Classification: Internal Status: Draft

Low Salinity Waterflooding: Opportunities and Challenges for Field Pilot Tests

Dagmar Spangenberg, Peimao Zhang

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Outline

• Introduction

• Lab experiments – overview

• Field experiments – overview

• Mechanisms – discussion

• Snorre – Heidrun – Gullfaks field pilot

• Summary

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Introduction - LowSal history

• 1970s: first IOR observation (SPE 6771)

• 1990s-: studies as a stand-alone IOR method

(SPE…)

• 2004-: field experiments

– Well-Log-Injection - BP (SPE 89379)

– Single well test - BP (SPE93903)

– Field statistics (SPE 109965)

– Field evaluation - BP (SPE 113480)

• 2008: pilot in Endicott (BP)

• 2009: possible pilot tests in Snorre or Heidrun

(StatoilHydro)

• Polymer flooding in Daqing, China

Lab Lab experimentsexperiments

1965-1972

Large scaleLarge scalecommercializationcommercialization

1996

CommercialCommercialfield testfield test

1991

Pilot Pilot field testfield test

1989

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Introduction - LowSal related activities in StatoilHydro

• R&D

– Extensive lab studies

– IOR mechanism

– Modelling tool

• Corporate IOR initiative

– Qualification of LowSal pilot tests

• Assets

– Heidrun

– Snorre

– Gullfaks

– Norne

– Partner operated fields

Snorre

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Lab experiments – overview (1)

• Typical LowSal core flooding performancein lab (Zhang, Xie and Morrow, 2007, SPE)

– Constant rate injection

– Increase in recovery of 5-15% OOIP

– Large PVs injected

– Slight increase in effluent pH

– Significant increase then decrease in ∆P

• The LowSal recovery response, without corresponding increase in pressure drop, is unusual (Loahardjo et al., 2007).

• Very few experiments showed IOR potential without significant changes in ∆P (e.g. Heidrun) SPE 109849

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Lab experiments – overview (2)

• LowSal: necessary conditions (Morrow et al., 1998&1999)

– Sandstone with presence of clays (but: latest findings (SPE 113410) show positive lowsal response without clays)

– Polar organic compounds from crude oil

– Initial water saturation (core floods)

– Brine salinity: 500-5000 ppm

– Salinity contrast between connate water and invading water

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Field Experiment - Well-Log-Injection – 2004

• SPE 89379

• Clastic reservoir, 70-95% quartz, plus kaolinite, plagioclase, illites and smectites

• 3000 ppm low salinity water

• Variation in water saturation with depth shows low salinity achieving higher water saturation and hence better oil recovery

• Top perforated interval

– decrease of remaining oil up to 50%

• Middle and bottom perforation

– decrease of remaining oil 10-20%

SPE 89379

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Field Experiment - BP

• BP Alaska Prudhoe Bay – SPE 93903, 2004

• Single well tests

• Tests in 4 areas, salinity of the water between 1500 and 3000 ppm

• Increased oil recovery between 8 and 19% of OOIP

SPE 93903

• Alaska Journal of Commerce, 21. October 2007

– BP will start early 2008 pilot test Endicott

– Endicott now: 65% oil recovery

– If pilot shows potential → Endicott full field implementation: 75-80% recovery

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Field Observation – Robertson, 2007

• SPE 109965 - Low Salinity Waterflooding to improve oil recovery – historical field evidence

• 3 fields in Wyoming, same formation, crude oil and reservoir temperature very similar, production started in the 70’s and 80’s

(Robertson, SPE 109965)

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Field Observation – Robertson, 2007

• Results corroborate laboratory results of improved recovery from low-salinity floods

• A trend in oil recovery from historical field data was identified with respect to injection water salinity

• Data showed that oil recovery tended to increase as the salinity ratio of the waterflood decreases, which generally means that lower salinity floods tended to have higher oil recoveries

Good statistics?

Salinity contrast is potentially important!

(Robertson, SPE 109965)

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Hypothetic IOR mechanisms

• Hypothetic IOR mechanism proposed in the literature

– Detachment/stripping of mobile fines/clays (Morrow et al, 1999)

– Generation of in-situ surfactants (SPE 93903)

– Multi-component ionic exchange and wettability alteration (SCA2006-36)

– Multicomponent ion exchange that causes reduction in ion binding between the crude oil and the rock surface (Lager et al., Symposium of Improved Oil Recovery, Egypt, 2007)

• StatoilHydro is evaluating different possible IOR mechanisms

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Strategy for qualifying LowSal for implementation

Lab study IOR Mechanism

Success criteria

Field pilots

Upscaling oflab results

Potential evaluation

Well pair selection

Modellingtools

Full fieldimplementation

Economicalevaluation

Fines migration /clay swelling?

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Upscaling Procedure to Estimate the EOR Potential

• Core flood experiments - displacement efficiency

• Pore volumes injected, salinity of the injected water, oil recovery

• Method - tracer simulation

– Tracer study - sweep efficiency

– Results from the core floods and the tracer study give a possibility to estimate the recovery improvement

• Method – relperm curves versus salinity (SPE 102239, ref. BP)

– Two relperm-curves, one with high salinity water injection, one with low salinity water injection

– Include both curves in ECLIPSE with a surfactant option

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Heidrun - Pilot Candidate

• Reverse osmosis plant on the platform

• First lab results from the Upper Tilje and Åre formation show low salinity water injection potential

• Simulation work is ongoing

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Snorre - Pilot Candidate

• Lab experiments ongoing

• Upper Statfjord, lower Stafjord, Lunde Formation

• Simulation work ongoing

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Gullfaks - Pilot Candidate

• Lab experiments ongoing

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Summary – LowSal pilots

• LowSal advantages

– High IOR potential

– Environmentally friendly

– Combination with other recovery methods possible (such as polymers, silicate, alkaline…)

• LowSal challenges

– Upscaling from lab scale to field scale

– LowSal mechanisms not fully understood

– Costs for the production of the low salinity water

– Favourably isolated injector/producer well pair without long distance from each other

– Pore volumes injected

– Danger at too low salinity: formation damage, plugging of the pores

– Composition of the injected water important, proportion between monovalent and divalent ions

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Thank you for your attention