A Technology Optimization Study Of Chemical Selective Water Shutoff Agent

Aimed to the characteristic of the Eight Production Plant, such as low abundance of oil reserves,few layers for single well and thin thickness, we study the cationic polymer-based selective chemical water shutoff technology. This technology has developed the craft adaptability of the characteristic. Selective Water shutoff agent is squeezed into the target stratum through the annulus without amemding the pump. The agent reacts with the rock surface, forming chemisorption with the cation group and negative charge on the rock sandstone surface, developing resistance to water and plugging the high water permeability layer.Through the experiment, we determine the cationic polymer-based formula blocking agent which is suited for eight production plants with the improvement of the crosslinking agent system of the blocking agent. The plugging rates of oil layer were lowered but the water layer increase along with an increasing concentration of cationic polymer. Oil layer plugging rate dropped from 35.6% to 15.5% while the plug on the water rate has little effect. The plugging rate was more than 95%. Organic crosslinker gelling time which is controllable range from 6～48h. The gel strength which is also controllable range from 10000～80000mPa.s. And there is nodehydration phenomenon during the whole process. For the first 10 hours, gel still has mobility. Next to the 10～15h, the gel strength changes rapidly. After 15 h, gel has lost mobility. The gel strength change little after 10h with the absence of dehydration phenomenon.With the irreducible water saturation increasing, both the oil layer and water layer plugging value increase. In order to reduce the oil layer plugging value, we adjust the formulation of plugging agent systerm by reducing the polymer cationic concentration and the amount of crosslinker. It can reduce the polymer adsorption ability and gel strength and lows the oil layer plugging rate. With the formation permeability increase, both the oil layer and water layer plugging value decrease correspondingly. Therefore, in order to minimize the plugging value of the low-permeability layer, we select the plugging agent with low intensity. For the high-permeability layer, we can choose the higher gel strength plugging agent to increase the plugging rate.Since 2004, we have implemented chemical water plugging on 61 wells. 56 of these wells have been constructed successfully and 48 of these have effect. Including 33 wells decrease the water production rate but increase the oil production rare, accouting 16.6% of the statistical number. 8 wells did not decrease the water production rate but increase the oil production, accounting 14.6% of statistical number. For the 61 wells implemented chemical water plugging. The success ratio is 85.7%, increasing 5374t oil, decreasing 3866t water, creating 14.4668 million RBM. The investing is 3.439 million RBM and the pure benefit is 11.0278 millom RMB. The ratio between investment and deliver is 1:4.2. It obtains better economic efficiency.