The Development and Application Offshore of a Direct Test of Well Fluid Scale Inhibition

摘要

Where wells are protected by scale inhibitor squeeze treatments, it is critical that there is an effective means of determining whether the produced fluids are inhibited against scale formation. Conventionally this is achieved by determining the minimum concentration of inhibitor required to prevent scale formation in the laboratory and then taking wellhead samples which are sent to an offsite laboratory for analysis to determine the concentration of inhibitor that they contain. Whilst this method can be an effective monitoring technique for inhibitor concentrations in excess of the minimum inhibitor concentration (MIC), it can introduce risk when wells are close to the MIC owing to the time required to turn around samples. Additional problems arise with poor sample preservation and the often-low frequency of sampling. A more robust approach to managing producing well scale risk is to utilise an on-site test that can be simply performed on freshly taken wellhead samples. The greatest value arises from a test, moreover, that is independent of laboratory determined measures of scale inhibition effectiveness. In this paper we report the development, field validation, and routine application on the Miller Field in the North Sea of a direct test for the degree of scale inhibition exhibited by wellhead samples. The test, as described, relies upon the stressing of samples with excess barium or sulphate ions and the monitoring of turbidity developed in the solution. In contrast to other stress tests that have been reported previously, the test described relies upon simple robust equipment and is straightfoward to perform allowing samples to be taken routinely and monitored in near-real time. The recent introduction of the stress testing technology on the BP operated Miller Field has already provided significant rewards with respect to HSE and scale management in one of the harshest barium sulphate scaling environments in the world.