抗240℃高密度复合有机盐钻井液在翼探1井的应用

翼探1井是中油股份公司在青海油田柴达木盆地柴西北区南翼山构造较高部位部署的一口重点风险探井，设计井深6500 m，完钻井深6194.22 m，目的层E₃1、E₁₊₂、基岩。钻探目的是探索南翼山构造E₃1和基岩含油气性，为下一步研究和勘探部署提供依据。南翼山地区E₁₊₂下部地层以前无钻井史，钻遇地层条件复杂，高陡构造，存在3条断裂带、破碎带和膏泥岩。其E₃2、E₃1、E₁₊₂地层裂缝发育，易漏易涌，多层高压盐水伴CO₂酸性气体，盐水中Cl-含量达235 000 mg/L，CO₂侵地面监测浓度高达75%以上，钻井液密度高达2.32 g/cm3，且存在多套硬脆性碳质泥岩破碎地层，极易发生垮塌掉块、井斜。该区域显示异常高温，因为测井公司高温仪器受限，无法实测井底温度，该区地温梯度在（3.80~4.30）℃/100 m之间，以及钻井液出口实测温度达到102℃，钻井液维护处理量达到井眼容积的10倍以上，从以上资料计算，以及钻井液材料与体系循环稳定周期等综合分析，预测该井井底温度在235~266℃之间，给钻井液工作提出了严峻挑战。为解决超高温、高密度、井壁稳定、酸性气体污染、窄窗口漏失等技术难题，优选采用了渤海钻探泥浆技术服务分公司的发明专利技术，即抗240℃高温的高密度复合有机盐钻井液。在此技术基础上，结合井下地质、工程实际情况，施工现场对配方进行了优化调整，引入抗240℃高温的滤失控制材料，引入刚性和塑性材料组配的随钻锲入封堵防漏材料，以及纳米类化学吸附护壁防塌材料，并提供良好的“非氧还原”钻井液环境，通过精心施工，取得了较好效果。全井施工顺利，钻井液高温流变性良好，高温高压滤失量控制在12 mL以内，较好地解决了高温流变性、沉降稳定性、漏失、破碎性地层垮塌、酸性气体污染等一系列钻井液技术难题。 

Application of Ultra-high Temperature High Density Compound Organic Salt Drilling Fluid in Well Jitan-1

The well Jitan-1 is a key exploratory well drilled by PetroChina Company Limited in the upper part of the Nanyishan structure in the northwest area of the Qaidam Basin (Qinghai Oilfield). The well, targeted to the E₃1, E₁₊₂ and the bedrock zones, was designed to drill to 6500 m, and was actually drilled to the total depth of 6194.22 m. The well was drilled to ascertain the petroleum production potential of the E₃1 and bedrock zones and hence to provide the basis for further research and exploration of the Nanyishan structure in which the formations beneath the E₁₊₂ zone had never been drilled before. These formations are complex and are located in a high and steep structure. Three fault zones, some broken belts and mudstone with gypsum have to be penetrated during drilling. The E₃1, E₃2 and the E₁₊₂ zones are developed with plenty of fractures, which may result in lost circulation. Several high-pressure saltwater zones with CO₂ exist with chloride content up to 23,500 mg/L, and CO₂ content up to 75% (measures on the surface). The high-pressure saltwater and CO₂ zones may result in well kick or even well blowout. Multiple zones of hard, fractured and brittle carbonaceous mudstone formations are a potential of borehole collapse and well deviation. To maintain the well in stable conditions, a mud weight of 2.32 g/cm3 was required. Abnormal high formation temperatures were encountered. The formation temperatures are too high for the logging instrument to measure, and thus the bottomhole temperature cannot be obtained. The formation temperature gradient in this area was (3.80-4.30) ℃/100 m, and the temperature of the mud at the exit of the flowline was 102 ℃. Volume of mud for dilution was at least 10 times of the hole volume. From these data and the stability cycle of the mud in circulation it was predicted that the bottom hole temperature was between 235 ℃and 266 ℃. These potential downhole troubles imposed serious challenges to the drilling fluid operation. To solve the problems such as ultra-high bottom hole temperature, high density, borehole wall instability, acid gas contamination and narrow safe drilling window, a high-density compound organic salts drilling fluid, which was a proprietary technology of the Bohai Drilling and Exploration Drilling Fluid Technical Service Company, was adopted to drill the well. This drilling fluid can be used at high temperatures up to 240 ℃ The drilling fluid was further optimized based on the geologic data and proposed drilling program; a filtration control agent functioning at 240 ℃ was used to control filter loss of the mud, a lost circulation material composed of rigid and plastic particles was used to minimized mud losses while drilling, a nano material was used to maintain borehole wall stability through chemical mechanisms, and a good “non-oxygen reduction” mud environment was maintained. By maintaining good mud rheology and low filtration rate (≤ 12 mL), potential downhole troubles such as high temperature rheology instability, settling of weight materials, mud losses, borehole wall collapse in drilling the fractured zones and contamination of the mud by acid gases, were all well solved.