Strong Damage Of Water-sensitive Reservoir Into The Well Fluid And Reservoir Protection Technology Research

Ke Xia formation, located in Wu 33 block of Wu Er He Oilfield, belongs to structural-lithological reservoir. Formation temperature is 35℃. Original reservoir pressure is 11.5MPa and the pressure coefficient is 0.98. Bubble point pressure is 9.3MPa. It belongs to elastic and dissolved gas drive. Porosity assemblages mainly include remaining intergranular pore and dissolution pore. Thus, the reservoir properties of Ke Xia formation are relatively bad. This type of formation has the problem of reservoir sensitivity. What's more, reservoir sensitivity has direct influence on the recovery ratio of low permeability reservoir.After analyzing rock, clay material characteristics and core flooding experiment, we found that Ke Xia formation of Wu 33 block has strong salt sensitivity, middle to strong water sensitivity, middle to strong alkaline sensitivity and has no velocity sensitivity and hydrochloric acid/hydrofluoric acid sensitivity.According to the reservoir sensitivity of Ke Xia formation, the damage mechanism of injection water, fracturing fluid, acidizing fluid, kill fluid and washing fluid have been completely analyzed.The damage mechanisms are shown as follows:Formation will be damaged by water sensitivity which is one of the main damage factors of Wu 33 block.The temperature of Ke Xia formation, located in Wu 33 block, is 35.0℃, which is relatively low. Normal guar fracturing fluid can not breakdown completely at this condition. It will lead to plug the pore throat. Hydrofracturing fluid loss is large and backflow is very difficult due to low reservoir pressure. Hydrofracturing fluid leads the formation to water sensitivity and alkaline sensitivity damage.Under the condition of formation temperature, the flow resistance of kill fluid is very high due to its high viscosity.The density and viscosity of flushing fluid is high and the fluid loss is very large.So, the formation protection plan has been put forward as follows: the newly synthesized SCH-1 has good anti-swelling effectiveness and can reduce the oil/water interfacial tension. Self-generation heat and pressure foam fracturing fluid and Clear fracturing fluid should been used. Novel solid-free well killing fluid and Foam flushing fluid can deduce damage degree.