Abstract

An erroneous production string cement job often leaves an operator with a tough decision to make; the technical and economic feasibility of a successful intervention must be considered and compared to sidetracking or, at worst, abandonment. CNX Resources, collaborating with Thru Tubing Solutions (TTS) and SLB, was able to develop and execute a unique (and record-setting) workover to save a 19,381 ft lateral in the Marcellus shale.

An incorrect mixture of cement slurry left CNX Resources with 20,489 ft (of 27,510 ft MD) of 5 1/2 in 23 ppf P110 production casing cemented off. A cement lead was pumped without issue. However, while pumping the cement tail and displacement, pressure gradually increased until it reached the pressure limitations of the rig equipment, resulting in a premature shut down. Utilizing a combination of traditional drilling and completions philosophy, a series of past lessons learned, and new-age technology, CNX, TTS, and SLB managed to clear the casing of nearly 20,500 ft of cement, perf and squeeze cement 6,019 ft into the lateral, and set the deepest (from KOP on US Land) casing patch ever set by SLB. This successful, more sustainable implementation offered upwards of 17% savings compared to the alternative.

Bottomhole assembly (BHA) selection, solids control, and fluid system management played a vital role in the cement drillout portion of the workover. Rates of penetration of up to 85 ft/hr were achieved and maintained throughout the job. In total, it took 19 days (approximately 17.5 days in hole) to drill the 20,489 ft of cement. Perforation depths were carefully determined at 14,130 ft via ultrasonic imaging and cement bond logging. Circulation was established and cement was squeezed to exceed state regulatory requirements. Due to the unique circumstance, a custom, fit-for-purpose expandable casing patch was designed and successfully installed to isolate the squeeze perforations while returning the casing to mechanical properties fit for fracturing operations. A casing integrity test to 10,500 psi was achieved post-installation of the casing patch.

This case study features the deepest 20,000+ ft drillout of cement for TTS (27,510 ft MD), a detailed look into a complicated extended lateral perforation and squeeze operation, as well as the deepest set (from KOP) casing patch for SLB on US Land (14,154 ft MD).