Full-Scale Experimental and Modeling Studies of Gas Migration and Suspension Behaviors During Wellbore Influx Management Using MPD
Authors: Wei Chen , S. Adeyemi Temitayo , Sharma Jyotsna , Mahmud Shahriar , Chen Yuanhang 
Published: October 2023

Gas influx management is critical in oil and gas drilling operations, which aims to prevent the uncontrolled outflow of formation gas and the potential consequences caused by blowouts. When gas influxes enter a wellbore or marine riser and migrate within the non-Newtonian drilling fluids, the gas suspension behaviors can noticeably impact the influx migration behaviors. This effect is particularly important to consider during the gas migration process in a non-circulating well, where the monitoring and accurate prediction of pressure changes in the well are essential.

This study investigates the distribution of gas influx and Interfacial Area Concentration (IAC) during gas migration through full-scale experiments and numerical simulations. Downhole gas influxes were simulated by injecting gas into the bottom of a 5,160 ft-deep experimental wellbore using a Synthetic oil-based Mud (SBM) system. Helium, which shows a minimum solubility in the SBM, was selected to simulate the downhole gas influx. The Distributed Fiber-Optic Sensing (DFOS) data was obtained in high-resolution to monitor the gas migration behavior, and the gas slip velocities, slug length, and suspension concentrations were analyzed based on the measurements. A numerical simulator was developed based on the Two-Fluid Model (TFM) and the Interfacial Area Transport Equation (IATE) to simulate the gas influx behaviors. The experimental data were compared with the model predictions.

The results of this study indicate that the numerical modeling framework utilizing IATE effectively captured the behavior of bubble breakdown, coalescence, and suspension by enabling the estimation of interfacial area distribution. The model predictions demonstrate a strong agreement with experimental data, including gauge measurements, Distributed Temperature Sensing (DTS), and Distributed Acoustic Sensing (DAS). The accuracy of model estimation was significantly improved compared to models such as the Drift-flux Model without the integration of IATE, particularly in the interpretation of gas suspension. Through sensitivity analysis, this study reveals the substantial impact of gas bubble dispersion and suspension on the level of surface pressure buildup, which can be attributed to significant changes in the overall system compressibility. In addition, the presented case study was translated into field predictions (the migration of methane influx in water-based mud (WBM)) based on the proposed and validated models. The obtained results provided valuable references for field applications.

The experimental data with Helium and SBM from this study is critical for better decoupling and facilitating the understanding of the underlying physics involved in gas migration. In addition, this is a novel practice to implement the IATE in well-scale multiphase flow simulations, which has proved to be an effective tool for predicting the dynamics of gas influx distributions. The results of this study provide critical insights into the design and optimization of gas influx management during Managed Pressure Drilling (MPD).