Application of fuzzy-ball workover fluid combined with solid plugging agent to the temporary plugging of deep low-pressure gas layers in Puguang Gas Field

In Puguang Gas Field, natural fractures, vugs and hydraulic fractures coexist in the deep carbonate formation and they will become leakage channels when there is pressure difference between wellbore fluid column and formation. Therefore, temporary plugging is needed. It is feasible to apply the fuzzy-ball workover fluid to plug low-pressure gas layers, but its consumption is too high while plugging large-scaled channels. The solid plugging agent was introduced to assist fuzzy-ball workover fluid, so as to decrease the fluid consumption. In the laboratory, the artificial cores (diameter 38 mm and length 60 mm) containing through-going fractures of 5.0 mm wide are connected in series to simulate large-scaled channels. After the fuzzy-ball workover fluid was added with calcium carbonate grains and fibers with the mass fraction of 0.1%-1.5%, the fluid consumption of single system in the fracture to reach the displacement pressure of 20 MPa was compared with that of complex system. After plugging, gel breaker was injected to remove the temporary plugging and then the recovery effect of the flow velocity of clear water was measured repeatedly. It is experimentally indicated that under the same pressure, the needed volume of fuzzy-ball workover fluid decreases by 12.3%-60.5% with the increase of the dosage of solid plugging agent and it is obviously in a direct proportion to the dosage of solid plugging agent. After gel breaking, the recovery rate of the flow velocity of clear water in fractures reaches 98%, indicating lower damage degree. The complex plugging technology of fuzzy-ball workover fluid and fiber and that of fuzzy-ball workover fluid and grain were tested in Well S-3X and Well P-2Y, respectively. According to the calculation results, the formation pressure was increased by 26 MPa and 32 MPa, respectively and the consumption of complex system is 30% less than that of single system. In conclusion, the fuzzy-ball workover fluid combined with solid plugging agent can meets the plugging and economic requirements of large-scaled leakage channels in Puguang Gas Field and it expands the application fields of fuzzy-ball fluid.