Maintaining Injectivity of Disposal Wells: From Water Quality to Formation Permeability

Abstract

Abstract Sustaining injectivity of disposal wells is a challenging task in oil industry because of inconsistent injected water quality and the need to meet disposal capacity of produced water. Disposal water contains large amounts of carry over oil, suspended solids and other associated water treatment chemicals. Such water property will damage near wellbore formation permeability and consequently decline well injectivity as documented by lab and field reported data. An extensive lab work was carried out to: 1) evaluate the effect of water quality on injectivity of disposal wells using reservoir core plugs, and 2) restore injectivity of damaged wells. Parameters such as core permeability and water quality in terms of suspended solids, particle size and oil content were examined at reservoir conditions using coreflood testing. Effect of natural clean up and different chemical treatment systems was also studied. The experimental work included water characterization in terms of geochemical analysis, total suspended solids (TSS), particle size distributions (PDS) and oil content. Solubility and compatibility tests were conducted to assess different cleanup systems. In this paper, water quality guidelines to minimize/prevent formation damage are recommended. In addition, an optimization of conventional chemical treatments for horizontal sandstone water disposal wells is discussed. Based on lab work, a novel chemical treatment was successfully applied to restore injectivity of several damaged disposal wells. This novel treatment reduced the long operation time and cost of a typical treatment practice, while effectively stimulated the well with over two folds increase in well potential and over 70% reduction in treatment cost and operation time.