九龙山构造欠平衡钻井提速的可行性分析

气体钻井技术在四川盆地九龙山构造提高机械钻速方面发挥了巨大作用,但在侏罗系沙溪庙组沙二段底部出现井壁坍塌,转换成常规钻井后钻速较慢。为了提高该井段的机械钻速,从岩石可钻性与井壁稳定两方面进行了欠平衡钻井的可行性分析,结果表明:沙溪庙组沙一段与千佛岩组层段设计的欠平衡钻井液密度应控制在1.10～1.25g/cm3,才能确保欠平衡工况下井壁稳定;欠平衡钻井与常规钻井相比,其岩石可钻性系数更低,有利于明显地提高机械钻速;沙一段至珍珠冲组上部岩石井壁稳定,适宜开展欠平衡钻井提速试验;对存在大量砾石层的珍珠冲组下部,欠平衡钻井提速效果不明显,可采用其他钻井措施提高机械钻速。龙110井的现场试验表明,沙一段至马鞍山组层段开展欠平衡钻井,能有效地提高机械钻速,且与邻井龙104井的常规钻井相比,最高可达206%。所提出的欠平衡钻井提速模式,为广泛开展九龙山构造欠平衡钻井提速提供了经验和技术支持。

A feasibility study of using UBD to improve the ROP at the Jiulongshan Structure, Sichuan Basin

Gas drilling technology has played an important role in the enhancement of ROP at the Jiulongshan Structure in the Sichuan Basin. Since well caving in was encountered at the bottom of the second member of the Shaximiao Formation, the gas drilling has been converted into conventional drilling, so the ROP has become rather slow. Therefore, a feasibility study of adopting underbalanced drilling to improve the lowered ROP there is conducted from two aspects of rock drillability and wellbore stability. The results show that only if the UBD drilling fluid is controlled to be 1.10~ 1.25 g/cm3 when drilling through Sha 1 and Qianfoyan formations, the wellbore can be kept stable during the UBD. Compared with conventional drilling, the UBD can improve the ROP remarkably with the rock drillability coefficient much lower. For the formations between Sha 1 and upper Zhenzhuchong, where it is the least possibility for the occurrence of well caving, the UBD can be used to improve the ROP. While for the lower Zhenzhuchong formation with a large amount of gravels, no obvious good results can be achieved by use of the UBD technology, so other drilling technologies will have to be adopted instead to improve the ROP. The drilling experience on the well Long 110 shows that the UBD has effectively improved the ROP when drilling from Sha 1 to Ma'anshan formations by up to 206% at most in comparison with the offset well Long 104 by use of conventional drilling technologies. This study will be a valuable experience for the ROP improvement by UBD at the Jiulongshan Structure.