| Unconsolidated sandstone reservoir has the characteristics of weak cementation, it is easy to produce sand whitch leads to erosion or damage of pipeline and casing during its recovery process,these can make a lot of accidents whitch endanger the production safety happen.So, sand control completion is always used in the development process of unconsolidated sandstone reservoir to prevent large amount of sand harm to oil well production. Completely sand control will lead to blocking of near wellbore zone formation that will reduce the oil well productivity while allowing sand production dredgs the formation and improves the structure of the pore permeability as well as well productivity. Moderate sanding technology is on a balance of completely sand control and sand production, on the premise of not exceedieng the maximum sand processing capacity, it allows moderate sanding that can improve the well productivity. It is called moderate sanding well whitch applys moderate sanding technology and can optimizes its capacity by optimizing well completion method and production pressure difference.Unconsolidated sandstone is selected as the research object of this article whitch targets to get the seepage mathematical model and productivity prediction model. On the basis of previous theoretical research and experimental simulation, begins from the perspective of the reservoir seepage, specific to the technical difficulties of the reasonable sand production, centers on sand production mechanism, the main work is as follows:(1) study of critical condition of sand production;(2) foundation of productivity calculating model and dynamic permeability mathematical model;(3) calculation of completion epidermis and the influence of sand production on it thus to the well productivity;(4) development of the moderate sanding well productivity evaluation softwear;(5) analysis of the influence on reservoir physical properties and well productivity of multiple parameters and the determination of reasonable production pressure difference.Depending on all above studies, the following conclusion can be reached:sand production critical condition is decided by critical sand production pressure gradient which has direct ratio relations with beginning coefficient of erosion, residual cohesion, reciprocal of particle radius, has inverse relation of effective volume stress, internal frictional angle, porosity;model of sand production and reservoir seepage process is a function of porosity, permeability, reservoir pressure distribution, critical sand production pressure gradient, erosion coefficient, collapse porosity, viscosity, differential pressure of production etc, the degree of sand production is controlled by pressure gradient, the process of sand production is descripted by erosion model, sand erosion ability of rock is presentated as erosion coefficient;relationship between sand fluid production and well productivity in the development is analyzed:with the sand fluid production, oil well productivity of unconsolidated sandstone gradually increase, higher concentration of sand, larger productivity improvement;sand production wells productivity evaluation software that can study the influence on reservoir physical properties and well productivity of multiple parameters and determinate a reasonable production pressure difference is developed;the influence process of sand production on the structure of formation porosity and permeability is researched, the reasons of reservoir productivity enhancement due to sand production is because of the improvement of porosity and permeability, and the improvement of concrete porosity and permeability distribution picture is given, analyzes of influence on formation porosity is finished, influence of permeability and well productivity of different factors including:critical sand production pressure gradient, erosion coefficient, collapse porosity, differential pressure of production, sand control precision, completion skin is studied. |
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