Rejuvenating First Shale Gas Field of China by Introducing Innovative and Tailored Casing in Casing Cementing Solutions

China discovered Fuling shale gas field in 2012. The production dropped dramatically for early drilled wells with the time. Refracturing the wells to maintain production is a must to keep the field economically viable. A new method of cementing a smaller inner casing inside legacy production casing and then plug-and-perf fracturing was executed and the production was rejuvenated. The procedure consists of well kill, wellbore cleanout and reaming, cure losses and then cementing. The wellbore re-construction process will isolate all existing perforations in the wellbore, and it can pass the pressure test for fracturing. The legacy wellbore is 5.5 inch size and a specialized 3.5 inch semi-flush joint casing was selected as new production string. A dependable cement barrier in this extremely tight annulus is required to carry on future re-fracturing operation. 2D hydraulic simulations and computational fluid dynamic was performed to optimize slurry density, rheology, and the method of cement placement. The cement mechanical property is enhanced to withstand the high pressure of fracturing. The top of cement in the annulus will be above the topmost existing perforation. The remaining 3.5 inch casing above the designed depth was disconnected and pulled out. The wellbore was cleaned, and the losses were treated prior cementing. Tailored ceramic centralizers were installed on the casing surface to achieve optimum stand-off. The centralizer's friction factor is low to casing running to bottom successfully. A low rheology slurry tailored for optimum mechanical properties of fracturing operation was pumped, and the cement returns to designed depth were noted. The casing string disconnected at designed depth and pulled out successfully. After waiting on cement, the wellbore passed pressure test. Cement bond log showed excellent results and the top of cement reached the designed depth. The stage fracturing operation was performed with no issues of wellbore integrity. A typical procedure of casing-in-casing cementing were recognized. Tailored slurry and centralizers design helped to achieve zonal isolation objective in the low clearance Casing-in-Casing cementing. The critical wellbore re-construction objective achieved and well was re-fractured with substantial increase in production.