Magnesium Depletion and Impact on Produced Brine Compositions in a Waterflooded Reservoir
- Oleg Ishkov (Heriot-Watt University) | Eric Mackay (Heriot-Watt University) | Myles Jordan (Nalco Champion, An Ecolab Company) | Sarah Blair (Nalco Champion, An Ecolab Company)
- Document ID
- Society of Petroleum Engineers
- SPE International Conference on Oilfield Chemistry, 8-9 April, Galveston, Texas, USA
- Publication Date
- Document Type
- Conference Paper
- 2019. Society of Petroleum Engineers
- squeeze, Waterflood, Produced water, scale, magnesium, brine, geochemistry
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- 76 since 2007
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Produced water composition analysis provides evidence of what geochemical reactions are taking place in the reservoir. This information can be useful for predicting and managing oilfield mineral scale resulting from brine supersaturation.
This paper presents results of a study of the produced brine compositions from three wells in a field operated in the North Sea, with geochemical modelling complementing the analysis. The findings presented in this work provide evidence of magnesium depletion and sulphate retardation in a sandstone reservoir at 130° C.
This adjusted formation water composition was then used for calculations of the injection water fraction in each of the produced water samples. The Reacting Ions Toolkit was used to plot data in a variety of formats, including ion concentration vs. ion concentration, ion concentration vs. injection water fraction and ion concentration vs. time to identify trends and to examine the extent of involvement of the various ions in geochemical reactions.
The breakthrough of sulphate, a component primarily introduced during seawater flooding, was retarded during injection water breakthrough. Observed sulphate concentrations were lower than predicted for the case of brine/brine interactions only. The implication of this sulphate reduction was lower minimum inhibitor concentration required to control scale formation and longer squeeze treatment lifetimes for the operator.
A brine/rock interaction mechanism was proposed that involves magnesium depletion and is reproduced in the reactive transport model. 1D reactive transport modelling was performed to match possible in situ geochemical reactions (precipitation, dissolution, ion exchange) and account for observed ion trends. The model predicts that the process, which is beneficial in terms of reducing the scale risk, is more pronounced at higher temperatures. It has been observed previously that high temperature (130°C) chalk reservoirs may act as natural sulphate reduction plants during seawater flooding, reducing sulphate scaling and souring risks, and so reducing the operating costs (scale squeeze treatment frequency, chemical volumes) of these fields. This work illustrates new evidence of magnesium depletion and sulphate retardation above levels expected for just brine/brine interactions for a 130° C sandstone reservoir with the implication that the geochemical reactions may lead to reduced operating costs (in terms of squeeze treatment volumes and treatment frequencies) in sandstone reservoirs with low carbonate mineral content that are undergoing seawater flooding.
|File Size||3 MB||Number of Pages||29|
Jordan, M.M, Edgerton, M.C, Cole-Hamilton, J and Mackin, K.: "The Application of Wax Divertor to Allow Successful Scale Inhibitor Squeeze Treatment to Sub Sea Horizontal Wells, North Sea Basin," paper SPE 49196 prepared for the SPE Annual Technical Conference and Exhibition, New Orleans, Mississippi, 28-30 September 1998.
Bogaert, P.Berredo, M.C, Toschi, C, Jordan, M.M, Frigo, D.M, Morgenthaler, L, Bryson, B and Afonso, M.: "Scale inhibitor Squeeze Treatments Deployed from an FPSO in Deepwater, Subsea Fields in the Campos Basin", paper SPE 102505, presented at SPE Annual Technical Conference & Exhibition, 24-27 September 2006, San Antonio, Texas, USA.
Wright, R., McCartney, R. A., & Sorhaug, E. (2008, January 1). Predicting The Sulphate Content Of Produced Water In Reservoirs Under Seawater Flood And Containing Calcium-Rich Formation Water. Society of Petroleum Engineers. 10.2118/113974-MS
Ishkov, O., Mackay, E., & Sorbie, K. (2009). Reacting Ions Method To Identify Injected Water Fraction in Produced Brine. SPE International Symposium on Oilfield Chemistry;. 10.2118/121701-MS