Fractal Description Of The Heterogeneity In Low Permeability Rocks And Its Influence On Oil Productivity

As an important energy base of economic development,oil is increasingly demanded,with the gradual expansion of the scale of the world's industrialization.With respect to the development status of oil industry in China,the already developed oilfields are at high water-cut stage and extra high water-cut stage,leading to an increasingly difficulty in the production of crude oil.Expect exploring for new blocks,it is also an important method to solve the bottlenecks encountering in current oil industry through the detailed description of developed oilfields and identifying the deep potential of residual oil.The porosity and permeability of oil reservoir determine the reservoir reserve,the productivity of oil and gas wells,and the degree of development difficulties in reservoir development.Reservoirs with three low characteristics(namely,low abundance,low permeability,and low productivity)dominate a large scale in newly proved reserves.Thus with regard to the low permeability reservoir,a thorough understanding of the characteristics of the pore-throat is central to its evaluation,development and modification.This paper is seeking to characterize the heterogeneity of reservoir quality using fractal dimension,permeability variation coefficient,gradation and abrupt injection coefficient from the macroscopic view of the permeability heterogeneity of reservoir sands and the microscopic view of the pore and pore-throat distribution in the reservoir rocks.For the calculation of the fractal dimension of rock,four methods were chosen and the results were different,which was mainly caused by differential operation and equivalent substitution.The results comply with the law that the greater the fractal dimension is,the stronger the reservoir heterogeneity becomes.This was reasonable because in general,porosity and permeability of reservoir rock no internal relations with its heterogeneity in theory.But the Fractal dimension was positive correlate with the permeability variation coefficient,but almost no correlation with porosity or permeability.For the calculation of the permeability variation coefficient,three main methods exist: Dykstra-Parsons definition method,statistical theoretical formula method,and Lorenz coefficient method.Taking the detailed situation of oilfield data,the paper selected statistical theoretical formula method to calculate the permeability variation coefficient.This method has high practical value,and the results also comply with the law that the greater the permeability variation coefficient is,the stronger the reservoir heterogeneity becomes by using permeability variation coefficient to describe the heterogeneity.In single sand body with good homogeneity,reservoirs with medium porosity and high permeability have relatively more stable daily oil production,lower water production of per thickness unit and longer stable product time when compared to the reservoirs with high porosity and low permeability.For oil group of multi-sand developed commonly,the daily oil production,water production of per thickness unit average permeability and water breakthrough time show a positive relationship with the average permeability.