多分支井缓释自破胶完井液设计及性能

多分支井缓释自破胶完井液是一种新型井筒工作液，凭借其特殊的储层自破胶能力，可使完井施工避免常规酸化与破胶工序，是衔接后续裸眼砾石充填作业的重要技术体系。结合南海恩平油田多分支井储层特征，分析了缓释自破胶完井液的设计原理，筛选并表征了流型调节剂高丙酮酸黄原胶，并检测了构建缓释自破胶完井液的破胶效果与储层保护性能。研究结果显示，基于核心处理剂黄原胶大分子与完井液自破胶性能间的构效关系，结合破胶与护胶协同作用，建立了缓释自破胶完井液的设计方法；制备的丙酮酸改性黄原胶分子量为8.0×106，丙酮酸基含量达7.9%；与常规黄原胶相比，高丙酮酸黄原胶的构象转换温度及热稳定性均显著下降，且无温度阈值，具有较好缓释降解性；对构建缓释自破胶完井液体系，通过高丙酮酸黄原胶与护胶剂联用方式调节完井液自破胶效能，使破胶时间在5～17 d；自破胶后完井液对孔隙无封堵，岩心渗透率恢复平均值达到90.36%±0.23%，储层保护效果良好。 

Design and Performance of a Slow-Release Self-Gel-Breaking Completion Fluid for Multilateral Wells

Slow-release self-gel-breaking completion fluid for multilateral wells is a new kind of wellbore working fluid. With its special self-gel-breaking capacity in reservoir, this completion fluid helps avoid conventional acid jobs and gel-breaking operation in well completion, and is thus an important technology linking the acid job with subsequent open hole gravel packing. In laboratory study, based on the reservoir characteristics of the multilateral wells in block Enping in Nanhai Oilfield, the design principle of the slow-release self-gel-breaking completion fluids was analyzed, the flow pattern regulator high pyruvate xanthan gum was selected and characterized, and the gel-breaking capacity and reservoir protection performance of the slow-release self-gel-breaking completion fluid was examined. The study showed that the method of designing the low-release self-gel-breaking completion fluid was established based on the structure-function relationship between the core additive xanthan gum and the self-gel-breaking performance of the completion fluid, combined with the gel-breaking and gel-protection synergistic effect. The molecular weight of the synthesized xanthan gum modified with pyruvic acid is 8.06×106, and the content of pyruvate in the modified xanthan gum molecule is as high as 7.9%. Compared with conventional xanthan gum, the high pyruvate xanthan gum has conformation transition temperature and thermal stability that are both significantly reduced, and has no temperature threshold, rendering the high pyruvate xanthan gum better slow-release degradation property. For the slow-release self-gel-breaking completion fluid formulated, the self-gel breaking was adjusted through the combined use of high pyruvate xanthan gum and gel-protection agents, and the time for the self-gel-breaking was controlled between 5 days and 17 days. Blocking of pores of reservoir rocks was eliminated after gel-breaking of the completion fluid, and the average percent permeability recovery of cores taken from reservoir rocks can be as high as 90.36%±0.23%, proving that the slow-release self-gel-breaking completion fluid has good reservoir protection capacity.