Lead sulphide (PbS) is one of ‘exotic’ scales deposited in the oil and gas industry. The inhibition of lead sulfide scale deposition is notoriously difficult compared to calcium carbonate and barium sulphate. In addition, it is extremely difficult to test lead sulfide formation and inhibition in laboratory with the conventional static jar and dynamic loop tests and very little is still understood about its mechanism of formation and inhibition.
In this paper, a novel stress test method has been developed and applied to test the performance and understand mechanisms of lead sulphide inhibition. Compared with the traditional static jar and dynamic loop tests, this test method shows good reproducibility and provides a quick and effective way to evaluate the performance of lead sulphide scale inhibitors.
Typical commercial scale inhibitors, including six phosphonate based scale inhibitors, PPCA, polymaleic acid, polyacrylic acid, polyaspartate, PVS and patented environmentally friendly polyacrylic copolymers have been tested based on this newly developed method. The performance of scale inhibitors on PbS inhibition can be classified as three types:
Type 1: Dispersion inhibitors. These scale inhibitors showed a dispersion effect on PbS formation. The turbidity in stress curve in the presence of these inhibitors is slightly higher than that in the absence of scale inhibitors.
Type 2: Nucleation/growth dominated scale inhibitors. These scale inhibitors inhibit nucleation and growth of PbS formation, where the test can be stressed further in the presence of these inhibitors.
Type 3: Scale inhibitors with poor performance on PbS inhibition. These inhibitors showed less PbS inhibition performance. The turbidity in stress curve did not change obviously in the presence of these scale inhibitors.
This paper will give the comprehensive study of lead sulfide formation and inhibition, which includes development of the test method and scale inhibitors for lead sulphide inhibition.