Well RXY is located in the Ravva offshore field in the Krishna-Godavari basin (India) and was intended to produce significant crude from a secondary reservoir section. This paper presents a case study concerning rigless remediation of microchannels in the cement packer (placed in the annulus of the production tubing and casing to isolate the producing zone) and discusses laboratory development of a customized epoxy resin system, simulations to estimate channel size, three-dimensional (3D) displacement modeling, drillout after placement, and evaluation post-placement.
An epoxy resin system was selected to seal micro-annuli in a cement packer and restore zonal isolation because of its ability to develop high compressive strength, potential to resist significant strain, and its solids-free formulation. This resin system was pumped followed by an ultrafine cement slurry comprising a fine-particle high-surface-area cement blend that can penetrate small channels more easily compared to conventional cement. The top of fluids was simulated for various cases as per channel size estimations, and 3D displacement modeling was performed to incorporate fluid contamination.
The strategic placement of epoxy resin and ultrafine cement focused on isolating annuli above the zone of interest. Conventional cement testing equipment was used to customize resin formulations to downhole conditions. After placement and solidification of the designed treatment, cement remaining in the tubing was successfully milled. A positive hermetical test was conducted after 48 hours of setting time, and the result was confirmed as successful. Barrier evaluation was performed using a combination of a cement bond log (CBL) tool and ultrasonic scanner. Furthermore, the acoustic impedance was post-processed to generate a derivative acoustic impedance (DZ) data set before performing the data analysis workflow. On the basis of analysis of this evaluation, the well was perforated in the pay zone interval and produced approximately 2,000 BOPD. The well was observed for several days to confirm tubing and casing isolation. The epoxy resin plus ultrafine cement blend was designed to deliver a dependable barrier. This engineering solution proved to be a highly efficient and cost-effective method for treating narrow cement channels in a deviated tubing-production casing annulus using only pressure-balanced cement placement.
The epoxy resin technology has unique properties that make it best suited for remediation, particularly in tight geometries, such as in the current scenario of micro-annuli channels in a cement sheath. The resin system is solids-free (Newtonian fluid) and can provide a high-pressure seal. The system also withstands contamination (overcomes inefficient well fluid displacement), which is beneficial when prejob cleanup resources are limited. In addition, this drillable system develops compressive strength ranging from 5,000 to 15,000 psi.