Study On Splitting Grouting Sealing And Fracture Propagation In Oil Shale In-Situ Pyrolysis Zone In Fuyu Of Jilin Province

China's economy is in a rapid development stage with a large demand for energy.As oil is a non-renewable energy source,oil shale has attracted much attention as a supplementary energy source for oil.Oil shale are abundant in China,and a great deal of scientific research has been devoted to the research of oil shale.In-situ conversion of oil shale has become a trend of development.The existing in-situ conversion methods of oil shale at home and abroad mainly adopt heat transfer,heat convection and heat radiation.Consideration of in-situ conversion technology for seepage control and water stopping can not only improve the efficiency of in-situ conversion heating,but also avoid oil and gas pollution of groundwater and soil.Based on the demonstration project of underground in-situ development and utilization of oil shale,and in view of the geological environment of in-situ exploitation of Fuyu oil shale,this paper studies the sealing method of splitting grouting through laboratory tests and numerical simulation.The results are as follows:In order to understand the geological conditions of the project area,drilling,controlled source audio magnetotelluric technology,high density resistivity method and hydrogeology survey were applied to the geological survey of the Fuyu oil shale demonstration base.The geological data indicated that the oil shale reservoir and adjacent formation fissures in the oil shale demonstration project area are well developed and greatly affected by water flow.The purpose of this paper is to effectively prevent seepage and prevent water from fractures in oil shale formation and adjacent formation.K1340 superfine cement,sodium bentonite,silicon powder and polycarboxylic acid superplasticizer were selected as anti-seepage and water-repellent materials.The optimum formula of slurry is determined by orthogonal test and comprehensive analysis: water cement ratio 0.85,silica fume 6%,sodium bentonite 4%,polycarboxylic acid water reducer 0.5%.According to engineering experience,the slurry can be used as grouting material for anti-seepage and water-proof in-situ conversion zone of oil shale.According to the formation parameters of oil shale and taking 6)=(-)/ as the influence index of different stress levels on fracture propagation.The numerical simulation of single-hole splitting grouting fracture propagation and double-hole splitting grouting fracture propagation with perforations is carried out by using RFPA-2D software.The results show that(1)When k=0,the expansion of the single-hole splitting grouting fracture begins to expand around the grouting hole,and as the grouting pressure increases,the fracture will expand along the weak position of the rock mass;When k>0,the fracture initiation and expansion will occur along the direction of the maximum principal stress;in both cases,the cracking pressure and the model instability pressure increase with the increase of the confining pressure;(2)In order to achieve the directional splitting expansion,the perforation is introduced into the grouting hole.Compared with the non-perforated two-hole grouting,the double-hole splitting grouting with perforating has a certain directionality,due to the concentration of stress,the fractures are easier to expand and the cracking pressure is lower.(3)The fracture propagation of perforated double-hole split grouting is affected by the stress in the x and y directions,and the increase of the stress in the x direction is beneficial to the formation of the split grouting curtain.As the stress in the y direction increases,the stress difference gradually becomes the main factor affecting the expansion.The expansion of the fracture is gradually deflected by the grouting in the x direction to the y direction.It is the key to grouting that whether the slurry can be well combined with the oil shale surface in the fracture and whether the combination can effectively prevent seepage.The non-steady-state pulse attenuation method was used to compare the permeability of the slurry filled parallel layer fracture sample,the slurry filled vertical layer fracture sample,the cement stone sample and the split oil shale sample.By comparing the permeability of several samples,it can be seen that the slurry has a good combination with the oil shale fracture surface and can form a unified anti-seepage system.According to the geological conditions of oil shale demonstration base,the law of fracture propagation and the effect of slurry water stop,this paper proposes a method of combining seepage and splitting grouting to establish a slurry curtain for the formation and periphery of the oil shale in situ pyrolysis zone.In this paper,RFPA-2D is used to simulate the influence of in-situ stress difference on fracture propagation,and laboratory tests are used to verify the permeability effect of grout filling in fractured fracture.A method combining permeation with splitting grouting is proposed to prevent water in oil shale in-situ conversion zone,which provides a reference for oil shale in-situ water sealing engineering,thereby improving heating efficiency of oil shale in-situ conversion and reducing environmental pollution.