Summary The detection and control of gas kicks in oil-based mud/synthetic-based mud while drilling through narrow pore-pressure/fracture-pressure windows has always been a challenge because of gas solubility and mud compressibility. Continuous closed-loop monitoring of the well and automated early kick detection and control helps to keep the influx volume at a minimum before it reaches the well-control-threshold margin in the kick-tolerance matrix. This paper presents a case study and detailed analysis of the event through advanced simulations to examine the benefits of automated influx detection and control by use of a managed-pressure-drilling (MPD) system compared with a conventional-well-control method. In the case study, an automated-MPD system successfully detected and controlled a gas influx in oil-based mud while drilling in onshore western Canada. The analysis used dynamic well-control simulations to regenerate the event, and a close match with the field data was achieved. A sensitivity analysis was then conducted to study the effect of total response time on pressures at the surface and at the casing shoe during the application of the conventional “driller's method” of well control. The findings from the study demonstrate how automated early kick detection and control minimize influx volume and increase operational safety. The implementation of an MPD system with such capabilities significantly reduces nonproductive time by enabling influx circulation at full rate and eliminating the need for flow check, blowout-preventer closure, and operational delays inherent in conventional well control.

Summary The constant-bottomhole-pressure (CBHP) method of managed-pressure drilling (MPD) maintains wellbore pressure above the wellbore stability or pore pressure and below the fracture pressure (FP). It is common practice to perform frequent dynamic formation-integrity/leakoff tests (FIT/LOTs) to measure the FP. Several authors addressed the uncertainty in the measured value of the FP caused by mud compressibility and thixotropy. Moreover, field evidence indicates considerable variations in the effective FPs resulting from varying wellbore temperatures. This paper presents a mathematical model, validated with field data, to estimate the true FP from the leakoff-test data. The model accounts for the effect of mud compressibility and thixotropy, and considers the effect of transient wellbore temperatures on the geomechanical rock stresses. The study also presents application of quantitative risk assessment (QRA) to represent the probability-density distribution of FP associated with the uncertainties in the input parameters. The method was demonstrated with two examples from the Gulf of Mexico (GOM). The study shows that the operational parameter “pumps-off” time and two formation properties—Young's modulus of elasticity (E) and thermal-expansion coefficient (αT)—contribute most to the uncertainty in FP. Moreover, a log-normal distribution of the FP indicated a strong effect of temperature variation. It is also concluded that the uncertainty resulting from the temperature effect could be minimized by conducting the test after a characteristic 60-minute pumps-off period.

Realizing the potential benefits automation brings, many operators have turned to managed pressure drilling (MPD) techniques as a technical and cost-reward solution to hard-to-reach assets, an approach which not only saves time but also enhances the safety capabilities of the operation. The evolving industry shift toward MPD-ready rigs demonstrates the significant need for a reliable software system to interact with the equipment and simultaneously deliver enhanced models able to precisely control annular pressure in geological complexities where drilling windows are narrow. Several studies have demonstrated the operational benefits of MPD through the application of the constant bottom hole pressure (CBHP) method, imbedded automated kick detection, and control capabilities. MPD technology relies substantially on applying surface back pressure (SBP) using automated chokes to precisely control the annular pressure profile in a closed loop circulation system. During drilling, CBHP connections, mud displacements and fluid anomaly incidents, the SBP is dynamically adjusted in response to operational changes that yield annular pressure changes; such as circulation rate, top drive speed, and rate of penetration to name a few. The integrated MPD drilling software platform is used in combination with interactive models and surface and downhole data measurement in a unified computing system to enhance real-time analysis of drilling performance. By employing real-time models such as hydraulics, well control, pore and fracture pressure estimation, surge and swab, and drilling optimization torque and drag, the system quantifies the boundaries and aid in understanding the real operational limits. Additional software platform applications deliver the common integration baseline that enables both operations within the pre-drilling, while drilling and post analysis. The current automated MPD software has been successfully used in several onshore and offshore wells with narrow drilling windows. This paper discusses the applications and the newest developments in the MPD integrated software to automatically and precisely manage wellbore pressure. The results to be presented include the summary of planning, while drilling analysis, and post drilling analysis of an offshore case study where a detailed parametric analysis of measured and estimated data are compared.

The constant bottom-hole pressure (CBHP) method of managed pressure drilling (MPD) maintains wellbore pressure above the wellbore stability or pore pressure and below the fracture pressure. It is common practice to perform frequent dynamic formation integrity/leakoff tests (FIT/LOT) to measure the fracture pressure. Several authors addressed the uncertainty in the measured value of the fracture pressure caused by mud compressibility and thixotropy. Moreover, field evidence indicates considerable variations in the effective fracture pressures resulting from varying wellbore temperatures.This paper presents a mathematical model, validated with field data, to estimate the effective fracture pressure (EFP) from the leakoff test data. The model accounts for the effect of mud compressibility and thixotropy, and considers the effect of transient wellbore temperatures on the geomechanical rock stresses. The study also presents application of quantitative risk assessment (QRA) to represent the probability density distribution of EFP associated with the uncertainties in the input paramaters. The method was demonstrated with two examples from the Gulf of Mexico. The study shows that the operational parameter-"pumps off" time, and two formation properties-Young's modulus of elasticity (E) and thermal expansion coefficient (␣ T ) contribute most to the uncertainty in EFP. Moreover, a log-normal distribution of the EFP indicated a strong effect of temperature variation. It is also concluded that the uncertainty resulting from the temperature effect could be minimized by conducting the test after a characteristic 60-minutes pumps-off period.

Detection and control of gas kicks in OBM/SBM while drilling through narrow pore -fracture windows has always been a challenge due to gas solubility and mud compressibility. Continuous closed loop monitoring of the well and automated early kick detection and control helps to keep the influx volume at a minimum before it reaches the "well control" threshold margin in the kick tolerance matrix.This paper presents a case study and detailed analysis of the event through advanced simulations to examine the benefits of automated influx detection and control using MPD system in comparison to conventional well control method. In the case study, an automated MPD system successfully detected and controlled a gas influx in OBM while drilling onshore Western Canada. The analysis employed dynamic well control simulations to regenerate the event and a close match with the field data was achieved. A sensitivity analysis was then conducted to study the effect of total response time on pressures at the surface and at the casing shoe during the application of conventional Driller's method of well control.The findings from the study demonstrate how automated early kick detection and control minimizes influx volume and increases operational safety. The implementation of MPD system with such capabilities significantly reduces NPT by enabling influx circulation at full rate and eliminating the need for flow-check, BOP closure and operational delays inherent in conventional well control.