Reservoir heterogeneity, along with the oil to water viscosity ratio, cause fingering and water breakthrough along fractures or higher permeability layers of in water flooding oilfield. This in turn decreases the water sweeping volume and water drive effect, making the medium or lower permeability layers poorly productive or even unproductive. As a result, the production wells will be flooded before due or will have a rapidly increased water-cut. Blocking higher permeable layers with chemical reagents along the flow direction of water can efficiently increase the water-affected volume; adjust productive and absorptive sections of the reservoir. Therefore, the water-cut can be decreased, the oil production can be increased, and the objective of stable oil production and lower water-cut can be achieved. This paper presents the techniques used in a field test project conducted at Daqing Oilfield. Granular gel-polymer was used as blocking agent. Economically improved oil production and reduced water-cut were observed.
According to the geological characteristics and the behavior of reservoirs in north Xingshugang region of Daqing Oilfield, both domestic treatment agents and alien agents were investigated. The physical and chemical capability of agents were also compared and analyzed. In the end, the granular gel-polymer was chosen as the treatment agent.
This kind of granular gel-polymer was formed through a cross-linking system on ground. First of all, gel was formed. Then, the gel was made into particles, dried, smashed, and griddled into gel granules. The gel granules, which exist as dispersed spherical particles in water, have certain characteristic of volume inflation. After being injected into the porous pay zones, the gel granules are deformed and moved towards the producing wells. In formations that are far from the injection wells, the gel particles become stagnant inside the porous and choke the channels of the porous because of the small pressure difference. The stagnancy and choke will convert the flows of injected water. This technique has a very good effect as to solving the defects in the underground cross-linking system such as the difficulties of controlling the formation of gel, the strict range of usage, and the complexities of operational techniques.
The granular gel-polymer has undergone laboratory test and has the following of characteristics:
Granule diameter: There are three kinds of diameters granules. They are 1.5mm, 3mm, and 5mm respectively.
Expansionary multiples: The expansionary multiples are 60~80 times when the granules are combined with injecting water used in Xingshugang region.
Expansionary velocity: The expansion velocity is controlled at 30~60min under the temperature of 45°C.
Brine tolerance: The granules are not influenced by salinity.
Stability: It will neither dehydrate nor gelout within two years under room simulated filed conditions.
The well to be treated is X7–2-F24, which is located in north Xingshugang region in Daqing Oilfield. This well was put into injection in November 1992 and had injected 85.0036×104m3 of water before treatment. There are four production wells around this well as shown in figure 1. They are X 7–1–25, X7–2–23, X7–2–25, X7–2–27, and X7–3–28. All these wells constitute a well group, by which we called X7–2-F24 well group. Figure 2 illustrates the result of voltage logging of X7–2-F24. The injected water mainly flew toward two directions.