Sweep-Improvement Options for the Daqing Oil Field
- Dongmei Wang (Daqing Research Institute) | Peihui Han (PetroChina Co. Ltd.) | Zhenbo Shao (PetroChina Co. Ltd.) | Weihong Hou (Daqing Oilfield Company Ltd.) | Randall S. Seright (New Mexico Tech)
- Document ID
- Society of Petroleum Engineers
- SPE Reservoir Evaluation & Engineering
- Publication Date
- February 2008
- Document Type
- Journal Paper
- 18 - 26
- 2008. Society of Petroleum Engineers
- 4.3.4 Scale, 5.2.1 Phase Behavior and PVT Measurements, 4.1.2 Separation and Treating, 5.4.10 Microbial Methods, 5.7.2 Recovery Factors, 5.4.1 Waterflooding, 5.4 Enhanced Recovery, 5.4.7 Chemical Flooding Methods (e.g., Polymer, Solvent, Nitrogen, Immiscible CO2, Surfactant, Vapex), 5.1 Reservoir Characterisation, 5.3.4 Reduction of Residual Oil Saturation, 2.5.2 Fracturing Materials (Fluids, Proppant), 5.6.5 Tracers, 5.1.2 Faults and Fracture Characterisation
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This paper investigates the potential of various approaches for improving sweep in parts of the Daqing oil field that have been enhanced-oil-recovery (EOR) targets. Our studies indicated that the polymer flood should have provided excellent sweep throughout the vast majority of the patterns under consideration. However, because alkaline/surfactant/polymer (ASP) flooding is being considered to increase recovery efficiency from the Daqing oil field, mobility control and sweep improvement will be especially important and challenging during implementation of any future ASP process.
Fractures were present in a number of Daqing wells (both injectors and producers). Because the fractures were narrow and far from the wellbore, severe channeling did not occur. On the contrary, fractures near the wellbore aided reservoir sweep. Near-wellbore fractures increased the injectivity index substantially during the injection of polymer solutions and increased oil-productivity index in the production wells. These observations may be valuable during implementation of future floods where very-low-mobility chemical (i.e., ASP) banks must be injected to maintain mobility control.
Several modes of polymer degradation were considered, with mechanical (shear) degradation being of greatest concern. Appropriate use of near-wellbore fractures may mitigate mechanical degradation effectively, as well as improving injectivity.
Several new polymers show potential for cost-effective improvements at Daqing. Increased polymer concentration was also considered. A number of other approaches are (or have been) under investigation, including colloidal dispersion gels, foams, ASP foams, steam, microbes, and polymer solutions prepared with reduced salinity.
Laboratory research began in the 1960s, investigating the potential of EOR processes in the Daqing oil field. The use of polymer flooding was identified as a key method to improve areal and vertical sweep efficiency, as well as providing mobility control (Wang 1995). Consequently, the world's largest polymer flood was implemented at Daqing, beginning in 1996 (Wankui et al. 2000, Wang et al. 2002). By 2004, 22.7% of total production from the Daqing oil field was attributed to polymer flooding. Polymer flooding should boost the ultimate recovery for the field to more than 50% of original oil in place (OOIP), which is 10% OOIP more than from waterflooding.
ASP flooding also has experienced extensive laboratory testing in China. The ASP technique was gradually perfected for application at Daqing and has been pilot tested on a large scale (Wang et al. 1999; Jirui et al. 2001; Wang 2003). Results from two typical pilot tests in the south and north parts of the Daqing field revealed incremental-oil-recovery values as high as 20% OOIP. By the end of 2003, the Center Xinger pilot site showed a definitive increase in oil production and decrease in water cut. In the east area of this site (the largest portion included within the ASP pattern area), the predicted EOR was approximately 18% OOIP more than from waterflooding.
Although field tests of polymer and ASP flooding have been very successful at Daqing, concerns about sweep efficiency persist—particularly the possibility of channeling expensive chemical formulations through the reservoir. Therefore, the sweep efficiency at Daqing is receiving intense scrutiny, and possibilities for improvement are being considered. In this paper, we examine the nature of reservoir sweep in parts of the Daqing oil field that have been EOR targets. We investigate the potential of various approaches for improving sweep. Our objective is to establish better options in the future for improving sweep in the main producing zone.
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