Preventing abnormal pressure in the annulus to enhance the seal integrity of cemented rings are crucial for the safe and efficient development of shale gas wells.During the cement setting period,the slurry density loss leads to a decrease in annular fluid column pressure,allowing formation fluids to invade the annulus and causing channeling,which typically compromises cementing quality.To address the cementing challenges in shale gas wells,we studied the weight loss process and static gel strength development of the cement slurries used in the field.The results indicate that among the three cement slurries,the fast-setting slurry exhibited the fastest development of static gel strength with the shortest transition time(30 minutes).At a static gel strength of 48 Pa,the density loss rate of the slow-setting slurry was 1.04%,while the fast-setting slurry reached a density loss rate of 85.2%.During the transition period(between 48 and 240 Pa),the medium-setting slurry exhibited the highest density loss rate,while the slow-setting and fast-setting slurries showed slower rates.Based on simulated calculations of the annular backpressure process,a field test was conducted in well Z201.The results showed improved cementing quality,with a primary interface pass rate of 97%and a secondary interface pass rate of 95.9%.The cement bond in the gas-bearing section was also good.The staged annular backpressure technology shows promising application prospects.
cement slurrygas channelingstaged annular backpressureweight lossstatic gel strengthcementing quality
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