Study and Application of Slim Hole Cementing Technology for Ultra-deep Well Mashen-1

The Well Mashen-1 is the deepest well found in Asia, the gas zone of which has been sealed with 146.1 mm liner string. Difficulties encountered during drilling included HTHP, small annular clearance, low displacing efficiency, narrow drilling window, and severe U-tube effect. In combating these problems, it was considered that dynamic pressure-bearing experiment was able to more accurately simulate the borehole pressure change during well cementing, thereby helping prevent mud losses. Fluids entering the borehole with density grading and rheology grading were beneficial to increasing displacing efficiency. Three-stage flushing prepad had strong resistance to contamination and better flushing performance. A high temperature anti-channeling latex cement slurry was developed based on the optimized high temperature cementing additives. It had good high temperature stability and strong antichanneling ability. The set cement had high compressive strength and good elasticity and toughness. The U-tube effect can be mitigated with varied flowrates and effective laminar flow displacing, in this way the lost circulation during well cementing was avoided and the displacing efficiency ensured. By adding 0.7%BS200-G and 3%BS200R (retarders) in the cementing slurry, the thickening time became adjustable and was not vulnerable to the effects of density and temperature anymore. JR, a latex, was added at percentage of 12%, and the lead slurry and tail slurry had right-angle thickening characteristics, with values of 0.9 and 0.5, respectively. The gel strengths of the cement slurry had transit time of 28 min and 22 min, respectively. The cement slurry also had high mobility and good rheology. After adding 50% quartz sand, the effect of high temperature on the strength of set cement became weakened, and the strength of the set cement showed good late-stage development. Adding 1% BS6000, a plasticizer into the cement slurry, the set cement had elastic modulus 53.13% lower than that of conventional cement slurries, indicating that the cement slurry had good plasticity. The experimental results showed that the cement slurry had good high temperature stability, good rheology, strong anti-channeling ability, and excellent mechanical performance when set. The Well Mashen-1 was successfully cemented with high cementing job with the high temperature anti-channeling latex cement slurry and the technology discussed above.