川西下二叠统超深气井网络裂缝酸化优化设计

摘要

四川盆地西部下二叠统储层具有超深、高温、高压的特点,天然裂缝发育,钻井液漏失污染是制约该区储层增产改造效果的主要原因,酸化是彻底解除漏失污染的首选增产措施.为此,提出了最大限度降低污染表皮系数的酸化设计思路,建立了深层天然裂缝开启的临界排量计算模型;改进实验尺度天然裂缝岩样的酸化模型,建立了井筒条件下酸液有效作用距离和裂缝开度预测模型,在此基础上建立了网络裂缝酸化的表皮系数计算模型.现场应用结果表明:①当注酸排量为5.0 m3/min时,S1-1井任意倾角的天然裂缝均能开启;②当注酸量大于100 m3时,大排量注酸的优势逐渐体现;③以最大限度地降低表皮系数为目标,优选了S1-1井网络裂缝酸化的注酸排量为4.5 m3/min,注酸量为210m3.S1-1井按照优化设计思路成功实施了网络裂缝酸化,获得了83.7×104 m3/d的高产工业气流.结论认为:网络裂缝酸化技术是实现该区超深、高温、高压、天然裂缝发育储层增产改造最安全、经济、有效的模式.%The Lower Permian reservoirs in the western Sichuan Basin are ultra-deep with high temperature,high pressure and developed natural fractures.Leakage and contamination of drilling fluid is the main factor restricting reservoir stimulation effects,so the acidification will be the solution also as the first choice to enhance the gas recovery.In view of this,an acidification design was proposed to minimize the contamination skin factor to the highest degree.A model was first developed to calculate the critical pumping rate for opening natural fractures in deep beds.Then,the acidification model for the rock samples of natural fractures in the experimental scale was modified,and a model was established for predicting the effective penetration distance of acid and the fracture aperture in the conditions of wellbores.Accordingly,a skin factor calculation model for network-fracture acidification was developed.It is indicated that when the acid pumping rate is 5.0 m3/min,all natural fractures around Well S 1-1 can be opened,regardless of their dip angles.Besides,the advantage of high-rate acid injection emerges gradually when the injected acid is more than 100 m3.Moreover,for minimizing the skin factor,the network-fracture acidification in Well S1-1 was optimized by pumping 210 m3 acid at the rate of 4.5 m3/min.According to the optimal design idea,network-fracture acidification has been successfully applied in Well S 1-1,and a high-yield industrial gas flow was produced at the rate of 83.7× 104 m3/d.It is concluded that network-fracture acidification technology is a safest,most economical and effective mode for the stimulation of such ultra-deep reservoirs in the study area.