| At present,many oil fields have entered the middle and late stages of development,and the water cut in production well has increasingly higher.When the economic limit is reached,it is necessary to shut production wells,which affects the economic benefits of oil field.The injection-production technology can separate oil and water in the same wellbore,which reduce costs of groundwater gathering and treatment of production fluids and extend economically efficient production time of the productive layer.Besides,it can increase the number of injection well,change flow direction,and improve injection and production relations.In order to ensure injection-production technology can be implemented well,it is necessary to determine the boundary of water cut,reinjection layer,interlayer between injection layer and production layer and injection pressure to form selection principles of wells and layers of injection-production technology.Based on break-even principle,one well reaches its economic limit when profit after tax equals operating costs.The economic limit water cut of water drive is 97.49% and the liquid production limit is 17.53t/d.The economic limit water cut of injection-production technology is 99.24% by considering equipment,operating costs,saved costs of ground processing stations and pipeline and increased production of affected oil wells which are located at injection-production well and are connected with injection-production well.In order to ensure the separated water of injection-production technology can inject reinjection layer successfully,the relation plate among formation coefficient of reinjection layer-water injection-pressure difference is calculated according to the injection well percolation model.When the injection well spacing is 200 m and the pressure difference is 8MP and water injection volume is 80m3/d,the lower limit value of the formation coefficient of injection layer is 0.32?m2·m.In order to improve the development effect maximally,when well spacing is less than 200 m,it is preferred to choose layer of which one affected oil well connects less than 2 water wells on average as re-injection target.When well spacing is more than 200 m,it is preferred to choose layer of which one affected oil well connects less than 3 water wells.Meanwhile,the permeability contrast limit of reinjection layer is 4.5.The pressure difference between injection layer and production layer in the near-wellbore area increases after implementing injection-production technology,and inter-well crossflow and interlayer crossflow are prone to occur.In order to prevent crossflow at cement-formation interface,the anti-crossflow differential pressure gradient is 3.44MPa/m and thickness of interlayer is at least 2.62 m when the number of BI is 0.4 and the reinject pressure is 16 MPa.In order to prevent interlayer crossflow,the lower limit thickness of interlayer is 0.012 m when the production volume is 70m3/d and the permeability of interlayer is 0.01×10-3?m2.Besides,by the results of numerical simulations,the interlayer which distribution ratio is one well spacing and is located close to the injection-production well can get great development effect.This paper established material balance equation of mudstone expansion and calculation model of equivalent damage load of casing by using Maxwell theory.With the time of mudstone expansion goes by,equivalent destruction load resulting from maximum and minimum horizontal ground stress is equal to the load carrying capacity of casing and at that time injection pressure reaches its upper limit.Compared with the pressure which is smaller 0.5 MPa than overburden pressure,the injection pressure without casing damage is used as the limit of the injection pressure when the depth is greater than 800 m.Based on the above results,at a depth of 1000 m,the upper limit value of the injection pressure is 19.7 MPa.This paper has a strong guiding significance for the implementation and promotion of the injection-production technology. |
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