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New Tailored Spacer System Helps Reduce Lost Circulation and Enhances Cement Bonding during Multistage Cementing Operations in Fractured Formations in Kyumbinskoe Field, Eastern Siberia


 Lost circulation (LC) is commonly encountered in drilling and cementing operations and can significantly contribute to non-productive time (NPT). An operator in the Kyumbinskoe Field faced this challenge in a fractured production section of the formation, and conventional LC solutions had been ineffective at achieving strict regulatory top of cement (TOC) requirements and satisfactory cement bonding. This paper describes a tailored spacer fluid system engineered to effectively and efficiently prevent LC to meet the job requirements. The tailored spacer system includes additives that perform synergistically to help prevent LC in permeable and fractured formations and enables rheological hierarchy to facilitate effective mud displacement. The spacer was designed to meet operational parameters for cementing a production casing string in two stages through the use of a multi-stage tool and was subjected to thorough verification through lab testing and computer simulations to ensure job requirements could be met. The tailored spacer system was used in three trial jobs to assess its ability to minimize losses in a permeable and fractured formation with a history of LC with the ultimate goal to achieve planned TOC and improve cement bond quality as verified by Cement Bond Logs (CBL’s).
 Use of this tailored spacer system helped to minimize losses experienced on all three wells. CBL results were also significantly improved with an average of 70% of the cemented interval being classified as "good bond" on wells cemented without the tailored spacer system to 88% on the three wells where it was used. Barrier dependability with the new spacer system was improved through achieving strict regulatory requirements for TOC on two out of three wells and improved cement evaluation results, which is a critical requirement of well construction that allows for maximizing production over the life of the well.