The Productivity Study Of Composite Oil-gas Reservoir Based On The Fractal Theory Of Combonate Matrix Acidizing

Carbonate reservoirs account for about half of global reserves.The production has reached more than 60%of the total in the world,and about 38.5 billion tons.In the exploitation of carbonate reservoirs,the zone near the wellbore can be polluted by the treatments such as the working fluid invasion,the balance between reservoir pressure and temperature destruction,and the unreasonable exploitation so that the production of wells declines.The matrix acidizing is an important stimulation treatment for carbonate reservoirs.High conductive channels called wormholes can be formed by the fresh acid,which can recover or improve the productivity.At present,the wormhole study mainly stays on the physical and mathematical models which characterizing parameters,and its academic achievements are inadequate.Moreover,the study about the seepage characteristics of wormholes is vacancy,and the related the production of composite reservoir formed by the matrix acidizing are indefinitely.In this dissertation,the DLA diffusion-condensation theory,fractal-like tree-shaped network seepage theory and the law related the production of composite reservoirs are studied.The main content is depicted as follows:(1)According to the mechanism of the carbonate matrix acidizing,he simulation rule about the growth of wormholes in the radial direction is set up.by the analogy of the DLA diffusion-condensation model.Based on Visual Basic programming languages and computer monitor parameters,a accessor method of initial simulation parameters representing the radial growth of wormholes in the vertical well is established.For example,1 pixel in the computer model represents both 0.005m distance in the actual formation,and the occupied area of area of 3.76×1022(0.062 mol)hydrogen ions.(2)The wormhole shapes in the different acidizing conditions are simulated by the Visual Basic program.The simulated wormhole fractal dimension is int the range of 1.6435?1.6936,as the same value in other literatures(1.67±0.3).The results also shows the wormhole simulation radius as same as the treatment radius,and analyzed the impact of different perforation phase angle,different perforation depth,different natural fracture number with the same fractal dimension,different natural fractures length with the same fractal dimension and different fractal dimension with the same fracture number.(3)The similarities between the micro-capillary tube flow and seepage in porous medium was deduced in this dissertation.The simplified equivalent permeability model for wormhole radial flow—" point to circle" type of two branch tree-like shape fractal network seepage system was set up.Some impact fators was also analyzed,such as the fractal dimension of two branch length distribution Dl,the fractal dimension of two branch radius distribution Dr,the bifurcate series of two branch networkm,and the bifurcate angle of two branch network?.(4)The two models of wormhole zone equivalent permeability were established.First onw is the single wormhole extended model based on the equivalent seepage resistance theory.Second one is the radial nisotropy of fractal seepage model based on the fractal seepage theory.Finally,the two models calculation results show the sample value by example(60 mD?80mD).(5)With the steady seepage mechanics theory and equivalent seepage resistance theory,this dissertation deduced a model for production which can avoid use skin factor and analyzed the necessity for considering the gas seepage's non-Darcy flow for composite gas reservoirs.(6)By analyzing the well test interpretation principles and Blsingame method,this dissertation established dimensionless bottomhole pressure and dimensionless production's Laplace spatial expression in two cases which are without considering wellbore storage effect and considering the effect in composite reservoirs.And furthermore this dissertation analyzed the characteristics and factors of dimensionless bottomhole pressure and dimensionless production under space by the means of Sethfest numerical inversion algorithms to eight parameters:?seepage of composite reservoirs after acidzing is divided into three stages:linear flow stage,radial flow stage and pseudo-steady flow stage;?perrneability of acidzing zone which belongs to composite reservoirs after acidzing has an influence on the radia flow stage,and acidzing radius dimensionless production decreases with the increment of dimensionless bottomhole pressure,?permeability of acidzing zone which belongs to composite reservoirs after acidzing has an influence on the linear flow stage,and when the acidzing radius increases.dimensionless bottomhole pressure drops and dimensionless production escalates.?the more wellbore storage coefficient in composite reservoirs after acidzing is,the less dimensionless bottomhole pressure is and the more dimensionless production is.?Non-Darcy effect in composite reservoirs after acidzing has no influence on the dimensionless bottomhole pressure and dimensionless production.