Optimizing the Cement Performance on Wells Subjected to Losses and Revolutionizing Wellbore Integrity: With External Casing Packer Ensuring Long-Term Wellbore Integrity – A Pakistan Case Study

Abstract

In this case study, drilling into unexpectedly weak formations led to inadequate cement behind the 13-3/8-in. and 9-5/8-in. casings, threatening well integrity. A robust solution combined advanced formation strengthening using non-reservoir-damaging chemicals and deployment of four external casing packers (ECPs). This approach enabled precise ECD management during the 7-in. liner cement job. The ECPs were pivotal in achieving smart completion objectives and long-term zonal isolation, revolutionizing cementing in challenging, loss-prone environments. A strategic approach was adopted to strengthen the formation to mitigate losses prior to cementing. Formation strengthening was achieved using non-reservoir-damaging chemicals to enhance fracture resistance. An optimal mud weight of 1.55 S.G. was selected, and ECD simulations were performed based on offset well data due to the absence of caliper logs. These simulations accounted for four external casing packers (ECPs) which were required for zonal isolation to meet smart completion requirements, with incremental outer diameters, enabling controlled ECD profiles. The cement design included flexible, expandable, and self-healing cement to ensure long- term zonal isolation under cyclic stresses. The 7-in. liner cement job was meticulously planned and executed to address a series of operational challenges, including weak formations, total fluid losses, and annular restrictions at the Polished Bore Receptacle (PBR). A key milestone in this operation was the deployment of four external casing packers (ECPs); marking the first time such an approach was implemented in Pakistan. This configuration enabled precise control of equivalent circulating densities (ECDs), critical to achieving effective zonal isolation and supporting smart completion strategies. In the absence of caliper data, simulations based on offset well information were employed to optimize cement volumes and manage ECD profiles. Formation strengthening treatments enhanced fracture resistance, enabling the Lockhart formation to sustain an equivalent mud weight of 1.80 S.G. The cement system, comprising flexible, expandable, and self-healing components, along with scrubbing spacers, facilitated efficient mud displacement and minimized losses. The operation achieved long-term well integrity while minimizing remedial interventions and reducing environmental impact. This case represents Pakistan's first successful 7-in. liner cementing operation utilizing four individually deployed external casing packers (ECPs), effectively overcoming severe loss risks associated with weak formations and operational constraints. Through the integrated application of formation strengthening, advanced self-healing cement technology, and multidisciplinary planning, effective zonal isolation was achieved, as validated by wireline cement evaluation, with no remedial intervention required. The adopted approach ensured sustained well integrity under challenging conditions where external mechanical isolation was essential. This case study provides a valuable reference for future applications encountering similar loss-prone environments, both within Pakistan and internationally.