Ultra-Low-Pressure Layer Injection Plugging Agent Sealing Technology Practice

Aiming at a production well in Tazhong 4 oilfield, where the pressure coefficient of the layer was reduced to 0.26 due to long-term exploitation, and the loss of returned well fluid leakage occurred during the well workover operation and the conventional oil well cement system failed to block the layer, the research was carried out to study the high-efficiency plugging agent system and the supporting plugging process applicable to ultra-low-pressure layer, so as to realize the effective blocking of the target layer. Based on the ultra-low-pressure layer and the seepage characteristics at the end of the exhaustive development of the clastic reservoir, a temperature-resistant and salt-resistant plugging agent combined with a multi-stage plug high-pressure squeeze plugging process was adopted. By optimizing the rheology of the plugging agent (density 1.65–1.72g/cm3, fluidity 22 cm) and particle gradation (8−1000 μm), designing a multi-stage plug high-pressure squeezing plugging scheme (graded and segmented injection, the highest pumping pressure of 18 MPa), and adjusting the construction parameters in real time by using the whole wellbore pressure monitoring, it ensures that the plugging agent is sufficiently squeezed into the near-well zone and seals the leakage channels effectively. Field application shows that the temperature-resistant and salt-resistant plugging agent together with the multi-section plug high-pressure squeezing plugging process successfully seals the ultra-low-pressure layer at one time, and the pressure-bearing capacity of the whole wellbore is increased to 15 MPa after sealing, and the amount of leakage is reduced to zero. Research shows that: ① temperature-resistant and salt-resistant plugging agent with multi-stage plug high-pressure extrusion plugging process is an effective plugging program for the loss of return leakage of ultra-low-pressure layer; ② temperature-resistant and salt-resistant plugging agent's rheology and particle gradation matching with the pore permeability characteristics of layer is the key to the success of the plugging. This technical solution will provide a low-cost and high-efficiency technical path for the management of ultra-low-pressure layer in old oilfields, and support the old oilfields to play the role of ballast in a sustainable and stable manner.