Petroleum engineers use a variety of flooding agents (seawater, hot water, acids, CO 2, and alkali solutions) to displace fluids and increase production from oil and gas reservoirs. Injected fluid may sweep oil through the reservoir or up the wellbore, or react with formation to increase permeability or wettability, promoting easier oil migration. Unforeseen reactions can counteract any benefit gained from injection. Reservoir Flooding and Stimulation
Occurs when fluids far from chemical equilibrium with sediments and fluid in reservoir are injected into formation. Some minerals will dissolve, others will precipitate as scale. Scale can form in formation, the wellbore, or production tubing. Particularly damaging in immediate vicinity of wellbore. Scaling
Task 1 — Fluid Mixing Mix two fluids in all possible proportions – “flash” diagram. One SO 4 2− rich, the second rich in Ba 2+. Predict scale formation or calculate S.I. of barite in mixture.
Flash Diagram Barite (cm 3 ) Mixing fraction High SO 4 −− High Ba ++
Barite (cm 3 ) Mixing fraction High SO 4 −− High Ba Concentration (mmolal) SO 4 −− Ba ++
Uncheck “precipitation” Disabling Precipitation Config → Iteration…
Mixing fraction High SO 4 −− High Ba ++ Barite saturation (Q/K) Concentration (mmolal) No Precipitation SO 4 −− Ba ++
Scaling occurs when seawater, rich in sulfate, is used as a flooding agent in reservoirs rich in barium and strontium. When the fluids mix, sulfate scale such as barite and celestite form, reducing formation permeability and clogging the wellbore. Case Study: North Sea Basin Oil Fields
Task 2 — Sulfate Scaling In North Sea Oil Fields Mix sulfate-rich seawater with metal rich Miller formation water. Consider relationship between mineral saturation and volume of precipitate.
MillerFortiesAmethystSeawater Na + (mg kg −1 ) K+K Mg Ca Sr Ba Cl − HCO 3 − SO 4 −− T (°C) pH (20 °C) TDS (mg kg −1 ) North Sea Basin Oil Fields
Volume (cm 3 ) Barite Miller Barite Celestite Forties Seawater reacted (kg) Celestite Anhydrite Amethyst
Barite Celestite Anhydrite Celestite Miller Forties Amethyst Barite Seawater reacted (kg) Q/K