关于延安致密砂岩气田水平井钻井先导试验的几个问题

Some Questions on Pilot Tests of Horizontal Well Drilling in Yan'an Tight Gas Field

延安致密砂岩气田在开发初期,先导试验水平井在钻井过程中普遍表现井下复杂事故多、机械钻速低、钻井周期长等问题。通过对先导试验水平井整体钻井时效进行分析,确定了影响钻井周期的主要因素为生产时间中的起下钻和非生产时间中的组织停工耗时太长;通过对延安气田复杂情况分析,发现水平井钻井面临的最突出的问题是"双石层"及以下的井漏和阻、卡;通过地层岩石理化分析显示"双石"层段属于典型的硬脆性地层,微裂隙发育,在地应力作用下易扩展形成大的贯通裂缝导致井漏,并且该层段伊/蒙混层泥页岩遇水易产生不均匀膨胀,引起井壁坍塌掉块,导致频繁阻卡等复杂情况;通过对延安气田地层岩石力学性能分析,发现上古生界地层岩石强度变化大,岩石可钻性差导致钻头磨损严重。综上,对目前制约水平井高效建井的上述问题进行详细分析,为下一步天然气水平井开展高效提速研究提供有效的借鉴。

For economic and effective development of Yan＇an gas field,the early pilot horizontal wells faced many down-hole complications,low penetration rate and long drilling cycle.Based on the drilling efficiency analysis,determine the main factors of influencing the drilling cycle are long tripping operation of the productive time and long shutdown management of the unproductive time.Based on the down-hole complication analysis,found that the most prominent problems are well loss,drilling resistance and sticking in the＂double stone＂and below.By rock chemical analysis,it shows that the＂double stone＂section belongs to the typical brittle formations,micro fracture can become large extensible crack and cause well leakage,besides the formation has illite mixed layer shale and water can easily produce uneven expansion,causing wellbore collapse.By rock mechanics analysis,found that rock strength of Upper Paleozoic strata change a lot and rock drillability is poor drill which lead the bit wear serious.After the detailed analysis of the problems which restrict the horizontal well fast drilling,provide effective reference for the next step of natural gas wells drilling research.