Enhancing Mineral Scale Dissolution in the Near-Wellbore Region

Abstract Mineral scaling in the near-wellbore region of oil wells can cause significant formation damage and have a major impact on well productivity. Removal of scale from the reservoir is usually limited to chemical means, or, if the completion is a cased hole, to re-perforating through the damage. Chemical removal of scale from the reservoir is limited by the contact that can be achieved between the scale deposits and the scale dissolver chemical, and by the volume of chemical which can be injected. In addition, scale deposits can become coated in hydrocarbons, preventing contact between the deposit and the chemical dissolver. Furthermore, owing to the nature of the dissolvers (comprised of chelants and acids), there is the potential for the dissolver to cause formation damage by (i) dissolving cementing minerals thereby generating fines; (ii) swelling authigenic clays; and (iii) forming water blocks. We have developed a proprietary mixture of non-ionic materials which has been shown to enhance the dissolution of both calcium carbonate and barium sulfate scales in porous media (using commercial scale dissolvers in the tests). This chemical, when used as a pre-flush, removes hydrocarbon deposits on the scale surface thus increasing the surface area accessible to the dissolver. In addition, the pre-flush chemical might remediate some aspects of dissolver induced formation damage. In this paper we describe laboratory experiments validating the chemical package.