Study On Basic Theories Of Effective Development Of Low Permeability Reservoir

This paper studies on basic theories on three main issues to effective development of low permeability reservoirs: first, the developement difficulty and effects of low permeability reservoirs with similar air permeability is very different, and the existing reservoir classification and evaluation method can not reflect the characteristics of low permeability reservoirs. So, it's hard to guide rational and orderly development of it. Second, the basic theory of flow in low permeability reservoir is unclear. With the permeability of reservoir more lower, nonlinear flow becomes more strongly. Conventional non-Darcy flow model can not describe the nonlinear phenomenon. It is essential to study the flow theory of low permeability reservoir to establish numerical simulation and calculation method of development indicators. The optimization principle of low permeability reservoir is not well considering the effective driving pressure system, making it difficult to achieve in the development designing, and production declines rapidly. This makes the development level of the low permeability reservoir greatly low. To establish well optimization based on effective drivens is an important basis for effective development theory of low permeability reservoirs.By controlled mercury, NMR and seepage experiments, pore structure, solid-liquid interaction and flow characteristics of different areas of low permeability reservoir is studied. Five new parameters of reservoir evaluation are proposed, including main throat radius, movable fluid saturation, threshold pressure gradient, clay content and type, and oil viscosity. Fuzzy optimization method is used to form reservoir evaluation techniques and generate reservoir evaluation software. This technique is used in Changqing, Daqing and Xinjiang Oilfield. Results show that it is valid to evaluate low perservoirs, especially the Changqing oilfield.Capillary experiments and seepage experiments results show that tiny pore and throat effects seepage. The decreasing of the thickness of solid-liquid boundary layer as the driving pressure gradient increasing and the selective flow of the fluid in the throat with different size is the two main mechanisms of non-linear flow in the low permeability reservoir. So, the water permeability is no longer constant, but the function of driving pressure gradient. A new nonlinear flow equation of motion is proposed based on a large number of experimental data. Combined with existing large-scale numerical simulation program, new numerical simulation software considering nonlinear flow is developed.The relationship between the relevant development indicators and effective driven is analysed. The concept of the effective driving pressure system, the pressure system to maintain the expected production, is propesed. The main factors effecting effective driving system is the reservoir properties (permeability, thickness and oil viscosity), well pattern, well spacing, fracture length of manual crack and the pressure of intput water ahead. Establishment of an effective driving pressure system has to optimize these parameters to achieve expected production for a given yield.The development effect of the rectangular and diamond well pattern is evaluated in Bai 153 tight reservoirs in Changqing field. Results show that effective driving is not archeived under these two well patterns, failing the expected production 2t/d. Through the optimization, it's found that five points pattern with 480x200m can be achieved effectively driven system, single well production 2t/d. While the inversed nine point pattern with 480×130m can only be achieved production 1.5t/d.