Successful Deployment of Managed Pressure Cementing (MPC) System Across a Challenging Narrow Pressure Window Condition for a Critical Liner Cement Job: A Case Study From Saudi Arabia

Abstract

A major challenge that is being occasionally faced during the well construction phase is to cement the formations holding narrow pressure margins between the pore and fracture gradients without inducing losses. Losses can commonly occur in these cases, compromising the integrity of the cement barrier. Designed slurry densities generally lead to high equivalent circulating density (ECD) levels during the cementing operations. This condition, combined with mud weights conventionally designed to be above pore pressure, usually results in downhole pressures which approach or exceed the fracture limit. Commonly, operators implement strategies to mitigate losses during the cementing phase, however, in most cases the losses are unavoidable using a conventional cementing approach. Managed pressure cementing (MPC) is an important technique for primary cementing operations in wells with such narrow pressure margins. This paper presents the design considerations, methodology and results of a land well where high-pressure influx was encountered while drilling an 8-3/8-in hole across a water-bearing formation. Narrow pressure gradient persuaded to utilize managed pressure drilling (MPD) to continue the drilling. The well was drilled to the target depth using 138-lbm/ft3 oil-based drilling fluid while maintaining the ECD from 146.5 to 149.5 lbm/ft3. Careful attention was paid to estimate the bottom hole circulating temperature, using the temperature modeling simulator. A 150-lbm/ft3 slurry was designed to keep the ECD intact. The slurry was batch-mixed to ensure the homogeneity of the final slurry mixture. A special spacer system was designed to reduce the losses while cementing. Additionally, the spacer was loaded with optimum amounts of surfactant package to serve as an aid to remove the mud and to water-wet the formation and pipe for better cement bonding. The centralizers placement plan was optimized, and additionally the liner was rotated during the cement job to achieve the required displacement efficiency yet staying within the torque and drag (T&D) limits. The cement treatment was performed as designed and met all zonal isolation objectives. The managed pressure cementing (MPC) system provides safe isolation of problematic zones in cost effective manner even in challenging narrow pressure window scenarios. The system provides precise control of the pressure and flow during and after the cement job. Constant pressure can be achieved at weak zones, preventing losses to the formation. This case study presents an overview of the engineering process used to plan and design the MPC operations and the results obtained. This paper reviews a successful MPC operation and presents findings and lessons learnt. After the successful results on this job and subsequent operations, this technique is now being adopted to optimize cementing, where losses during cementing operations in the past had forced to modify the well construction.