Novel Equidensity Particle Agent And Channel Flow Control Mechanism In Fractured-vuggy Carbonate Reservoirs

Fractured-vuggy carbonate reservoirs have abundant reserves.Only the fractured-vuggy reservoirs in Tarim Basin have a reserve of more than 4.8 billion tons.Fractured-vuggy carbonate reservoirs have been the main position for increasing crude oil storage and production in China,which is of great significance for ensuring national energy security.Water injection is the main exploitation method for fractured-vuggy carbonate reservoirs.However,due to complex reservoir structure,variable scales and serious development of dominant flow channels,the response degree of water injection is only 33.4%and the recovery rate is only14.9%.Effective methods are urgently needed to control the development of dominant flow channels and improve the crude oil recovery of carbonate fractured-vuggy reservoirs.Based on the research status of enhanced oil recovery in fractured-vuggy reservoirs at home and abroad and the development of fractured-vuggy reservoirs in Tahe Oilfield,this paper proposes that the channel flow control(CFC)treatment combined with water injection development is the main research direction for enhanced oil recovery in fractured-vuggy reservoirs in the future in view of the development difficulties of dominant flow channels in large-scale high temperature and high salt fractured-vuggy reservoirs.Based on the conditions and geological characteristics of fractured-vuggy carbonate reservoirs,a new equidensity particle agent was developed and its CFC performance was studied.Combining mathematical simulation method and physical simulation method,the regulation mechanism of CFC treatment is clarified,and the mechanism of CFC treatment and enhanced oil recovery in fractured-vuggy reservoir is revealed.A temperature-resistant 120?,salt-resistant 21×10~4 mg/L gel particle type CFC agent and a temperature-resistant 140?,salt-resistant 21×10~4 mg/L composite organic particle type CFC agent have been developed,with controllable density and adjustable particle size of 0.5-6.0 mm.The CFC treatment experiments show that the CFC agent has better oil-water selective control ability under reservoir conditions.Under the reservoir condition of 120?,the injection pressure of gel particle type CFC agent increases 4.7 times after CFC treatement,while the CFC performance decreases 40.4%after encountering oil.Under the reservoir condition of 140?,the injection pressure of compound organic particle CFC agent increases by 19.2 times after CFC treatement,while the CFC performance decreases by 45.3%after encountering oil.In order to carry out industrial popularization and application better,an integrated method of on-line production and injection of CFC agents was established,and the industrial process of CFC treatment was simplified.In this paper,it is clarified that free flow area decrease is the main mechanism for controlling flow capacity of the dominant flow channel.Mathematical simulation and physical simulation show that equidensity is the main controlling factor to realize the deep migration of CFC agent.Equidensity reduces the cave retention of CFC agent from 77.3%-99.8%to 5.8%-22.7%,greatly improving the deep migration capability of CFC agent.Increasing the injection speed and the viscosity of the carrier fluid are beneficial to the deep migration of the CFC agent,while the"vug obstacle"is not conducive to the deep migration of the CFC agent.Blocking at the fracture entrance and accumulation in the fracture are the main ways to realize decreasing free flow area in the fracture.The barrier pressure of blocking at the fracture entrance is 10-20times higher than that before blocking.The accumulation of particles in the fracture reduces the free flow cross-sectional area of the flow passage,forcing the flow velocity in the fracture to decrease.The free flow cross-sectional diameter of the flow passage has a cubic relationship with the flow capacity.Deep flow passage diversion and balanced displacement are the mechanism of CFC treatment and enhanced oil recovery.The results of visual experiments show that the remaining oil shielded by the dominant channel is about 43.7%in the fractured-vuggy carbonate reservoir.The CFC treatment controls the flow capacity of the dominant flow channel through decreasing free flow area in the fracture to realize deep flow passage diversion and balanced displacement.The CFC treatment expand the swept volume of water flooding by 43.8%,and enhance the recovery by 22.2%.Nuclear magnetic resonance experiment results show that CFC treatment can effectively realize the balanced displacement and improve the recovery by 7.0%.Field test results show that the water cut of the main receiving well for CFC treatment is reduced to 6%,and the oil increase exceeds 1500 t,which proves that CFC treatment is the key and future development direction for enhancing oil recovery in fractured-vuggy carbonate reservoirs.