(68a) Introduction to Inorganic Scale in Oil and Gas Production

Scale deposits are undesirable in oil and gas production and can cause simultaneous blockage of the production line and dramatic decrease of yield. Oil and gas field scale formation and control becomes even more important in ultra-high temperature and pressure offshore fields due to the enormous costs of remediation and in unconventional production due to the marginal costs of drilling and operation.  From the reservoir to the surface pressure can change by as much as 20,000 psi, temperature by 300 F, and brine composition by ± 300,000 mg/L TDS due to water evaporation or condensation in low water cut wells.   Sampling and analysis protocols are needed for semi-continuous data collection remotely.  The solubility of calcite and barite at most T, P, and composition values is probably as good as is needed, but for few other scale types are similarly robust understanding available, e.g. halite, iron oxides and sulfides, calcium and strontium sulfate, and silicates.  Beyond descriptive solubility, there is a dearth of nucleation, growth, and dissolution rates at realistic field conditions.  Calcite and barite scale formation are typically prevented by adding milligram per liter of threshold inhibitors, but very little is known about inhibition of most other scale types.  Produced waters are naturally anoxic, but testing scale types formed from redox sensitive elements (mostly iron and sulfur) is rarely accomplished due to the difficulty of conducting experiments with strictly anoxic waters (O₂ <<1 mg/L, ppb).  This presentation will review the state of knowledge in scale formation, equilibrium modeling, a few kinetic results that appear reliable, and present recent lab and field testing at strictly anoxic conditions.  And finally this research will posit a priority list of research needs for economic scale control.