顺北油气田奥陶系破碎性地层油基钻井液技术

针对顺北多口超深井采用水基钻井液钻遇奥陶系地层时井壁失稳和井漏并存的技术难题，通过井壁失稳机理分析，设计合成了具有三头双尾结构的Gemini型高温乳化稳定剂和支化型流型调节剂，采用微胶囊化处理方法研制了一种可在156℃以上的温度下激发后膨胀5.37倍以上的温度敏感型膨胀性堵漏材料，开发了一种抗高温强封堵低黏高切油基钻井液体系。室内评价结果表明，该体系抗温不小于180℃，所形成的油包水乳化液滴尺寸为1.2～26.9 μm，具有较宽的粒径分布，高温高压滤失量为2.4 mL ；塑性黏度不大于40 mPa·s，动塑比为0.31～0.40 Pa/mPa·s，与传统油基钻井液相比，塑性黏度降低10%～15%，动切力提高15%～25%，表现出优异的低黏高切特性和微裂缝的匹配性封堵能力。该体系在顺北Y井进行了现场应用，破碎性地层平均井径扩大率仅为7.77%，钻井过程中除出现一次短暂的放空性漏失外，未见其他明显漏失，避免了奥陶系破碎性地层井壁失稳，减少了裂缝性储层段油基钻井液损耗，助力了亚洲陆上最深定向井纪录的创造和顺北油气资源的提速、提效开发。 

Oil Base Drilling Fluid Technology for Drilling Broken Ordovician Formation in Shunbei Block

Several ultra-deep wells were drilled in the Shunbei Block with water base drilling fluids, resulting in borehole wall collapse and mud losses in the Ordovician formation. Based on the analyses of the mechanisms of borehole wall collapse, a Gemini type high temperature emulsion stabilizer and a branched flow pattern additive with three heads and two tails have been developed. Using microencapsulation treatment method, a temperature-sensitive expandable lost circulation material was developed. This lost circulation material, when excited at 156 ℃, can expand to a volume that is 5.37 times of its original volume. With these additives, a high temperature oil base drilling fluid was formulated. This drilling fluid has low viscosity, high gel strength and strong sealing capacity. Laboratory evaluation results showed that this drilling fluid can be used at 180 ℃. The sizes of the emulsified droplets are in a range of 1.2-26.9 μm. The HTHP filter loss, plastic viscosity and yield point/plastic viscosity ratio of the drilling fluid are 2.4 mL, ≤40 mPa.s and 0.31-0.40 Pa/mPa·s, respectively. The plastic viscosity of the new oil base drilling fluid is 10%-15% lower than that of the conventional oil base drilling fluids, while the yield point of the new oil base drilling fluid is 15%-25% higher than that of the conventional oil base drilling fluids, demonstrating an excellent low viscosity high yield point characteristics and capabilities of plugging microfractures by size matching. Application of the new oil base drilling fluid in the well Shunbei-55X showed that the average percent hole enlargement in broken formations was only 7.77%. Apart from a momentary mud loss into a cave during drilling, there was no other obvious mud losses encountered. Use this new oil base drilling fluid, collapse of the Ordovician formation during drilling was avoided, mud losses into the fractured reservoir were reduced. It also helps set a record of the deepest onshore directional well in Asia and develop the oil and gas resources in Shunbei Block with high speed and high efficiency.