In this paper, development of a new well treatment method using in situ gelation as well as the pilot test have been presented. The result of the pilot test demonstrated good success in both technical and economic aspects.

For mature oilfields, water cut is normally very high. East part of Shenli oilfield in China is in such category. Water cut of most wells are high than 90%. Some of them are even higher than 95%. That means water flooding efficiency is very lower. Because of employment and economic problems, such oilfield must still keep on operation. In some regions, polymer flooding has been conducted. But it breaks through very quickly. From the break through and other diagnose, it is known that after long time of water flooding, the heterogeneous of the reservoir has been increased, even there are big channels between injection wells and production wells. In order to improve oil recovery in such reservoirs, a injection modification technique has been developed. This method is aimed to shut off big channel near injection wells. By this method, different chemicals were mixed together on the well location. The solution has low viscosity near as injected water. Such solution is pumped into the reservoir by removable pump and close the well 48 hrs for reaction. After reaction, such chemical solution became very strong gel filled in the pores of reservoir. Because during the time of injection, it flew into big channel first. After reaction, big channels has been shut off.

In a pilot test project, 14 injection wells have been treated with this injection modification technique. Reduction of water cut and increase of pressure indicate a good result. It also presented a very good economic benefit for mature oilfield. In this project, the chemical investment was US$. 335,400. Research cost was US$ 96385. Labour cost was US$ 34700.

The total cost was US$ 335422. Increased oil was 34300 Ton. With price of 1250 RMB/t and cost of 443 RMB, the benefit was 24896100 RMB, eg US$ 3 Mill.. From this can be seen that suitable well treatment is very important to mature oilfield. And it can also have obvious benefit.

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