油基钻井液体系在东海气田的试验应用

东海地区油气层系主要分布在花港组和平湖组，存在砂泥岩互层胶结疏松、裂缝性泥岩以及煤层发育等地层特性，井壁稳定和井眼清洁是导致钻井复杂情况的主要原因。研究气田的大位移井最大井深为6 716 m，最大水平位移达4686 m，垂深最大为4 429 m，井底温度最高在150℃以上，井口返出钻井液温度在115℃以上。大井斜、高水垂比和长水平位移，使井眼清洁难度更大；地层温度高，使设备维护难度大。为满足该气田大位移井安全高效作业要求，建立了一套低黏高切的油包水钻井液体系，并加入了2%封堵剂PF-MOLSF、2%成膜封堵剂PF-MOLPF和2%~3%疏水胶体封堵剂PF-MOHCP。在现场应用中，通过调节提切剂PF-HSV-4加量，该油基钻井液表现出了很好的携岩性，井眼净化效果好；在地层稳定性差的井段增加成膜封堵剂的加量，7口井没有发生漏失，井下事故率为零，个别井段遇阻均划眼通过，划眼时间相比探井减少70%以上，其他作业都安全顺利；钻井液在储层段的高温高压滤失量均在3 mL以内，且滤失的几乎全为油相，对储层液损程度小，避免了水敏等伤害。室内评价和现场应用结果表明，该油基钻井液具有良好的流变性、电稳定性和润滑性，井壁稳定和储层保护效果明显，加上钻井液维护及油基岩屑处理等配套措施的完善，使其在东海的应用获得了成功。 

Application of Oil Base Drilling Fluids in Donghai Gas Field

The target zones of the Donghai gas field are the Huagang Formation and the Pinghu Formation, whose formation characteristicssuch as poorly cemented sandstone-mudstone interbeds, fractured mud stone and developed coalbeds, are unfavorable to drilling operation. Unstable borehole wall and poor hole cleaning are the main causes of downhole troubles. Wells drilled in the gas field of interest have maximum hole depth of 6,716 m, maximum horizontal displacement of 4,686 m, maximum TVD of 4,429 m, highest bottom hole temperature of 150℃ and highest temperature at the wellhead of 115℃. High well angle and high ratio of horizontal displacement to vertical depth make it hard to clean the hole, and high formation temperature makes equipment maintenance difficult. A low viscosity high gel strength oil base drilling fluid has been introduced to safely and efficiently drill the gas wells. The oil bade drilling fluid was treated with 2% plugging agent PF-MOLSF, 2% filming plugging agent PF-MOLPF and 2%-3% hydrophobic colloidal plugging agent PF-MOHCP. In field operations, the concentration of the gelling agent PF-HSV-4 was adjusted for the drilling fluid to have good carrying performance, and hence good hole cleaning. In drilling the unstable sections, more filming plugging agent was used. During the whole drilling process of 7 wells, no mud losses and other downhole troubles had ever occurred. Tight hole can be easily removed by reaming, and time spent reaming the hole was reduced by 70% compared with exploratory wells. Other operations were all done safely and smoothly. The HTHP filter loss in drilling the reservoir section was controlled to less than 3 mL, and the filtrate was almost whole oil, helpful in eliminating reservoir damage by water invasion, to name but one. Laboratory evaluation and field application showed that the oil base drilling fluid had good rheology, electric stability and lubricity. Borehole wall stabilization and reservoir protection were both achieved. With the aid of property maintenance and cuttings disposal measures, the application of the oil base mud has made a great coup in the Donghai gas field.