Research On The Prediction Of Mechanical Parameters Of Shale Acidification Pretreatment In Longmaxi Formation

Shale gas is the focus of oil and gas development at home and abroad.With the development of shale development technology,the development of domestic shale gas has gradually turned to deep,but also encountered many new technical problems,one of which is the deep shale volume fracturing construction pressure is too high,leading to development Blocked.Taking the shale of the Longxaxi Formation in southern Sichuan as an example,the shale acidification pretreatment technique was used to reduce the construction pressure of some wells successfully.However,due to the theoretical study of the problem i5 still less,still can not effectively and rational design of technical parameters.In this context,this paper based on the shale acid treatment experiments to understand the shale mechanical properties of the law,the establishment of a set of Longmaxi shale acid processing parameters of the prediction model.In this paper,the experimental study of the process of acid treatment of shale mechanical properties of the law and the relevant paraneters of the understanding and access.The acidification pretreatment experiment of shale was carried out by static dissolution method with acid treatment time and acid concentration as influencing factors.The changes of shale mineral composition before and after acid treatment and the changing characteristics of various minerals under acid treatment were studied by X-ray diffraction experiment.It was found that the carbonate minerals of the acid treatment shale decreased with increasing time and concentration.Acidic environment,the illite spacing increases,the strength of their own nature to reduce.The chlorite crystal structure is susceptible to high concentration of hydrochloric acid.The feldspar nature changes,hydrophilic enhanced.The change of the overall structural properties of the shale after acid treatment is related to the change of the crystal structure of the single mineral.In this paper,the microstructural characteristics of shale acid were qualitatively and quantitatively observed by electron microscopy,nitrogen adsorption,mercury intrusion and nuclear magnetic resonance experiments.The seepage relationship of shale is revealed by helium porosity test.The influence of micro-pore properties of shale on the mechanical properties of shale during acid treatment was analyzed by means of triaxial mechanical properties.Experiments show that the treatment of shale acid treatment in Longmaxi Group stabilizes after 2 days.After 7 days of treatment,the compressive strength decreased by 51.53%,Young's modulus decreased by 60.53%,and the brittleness index decreased by 78.7%.Under different acid treatment time,with the increase of acid treatment time,the carbonate mineral content of shale decreased,porosity and permeability increased.Shale compressive strength,Young,s modulus and brittleness index showed a decreasing trend.When the concentration of acid is increased to 20%,the mechanical properties of shale are slowed down and stabilized.When the acid concentration is increased to 25%,the compressive strength of the Longmaxi Formation is reduced by 48.5%,the Young 's modulus is reduced by 28.9%,and the brittleness is reduced by 56.6%.During the acid treatment,the variation of the mechanical properties of the shale varies with the mineral composition,the pore structure and the pore-permeability relationship under different concentrations of acid.With the increase of acid concentration,the carbonate mineral content of shale decreases,the porosity increases and the permeability increases.Compressive strength,Young,s modulus and brittleness index showed a decreasing trend.The optimal hydrochloric acid treatment time of the Shixi Formation shale was optimized at 240 min?3 days and the acid concentration was 15%.Based on the BP neural network algorithm,the prediction model of shale acidification pretreatment mechanical parameters of Longmaxi Formation is established on the basis of recognizing the law of acid treatment and obtaining parameters.The average error of the parameters in the simulation results is 7.88%.The model has good applicability.In this paper,the research results of the acidification pretreatment technology in the fracturing of the shale are explored,and the more detailed understanding of the production and development of the shale in the Longmaxi group is discussed.For the fiuther theoretical research To the scene should have a certain guiding significance.