Causes of Trapped Annular Pressure in High Pressure Gas Wells in Central Sichuan and Well Cementing Solution
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摘要: 川中高压气井纵向上存在多产层、多压力系统，须家河之上浅层气及嘉陵江组、飞仙关组等高压气层显示活跃。区块整体固井质量较好，但钻完井期间有12口井B、C环空异常带压。通过固井情况、气源、带压时间分析，并采用水泥环完整性评价装置及软件分析后续工况对水泥环密封完整性的影响，推断常规水泥石力学性能不适应川中高压气井层间封隔要求，固井后管柱试压、钻井液密度降低易导致水泥环完整性受损，是C环空带压的重要原因。φ177.8 mm尾管固井质量差，后续工况进一步削弱固井胶结质量是B环空带压的重要原因。基于此，针对性地优化了韧性微膨胀水泥浆体系，形成了“以快治气”防窜固井工艺，推广应用封隔式尾管悬挂器。现场应用12口井，φ177.8 mm尾管固井质量声幅评价段平均合格率由52.98%提高至73.18%，较好地解决了钻完井期间环空带压问题。Abstract: High pressure gas wells drilled in the central Sichuan Basin penetrated multiple pay zones and encountered multiple formation pressure systems. Shallow gases above the Xujiahe Formation and high pressure formations such as the Jialingjiang Formation and the Feixianguan Formation have active gas show. Well cementing job quality has been good, yet there have 12 wells with abnormal pressure in the annulus B and annulus C. By analyzing the well cementing operations, the sources of gas causing the annular pressure and the time for the pressure trapped in the annuluses, and using apparatus and software for cement sheath integrity evaluation to analyze the effects of subsequent work conditions on the sealing integrity of cement sheath, it is inferred that the main causes of pressure trapped in annulus C are that the mechanical performance of the conventional set cement does not satisfy the needs for sealing interlayers in high pressure gas wells, and the integrity of the cement sheath is thus damaged during pipe string pressure test after well cementing, and decrease in mud weight further deteriorates the situation. It is also inferred that pressure trapped in annulus B because of poor job quality in cementing the φ177.8 mm liner string and the weakening of the cement bonding in subsequent operations. Based on the analyses, a micro-expanding cement slurry with good toughness has been developed to fast cement the well to prevent gas from invading into the borehole and to prevent gas channeling from happening. This cement slurry has been applied on 12 wells into which packer type liner hangar was run. Rate of certified job quality of cementing the φ177.8 mm liner string as measured with acoustic amplitude evaluation was increased from 52.98% to 73.18%, indicating that trapped annular pressure problem has been satisfactorily resolved.
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