Unconventional Single Slurry Solution for ERD Wells with Depleted Formations

Abstract

Tailoring slurry designs using amorphous liquid silica base has been a success for Cementing Extended Reach Drilling (ERD) wells in Brunei in development fields. The use of this unconventional slurry density and design has helped to achieve the necessary top of cement and required zonal isolation for the production string of these wells. Cementing across depleted formations has been a challenge for the drilling sector within the oil industry. Isolation of production zones with competent cement slurries has become a necessity in fields, especially where a low Equivalent Circulating Density(ECD) during the cementing operation is required to achieve the desired top of cement in low fracture gradient formations. For Brunei offshore operations a novel approach has been proposed that uses an amorphous liquid silica-based slurry system to design a new 14 ppg lightweight cement slurry. The slurry properties were tailored to eliminate the need for a dual slurry system. Planning, execution, and post-operation evaluation methods have been developed for this new design. Extensive laboratory testing has been performed for the 14 ppg extended slurry which includes basic slurry testing as well as more advanced evaluations such as a full mechanical properties study and finite element analysis that was used compared to conventional slurry designs. Various optimizations were done for the slurry design to overcome mixability challenges and deployment using a conventional offshore liquid injection system or by premixing the water with liquid additives on a mixing tank or rig pits. To validate this technology, a field trial was performed at the rig site where a production liner for an extended reach well was cemented and subsequently evaluated using cement evaluation logging tools. The first Brunei offshore trial operation, executed in Q2 2020, was a 4.5-in. production liner where 16.5 m3 of a 14ppg novel slurry design was mixed, pumped and successfully placed within the annulus. Since the initial trial, a total of 8 jobs have been executed successfully in Brunei, with a few more wells identified as candidates for this solution. The paper provides laboratory testing details, hydraulic simulation validations along with job execution and post-operation cement evaluation.