Low Permeability Oil Field Oil-water Two-phase Low-speed Non-darcy Flow Law Study

Basted on three fundamental factors of fluid, porous medium and fluid condition, by plentiful experimental studies and theoretical analysis, the single-phase and oil-water two-phase flow seepage rules have been researched in Daqing periphery low permeability oil field. And using the non- Darcy seepage theory, some improving measurements that reduce and eliminate the negative influence of starting pressure have been proposed. The research work of this article includes:Based on the methods of clay mineral analysis, pressure mercury analysis, scanning electronmicroscope (SEM), thin section analysis and so on, the type of pore result on Fuyang oil layer in Daqing periphery low permeability oil field has been studied. It is pointed out that the main flow throat radius of the reservoir was 0 .25 - 1.6um . Th i s kind of slight passageway increased the oil and water flow resistance, and this was the main reason of non- Darcy seepage in the low permeability reservoirs.Through the analysis of rheological property to crude oil under the different temperature, the study pointed out that the crude oil of low permeability oil field in Daqing periphery has the ge11ing-thixotropy, and it is anon - Newtonian flow at a specific temperature, it is a yield value plastic fluid when the temperature is lower than the specific temperature. This is also a reason that the low permeability oil field has a non- Darcy seepage.By adjusting temperature to change fluid viscosity, the impacts of viscosity on fluid transfusion curve were examined and also the impacts of viscosity on non-Darcy seepage were clarified.According to the need of test, a method was designed that "unsteady displacement-capillary measurement" determines the minimum starting pressure gradient of low-permeability core and the average starting pressure gradient using the conventional "flow-differential pressure" measurement.According to a series of single-phase or two-phase flooding of oil and water, the characteristics of non- Darcy flow curve and its influence factors have been studied. It pointed out the initial pressure gradient of oil-water two-phase flow are functions of the water saturation, it namely is bigger than the initial pressure gradient of water single-phase flow on residual oil condition, is also bigger than the initial pressure gradient of oil single-phase flow on inreducible water condition. At the same time, the oil layer with low permeability mainly existed two phase, even if it is the single-phase flow in the condition of inreducible water or the residual oil, the initial pressure gradient is bigger than the oil single-phase or the water single- phase initial pressure gradient. The oil single-phase flow has the non-Darcy flow with the permeability limit of 5×10^-3um², and water with1×10^-3um². This conclusion was confirmed by the oil-water two-phase flow experimental.Based on two-phase flow theory, a set of two-phase seepage formula describing especially ultra-low permeability reservoir has been established. This formula has considered not only the influence of oil- water non-Darcy seepage, but also the influence of capillary pressure. By testifying, this formula can be applied to the determination of oil-water relative permeability curve when low seepage core is low speed seepage.Through the theory analysis and application of non- Darcy seepage in Daqing periphery low permeability oil field, some improving measurement for the development of low permeability oil field——the infill of well pattern, the determination of reasonable water injection pressure, reducing water injection pressure by injection of surfactant water and so on has been proposed and has obtained certain practice effect and understanding.