Enhancing Retention Properties of Sulphide Scale Inhibitor for High Pressure and Temperature Environments with High Salinity

With the raising potential for nearly all producing oil wells to sour over time, prevention of sulphide scale is a developing area of focus, specifically in relation to sandstone reservoirs. Market demand has pushed the industry to extract oil and gas from wells with harsher reservoir conditions i.e. high temperatures and pressures (HTHP) containing high saline formation water that is accompanied by a range of scaling issues such as barium sulphate, calcium carbonate (BaSO4 and CaCO3), mixed zinc, lead and iron sulphide (ZnS/PbS/FeS).

Based on laboratory test results, sulphonic-co-maleic acid-based scale inhibitor (SI), FL1-DETA successfully disperses freshly formed ZnS scales at threshold concentration. However, Elgin field trial at HTHPHS (i.e. 196 C, 15000 psi, 292.3 g/L) conditions has shown that the inhibitor suffers from poor retention properties on sandstone reservoirs when applied as a squeeze treatment and has no effect on PbS scale.

By characterising FL1-DETA, the source of its poor retention on sandstone particles was identified and a modified version based on soluble polyaniline structure was synthesised. PSS-co-MA|PANI, showed enhanced adsorption on sandstone with thermal stability up to 385 C. The SI was fully compatible with Elgin production water composition, i.e. [calcium] > 20 g/L, [barium] > (3 g/L, [zinc] >100 g/L and [Pb] > 10 g/L.

Static test results indicate disrupted sulphide scale crystal growth caused by PSS-co-MA-PANI wrapping around ZnS crystals and successful inhibition of BaSO4 and CaCO3 crystals. The minimum effective dose at 125 C and 635 psi were identified as <5 mg/L against ZnS and <100 mg/L against PbS, using dynamic tube blocking tests. Sandpack profiles show pure adsorption and gradual release of the inhibitor at room temperature over more than 200 pore volumes. Therefore, it is anticipated that PSS-co-MA-PANI can perform as a successful squeeze treatment candidate against ZnS with performance against PbS.