Complexity treatment technologies for Sinian gas wells in eastern Sichuan Basin:An example from YT1 well
For both active and safe development for Sinian gas reservoirs,eastern Sichuan Basin,and ensuring effective re-placement of natural gas in Sichuan-Chongqing area,it is essential to figure out development challenges in Sinian gas wells to further deal with usual complexity and accidents.So,YT 1 well,the key exploration one which belongs to Petro-China Southwest Oil&Gasfield Company,was taken as an objective.And then,some geological difficulties existing in this drilling were put forward,including multiple sets of formation pressure,large window of pressure system,heavy lost circula-tion and wellbore shrinkage.Additionally,many treatment technologies were established for the complexity in terms of cas-ing program,leakage stopping,anti overflow and anti collapse.Results show that(ⅰ)five-spud nonstandard program should be optimized as an optimal one for setting position in effective package;(ⅱ)three schemes of leakage stopping while drill-ing,compound leakage stopping and cement plugging should be employed at big hole from the Lower Jurassic Ziliujing For-mation to the Upper Permian Longtan Formation.As a result,the success ratio of leakage stopping can be improved with effect to decrease the complexity's incidence rate;and(ⅲ)bottom hole assembly should be chosen at the hole of 241.3 mm from the Ordovician Shizipu Formation to the Upper Cambrian Xixiangchi Formation.And some complexity,like over-flow,lost circulation and collapse,is treated to increase drilling efficiency.Five conclusions are made.First,there are no complexity or accidents during air and mist drilling from Shaximiao to Lianggaoshan formations,obtaining an obvious effect in anti-leakage and ROP increase.Second,hydroscillator + compound bit + MWD directional drilling,as the best technol-ogy for Longtan to the Lower Cambrian Qiongzhusi formations,runs 23 trips in the gypsum salt bed with the well interval of 3150.94 m.Third,185 mm bidirectional microreamer is tested after drilling 190 mm hole,which may solve hole shrink-age in long gypsum salt bed and ensure smooth running to the expected position after triple ream.Fourth,after the applica-tion of treatment technologies to YT1 well,the incidence rate is decreased by 17.47％to avoid heavy pipe sticking.Fifth,these treatment technologies established for the Sinian gas reservoirs in eastern basin are meaningful for studying technolo-gies used in deep wells of the same reservoirs in the whole Sichuan Basin.
Eastern Sichuan BasinSinian gas wellComplexity treatmentLost circulationGypsum salt bedDirectional operation
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