Rigless Cementation and Completion Integration: A Novel Strategy for Unconventional Reservoir Development in China and Its Middle East Potential

Abstract Low-permeability reservoirs account for approximately 56% of China's total hydrocarbon reserves. Horizontal drilling combined with staged hydraulic fracturing remains the most effective development approach for these formations. However, conventional cementing, completion, and perforation techniques often prove too intrusive for such sensitive reservoirs. In particular, horizontal sections tend to exhibit poor cement bonding, while traditional fracturing methods struggle to effectively stimulate the reservoir at scale. To address these challenges, a novel approach integrating rigless cementing and completion has been proposed to enhance the development of low-perm formations. Building on principles of rock mechanics and classical hydraulic fracturing theory, this study compares two completion scenarios—using either casing joints or coiled tubing strings as fracturing conduits. The comparison focuses on evaluating fluid friction losses and stimulation effectiveness. A specially engineered casing joint system was developed and evaluated, incorporating external packers, stage collars, multiple oil-swelling packers, sliding sleeves, and coiled tubing-deployable downhole tools such as mechanical switches and wash-over choke valves. Laboratory testing and pipe string mechanics analysis were conducted to assess system performance. One of the critical limitations in traditional fracturing lies in high fluid friction caused by both borehole geometry and perforation tunnels. The proposed rigless integration eliminates the need for perforations by utilizing casing joints directly for fluid injection. During staged fracturing of the horizontal section, fracturing fluids are pumped through the annular space between coiled tubing and 5-1/2″ casing, significantly expanding the flow area. This design results in fluid friction reduction of up to 90% compared to conventional tubular strings. The operational sequence begins with zonal isolation of the upper horizontal section via a pair of expandable packers. Cement is then placed above this interval using stage collars, thereby minimizing slurry invasion into sensitive formations. Subsequently, oil-swelling packers expand within the horizontal interval, while a coiled tubing-conveyed mechanical switch and wash-over choke valve selectively actuate sand-control sliding sleeves. This enables targeted, stage-by-stage stimulation of each reservoir segment. This integrated, perforation-free rigless design represents a breakthrough for low-perm reservoir development. It simplifies completion, improves stimulation efficiency, and mitigates common operational issues such as sand blockage. Field trials conducted in Iraq’s Missan Oilfield have demonstrated promising performance, highlighting the concept’s potential for broader application across the Middle East.