控压钻井用凝胶隔段工作液性能评价及机理分析

A Brittle and Drillable Gel Slug for Use in Managed Pressure Drilling

精细控压钻井技术在四川磨溪高石梯和下川东等地区应用,解决了因窄安全密度窗口引起的严重井漏、喷漏同存、难以钻进的工程难题,但在起下钻及完井过程中缺乏有效且安全的过程控制工艺,导致钻井液漏失严重,且井控风险极高。为此,笔者基于无机水硬性胶凝理论、密实充填理论、固化增强理论,提出了一种脆性可钻凝胶隔段封隔技术,并通过处理剂优选、配方优化形成凝胶隔段工作液。性能评价结果表明:该凝胶工作液初始流动性能和稳定性好、40 Bc稠化时间0.5～4 h可控,满足温度80～150℃要求、抗钻井液污染能力强;固化后段塞抗压强度高,达到8.02 MPa,与套管壁面胶结强度高,达到1.45 MPa/m^2;同时固化段塞自身胶结性能好,承压封气能力不小于2.69 MPa/m;固化后段塞可钻性级值为1级,采用钻头钻除即可快速恢复钻进。

Severe mud losses,coexistence of blowout and mud loss and difficulty of drilling are problems associated with narrow safe drilling windows found in Moxigaoshiti and Xiadongchuan,Sichuan,and were all overcome thanks to the use of precisely managed pressure control drilling technology.In managed pressure control drilling,lack of effective and safe process control techniques during tripping and well completion also resulted in severe mud losses and high risk of well control.To resolve these problems,a brittle and drillable gel slug separating technology has been presented based on inorganic hydraulic cementing theory,close packing theory and strengthening through solidification theory.By selecting the best additives and optimizing,a gel slug-forming working fluid was prepared.Evaluation of the working fluid showed that it has good initial mobility and stability.The 40 Bc thickening time of the working fluid is manageable in 0.5-4.0 h.It functions normally at 150℃,and is resistant to contamination from drilling fluid.The gel slug,after becoming hardened,has compressive strength of 8.02 MPa.When bonded with the surfaces of the casing,the bond strength can be 1.45 MPa/m2.The hardened slug itself has good cementing performance,with gas containment capacity of no less than 2.69 MPa/m under pressure.Thus gel slug,after hardening,has drillability of grade 1,and can be drilled out with drill bit.