Analysis of field responses to low-salinity waterflooding in secondary and tertiary mode in Syria
- Hassan Mahani (Shell Intl E&P Co) | Tibi Sorop (Shell) | Dick Jacob Ligthelm (Shell Intl E&P BV) | David Brooks (Shell Intl E&P Co) | Paul Vledder (Syria Shell & AFPC) | Fadwa Mozahem (Al Furat Petroleum Co.) | Younes Ali (Al Furat Petroleum Co.)
- Document ID
- Society of Petroleum Engineers
- SPE EUROPEC/EAGE Annual Conference and Exhibition, 23-26 May, Vienna, Austria
- Publication Date
- Document Type
- Conference Paper
- 2011. Society of Petroleum Engineers
- 5.7.2 Recovery Factors, 5.6.1 Open hole/cased hole log analysis, 5.5 Reservoir Simulation, 2.2.2 Perforating, 5.1.2 Faults and Fracture Characterisation, 5.5.8 History Matching, 6.5.2 Water use, produced water discharge and disposal, 5.3.4 Reduction of Residual Oil Saturation, 4.1.5 Processing Equipment, 5.6.2 Core Analysis, 5.1.5 Geologic Modeling, 4.1.2 Separation and Treating, 5.4.1 Waterflooding, 1.6.9 Coring, Fishing, 4.3.4 Scale, 5.3.2 Multiphase Flow, 5.2 Reservoir Fluid Dynamics, 5.2.1 Phase Behavior and PVT Measurements
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Low-salinity water injection is an emerging IOR/EOR technique, applicable to mixed-to-oil-wet sandstone reservoirs. This paper describes the field response for two large fields: Omar (secondary flood) and Sijan (tertiary flood). The data were analyzed using analytical and numerical modelling tools. This included evaluation of scaling numbers, mixing and dispersion and calibration. Insight was obtained on relevant drive mechanisms.
The responses to low-salinity flooding differ for the two fields:
• In Omar, a dual-step water-cut development was observed, which is characteristic for a change in wetting state. Our interpretation is that in this field, viscous forces provide the dominant drive mechanism, which is favorable to low-salinity flooding. We were able to history match the low-salinity response using a simple conceptual model.
• In Sijan, the low-salinity flood appears to be still immature and breakthrough of low-salinity water has not (yet) been observed. The reasons for the muted response thus far are explored, including a rather strong buoyancy effect caused by the higher permeability of the block, and the significant effect of injectant mixing with the highly saline aquifer.
A proposal is made for a workflow on how to apply this analysis to future low-salinity flooding implementation in field cases.
Low-salinity (LS) waterflooding (in general Designer WaterTM flooding (DWF)) is a novel IOR/EOR technology which has been developed to improve microscopic sweep efficiency with reduction in remaining oil saturation. Low-salinity flooding is defined as injection of a low-saline brine with well-manipulated ionic composition into a sandstone reservoir (with appropriate clay mineralogy such as kaolinite and illite) that contains relatively saline formation water, particularly containing a fair concentration of bivalent cations. LS flooding into mixed-wet to oil-wet reservoirs causes wettability modification towards a more water-wet state.
LS waterflooding is a low-cost, low-CO2 footprint IOR/EOR technology and is operationally (virtually) identical to conventional waterflooding. Additional oil recovery gain from LS water flooding varies depending on the history of water injection in the field and reservoir complexities. Recent field evidences indicate that the estimated incremental oil recovery of LS flooding can be as much as 5-15% of STOIIP in field scale in Syrian fields (Vledder et al. 2010).
Recent publications reporting both laboratory (Boussour et al. 2009, Yousef et al. 2010) and field experiments (Seccombe et al. 2010, Skrettingland et al. 2010) indicate that this technology is gathering momentum in the oil industry. In Shell there is an intensive program to deploy this technology in many potential candidate fields. Spontaneous imbibition and unsteady-state core flow experiments for a number of Syrian oil fields as well as one single-well Log-Inject-Log experiment (Vledder et al. 2010) have shown that LS water may improve on oil production by wettability modification. Consequently, some of these fields may be considered for implementing LS waterflooding. In addition there are other fields, such as Omar and Sijan, in which LS water injection was not originally intended as IOR technique, but rather used due to other operational reasons. Obviously these fields provide a good opportunity to compare the field data with the laboratory results and test the current understanding of the theoretical models used to describe low-salinity.
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