Drilling Fluid Technology for Well Ming-15 in Mingbulak Oilfield, Uzbekistan
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摘要: 乌兹别克斯坦明格布拉克油田,地质构造极其复杂,井深800~3850 m存在盐水层、大段硬石膏、膏泥混杂层以及强水敏性地层,地层内CO2气体浓度高,中下部3850~5900 m地层存在断裂带,孔洞裂缝发育,石膏蠕变缩径,高压油气水同层,溢漏矛盾突出,针对“四高一超”井(地层温度≥ 170℃、压力系数≥ 2.3、含盐≥ 20%、含硫5%~6%、超深井)施工,钻井液既要满足压稳上部高压层,又要兼顾下部低压层防漏堵漏和防H2S需要,为解决大段石膏层蠕变缩径、高压盐水侵入造成井壁失稳垮塌以及高密度钻井液流变性调控难度大,循环压耗高,油气层保护等技术难题,通过钻井液体系优选,确定二开以下异常复杂井段采用高密度复合有机盐钻井液。现场应用结果表明,复合有机盐钻井液抑制润滑性好,抗盐钙污染能力强,固相含量低,即使在加入高浓度堵漏材料后,钻井液流变性依然可控,成功解决了该油田高密度钻井液压差卡钻、盐膏层阻卡、溢漏同层造成井下复杂事故频发以及无法钻遇深部油气层的技术难题,实现了打成目标,为后续施工提供了技术支撑和宝贵经验。Abstract: Formations drilled in the Mingbulak Oilfield in Uzbekistan have very complex structures. Wells drilled in this oilfield with depths between 800 m and 3,500 m penetrated saltwater-bearing zones, long segment of anhydrite, gypsum/shale mixed formations and highly water sensitive formations. Part of the formations also have high concentration of CO2. Formations between 3,850 m and 5,900 m are full of fault zones, vugs and fractures, and gypsum segments that may creep and form tight hole during drilling. Coexistence of high-pressure oil, gas and water may cause well blowout and mud losses to happen simultaneously. When drilling an ultra-deep well with high temperature (≥ 170℃), high pressure (pressure gradient ≥ 2.3), high salt content (≥ 20%) formation water, high H2S content (5%-6%), the drilling fluid should satisfy the needs of both stabilizing the high pressure formations in the upper section of the well as well as preventing mud losses and flowing of H2S in the lower section of the well. Difficulties associated with ultra-deep well drilling include creeping of long section of gypsum/anhydrite which leads to tight hole, borehole wall collapse caused by high pressure saltwater invasion, difficulties in controlling the rheology of high-density drilling fluid, high circulation pressure and reservoir protection etc. By optimizing the composition of the drilling fluid and carefully selecting mud additives, it was decided that a highdensity compound formates drilling fluid was used to drill the extremely complex second interval and the sections beyond that. Filed operations showed that the compound formates drilling fluid had good inhibitive capacity and lubricity, strong resistance to calcium contamination and low solids content. The compound formates drilling fluid had controllable rheology even when the drilling fluid was treated with high concentration of lost circulation materials. With this drilling fluid, downhole problems previously encountered such as pipe sticking (because of high mud weight and creeping of salt/gypsum layers), coexistence of well blowout and mud losses, as well as inability to drill deeper reservoirs, have all been wiped out. The aim of drilling the well successfully has been realized, and technical support and experiences have been provided to subsequent operations.
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