摘要:
Horizontal well open hole completion is a way of well completion to maximize well production rate.In offshore drilling,well completion is generally done with solids-free drill-in fluid,supplemented with gel-breaking well completion.Direct flowback of drill-in fluid is a technology developed on the basis of this way of well completion.In this paper,parameter design,additive selection and well completion technique were systematically analyzed and evaluated,and the mechanism of reservoir protection of this technology was also analyzed.The composition of the drill-in fluid is as follows:seawater + soda ash/caustic soda + rheology modifier VIS + starch filter loss reducer STARFLO + soluble salt (shale inhibition and mud weight) + high purity sized calcium carbonate MBA.The three functional additives of the formulation can all be liquefied by 0.3% HTA (a chelating agent) solution.The liquefaction of the additives left no residue and the mud cakes in the wellbore and near the borehole wall were all converted to clear saltwater.MBA is a mixture of calcium carbonate powders with five particle sizes.The particles of MBA can be "inter-inserted" with starch to form a mud cake that is much denser.Laboratory experiment has shown that the drill-in fluid had low-shear-rate viscosity of around 30,000 mPa · s,optimum contamination-resistance and flowback ability,and the highest permeability return.After contaminated with 15% drill cuttings,the drill-in fluid still had permeability return of more than 80%.This drill-in fluid was used in twelve wells in three oil fields and one gas field in the east of South China Sea.The maximum temperature at the hole bottom was 60-130 °C,and the highest mud density was 1.20 g/cm3.Three of the twelve wells penetrated low porosity low permeability reservoirs and the rest nine wells penetrated reservoirs with medium to high porosity and permeability.The drilling operation was successful.The use of this technology simplified the process of well completion,saved operational time and cost,and protected the reservoirs from being damaged.%水平井裸眼完井是一种最大限度提高储层开采能力的方式,海上油田常采用无固相钻井完井液并辅以破胶完井的方式来完成钻完井作业.直接返排钻井完井液是在此基础上开发的,对其在参数设计、材料选择、完井工艺等方面进行了分析与评价,并分析了其储层保护机理.该体系基本组成为海水+纯碱/烧碱+流型调节剂VIS+淀粉降滤失剂STARFLO+可溶盐+高纯粒径匹配碳酸钙MBA,3种功能材料均能够被0.3%HTA隐形酸螯合剂溶液液化,液化后无任何残留,使井筒内及近井地带的泥饼全部转化为清洁盐水,MBA由5种不同粒径的碳酸钙复配而成,且和淀粉可以达到互相“镶嵌”的作用,使泥饼更加致密.通过实验评价,该钻井完井液的低剪切速率黏度控制在30 000 mPa·s左右,具有最佳防止污染和返排的能力,且渗透率恢复值最高,可抗15%左右钻屑污染,渗透率恢复值大于80%.该体系在南海东部3个油田、1个气田已应用12口井,井底最高温度为60~130°C,密度最高为1.20 g/cm3,3口井属于低孔渗油藏,9口井属于中、高孔渗油藏,钻井过程顺利.该技术简化了完井方式,节省了作业时间与费用,并具有较好的储层保护效果.