The Fuyu fractured sandstone reservoir is characterized by low permeability and medium high crude viscosity. There is insufficient natural energy because of its shallow depth of burial. The field was put into development in 1970 under solution gas drive. Water injection was started in 1973 and an overall adjustment of the development program was made in 1982.
The following methods have been used successfully according to the geologic features of the field as well as the problems occurring during development:
To supply more energy by active water injection.
The rapid decline of the production and reservoir pressure under solution gas drive has been stopped and gradually restored.
Well-developed vertical fractures and horizontal bedding in the overlying shales result in a good permeable zone. Under high injection pressures, water runs from the reservoir formation into these layers and causes swelling of the clay minerals in them, so that a lot of casing damage occured with a serious effect on the production of the field. Thus it is important to control injection pressure and to take comprehensive measures to eliminate the casing damage. Good results have been obtained.
The data from non-invasion cores and from newly drilled wells have been used to study the status of water flooding, the reserves affected by current status development program and the distribution of the remaining oil in the reservior. Based on such a study, the adjustment wells are located in the areas where the majority of the remaining oil exists. The zones with medium and low Water cut have been perforated for production, thus more reserves will be put into water drive production.
According to the characteristics of fracture development in the reservoir, a linear injection pattern has been used to restore the reservoir pressure and to prevent water channeling through fractures. Good results have been achieved.