Study on the law of waterflooding enhancement in tight reservoirs

Waterflooding is widely used to enhance formation pore pressure and oil recovery, which is crucial to determine the waterflooding timing with varying injection rate. This paper proposed an experimental method to illustrate the variation law of micro-pores in rocks during waterflooding using online nuclear magnetic resonance and dynamic computed tomography scanning. A theoretical model is used to optimize the waterflooding time depending on the effective porosity and pressure propagation velocity. The results show that, when subjected to confining pressure, the pores and cracks inside the rock sample are compressed, resulting in decreased permeability. Under reasonable confining pressure, the small pores can be increased to the largest by 121.60%. By controlling the water injection pressure, the quantity and proportion of large and small pores in the reservoir rock mass can be regulated and then the permeability of the reservoir can be quantitatively and controllably increased, ensuring the feasibility of increasing the waterflooding in improving the oil and gas recovery. Considering effective porosity and pressure propagation velocity, the timing of water injection is deduced. Based on the laboratory experiments and theoretical derivations, this paper proposes a method for determining the optimal water injection time, which helps to solve the problem of process parameter design of waterflooding and gives an increased recovery of the three adopters by 18%–35%. This study provides theoretical support and practical guidance for the waterflooding development of tight oil reservoirs.