KT worksheets or it is assumed zero while, as an additional stress load to wellbore, it impacts the kick budget and must be taken into consideration. Casing Pressure (CP) reduction method is a non-standard well killing procedure through which can compensate APL by adjusting choke pressure, the study discusses the CP method to show how can eliminate the APL properly and increase KT by changing operational practices. Pore Pressure (PP) reversal trend also could potentially increase operational risks should engineers calculate KT only at section Total Depth (TD) where PP is less than its maximum value along the section, KT sensitivity analysis to drill depth reduces the risk of overestimation. Simulator D, a dynamic drilling simulator, used for comparison and verification of the company model in different scenarios. This study doesn’t compare steady-state model accuracy against a dynamic simulator, but rather focuses on proof of the concept of the proposed model and sensitivity to the mentioned criteria/parameters. The primary objective of this project was to perform a QA/QC to assess the risk of simplistic KT worksheets for the company but later on, a lack of adequate references on swabbing kick tolerance, the effect of APL, mud weight and temperature became main drivers for conducting this study that may provide more insight into KT calculation and hopefully open up other areas of research leading to realistic approaches for KT calculation.