压裂酸化中近缝区灰岩强度弱化效应试验研究

EXPERIMENTAL STUDY ON STRENGTH REDUCTION EFFECTS OF LIMESTONE NEAR FRACTURE AREA DURING ACID FRACTURING

采用静态高温酸蚀试验和常规岩石力学试验,探讨胶凝酸对于灰岩的强度弱化效应,给出灰岩的应力-应变曲线,分析灰岩的破裂特征。试验结果表明,在与相同配方的胶凝酸反应后,灰岩弹性模量大幅降低,泊松比略有上升,单轴强度约为酸蚀前的20%,强度弱化效应明显;在反应过程中,基质型灰岩和裂缝型灰岩在反应速度、刻蚀模式上存在明显差异。在与相同配方的胶凝酸反应过程中,塔中裂缝型灰岩的反应速率约为轮古基质型灰岩反应速度的3倍。在与胶凝酸反应过程中,裂缝型灰岩的刻蚀模式为局部深度刻蚀,基质型灰岩的刻蚀模式为表面均匀刻蚀。该项研究可为现场酸压设计及优化提供有效的技术参数,具有重要的工程意义。

Reducing effects of limestone strength on the unconfined compressive strength of limestone are studied according to acid-rock reaction experiments of the static high temperature and the rock compressive strength tests,and analyzed stress-strain curve and mechanics of damage for limestone.Test results indicate that after reaction with the same gelled acid used on the test,elastic modulus highly decreased and Poisson′s ratio increased a little,unconfined strength are about 20% compared with the same parts of limestone before acidized.During the acid-rock reaction,difference of reaction rate and acid etched pattern are obvious between matrix limestone with fractural limestone.Reaction with the same gelled acid used on the test,the reaction rate of Tazhong fractured limestone is about two times of Lungu matrix limestone.The etched pattern of fractured limes is local and deep,the matrix limestone is superficial and symmetrical.Different limestone pattern determined different etched pattern,and together with acid system,different etched patterns resulted in different strength reducing effects of limestone near fracture area during acid fracturing.The research results can provide effective technical parameters for designing and optimizing of acid fracturing.