The Research On Protection Technology Of Fractured Carbonate Reservoir In Tarim Basin

The carbonate reservoir is the important reservoir rock, which is 20% of the all sedimentary rock areas in the world and its hydrocarbon reserve volume is the 50% of the all reserve volume of the world. In recent years, the major carbonate oil and gas resources are found in Tarim, Sichuan of China. The carbonate reservoir have many characteristics, such as the more deep buried reservoir, the growing natural fracture, the bad trait and the strong nonuniformity. So the heterogeneous formation is easily damaged, and the damage are hard to ponderate by the lost circulation. The effect of exploratory development is constrainted seriously in these regions. Therefore, relying on the major projects of national science technology, it is urgently necessary to do research on the reservoir protection of fractured carbonate reservoir. In this paper, the fractured carbonate reservoir protection technology is studied in Tarim Basin.The rock properties, the sensitivity of mineral content, reservoir properties, reservoir fluid composition and reservoir sensitivity of the fractured carbonate reservoir were studied, the main damage mechanism of reservoir is revealed, that it show us the main factors which are the invasion into the fractures by drilling fluid, the stress-sensitive, and water-blocking.On account of the special damages of fractured carbonate reservoir, a new damage assessment method of fractured carbonate reservoir is established. Using the new artificial fractured cores and steel mold to evaluate the damage extent on fractured carbonate reservoirs of drilling fluid and the protective effect on fractured carbonate reservoirs of efficient plugging-off drilling fluid.The mechanical theory which is called "stress cage" is applied into the reservoir protection technology, the leakaged mechanism is analyzed, a fractured carbonate reservoir plugging technical method is established. The method is that to form the pressure isolation through the bridge material blocking the cracks, thereby increasing the well wall hoop stress, improving the system bearing capacity and optimizating distribution particle size of the drilling fluid.Based on the damage mechanism of fractured reservoir and plugging technical method, the film former, the anti-water-locking agent and the special fiber blocking agent are selected and invented, the drilling fluid technology of"double membrane"collaborative protection is formed, and it is suitable for the low porosity and low permeability fractured reservoirs. The drilling fluid technology of lost circulation prevention is formed by selecting the the sealing materials.Laboratory evaluation and field test show that the "double membrane" system can quickly form a dense protective barrier to prevent the invasion of solid phase and liquid by drilling fluid, which can block a large pore, different crack width of reservoir effectively. The protective effect of this technology are significant. It is a set of drilling fluid technology on protection of oil and gas reservoir in Tarim Basin. It can meet the requirements of reservoir protection during drilling operations, and provide technical support for marine fractured carbonate reservoir protection technology of home and abroad.