Application and Design of Alkaline-Surfactant-Polymer System to Close Well Spacing Pilot Gudong Oilfield
Authors: Wang Chenglong , Wang Baoyu , Cao Xulong , Li Huanchen 
Published: December 2007

Abstract
In order to construct a formula applied to the Close Well Spacing, various surfactants alkali and polymers have been screened by IFT, emulsion screening, chemical consumption and compatibility tests. The effects of both type and concentration of surfactant, alkaline on the feature of IFT, emulsion and oil recovery have been investigated in this paper. The realizable formulation has been proposed after the detailed investigation and applied to the Close Well Spacing pilot. Incremental oil from the pilot is 20667.7 tons and enhanced oil recovery from central well No.7 13.4%(OOIP).Chemical performance from pilot has been presented in this paper.

Introduction
The ASP system used in EOR process is a new technology that has been studied since 1980's. Not only can the IFT be lowered and sweep efficiency be improved, but also chemicals in this system can compensated deficiency that occured in independent system when alkaline, surfactant and polymer are mixed together, Therefore the ASP system has more advantage over the independent chemical flooding. Both interaction between chemicals, activity map and IFT have been investigated since 1980's. The ASP process has been applied to West Kiehl and field performance presented that time was attractive after ASP injected.
Before ASP solution injection, water out in Close Well Spacing pilot, Gudong oilfield was up to 98%. In order to maintain the balance between pilot and oilfield, water has been continuously injected for some three years when water flood test has been completed. Oil recovery from well No. 7 was 54% (OOIP) before ASP flood. Based on the study of IFT, emulsion screening, chemical losses, compatibility etc tests, the ASP system has been designed and applied to Close Well Spacing pilot in August 1992, and completed in February I994.Incremental oil from pilot is 20667.7 tons and oil recovery from central well No. 7 13.4%(OOIP). This practice of ASP process is a good reference to EOR in the stage of very high water cut.

Reservoir data:
Most data of Close Well Spacing pilot was listed in Tab 1. Generally speaking, this reservoir was suitable to ASP flood for its high porosity, permeability and homogeneity. Clay content in unconsolidated sand is 6.4% and montmorillonite in clay 25.5%. Acid number is 3.11mgKOH/g oil which was determined by titration method. Total dissolved solid is 4454 mg/L.
Content of calcium plus magnesium is 92 mg/L. Therefore water quality is good for ASP flood. Well pattern of Close Well Spacing pilot was shown in Fig 1.

Chemical screening in ASP system:
The factors of water quality, chemical interaction and costs, emulsion and IFT have been considered during alkaline and surfactant screening while rheology of polymer solution has been taken account in polymer screening.
Alkaline screening: Normal alkali used in alkaline flood and their emulsion screening results when they were mixed with Gudong oil was listed in Tab 2. We can draw a conclusion that low salinity requirement, which is the salinity that optimum emulsion occured in activity map for, sodium carbonate is the lowest one when the content of cation in alkaline is nearly the same. Because IDS from produced water is only 4454 mg/L as shown in Tab 1, alkaline used in ASP system should be selected the one that needs the lowest salinity requirement according to Nelsons results. We have found that flocculate does occure if we use sodium silicate solution which was made up from Yellow River water when temperature is up to 68 C or more.
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