The production performance of waterflood reservoirs with years of production is severely challenged by high water cuts and extensive water channels. Among IOR/EOR methods, weak gel injection is particularly effective in improving the water displacement efficiency and oil recovery. The visualized microscopic oil displacement experiments were designed to comprehensively investigate the weak gel mechanisms in porous media and the numerical simulations coupling equations characterizing weak gel viscosity induced dynamics were implemented to understand its planar and vertical block and movement behaviors at the field scale. From experiments, the residual oil of initial water flooding mainly exists in the form of cluster, column, dead end, and membranous, and it mainly exists in the form of cluster and dead end in subsequent water flooding stage following weak gel injection. The porous flow mechanism of weak gel includes the preferential plugging of large channels, the integral and staged transport of weak gel, and the residual oil flow along pore walls in weak gel displacement. The profile-control mechanism of weak gel is as follows: weak gel selectively enters the large channels, weak gel blocks large channels and forces subsequent water flow to change direction, weak gel uses viscoelastic bulk motion to form negative pressure oil absorption, and the oil droplets converge to form an oil stream, respectively. The numerical simulation indicates that weak gel can effectively reduce the water-oil mobility ratio, preferentially block the high permeability layer and the large pore channels, divert the subsequent water to flood the low permeability layer, and improve the water injection swept efficiency. It is found numerically that a weak gel system is able to flow forward under high-pressure differences in the subsequent water flooding, which can further improve oil displacement efficiency. Unlike the conventional profile-control methods, weak gels make it possible to displace the bypassed oil in the deep inter-well regions with significant potential to enhance oil recovery.

Ultra low permeability reservoirs are significantly affected by the pressure sensitive effect, resulting in severe permeability loss, leading to a larger starting pressure gradient and increasing the difficulty of establishing effective displacement. At present, the existing technical limit well spacing formulas only consider the static starting pressure gradient and do not consider the reservoir pressure sensitivity effect, which leads to the problem of dynamic changes in the starting pressure gradient, resulting in the calculation results not being consistent with the actual situation of the mine. In response to this issue, a formula for calculating displacement pressure near oil and water wells considering pressure sensitivity effect and a formula for calculating variable starting pressure gradient were first established. Combined with the traditional formula for calculating the maximum well spacing, a formula for calculating the maximum well spacing between injection and production wells that can establish displacement considering dynamic starting pressure gradient was derived. The relationship between the permeability of ultra-low permeability reservoirs in Chaoyang Gou Oilfield and the technical limit well spacing was calculated. The analysis results indicate that compared with traditional methods, the new method needs to reduce the well spacing by 10m; The technical limit well spacing of Y-3 block is 47m; The demonstration results and case analysis results demonstrate the correctness and applicability of the formula. The results of this article can provide theoretical guidance for infill adjustment and potential tapping measures in ultra-low permeability reservoirs.

Ultra-low permeability reservoir fluid presents nonlinear flow, pressure sensitive effect, permeability changes, resulting in starting pressure gradient changes. At present, the problem of variable-start pressure gradient and pressure-sensitive effect is not considered in the existing production calculation method. To solve these problems, based on the percolation theory of ultra-low permeability reservoir, this study established the variable-start pressure gradient production calculation model based on the pressure sensitivity effect by using the pressure-sensitive effect formula and other laboratory experiment results. Taking Block C of Chaoyanggou Oilfield as an example, the main influencing factors of development effect under the condition of variable start-up pressure gradient are analyzed. The results show that the start-up pressure gradient leads to a significant decline in oil well production. When the variable start-up pressure gradient and pressure sensitive effect are considered simultaneously, the effective production radius of the oil well decreases, and the production of the oil well varies nonlinearly with the change of pressure. Compared with the calculation results of the non-Darcy seepage production model, the calculation accuracy of the model in this paper is improved by 4.17%.

Low permeability fractured reservoirs have strong heterogeneity, low efficiency and ineffective circulation, high water content, and low recovery rate. Conventional profile control measures significantly stabilize oil and control water, but the increase in recovery rate is small. Taking low-permeability fractured reservoirs in the periphery of Daqing as the research object, this study conducts research on the synergistic potential tapping technology of plugging, regulating and driving, and conducts pilot tests to verify the feasibility and adaptability of the technology. The effect of plugging, adjusting and driving is significantly better than that of deep profile control, and the experiment can increase the recovery rate by more than 10 percentage points; Injecting three cycles of rock cores can increase the recovery rate by 16.8 percentage points. During the pilot test of plugging, adjusting and driving, the recovery rate was increased by 1.95 percentage points within 2 cycles. This technology has important practical significance for improving the recovery rate of similar oil reservoirs in China.