The development of shale gas is faced with low reservoir porosity,low reservoir permeability and high formation fracture pressure.In order to deal with these problems,this paper selected shale samples from the bottom ...The development of shale gas is faced with low reservoir porosity,low reservoir permeability and high formation fracture pressure.In order to deal with these problems,this paper selected shale samples from the bottom of the Lower Silurian LongmaxieWufeng Formation of Upper Ordovician in the Weiyuan Block of the southern Sichuan Basin as the research objects.After acid dissolution experiments were carried out,the microstructures and the mechanical parameters of shale after acidizing treatment were investigated by means of X-ray diffraction,scanning electron microscopy and triaxial mechanical test.Then,the effect of acidizing treatment on the microstructures and the mechanical properties of shale were analyzed.And the following research results were obtained.First,after acidizing treatment,the carbonate mineral content of shale decreases and the number and size of pores increase.In the process of dissolution,micro-fractures occur,leading to the increase of shale porosity and permeability.Second,after acidizing treatment,the mechanical properties of shale change.Its deformation mode transforms gradually from elasticebrittle deformation to elasticeplastic deformation,and its fracture mode transits from brittle to semi-brittle and semi-ductile.Third,after shale is treated with the acid with the concentration of 15%for 240 min,its permeability is increased by 3.09 times.After 3 days,its porosity is increased by 1.65 times.And after 7 days,its compressive strength,Young's modulus and brittleness index are decreased by 50.1%,58.1%and 32.8%,respectively.Fourth,the mechanical parameters of shale of the LongmaxieWufeng Formation in the Weiyuan Block is in a quadratic relationship with an average pore size and permeability and in a quadratic or linear relationship with porosity,and their correlation is strong.In conclusion,the research results provide technical support for the prediction of the mechanical parameters of shale in this block after acidizing treatment and for the design of acid fracturing scheme.展开更多
基金supported by the National Natural Science Foundation of China"Flow mechanism of induced fractures and conductivity prediction model of shale fracture network in deep strata under high pressure"(No.:51704251)"Fracturing and acidizing of low-permeability and tight reservoirs"(No.:51525404).
文摘The development of shale gas is faced with low reservoir porosity,low reservoir permeability and high formation fracture pressure.In order to deal with these problems,this paper selected shale samples from the bottom of the Lower Silurian LongmaxieWufeng Formation of Upper Ordovician in the Weiyuan Block of the southern Sichuan Basin as the research objects.After acid dissolution experiments were carried out,the microstructures and the mechanical parameters of shale after acidizing treatment were investigated by means of X-ray diffraction,scanning electron microscopy and triaxial mechanical test.Then,the effect of acidizing treatment on the microstructures and the mechanical properties of shale were analyzed.And the following research results were obtained.First,after acidizing treatment,the carbonate mineral content of shale decreases and the number and size of pores increase.In the process of dissolution,micro-fractures occur,leading to the increase of shale porosity and permeability.Second,after acidizing treatment,the mechanical properties of shale change.Its deformation mode transforms gradually from elasticebrittle deformation to elasticeplastic deformation,and its fracture mode transits from brittle to semi-brittle and semi-ductile.Third,after shale is treated with the acid with the concentration of 15%for 240 min,its permeability is increased by 3.09 times.After 3 days,its porosity is increased by 1.65 times.And after 7 days,its compressive strength,Young's modulus and brittleness index are decreased by 50.1%,58.1%and 32.8%,respectively.Fourth,the mechanical parameters of shale of the LongmaxieWufeng Formation in the Weiyuan Block is in a quadratic relationship with an average pore size and permeability and in a quadratic or linear relationship with porosity,and their correlation is strong.In conclusion,the research results provide technical support for the prediction of the mechanical parameters of shale in this block after acidizing treatment and for the design of acid fracturing scheme.
