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Importance

Kinetics Of Scale Deposition And Dissolution - Issues Important To Seawater/Brine Injection And Control. Importance. Seawater injection Tolerance of low sulfate seawater (LSSW) Mixing of incompatible brines Brine disposal Efficiency of inhibitors in porous media. State of the Art.

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Importance

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  1. Kinetics Of Scale Deposition And Dissolution - Issues Important To Seawater/Brine Injection And Control

  2. Importance • Seawater injection • Tolerance of low sulfate seawater (LSSW) • Mixing of incompatible brines • Brine disposal • Efficiency of inhibitors in porous media

  3. State of the Art • Kinetics of mineral scale formation is not well understood. • Most kinetics studies are conducted in laboratory systems, synthesized minerals, low ionic strength, and temperature. • Kinetics of mineral deposition and dissolution in porous media at oilfield condition of high temperature, pressure, and salinity has not been studied.

  4. Attachment/Detachment • Four steps to attach or detach • Diffusion in the solution boundary layer adjacent to the surface. • Adsorption-desorption reaction with the solid surface. • Migration on the surface to or from a step edge. • Migration along a step edge to or from a kink. • Mineral dissolution and crystal growth are typically controlled by surface reactions. • Highly dependent on solution and solid conditions, e.g., I, T, pH, particle size, surface defects Morel, Hering 1991, adopted from Nancollas, Reddy

  5. Typical Dissolution/Precipitation Rate Barite Dissolution Rate: Rate(mol/L/sec) = k · A/V·(Ce-C)2 k = 3.6·10-5L2mol-1s-1m-2, 25 C (Liu and Nancollas, 1976) Rate (mol/L/sec) = k· Ce·(1-C/Ce)2 k = 3.2 Lmol-1s-1, 25 ºC (Cheng et al., 1984) Rate (mol/L/sec) = k·A/V·(Ce-C) k = 3.3·10-3 Lm-2s-1, 25 C, (Christy & Putnis 1993) Barite Precipitation Rate: Rate(mol/L/sec) = k · A/V·(C-Ce)2 k = 36-160 L2mol-1s-1m-2, 25 C (Liu and Nancollas, 1976; Christy & Putnis 1993) Dove&Czank, 1995

  6. A B Experimental AEG: 40% Quartz, 40% feldspar, clay 20% calcite, 0.06% Barite LS (Low Sulfate) Brine: 1 m NaCl, 4.55 mm SO42-, 4.03 m HCO3- SW (Seawater): 0.49 mNa+, 0.01 mCa2+, 0.01 m K+, 0.05 m Mg2+, 0.57 m Cl-, 0.029 m SO42-,0.002 m HCO3- Column: 0.5 cm ID, 7.6 and 15 cm L, Porosity~0.35, A/V~ 1000 m2/L AEG LS Brine SW EDTA 210 ºF

  7. Preliminary Testing Protocol • Barite and calcite dissolution kinetics from AEG core by low sulfate brine at 210 ºF. • Barite and calcite precipitation kinetics from AEG core due to seawater flooding at 210 ºF, followed by low sulfate brine. • Barite and calcite dissolution inhibition from AEG core by low sulfate brine in the presence of BHPMP at 171 ºF.

  8. Barite Dissolution from AEG Sulfate Brine, 210 ºF Radius form Center of Well Radius form Center of Well Both barite and calcite dissolution were not affected by flow rate and had reached equilibrium solubility at flow rates equivalent to the flow rates within 1 – 20 ft radius from the center of the well.

  9. Seawater and Low Sulfate Brine Injection Ion exchange of Mg in seawater with solid phase may release Ca into the pore water

  10. Seawater and Low Sulfate Brine Injection Ca in seawater and Ba in pore water are expected to precipitate during seawater injection due to temperature and pore water composition changes

  11. Barite and Calcite SI During seawater and LS brine injection, the pore solution is supersaturated with respect to both calcite and barite, i.e., Kinetics of precipitation is slow.

  12. Flow interrupted overnight Flow interrupted overnight Calcite/Barite Dissolution in the Presence of BHPMP

  13. Dissolution in the Presence of BHPMP - Barite and Calcite SI

  14. Conclusions • A new apparatus to study mineral precipitation/dissolution kinetics in porous media at oilfield condition has been developed. • In the absence of inhibitor, dissolution of barite and calcite is very fast, while precipitation can be kinetically slow at the oilfield condition. • In the presence of inhibitor, dissolution of barite and calcite is not at equilibrium and is not affected by changes in flow rates. • This research can be important to better design scale control strategies for seawater injections, brine mixing and disposal.

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