The Study Of Dynamic Simulation In Mudstone Rheology And Optimum Balance Of High Pressure Of Injection And Production

Based on the research of basal geology, depositional evolution, stress and fluid of the development area, this thesis simulated the sandstone of SI and its cap mudstone which located at the Beibei Transition Strap of Lamadian in Daqing Oil field by limited difference method to learn mudstone rheological property and optimum balance of injection-productionin in high-fluid-pressure system. The following main results have been achieved:During the oil production, the procedures of water-injection can significantly change the distribution of principal stress both on its power and direction. Field experiments indicated that changing the methods of water-injection could change the main principal stress (MPS) up to 3～5MPa in power and from N84°E to N80°W in direction. The changes of MPS were actually controlled by the pressure difference in the fluid (i.e., water and oil). The strata would creep or break when the main stress in the oil layer increased to the pressure-difference threshold of the local strata. To deep layers, changes in pore pressure would only cause deformation of strata in vertical direction and nearly nothing in horizontal direction if the ratio between the thickness of vertical direction and plane is very small.Numerical simulation on study area indicated that the maximum principle stress in this area is between -25.87—24.88MPa, and the minimum principle stress is -19.95～-18.44MPa. The distribution of strain consistent with stress which mainly behaved at vertical direction. The maximum increment of strain (about 0.53) is at the bottom of the mudstone and to the top is gradually diminished. The displacement is upward with relative maximum shift (～3.4 mm) at the bottom and nearly zero at the top. Whether the mudstone was soaked or not, all of the stress, strain and displacemen increased with bracing pressure of underlying sandstone, and became being stabilized in short time. Once mudstone was soaked, its rheological effect is significantly enhanced. Compared with un-soaked mudstone, when uploading stress of the sandstone increased 1 MPa, the increments were separately as below: principle stress is 0.2MPa, displacement is 0.73mm, and strain is about 0.1. Moreover, with the continuous stress increasing of underlying sandstone, the gaps of principle stress and strain between soaked or un-soaked mudstones became larger while the gap of displacement became smaller. When mudstone became saturated in water, its pore pressure started increasing from zero. Experiments indicated that pore pressure of mudstone would increase about 1.9MPa when bracing pressure of sandstone increase 7MPa.Based on the theories of Mass-balance and Seepage Mechanics, the relationship among oil productivity, water-injection rate and fluid pressure was calculated and discussed by applying dynamic analyses methods. During stable production period, the natural logarithm value of oil productivity was negatively correlated with reciprocal of water-injection rate. And fluid pressure of oil layer was mainly determined by annual water-injection rate and annual oil productivity. When annual water-injection rate was higher than annual oil productivity, the pressure would rise, and vice versa. If both of them were in equal, the original pressure of oil-layer would be maintained. Then this time must be in balanced state.Stress thresholds for SI oil layer in studying area were also calculated in this study. Results showed that the maximum bearing pressure is 13.0MPa. If the relationship of the pressure and recovery efficiency was thought about, the optimal pressure for SI oil layer should be 10.7MPa. And if considering the factors of casing damages, default and oil-layer breaking, the maximum water-injection pressure should be 13.4MPa. Based on the relationship between fluid pressure and oil-well flowing pressure, the optimal flowing pressure for study area was 6.8MPa. Dynamic simulation of oil layer further demonstrated that pressures from water-injection and oil production are not balanceable at present. The bracing pressure from oil layer would be over the maximum bearing pressure of cap mudstone if keeping current water-injection rate. However, if keeping strata pressure at 10.7MPa, oil productivity would increase 1.7m~3/(d · m) with constant water-injection strength. Recoverable reserves of study area was also calculated in this thesis, which is 2111.4×10~4t with a theoretical recovery efficiency of 36.24% which enhanced 1.79%.