Effective Zonal Isolation in Umusadege Field Wells with Expansive Cement Additives and Best Practices for Displacement: Case Study from OML 56

Abstract

The development of new fields in the Niger Delta presents unique challenges to successful production. One critical issue faced by an onshore operator in the Umusadege Field involved poor zonal isolation, as indicated by suboptimal cement bond logs (CBLs) from previous wells. The Umusadege Field, located in OML 56, contains multiple sand and shale intervals deposited during transgressive and regressive cycles, which create complex reservoir-seal systems. CBLs from previous wells indicated poor zonal isolation that could jeopardize well completion integrity. A tailored cement design that incorporated expansive additives applied through best-practice displacement techniques addressed this issue and resulted in improved zonal isolation and production in multiple wells. Target wells in the Umusadege Field exhibit various reservoir pressures and temperatures, with sands of interest at pressure between 3,080 and 3,635 psi and temperature between 157 and 226°F. The deepest well reached a total measured depth (MD) of 12,992 ft and a true vertical depth (TVD) of 11,342 ft. These conditions required cement solutions capable for long-term zonal isolation. After review of the operator's concerns and historical well data, a cement slurry with expansive additives was designed and validated in the laboratory to help mitigate microannulus development. The execution plan included best-practice displacement techniques to ensure proper placement and minimize cement channel formation. This innovative approach aimed to: Seal microannuliImprove cement bond qualityMinimize remedial cement applications Key execution practices included: Wellbore Preparation: Cleanup and conditioning to ensure proper cement adhesionCentralization: Optimal centralizer placement to promote uniform cement distributionSpacers and Preoperation Circulation: Use of appropriate spacers and fluid circulation to help prevent mud contamination and improve displacement efficiency The cement design and execution approach were applied to five wells within the field. Post-operation CBLs confirmed significant improvements in zonal isolation, with a strengthened bond quality at all key intervals. These wells entered production, and early results indicate stable flow rates and reduced remedial interventions. The effectiveness of expansive cement additives combined with best-practice displacement techniques to address zonal isolation challenges in the Umusadege Field are demonstrated in this case study. The tailored design and rigorous execution improved well integrity and long-term production efficiency. The methodologies outlined could apply to similar fields in the Niger Delta and support more reliable and cost-effective well completions