Research On The Water Blocking Mechanism Of Low Permeability Sandstone Reservoir And Preventing And Controlling Methods In Su-6 Well Block

The gas reservoir of Su-6 well block is a typical low pressure and permeability sandstone reservoir. So far, the gas reservoir is At the middle and final stages of gas field development. There is a serious decline of gas productiom of the reservoir. In order to improve the development effectiveness, through the evaluating formation sensitivity, the two-phase flow experiment and the rock electrical experiment, this paper recognizes and evaluates the major damage factors of the reservoir and its damage degree. The paper systematically and comprehensively studies the water blocking damage process and evaluating methods, and optimizes and selects the drilling fluids of protecting the reservoir. Meanwhile the water blocking control methods were discussed based on the research of the reservoir geological characteristics. The following knowledge and achievements have been primarily obtained:(1) The most serious damage of the reservoir is the water blocking damage, then stress sensitivity, water sensitivity, velocity sensitivity, acid sensitivity and alkali sensitivity. Its damage degree is related to the reservoir types. There exists has a most serious water blocking damage in the reservoir type II.(2) The evaluating results that is get by using of the normalized relative permeability curve is consistent with the core assessment results of water blocking..(3) It is possible for the rock electrical parameters to forecast the water blocking damage degree of H8 and S1 reservoir with logging and APTi water blocking index. The results is consistent with core assessment results. This method is suitable for the reservoir of Su6 well block.(4) The main damage of drilling fluid for the reservoir includes invading of liquid phase,self-absorption of water phase,sensitivity and salt sensitivity, etc. Water blocking effect is the most serious damage for the reservoir;next is the water sensitivity, salt sensitivity, acid and alkali sensitivity damage.(5) Put forward to a set of the polymer drilling fluid which is the low cost, less-damage and no-solid. The formula is as follows:Water+0.5% Low Viscosity CMC+0.2% CJ2-3+0.125% LMJL-2+0.01% Fungicide+0.3% Anti-swelling Agent+0.3% Reverse Wetting Agent+0.05% Na2CO3+1% KCl. (6) Water blocking damage can be removed by increasing the differential pressure, decreasing interfacial tension, dry gas injection, heat treatment, etc. Injecting no-water ethyl alcohol into the layer can decrease interfacial tension. The method has the most obvious effect to remove the water blocking damage of the reservoir type III, next is the reservoir type II and the reservoir type IV.(7) When there is not constant external water invading into the reservoir, invaded external water still will enlarge in the reservoir gradually as the increase of time. However, the water saturation of the reservoir in the invaded area will gradually decrease. Therefore, cutting the invading of external water, the water blocking effect can be weakened.It is significant for the results to improve the development of the reservoir of Su-6 well block and protect the reservoir. And the results provide a new idea for the protection technology of the low-pressure and low-permeability reservoirs.