Abstract
At present, in the workover operations of old gas wells in the Changqing Gas Field, due to years of exploitation in the production layer, pressure deficits, and general leakage during the well killing, the well must be plugged before the well can be killed. In particular, the fracture-cavity type fractures of the lower paleocarbonate reservoirs have serious leakage. Traditional plugging materials and traditional plugging materials and methods have some limitations in dealing with leakage problems. Therefore, a composite plugging system using polymer solution as the base carrier fluid, multi-particle size rigid particles, expandable particles and modified fibers is developed. Its formula is: water + 2% polyacrylamide + 0.1% N, N-methylene bisacrylamide polymer gel is the base carrier fluid; the formulation of the particle plugging agent was continuously optimized through the CDL-II high temperature and high pressure dynamic and static plugging ability to plug the core. The final formulation of the plugging agent is: 1) 20% rigid particles (5 mm, 1 mm, 0.5 mm CCP-3 ratio 4:2:1) + 1% 3 mm expanded particles SMK-1 + 1% 1 - 2 mm fiber SRXW-10; 2) 20% rigid particles (3 mm, 0.1 mm, 0.05 mm CCP-3 ratio 3:2:1) + 1% 3 mm expanded particles SMK-1 + 1% 1 - 2 mm fiber SRXW-10. The water swelling multiples of the granular plugging agent in salt water are all above 7 times, which meets the requirements of leak-proof plugging operations under high salinity; 3% HCl is selected as the gel breaker, and the plugging system has a gel breaking rate of 95%; through the water plugging and profile control experimental system, the sand-filled pipe is used to simulate the plugging effect under high temperature and high pressure, and the plugging system can be sealed for 5 days at a high temperature of 110°C and a high pressure of 20 MPa to achieve a good plugging of the formation. It is expected that the developed plugging system has a good application prospect in future workover operations.
Highlights
The Changqing Gas Field is a typical gas field with “low permeability, low pressure and low abundance”
Its formula is: water + 2% polyacrylamide + 0.1% N, N-methylene bisacrylamide polymer gel is the base carrier fluid; the formulation of the particle plugging agent was continuously optimized through the CDL-II high temperature and high pressure dynamic and static plugging ability to plug the core
The water swelling multiples of the granular plugging agent in salt water are all above 7 times, which meets the requirements of leak-proof plugging operations under high salinity; 3% HCl is selected as the gel breaker, and the plugging system has a gel breaking rate of 95%; through the water plugging and profile control experimental system, the sand-filled pipe is used to simulate the plugging effect under high temperature and high pressure, and the plugging system can be sealed for 5 days at a high temperature of 110 ̊C and a high pressure of 20 MPa to achieve a good plugging of the formation
Summary
The Changqing Gas Field is a typical gas field with “low permeability, low pressure and low abundance”. After long-term mining, the formation pressure coefficient dropped to about 0.5 [1] [2] [3]. In order for the oil and gas wells in the Changqing block to resume normal production, it is necessary to restore the formation force coefficient through workover operations. In workover operations, due to years of mining, pressure deficits, and common losses during well killing, the well must be plugged before killing, especially the fractures of the lower paleocarbonate reservoir, where the leakage is more serious [4] [5] [6]. In the process of workover operations, traditional plugging materials and methods are prone to poor plugging effect, repeated leakage or flowback difficulties when dealing with leakage problems, and plugging the pay zone, affecting productivity after workover, etc. This research relies on the Yangtze University Oilfield Chemistry Laboratory and project team members to develop a composite plugging system that uses polymer solutions, multi-particle size temporary plugging particles, and modified fibers to realize the effective plugging of perforation holes
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