Abstract
This paper presents the findings from the study and application of profile modification in offshore fields and discusses how to select the proper agents and manage the operation for reservoirs with different geological characteristics.
China inner sea-Bohai is one of the most important oil-producing areas in China. The reservoirs are complex with a great variety in geology and properties of rock and oil. Most of them are medium to high permeability heavy oil reservoirs. Because of high viscosity ratio of oil to water and strong heterogeneity of formations, injected water break through quickly along one direction/layer after waterflooding starts. In order to enhance the water sweep efficiency and improve the oil recovery, the study of profile modification from injectors has been conducted since the year of 2003. Through the study and practice for several years, the technology of profile modification for different types of reservoirs has been developed.
There are six main factors affecting the performance of profile modification in offshore fields. First is the available space on platform for the installation of the operational equipment. Second is the type of profile modification agents. Third is the property of formation liquids, specially the salinities of formation and injected water. Fourth is the procedure of applying the technology. For medium to low permeability formations, the concentration of slugs injected should be in the order of: low-medium-high; for high permeability multiple zones, the order should be: high-medium-low. Fifth is the injection rate of the agent (especially for polymer). Sixth is the amount of agent injected.
The application of this technology has improved the performance of waterflooding and played an important role in sustaining oil production in Bohai. Up to date, 53 times of all kinds of profile modifications have been applied and the incremental oil is about 4 MMBO.
