Application of an Innovative Cement Spacer to Improve Zonal Isolation - Indonesia Case Histories

Abstract

This paper reviews the challenges faced during well cementing in the fields of Indonesia and describes the use of an innovative cement spacer to successfully solve these issues. Unconsolidated formations, natural fractures, and depleted reservoirs are the main causes for lost circulation during drilling and cementing operations, often resulting in poor zonal isolation and failed Top of Cement (TOC) requirements. The common practice to address these well integrity problems is to apply lost-circulation materials and low-density cementing systems which did not always yield the desired results. As a result, remedial cement squeeze jobs were needed in many primary cement jobs. To overcome these challenges, an innovative cement spacer system was engineered and applied. The environmentally preferred spacer system contains a biopolymer to mitigate lost circulation issues during cementing. It strengthens the wellbore wall by forming an effective seal along the formation, minimizing losses and preventing cement fallback after placement. In cases of severe or total loss of returns, a special Lost Circulation Material (LCM) can be added to the spacer system which enhances the performance of the spacer by allowing it to adhere to the lost circulation zone(s). The special LCM technology is a blend of 100% organic biodegradable, lost circulation materials. The initial field application was immediately successful in obtaining full circulation returns during cementing, a constant challenge on many jobs in the fields of Indonesia. An additional advantage in some areas was that the cement slurry density could be increased from lightweight (10.5 ppg) to conventional (15.8 ppg) without encountering losses, despite exceeding the maximum theoretically allowable equivalent circulating density (ECD). The increased slurry density improved early cement strength development, which reduced wait-on-cement times and eliminated the requirement for expensive lightweight cement materials. This, in turn, simplified operations and logistics, and reduced costs. Multiple case histories are presented covering more than 70 successful cement jobs using the innovative sealing spacer system. Specific cases are discussed where successful results were achieved despite partial to total losses during the drilling phase; where cement bond logs have improved; where severe to total losses have been cured by the addition of special LCM and where remedial jobs have been eliminated. Conservative cost savings with the new spacer design were conservatively estimated to be more than 4 million USD.