Damage Properties Of Oil Shale Under Acidizing Fracturing Fluid

Oil shale is a very important alternative energy source.China's oil shale reserves rank second in the world.Fully exploiting and utilizing China's oil shale resources to make up for the shortage of conventional oil and gas production in China will play an inestimable role in promoting the development of our national economy and social stability.On the basis of in-situ transformation technology of oil shale,this paper optimizes hydraulic fracturing technology,uses acidizing fracturing fluid based on hydrochloric acid to acidize oil shale in Wangqing mining area,studies the macro-mechanical characteristics of acidized oil shale,and combines with its nuclear magnetic resonance characteristics,characterizes the micro-structure of acidized oil shale,and explores acidizing fracturing fluid.The chemical damage characteristics of oil shale under action can provide technical reference for in-situ fracturing technology of oil shale and improve production efficiency.Firstly,the basic principle of rock damage is elaborated,and the process of acid erosion of oil shale in acidizing fracturing fluid is that inorganic minerals(carbonates)in oil shale are dissolved and decomposed by acid solution,which results in acid corrosion holes in oil shale;the mechanical properties of oil shale are deteriorated by acid erosion,and combined with the macroscopical of acidized oil shale under uniaxial compression.The damage evolution equation of oil shale under the coupling action of chemical and stress is deduced according to the mechanical characteristics.Taking WangQing oil shale in Jilin Province as a rock sample,acidification test and mechanical properties test are carried out,and the change rules of physical and mechanical properties such as quality,uniaxial compressive strength and tensile strength of oil shale before and after acidification are obtained.The test shows that with the increase of acidification time,the quality of oil shale increases.With the increase of time,the uniaxial compressive strength and tensile strength decrease in varying degrees,and have layer rationality.At the same time,the chemical damage evolution equation of oil shale is established,which takes the change of elastic modulus as the damage variable.At the same time,the X-ray diffraction tests of oil shale before and after acidification are carried out,and the XRD diffraction patterns before and after acidification are obtained,and the carbonates of oil shale after acidification are found.The disappearance of characteristic peaks of minerals indicates that acidizing fracturing fluid mainly reacts with carbonate minerals in oil shale;NMR characteristics of oil shale before and after acidification are measured by NMR technology,and the distribution of T2 relaxation time,total T2 atlas area and porosity of acidified oil shale after different time are obtained,and the NMR T2 characteristics of acidified oil shale are obtained.The relationship between the area,porosity,pore size distribution and acidizing time was studied.The physical and mechanical properties of oil shale under different conditions of nuclear magnetic resonance(NMR)were studied through the mechanical properties test and NMR test of acidified oil shale,and the relationship between the micro-structure characteristics and macro-physical and mechanical properties of oil shale was established.