A new method of water control for horizontal wells in heavy oil reservoirs

It is more difficult to control water production in horizontal wells than in vertical wells. It is challenging to predict the water-producing section of a horizontal well and realize staged oil recovery. With water breaking through the oil layer, the water cut of production wells sharply rises. This can even lead to early closure of production wells, which can seriously affect the economic benefits. When researchers explore water control of horizontal wells, they usually use the method of plugging the water-producing section. The success rate is often low due to water flow around the plugged section and pollution of plugging agents in the high-oil saturation area. On the basis of nitrogen for water cresting control, this paper studied the ability of a viscosity reducer (VR) and nitrogen (N2) compound system to inhibit the rise in the water crest. First, a series of two-dimensional quanti-tative experiments and visualization experiments were conducted to study the influence and mechanism of the VR and N2 system in controlling water cresting. The results show that compared to N2 control of water cresting (recovery improved by 2.70%), the compound system greatly improved the water control and oil increase effects of the horizontal well (recovery improved by 26.38%). The VR enters the area with high oil saturation through osmosis to reduce the viscosity of heavy oil and the water-oil mobility ratio. N2 enhanced the osmosis of the VR in the reservoir. In addition, rheological tests were performed of heavy oil mixtures, and the viscosity reduction mechanism of the VR was analyzed via diffusion-ordered spectroscopy (DOSY) and scanning electron microscopy (SEM). The experiment shows that after addition of the VR, the size of heavy oil deposit was reduced and the asphaltene surface was broken. The VR reduced the viscosity of heavy oil by depolymerizing macromolecular aggregates in heavy oil and preventing them from coming together again. Finally, a field test was conducted in a horizontal well, with a cumulative oil increase of 9286.86 bbl. The research results provide an important guiding significance for water control and oil recovery of horizontal wells.