Innovative Cement Spacer Improves Well Cementing Integrity - 60 Case Histories Reviewed

Abstract

Abstract This paper reviews the challenges faced during well cementing in the fields of East-North Kalimantan, Indonesia and describes utilizing an innovative cement spacer to successfully solve these issues. Unconsolidated formations and depleted reservoirs are main causes for lost circulation during drilling and cementing operations often resulting in poor cement bond logs and failed Top of Cement (TOC) requirements. The common practice to address these well integrity problems is to apply lost circulation material and low density cementing systems designed at 10.5 to 11.0 ppg. This strategy did not always accomplish the desired results and remedial cement squeeze jobs were needed for many primary cement jobs. To overcome these challenges, an innovative cement spacer system was engineered and successfully applied. The new environmentally friendly spacer system contains a biopolymer to mitigate loss circulation issues during cementing. It strengthens the wellbore wall by forming an effective seal along the formation, minimizing losses during cementing and preventing cement fall back after placement. The initial field application was immediately successful in obtaining full circulation returns during the cement job, a constant challenge on prior jobs. An added advantage was the cement slurry density could be increased from 10.5 up to 13.5 ppg without encountering any losses; despite exceeding the maximum theoretically allowable equivalent circulating density (ECD). As a consequence the increased slurry density improved early cement strength development which reduced wait-on-cement times and required using less concentration of expensive light weight cement materials. This, in turn, simplified operations and logistics and reduced costs. Case histories are presented covering more than sixty successful cement jobs using the new spacer system. Specific cases are discussed where: 1. successful results were achieved despite partial to total drilling related losses during the drilling phase, 2. cement bond logs have improved and 3. Remedial jobs have been eliminated. Conservative cost savings utilizing the new spacer design is more than $2.5 million USD. The product can be applied on high-temperature, high-permeability formations, those with low fracture gradients and fragile, unconsolidated, and fractured formations.