Abstract
Application of scale inhibitors by the formation squeeze technique is a common method for mitigating downhole scale in oil and gas wells. Factors which can adversely affect inhibitor returns include high fluid velocity and high calcium concentrations in the produced water. It has been observed that high calcium levels, particularly at higher temperatures, can suppress inhibitor returns both immediately following the squeeze and thereafter. When coupled with high velocity, wells must be retreated frequently to maintain adequate inhibitor residual concentrations. By increasing inhibitor levels through improved adsorption-desorption properties, squeeze life can be lengthened.
Laboratory data have been reported that polymer/phosphonate combinations can improve both inhibition of calcite and the desorption rate of the phosphonate.1 In the current study, dynamic tube blocking and longer term static scale inhibition tests were conducted against both calcite and barite to evaluate the effectiveness of polymer/phosphonate blends for preventing scale. Flow tests in sandpacks were run to determine dynamic adsorption and desorption characteristics of both polymer and phosphonate from blended formulations. Simultaneous or coadsorption of polymer and phosphonate appeared to be a factor in increasing inhibitor returns.
Data from field squeeze applications show the combination inhibitors provided longer squeeze life compared to phosphonate alone in the presence of calcium concentrations in excess of 10,000 mg/L, at temperatures up to 200F and at near wellbore fluid velocities of 0.01 ft/sec. Field data are presented which are in good agreement with computer modeling results that predict the sensitivity to increased velocity.
