A new EOR method of Crosslinked polymer displacement technology is introduced in this paper. The crosslinked system is based on the reaction of Cr(III) in crosslinker with hydrolysed polyacrylamide(HPAM). After gelation, the system has some character such as good viscoelasticity, good thermal stability, and high salinity resistance. The viscoelasticity of crosslinked system can reach 2–3 times simple polymer solution. As a new system combining profile modification and flooding, it can be applied in high water-cut and severe heterogeneous reservoirs. Because of delayed crosslinking property, it can not only improve profile during injection, but also flow increase volumetric sweep efficiency. Having been injected into reservoir, crosslinking polymer can block and adjust high permeability zones in deep section, and improve sweep volume, and decrease water to oil mobility ration, thereby enhance recovery efficiency.
The pilot is is in BO-19 block in GUDAO oilfield, which is characteristic of positive rhythm deposit, loosed sand cement, high density and high viscosity etc. The reservoir temperature is 73°C, the viscosity of crude oil is 80mPa.s, density is 0.9030g/cm3 at reservoir conditions, permeability is 1000–2000×10-3µm2 and the formation water salinity is 6453mg/L. It has 21 injection wells and 40 production wells, the oil-bearing area is about 2.4km2 and reserve in place is about 737.3×104 tons. From 1999 to 2001, 0.15PV (pore volumes) of crosslinked polymer solution has been injected, and a good effect of increasing oil and decreasing water appears, oil production increases from 201 to 350 tons per day, composite water cut decreases from 91.3% to 84.6%, cumulative incremental oil reached 5.0×104 tons.
Introduction
Gudao is one of the main oilfields in Shengli Petr.Admn.Bureau and characterized by high permeability, high oil viscosity, unconsolidated formation, sand production, and heterogeneous reservoirs, are now at special high water cut development stage. New technologys are needed to improve recovery of this kind of oilfield.
A new system of crosslinked polymer for profile modification and flooding technology was developed in Shengli oilfield as the first in China in the late 1980s. With gellant concentration lower or similar to polymer system for flooding and low concentration of delayed crosslinker, the system has a great improvement in viscosity, thermal stability and salinity resistance when crosslinked. Injected into formation it can increase the resistance factor and residual resistance factor of the formation. Heterogeneous conditions of oil reservoir and profile control can be improved when a great bulk of solution enters reservoir, and then flooding fluid can change its path and increase sweep volume. In the meantime weakly crosslinking and uncrosslinking polymer solution can displace oil when injecting crosslinking polymer solution.
Laboratory study on optimization of rosslinked polymer system
Development of Crosslinker. Polymer crosslinker commonly used at present are aluminium citrate, organic chromium and phenolic system, etc. Evaluation of performance of those systems shows that all the crosslinking systems listed above possess delayed crosslinking performance (refer to table 1).However aluminium citrate crosslinked gel has low strength and thermal stability and so small applicable reservoir type. The costs of chromium propylene acetate and phenolic system are too high. In addition crosslinking condition of these all the
