大牛地气田盒1段气层氮气泡沫钻水平井技术

大牛地气田二叠系下石盒子组盒1段气层具有低孔隙度、低地层压力、特低渗透率、高基块毛细管力、强非均质性的特点,常规直井和水平井几乎不能实现自然建产,截止到2008年底探明储量动用率仅为8.42%。为了有效地动用该气层储量,针对盒1段气层开展了氮气泡沫欠平衡钻水平井的研究与现场试验。考虑到该气层的工程地质特征,首先优选了氮气泡沫基液配方;然后分析了该气层的产水情况和井壁稳定性,认为对盒1段储层实施氮气泡沫钻水平井是可行的;最后介绍了DP14井、DP19井和DP22井的现场试验情况和应用效果。DP14井、DP19井和DP22井在氮气泡沫水平段钻进过程中油气显示良好,且均实现了随钻点火;其中DP14井完井后,在油压为7.1MPa,套压为9.3MPa时,产气量为1.07×104m3/d,首次在盒1段气层实现了自然建产。现场试验表明:氮气泡沫欠平衡水平井能有效地动用该气层储量,为提高大牛地气田盒1段气层的探明储量动用率提供了新途径,也值得类似探区借鉴。

Horizontal well drilling by nitrogen foam through the first member of lower Shihezi Formation at the Daniudi Gas Field

The pay zone of the first member of lower Permian Shihezi Formation (He 1), Daniudi Gas Field, is featured by low porosity, low formation pressure, extremely low permeability, a high matrix capillary force, and strong heterogeneity. Wells here can hardly achieve industrial flow by conventional vertical or horizontal well drilling, which is the reason that the ratio of producing proven reserves had been only 8.42% by the end of 2008. In order to effectively produce more reserves out of He-1, studies and field tests of underbalanced drilling with nitrogen foam were carried out here. With the geologic conditions of He-1 taken into consideration, base fluid for nitrogen foam was first optimized, then the water production and wellbore stability at He-1 were studied, which suggests that the horizontal drilling with nitrogen foam was proved to be practical for He 1. Finally the field test results on the DP14, DP19 and DP22 wells are introduced as follows: Good oil/gas flow was observed in all the three wells during drilling, and gas flaring was performed while drilling; After completion of the well DP14, the tubing pressure was 7.1 MPa and casing pressure 9.3 MPa, and the gas rate reached up to 1.07×104m3/d, an industrial flow of which was obtained at He-1 for the first time. The field tests also prove that the horizontal drilling with nitrogen foam can effectively help produce reserves out of He-1, providing not only a new approach for improving the ratio of producing proved reserves out of He-1 at the Daniudi Gas Field, but good reference for similar exploration areas.