Scaling problems were identified in a typical tight carbonate gas reservoir. Selecting an effective iron carbonate scale inhibitor in low-permeability (≤ 1 mD), high-temperature, low-pressure, and low water-cut gas wells of this reservoir type can be challenging. The scale treatment strategy focused on the application of a downhole scale inhibitor squeeze treatment as one of the most effective methods for controlling scale deposition from the reservoir to the wells.
The scaling index from the scale prediction work indicated a moderate to high scaling potential for siderite and calcite. This paper concentrates on the selection of a scale inhibitor to inhibit scale formation of siderite and calcite under downhole conditions. The approach used to select the most appropriate scale inhibitor formulation consisted of a series of laboratory screening tests, such as anaerobic dynamic scale loop tests and static compatibility tests.
Based on the testing results, the performance of the selected scale inhibitor was evaluated under anaerobic dynamic conditions at high temperature and high pressure on a dynamic loop rig. The dynamic loop test results provide a low MIC of 5 ppm for the qualified scale inhibitor. Additionally, a coreflood experiment was conducted to evaluate potential formation damage to the limestone reservoir.
The results indicate that the scale inhibitor brine at the tested concentrations did not cause damage to the core. The regained permeability of the core plug was greater than 90% after scale inhibitor injection under the reservoir conditions. The static compatibility tests were also conducted to evaluate 10% scale inhibitor compatibility with the brine as well as the field condensate to confirm that the selected scale inhibitor was fully compatible with the contacting fluids.
The novelty of laboratory testing for the selected scale inhibitor to inhibit iron carbonate scale formation has led to a field trial, and a scale inhibitor squeeze treatment was performed successfully.