Design and Testing of the Stimulation Tool for Pinnate Branch Tubes
摘要: 针对缝洞型碳酸盐岩储层酸压改造投入高、效果不理想的问题，基于羽状分支管增产原理，设计了羽状分支管增产管柱和羽状分支管增产关键工具——分支管短节。分支管应力分布和屈曲特性的有限元法分析结果发现，ϕ8.0和ϕ10.0 mm 316L型不锈钢分支管的最大应力小于材料的屈服强度，属于弹性变形范畴，满足使用要求。地面试验结果表明，分支管可以从分支管短节中伸出，启动压力3.0 MPa，最高压力3.5 MPa。性能测试结果发现，分支管启动前经喷嘴高速喷出的酸液可以在岩心上造孔，分支管伸出短节后可以进入岩心并在岩心中穿行。羽状分支管增产技术在塔河油田碳酸盐岩储层改造应用的可行性分析表明，目标区块碳酸盐岩岩样的溶解率达100%，喷酸造孔速率达2.6～14.4 m/h，具备实施该技术的条件。研究结果表明，羽状分支管增产技术具有施工压力低的优点，在塔河油田碳酸盐岩储层改造中应用具有很强的可行性，前景良好。Abstract: In view of the problems of high investment on acid-fracturing and unsatisfactory effect in the stimulation of fracture-cavity carbonate reservoirs, and based on the principle of pinnate branch tube stimulation, a pinnate branch tube stimulation string and the key tools (i.e., branch tube nipple) were designed. Combined with the working state of the branch tube, the stress distribution and buckling characteristics of branch tube were analyzed by the finite element method, and it was found that the maximum stress of the 316L stainless steel branch tube with a outer diameter of 8.0 and 10.0 mm was less than the yield strength of the material, which belonged to the category of elastic deformation and satisfied the requirements. Through surface tests, it was verified that the branch tube could extend from the branch tube nipple, with a starting pressure of 3.0 MPa and a maximum pressure of 3.5 MPa. By testing the performance of branch tube nipple, it was found that acid jetted out through the nozzle at high speed could make a hole in the core prior to initiating the branch tube, and the extended branch tube could enter the core to enable the branch tube run through the core. Based on carbonate reservoirs in Tahe Oilfield, the feasibility of pinnate branch tube stimulation was analyzed. It was found that the dissolution rate of carbonate rock samples from the target block reached 100%, and the rate of acid jetting to create holes reached 2.6～14.4 m/h, which possessed the conditions to implement the pinnate branch tube stimulation technology. Studies have shown that the principle of pinnate branch tube stimulation technology is feasible, and it has the advantage of low operation pressure. It is highly feasible and promising to apply this technology in the stimulation of carbonate reservoirs in Tahe Oilfield.
表 1 壁厚1.0 mm、不同外径316L不锈钢分支管承压30 MPa时的变形情况
Table 1. Deformation of 316L stainless steel branch tubes with a wall thickness of 1.0 mm and different outer diameters under pressure of 30 MPa
8.0 1 078 8.982 0.028 否 10.0 1 146 14.926 0.037 否 12.0 1 248 22.240 0.113 是 14.0 1 459 29.500 0.351 是 16.0 1 563 36.000 0.620 是
表 2 酸岩反应试验结果
Table 2. Test results of acid-rock reaction
岩样编号 岩样质量/g 溶解时间/min 溶解速度/（g·min–1） 1# 3.9 7.0 0.56 2# 4.1 9.5 0.43 3# 1.4 6.0 0.23
表 3 喷酸试验结果
Table 3. Test results of acid spraying hole-forming
岩样编号 测试时间/s 造孔深度/mm 造孔速率/（m·h–1） 1# 14.0 56 14.4 2# 15.0 18 4.3 3# 13.6 10 2.6
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