Researches On Formation Damage Mechanisms And Protective Measures Of Low Permeability Reservoirs Of WeiZhou Area

Low permeability oil fields spread widely in china. According to statistic data, by the ending of 2000 the produced geologic reserves of low permeability oil fields in china is 26.66 × 10~8t, accounting for 25.5% of the total produced reserves. It has great significance to the continuous and stable development of oil industry of china that exploits low permeability oil fields excellently. Because of compacting lithology, low permeability and high flow resistance, low permeability oil fields are sensitive to formation damage and very difficult to exploit, it has become choke point that restrict the exploitation of low permeability oil fields. Thus it is very important for the exploitation of low permeability oil fields that study damage mechanisms of low permeability oil fields and suggest protective measures accordingly.The thesis takes example for low permeability reservoirs of WeiZhou Area (WeiZhou 11-1 oil field in chief), through the systematic study of the basic geologic characters of low permeability reservoirs, analyze the potential damage fountainhead of reservoirs, get the main formation damage mechanisms, and put forward the protective measures.The thesis primarily obtains the following achievements: (1) Through the researches on reservoirs geological characters, the main damage mechanisms of the low permeability reservoirs of WeiZhou Area are water-sensitivity, brine-sensitivity, velocity-sensitivity, water blocking and scaling because of incompatibility between injective-water and formation water; (2) Utilizing the rock and mineral testing technologies for the first time, such as X-ray, SEM, mercury-injection and etc, to analyze the collapse mechanism of brittle shale. According to the analyzing result, it is the main mechanism resulting to wellbore collapse that the water of the drilling fluids invades the shale through the micro-fracture, resulting in swelling of the clay minerals of the shale. and suggest that mix some very fine particles into drilling fluids to plug the micro-fracture, maintaining stability of wellbore; (3) Through the experimental test of formation sensitivity, the degree of various type of formation sensitivity has been acquired, and put forward advise of reservoir protection accordingly; (4)Through dynamic damage experiment the paper choose the drilling fluids system that is appropriate for geologic characters of researching area, evaluate the reservoir's protective effect of the drilling fluids system, provide the beneficial advise for the low permeability reservoirs development of WeiZhou Area.