Summary Low salinity water injection is an emerging EOR technology, applicable to mixed-to-oil-wet sandstone reservoirs. Flooding with low salinity water causes desorption of petroleum heavy ends from the clays present on the pore wall, resulting in a more waterwet rock surface, a lower remaining oil saturation and higher oil recovery. A secondary flood application is discussed in the Omar field in Syria showing a change of wettability from oil wet to a water-wet system. This change in wettability is supported by the observation of dual steps in watercut development. In between the two steps the watercut was constant. This behaviour is a known indicator of changing wettability. Moreover, direct connate water banking measurements confirm the change. The field observations are supported by spontaneous imbibition experiments in core material and a single well Log-Inject-Log test in an analogue field. From the field observations, the change in wettability is estimated to be nearly complete, leading to an associated incremental recovery of 10–15% of the Stock Tank Oil Initialy In Place (STOIIP). The significance of this work is that this is one of the very few documented proofs of concept on a reservoir scale. Work is ongoing to prove this concept in a tertiary flood as well.

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.

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With an approximate STOIIP of 760 MMbbls, the Omar field is the largest field in Al Furat Petroleum Company's portfolio. The field -located in the Euphrates Graben 45km SE of DeirEzZor -was discovered in 1987 and holds a maximum undersaturated oil column of more than 500m with two original oil-water contacts of 3750 and 3778 meters subsea. The oil production almost exclusively originates from two sandstone formations: the Cretaceous sheet-like shallow marine Lower Rutbah (RUL) and the Triassic coastal fluvial plane Mulussa F (MUF) formation. The Omar Field is formed by an elongated, high relief tilted horst block, which is internally compartmentalised.Originally, the field produced naturally at a peak net oil rate of some 80kbpd but production declined rapidly because of the lack of any pressure support. Following the implementation of water injection from 1991 onwards a plateau production of around 60-70kbopd was achieved for some five years (1994)(1995)(1996)(1997) declining to the current net oil production of 20 kbopd.Despite the structural complications, the injector-producer connectivity in the laterally extensive RUL sands could be established rather confidently and recoveries in excess of 55% should eventually be achievable. Predicting water-flood efficiency in the Mulussa F 3D sand channel labyrinth turned out more complicated. As a matter of fact, it was demonstrated that the resolution achievable by static reservoir modelling was not sufficient to predict the water-flood efficiency meaningfully. As a consequence a statistical infill campaign was launched with a focus to infill the existing major gaps between the MUF wells and secondly to establish a line drive waterflood pattern while investigating the merits of a dense five spot.The results of this infill drilling campaign (executed in 2005-2006) and a new 600-fold high-resolution seismic survey gave a multi-disciplinary team the challenge to improve in identifying more attractive targets while reducing the downside drilling results observed during the infill campaign. A combination of the new structural data with a regional geological well correlation fully and iteratively integrated with dynamic well information and production data, indicates that the recovery in the MUF formation could well be optimized through a more deterministic instead of the previously adopted statistical infill drilling approach.