2. 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

3. 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

4. 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.

5. 0.25.5.751.001.01.1 Flash Diagram Barite (cm 3 ) Mixing fraction High SO 4 −− High Ba ++

6. Barite (cm 3 ) 0.25.5.751.001.01.1 Mixing fraction High SO 4 −− High Ba ++ 0.25.5.751 0 5 10 15 20 25 Concentration (mmolal) SO 4 −− Ba ++

7. Uncheck “precipitation” Disabling Precipitation Config → Iteration…

8. 0.25.5.751 1 10 100 1000 Mixing fraction High SO 4 −− High Ba ++ Barite saturation (Q/K) Concentration (mmolal) No Precipitation 1 0 5 10 15 20 25 SO 4 −− Ba ++

9. 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

10. 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.

11. MillerFortiesAmethystSeawater Na + (mg kg −1 )27 25027 34051 90010 760 K+K+ 1 7303461 100399 Mg ++ 1104692 6401 290 Ca ++ 9952 61516 320411 Sr ++ 1055341 0008 Ba ++ 995235100.01 Cl − 45 15048 753121 55019 350 HCO 3 − 1 98046285142 SO 4 −− 01002 710 T (°C)121968820 pH (20 °C)776.78.1 TDS (mg kg −1 )78 30080 800194 60035 100 North Sea Basin Oil Fields

12. Volume (cm 3 ) 0.1.2.3.4.5 Barite Miller 0.1.2 Barite Celestite Forties 0246810 0.5 1 1.5 2 Seawater reacted (kg) Celestite Anhydrite Amethyst

13. 1 10 100 1000 1 10 100 1000 Barite Celestite 0246810.5.6.8 1 2 3 4 5 6 8 10 Anhydrite Celestite Miller Forties Amethyst Barite Seawater reacted (kg) Q/K