The Research On Oil Well Capacity And Reasonable Well Spacing In Low Permeability Anisotropy Reservoir

Low permeability sandstone reservoirs widely exist in the petroliferous basins in China, accounting for about30%of the total of oil resources. In recent years, the reserves proportion of low permeability and extra-low permeability has exceeded60%in the new reserves of crude oil. Therefore, how to develop the low permeability reservoir efficiently has a long-term strategic significance to the sustained and steady development of China’s oil industry.Low permeability reservoirs have the characteristics of large specific surface、small pore and throat as well as complex flow patterns. Due to the orientation of rock particles during the sedimentary process and a large number of micro-cracks, which caused the serious permeability anisotropy, the hydraulic fractures of low permeability reservoirs exacerbate the permeability anisotropy and complexity of fluid flowing, which will affect the types of well patterns and the arrangement of well spacing, even the ultimate recovery of reservoirs. To analysize the influence permeability anisotropy on the oil well productivity, producing a set of reasonable well spacing charts considering the low permeability anisotropy and fractures is of important practical significance for production guidance.Based on the low anisotropic permeability reservoirs, this paper has investigated the geologic characteristics of low anisotropic permeability reservoirs, researched the developing characteristics of different types of the well patterns, obtained the following main results:①Establish the dynamic model of the fracture well productivity considering the anisotropy effectBased on the effect of anisotropy on the fractured wells capacity, using the conformal transformation method, the well productivity calculation model of infinite conductivity single crack and double fracture is established which considering the permeability anisotropy, and is verified. The method is proved to be correct by using the conformal transformation method to establish the fractured well productivity calculation model.②Based on the low permeability anisotropy characteristics, a theoretical calculation formula is proposed for the reasonable well spacing of different types of well patterns.According to the flow-tube method and the Buckley-Leverett immiscible flooding mechanism, prediction formula of the reasonable well spacing has been set up for different anisotropy coefficients and different types of well patterns, with analysis of the anisotropic coefficient’s impact on the well spacing. Using the ideas of vector well pattern, this paper has deduced a dynamic analysis theory and well pattern optimization theory for the development of anisotropic reservoirs.③Combining water flooding type-curves and Weibull prediction model, research the oilfield dynamic prediction method.Based on well productivity, combined with Weibull prediction model, a solution to the water drive curve can be obtained, which can be used to predict the dynamic parameters of the entire oilfield varying with the time. The new method maintains the original advantages of the two models, overcomes their limitations and expands the scope of their application. It has been proved that the new method is accurate and practical through the actual production data of two oil fields at home and abroad. Meanwhile, comparing the combined solution model of four types of water drive curve, type I water drive curve has the highest prediction accuracy.④Based on mechanism model, this paper has established theory charts of different anisotropic coefficients, different well spacings and the best flooding sweep efficiency for different well patterns.Equilibrium displacement can be reach in heterogeneous reservoirs when well spacing is equal. However, for the anisotropic permeability reservoirs, the arrangement of well pattern need not to follow the regular cases, but extend the well spacing in the principal permeability direction and shorten the row spacing in lateral permeability direction, so that water breakthrough of different wells is at the same time. When anisotropic coefficient is different, the dimensionless well spacing has the best flooding sweep coefficient, and fractures aggravate the complexity of flow process in low anisotropic permeability reservoirs. The charts provide theoretical basis and convenience for the layout of well pattern in low anisotropic permeability reservoirs. According to the charts, the reasonable well spacing and row spacing can be calculated. With the combination of reservoir numerical simulation and reservoir engineering method, taking H56well area in Changqing oilfield for example, the calculations show that the development effect of inverted nine-spot rhombus pattern is obviously superior to that of the inverted five-spot rhombus pattern, it is easy to establish an effective driving pressure system with short well spacing, so that a better development effect can be obtained for in low anisotropic permeability reservoirs, and that the recovery of well pattern whose fractures are parallel to the principal permeability direction is higher than the well pattern whose fractures are vertical or well pattern without fracturing. Therefore, the development of low permeability anisotropic reservoirs should obey the principle that inject water in the direction parallel to fractures and produce oil in the direction perpendicular to fractures.This paper not only improves the prediction and impact factors on single well productivity in low anisotropic permeability reservoirs, but also analyses the dynamic analysis theory in low anisotropic permeability reservoirs and well pattern optimization theory, which provides the important basis for the reasonable arrangement of well pattern and optimization of injection/production program in low permeability anisotropic reservoirs, and has certain referential value for oilfield development.