Numerical Simulation Of Temperature Field And Development Scheme Optimization For IFCD Oil Shale In-situ Mining

With China's sustained economic growth and increasing energy demand,petroleum,a non-renewable energy source,is no longer able to meet the needs of current economic development.Moreover,Conventional oil and gas resources will eventually be exhausted.At present,the supply of domestically-owned mining is far from meeting the demand.Therefore,the search for alternatives to petroleum has become a top priority.Oil shale is a kind of flammable sedimentary rock,rich in organic matter.It is an unconventional oil and gas resource with huge resources.The dry distillation can cause the kerogen in oil shale to decompose at a certain temperature and produce shale oil.According to the new round of oil and gas resources assessment,China's total oil shale resources reserves rank fourth in the world,and the conversion to shale oil can reach 47.64 billion tons,1.5 times that of conventional oil and gas resources.The total amount of oil shale in the Songliao Basin in Northeast China accounts for 47% of the national resources,with the largest domestic possession,but deeper burial.At this stage,the factors restricting the exploitation and utilization of oil shale are mainly the immature development and utilization technology of oil shale.The current oil shale mining technology mainly includes ground retorting and in-situ mining technology.Ground retorting technology is often used for shallow oil shale mining with high pollution and low efficiency.In contrast,underground in-situ mining technology has the characteristics of low cost,environmental protection and high heating efficiency.But geological conditions and engineering factors have a great influence on the application of oil shale in-situ mining technology.The use of field trials will consume huge financial and material resources,while numerical simulation experiments provide a safe,fast,and low-cost method.Based on the IFCD technology developed by Zhongcheng Oil Shale Company and the on-site test of oil shale in-situ mining in Fuyu Songyuan Songliao Basin Northeast China,The author carried out numerical simulation study on the well pattern of simple well group,the well pattern of parallel well group,the well pattern of hexagonal well group and the superiority of IFCD technology.The main research and results are as follows:(1)When numerically simulating a model with a large size difference,dicing the established model entity can improve the success rate of automatic generation of the model unstructured grid.(2)Based on the engineering geological conditions of in-situ mining in situ test in Songliao Basin,the basic model of single-fracture-single gas injection well(model I),Double-fracture-single gas injection well model(model II),double-fracture-double equal-depth gas injection well model(model III),double-fracture-double unequal depth gas injection well model(model IV)was established.And numerical simulation studies of each model were carried out.It was found that when the gas injection well penetrates the fracture to heat the oil shale formation,increasing the degree of fracturing of the oil shale layer,the gas injection rate,and the number of gas injection wells in the gas injection well will significantly improve the oil shale production,which makes the development and utilization of the oil shale more thorough.(3)Through the establishment of 55 multi-gas injection wells,multi-production wells,parallel well groups with different well spacings,and the numerical simulation studies were carried out,it is found that the gas injection shale heating effect of the gas injection well-injection well spacing and the gas injection well-production well spacing The impact of the parallel well group model is selected.The relatively preferred gas injection well-injection well spacing is about 8-10 m,and the gas injection well-production well spacing is about 20 m.(4)In order to study the heating effect of oil shale during the in-situ mining process of the hexagonal well group,the numerical simulation study of the double-fracture model with different well spacing(30-45m)was carried out,and it was found that the duration of gas injection heating was not At the same time,the optimal well spacing is different.When the gas injection time is less than 500 days,the optimal well spacing is 30m;when the gas injection time is 500-1000 days,the optimal well spacing is 35m;when the gas injection time is 100-1500 days,the optimal well is The distance is 40m;when the gas injection time is more than 1500 days,the optimal well spacing is 45m;therefore,when the gas injection time is sufficient,the proper well spacing should be increased.(5)In order to study the influence of the spacing between the fractures on the heating effect of the oil shale during the in-situ mining of the hexagonal well group,the model BI(d=2.5m)and the model BII(d=3.5m)of the different fracture spacing were established.and numerical simulation studies were carried out,found that the model BI heating effect is good when the gas injection time is less than 600 days;when the gas injection time is more than 600 days,the model BII heating effect is good;when the gas injection time is sufficient,The spacing between the fractures can be appropriately increased.(6)When the in-situ mining simulation is not carried out by using the IFCD technology,the gas field is only heated by the gas injection without dissipated,which causes the temperature field diffuses slowly,and the heat in the early stage is mostly absorbed by the Overlying rock formation.For the deep and thin oil shale buried in the Songliao Basin,compared with the IFCD technical method,simply injecting heat from the wellhead of the gas injection well will cause heat consumption and loss;using the IFCD technology to carry out in-situ mining in the Songliao Basin has more Great advantage.