SZ361 is an offshore oilfield in China. It is characterized by thick oil layers, high permeability contrast, high oil viscosity and high water salinity. All injection wells were completed by liner gravel-packing. The oilfield has been developed since 1993. Water cut of some production wells is above 90%. To control water conformance, a large volume of weak gel treatment was proposed. Based on the specific features of offshore oilfields, such as small space of platform, high salinity on injection water, a new weak gel was developed. This paper introduced the properties of each composition of the gelation and the effect of each composition on gel properties. The salinity and temperature on the thermal stability of gel were evaluated. The plugging efficiency of the gel was carried out on different permeability cores. Results show that the selected polymer and cross-linkers can be well dispersed and solved within 30 minutes when mixing with sea water or produced water. The gelation time can be controlled by adjusting compositions of gellant. The novel gel can be applied in the reservoirs with a temperature range of 30–70 °C and salinity below 40,000 mg/l. The residual resistance factor of the gel is above 10 for the cores with permeability from 0.5 to 12 μm2. The gel was piloted in one injection well in SZ361 oilfield and an economically efficient result was obtained. The pilot was introduced in details to show how to well select well candidate and operate gellant injection process so that a better placement can be attained.
After years of research, the technique of profile modification has been successfully used in China's oilfields on land and has been becoming one of the key techniques which can effectively improve the development of mature fields with high heterogeneity and high water cut. Offshore oilfields usually have unique production conditions and techniques, such as liner gravel-packing, lack of fresh water, limited space on platforms and high requirements on environment. Though much experience of profile modification in onshore oilfields has been accumulated and the technique itself is mature, it can't be easily copied and applied in offshore oilfields. A new profile modification agent, which is characterized by fast dissolving, tolerance of salt and simple operation of injection, has been specially developed to fit suit the conditions of Suizhong36–1 oilfield.
Suizhong36–1 oilfield, located in Liaodong Gulf of Bohai Sea, is a large offshore sandstone heavy oil field. Depth of the reservoir is between 1400 and 1600 m and reservoir temperature is about 65 °?C. Initial reservoir pressure is 14.28MPa. The oilfield has been developed since 1993 and water injection began in 1995. At present, there are 4 platforms and 64 wells in the oilfields. Among these, there are 13 water injection ells(Fig.1). Both production and water injection wells were completed by liner gravel-packing. Injection pressure is between 4 and 5MPa.
For well group of A21 which was chosen to have the treatment of profile modification, daily water-injection rate averages 711m3. Average water cut is approximately 50% and water cut of some wells reaches 90%.
