Study Of The Fluid Flow In Ultra-low Permeability Reservoir With Fractures And Its Application At Daqing Oilfield

This study was performed to make clear the flow characteristics of the ultra-low permeability reservoir with fractures in the periphery of Daqing Oilfield, like the Fuyu oil layer in Toutai oilfield and Yushulin oilfield. Aiming at such problems existing in the low permeability reservoir development by water flooding at Daqing Oilfield as the fast decrease of oil production, the low recovery ratio and poor use of reserves, after comprehensive analyses of the research methods, results and literatures concerning non-Darcy flow at low-permeability reservoir home and abroad, the research ideas and contents were determined. Much efforts were put to both the theoretical and the experimental studies on the non-Darcy flow.Through the comprehensive studies by Clay-mineral Explanation, Scan Electron Microscopy, Cast Thin Section, Constant-rate Mercury Injection, Nuclear Magnetic Resonance and so on, it was found out that there are five primary types of reservoir spaces as intergranular pores, corrosion holes, micro-pores, intercrystal porse and the fracture at the low-permeability oil layers of Fuyang in the periphery of Daqing. The fracture takes the tubular and sheet-based thin throat as the major types, and the pores are the main flow channels of reservoirs. Inevitably, the fine pores increase the oil&water flow resistance. Also, such reservoir matrix pores, throat, fractures and their mutual links control the fluid flow characteristics at different extents.Laboratory Experiments proved that the flow of single-phase oil or single-phase water in the low permeability oil layers of Fuyang at Daqing oilfield shows non-Darcy characteristics; the lower the permeability, the more obvious characteristics of the non-Darcy flow, then the larger the minimum pressure gradient and the quasi-starting pressure gradient required. The limit of the permeability for the non-Darcy flow of a single water phase is 1×10-3μm2, the number for oil phase is approximately 5×10-3μm2.When two phases of oil & water flow in the low permeability reservoirs, the flow curve is more significant in the non-linear characteristics. Now the quasi-starting pressure gradient is not only a function of the water saturation, but also associated with the displacement process. It is greater than number of the single-phase flow of water in the state with residual oil and than the value of oil in the state of the irreducible water. The oil-water relative permeability curves of the ultra-low permeability cores at low speed are characterized by a high irreducible water saturation, a high residual oil saturation, a small range of two phase flow of oil and water, fast decline speed of the oil phase relative permeability and the low water-phase relative permeability at the state of residual oil.A great many researches were carried out about the flow characteristics and development features of ultra-low permeability reservoirs with fractures. A concept of the effective drive system was put forward. In combination with the actual oilfield development, several measures were explored to build the effective driving system, such as fracturing for production to increase the movable fluid saturation, using rectangular well pattern to enlarge the flow area, combining the matrix and fracture to improve the oil displacement capacity and so on.