Research And Application Of Seawater Blocking Agent

In Chengdao Oilfield which belongs to Shengli Offshore Oil Exploration Company, the reservoir temperature and stratum salinity is 70℃ and 8346 mg/L respectively. Heterogeneity in the reservoir is serious for there are high permeability holes, and the permeability reaches to 8.0462um2, which causes the water influx profile is not uniform and the high water production in production well reaches to 95%. Water shutoff and profile modification are effective measures to enhance oil recovery. For the fresh water is limited in offshore oilfield and the brine salinity is high (30731.15 mg/L), the brine-based selective water shutoff and profile modifier is needed.This paper, according to the selection from the HPAM/AlCit, HPAM/organic phenol aldehyde and Hydrophobic Water-soluble Polymer AP/ organic phenol aldehyde systems, the optimum brine-based selective water shutoff formulation which suits to Chengdao Oilfield is exploited: Hydrophobic Water-soluble Polymer AP is 0.8%, organic phenol aldehyde is 1.2% and the anti-thermal/anti-salinity agent content is 75mg/L. The strength of the water shutoff is grade G, which is middle metamorphous unflowable gel. The gelling time is from 24 to 93 hours and it is changeable. The breakthrough pressure gradient is 37.54 MPa/m. At 70℃, the shutoff is stable in brine or stratum salinity. The parallel core experiments make it clear that the exploited water shutoff can modify water profile effectively, and the enhanced oil recovery rates of high and low permeability reaches to 8.2% and 25.1% respectively.In this paper, in order to discover the laws of affecting the selectivity, the gel selectivity property is studied, such as different gel formulations, core wettability, and water injection rate experiment on selectivity, the oil-riched saturation and core permeability. The experiments results indicate that: the injection pressure curve of water/oil to the heterogeneity models with HPAM/AlCit, HPAM/ organic phenol aldehyde and AP/ organic phenol aldehyde shows the different gel selectivity in different gel formulations, whereas, the AP/ organic phenol aldehyde formulation is the best among them; wettability experiments display the selectivity in water-wetted cores is strongger than the gel in oil-wetted cores; The increasing water injection rate is an disadvantage for the gel to blocking the thief zones according to modeling the water injection course with heterogeneity model; The higher oil saturation in the reservoir, the lower water blocking efficiency will be occurred; In the high permeabilityreservoir, the gel exhibits good selectivity which can prevent water flowing in the big holes and permit oil flowing in the wall.On the basis of the studies above, the water shutoff and profile modification project was designed. After that, the fomulation was used in-situ on the grounds of the geological condition and dynamic exploitation feature of the CBllE-4 injection/production wells in Chengdao Oilfield. The production was increased in three wells from September 2003 to December 2004. And the net increased oil production is 2165 tons since in-situ application was performed.