西藏伦坡拉地区固井工艺技术探讨

西藏伦坡拉地区海拔4700m,气候恶劣,年平均温度7℃左右。地层主要为大段泥岩,水敏性强,裂缝发育;孔隙压力一般为0.92~0.97g/cm3,多数层段呈负压特性;地温梯度4.0~4.8℃/100m,平均4.26C/100m,属温度异常。钻井时漏失频繁,固井时水泥浆漏失,返深达不到要求,固井合格率56%~76%,优质率38%~47%。针对该地区固井漏失和水泥胶结质量差的突出问题,模拟真实的井底温度和压力,以提高低密度水泥强度为重点,优选出适合低密度水泥浆的外加剂,达到低密度、高早期强

DISCUSS ON CEMENTING TECHNOLOGY IN LUNPOLA AREA OF TIBET

Lunpola area in Xizang is 4700m above sea level with a harsh climate and the annual average temperature is 70o or so. The formation is mainly made up of shale with strong water sensitivity and developed fracture, its pore pressure is generally 0. 92~0. 97g/cm3 and the pressure of most intervals behaved negative; the geothermal gradient is 4. 0~4. 8℃/100m, the average is 4. 26℃/100m, the temperature is of abnormality. The frequent leakage occurred during drilling and cement slurry leakage occurred during cementing,the cement slurry did not return to the required depth with 56%~76% qualified rate and 38%~47% high-grade rate of cementing. Regarding to the problems of cementing leakage and cement consolidation with bad quality in this area, the true bottomhole and pressurewere simulated to optimize the addition agent suitable for low-density cement slurry in terms of improving lightweight cement strength. And then the cement slurry formulations with low-density, high early strength and flow pattern index can be obtained. No leakage occurred in practices of three wells, the qualified rate of cementing for west well Lun-5 is 98%, and high-grade rate is 89%.