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Low Salinity Evaluation in Low Permeable Sandstone Reservoirs with Intermediate Clay ContentNormal access

Authors: E. Hoffmann, R.E. Hincapie and L. Ganzer
Event name: IOR 2019 – 20th European Symposium on Improved Oil Recovery
Session: Turning Resources into Reserves
Publication date: 08 April 2019
DOI: 10.3997/2214-4609.201900102
Organisations: EAGE
Language: English
Info: Extended abstract, PDF ( 1.65Mb )
Price: € 20

Summary:
Within this work, we evaluate the Low Salinity Waterflooding (LSWF) effects in the German Wealden Sandstone (intermediate clay-content). Therefore, we present a comprehensive workflow that combines different experimental approaches to determine LSWF effects in oil mobilization. Experiments included fluid optimization-characterization, spontaneous imbibition and coreflooding evaluations. The workflow comprises the following steps: 1) Detailed fluid optimization/characterization based on typical German reservoir characteristics (including oil samples, brine composition and polymer solutions)-for mobility control-, 2) Routine core analysis (such as porosity, permeability, contact-angle and pore-size distribution), 3) Spontaneous imbibition evaluations for selected fluids -to assess wettability changes-, 4) Investigation of LSWF combined with polymer in coreflooding experiments (monitoring pressure response and mobilized oil vs PV injected), 5) Assessment of Streaming-Potential response for selected cores, to link with the LWSF effects and 6) Cross-checking the acquired data by performing a quantitative and qualitative analysis. Results of this work allowed to validate three main mechanisms out of those reported in literature: 1) Wettability Alteration (contact angle and spontaneous imbibition), 2) Fine Migration (pressure responses along with fine production), and 3) Multi-ion exchange (Streaming-Potential decline). Half of the experiments in secondary-mode depicted a higher Recovery Factor. The less saline brine LSW2 (50-times diluted FW), injected after LSW1 (10-times diluted), did not recover any additional oil. This suggested that a higher reduction in salinity should be aimed for in future investigations. Tertiary-flooding with solely LSWF, showed a lower recovery than tertiary LSWF-PF flooding. This observation confirms the potential of polymer-combined LSWF in sandstones. Streaming-Potential measurements enabled the verification of the multi-ion exchange inside the rock pores during flooding. Results have shown a declining trend in voltage response, indicating the exchange of dissolved ions with the rock surface. Moreover, results of the Spontaneous Imbibition tests refuted the Low Salinity Effect (LSE) in aged cores. On one hand, the immersion in formation water has yielded 3.2% more oil compared to LSW1. On the other hand, in the case of non-aged cores the low saline brine released additional oil. To the best knowledge of the authors, Low Salinity Water Flooding has yet not been investigated in the German Cretaceous Wealden Formation. This investigation provided excellent insights on recovery factor in secondary and tertiary-mode. Tertiary-mode flooding experiments provided clear evidence of the advantages of LSWF-PF. This could yield that the processes -when applied in tandem- become a leading EOR strategy. Moreover, fellow researchers can benefit with the presented data and workflows.


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