Predicted and Observed Evolution of Produced Brine Compositions, and Implications for Scale Management

Hu, Yisheng; Mackay, Eric James; Ishkov, Oleg; Strachan, Alistair

doi:10.2118/169765-ms

Cited by 2 publications

(1 citation statement)

References 13 publications

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“…The modelled concentration of SO 4 in the produced brine significantly deviates from its pure dilution line, which is abnormal behaviour in sandstone reservoirs where produced SO 4 usually lies close to its pure mixing line, in spite of significant barite precipitation (Houston et al, 2006;Fu et al, 2012;Hu et al., 2014), due to the fact that it is usually in excess. This type of SO 4 depletion is more commonly observed in carbonate reservoirs, such as Ekofisk.…”

Section: Mineral Dissolution and Precipitation Reactions Chemical Equmentioning

confidence: 98%

Analysis of Mineral Reactions Occurring in the Gyda Field Under Seawater Injection with the Help of Geochemical Non-Isothermal Model and Produced Water Data

Hu¹,

Mackay²

2016

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The evidence from the produced brine chemistry suggests that the Gyda field has experienced a variety of geochemical reactions due to the high temperature and initial calcium concentration, and so it is worth reviewing the produced water dataset and studying what in situ geochemical reactions may be taking place.Produced brine chemistry data from 16 wells in the Gyda field are plotted and analysed in combination with general geological information and the reservoir description. A one dimensional reactive transport model is developed to identify the possible geochemical reactions occurring within the reservoir triggered by seawater injection, then extended with the inclusion of thermal modelling and also to be a two dimensional vertical cross section model.Three possible classes of formation water compositions in different regions of the Gyda field have been identified by analysis of the produced water dataset. Anhydrite and barite precipitation are the two dominant mineral reactions taking place deep within the reservoir. Magnesium stripping may be a result of multi-component ion exchange, dolomite precipitation or a combination of both. Reservoir temperature is lowered during cold water injection. The solubility of anhydrite increases at lower temperature, and anhydrite will gradually dissolve in response to the movement of the temperature front, which is much slower than the formation/injection water mixing front. The extent of mineral precipitation within the reservoir can be reduced by the heterogeneity; the modelling shows that the extent of ion stripping caused by mineral reactions in the reservoir is greatest when simulating a single uniform layer. Brine mixing and the occurrence of geochemical reactions due to vertical mixing are not observable, even when assigning a high vertical permeability in a heterogeneous model.Thermal modelling is included to evaluate the effect of non-isothermal processes and heat transport on the geochemical reactions, especially the anhydrite mineral reaction. We have investigated how the difference in horizontal permeability in the two layers affects brine mixing of formation and injection water and geochemical reactions.

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Section: Mineral Dissolution and Precipitation Reactions Chemical Equmentioning

confidence: 98%

Analysis of Mineral Reactions Occurring in the Gyda Field Under Seawater Injection with the Help of Geochemical Non-Isothermal Model and Produced Water Data

Hu¹,

Mackay²

2016

All Days

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Kinetics of in Situ Calcium Magnesium Carbonate Precipitation and the Need for De-Sulphation in Seawater Flooded Carbonate Reservoirs

Al-Behadili,

Makcay

2024

Day 1 Wed, February 21, 2024

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Mixing of incompatible injection and formation brines leads to the deposition of inorganic sulphate scales such as barite, celestite and anhydrite in and around production wells. This process is well documented in seawater-flooded clastic reservoirs. One technique to avoid the resulting formation damage is to remove sulphate from seawater before injection, using nanofiltration; however, this process is costly. This paper identifies that it may not always be necessary in higher temperature carbonate reservoirs. This paper describes the use of reactive transport reservoir simulation to investigate the impact of carbon dioxide partitioning and changes in pH, ionic concentrations and temperature on carbonate reactivity and the sulphate scaling risk in waterflooded carbonate reservoirs. Dissolution and precipitation of calcite, dolomite, gypsum, anhydrite, barite and celestite are all modelled and found to be coupled through (various) common ion effects. The produced brine compositions are used to calculate the saturation ratios and mass of precipitate that may form in the production system. Sensitivity to mineral reaction kinetics, particularly for the dolomite reactions, is accounted for. Results identify that there is a strong relationship between calcite dissolution and dolomite (or other calcium/magnesium carbonate mineral) precipitation reactions, which drive each other and are affected by availability of carbon dioxide in the residual oil phase. This evolves over time and as the thermal front propagates, impacting the concentration of calcium and magnesium in the brines traversing the reservoir. Temperature changes around the injection wellbore impact carbon dioxide and mineral solubilities. The concentration of calcium in the displaced brine mix is thus determined more by contact with rock and temperature than by mixing between injection and formation brines. Depending on location relative to the thermal front, this may lead to gypsum or anhydrite precipitation, thereby stripping sulphate out of the injection brine. Thus, the sulphate scaling risk at the production wells is significantly reduced by this sulphate depletion process: the sulphate is stripped out of the seawater as it warms up in the reservoir, before it mixes extensively with the formation water, and significantly before any mixture of the two brines reaches the production zone. Thus, any loss of permeability is restricted to deep within the reservoir, where the pore volume that can accommodate mineral precipitation is very large. This work identifies that for carbonate reservoirs above 90°C to 100°C, stripping of sulphate due to coupled mineral reactions may reduce or eliminate the need for use of a sulphate reduction plant. The process is modelled for the first time, accounting for the impact of carbon dioxide partitioning and thermal front propagation. Knowledge of the kinetics of calcium/magnesium carbonate precipitation is shown to be critical in predicting the extent of sulphate depletion.

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Predicted and Observed Evolution of Produced Brine Compositions, and Implications for Scale Management

Cited by 2 publications

References 13 publications

Analysis of Mineral Reactions Occurring in the Gyda Field Under Seawater Injection with the Help of Geochemical Non-Isothermal Model and Produced Water Data

Analysis of Mineral Reactions Occurring in the Gyda Field Under Seawater Injection with the Help of Geochemical Non-Isothermal Model and Produced Water Data

Kinetics of in Situ Calcium Magnesium Carbonate Precipitation and the Need for De-Sulphation in Seawater Flooded Carbonate Reservoirs

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