Phosphonate scale inhibitor adsorption/desorption and the potential for formation damage in reconditioned field core

Scale inhibitor `squeeze' treatments are used extensively to control problems with downhole carbonate and sulphate scale formation. The return curve from an adsorption/desorption squeeze is governed by the inhibitor/rock interaction which, in turn, is described by the adsorption isotherm. Several factors, such as pH, [Ca<sup>2+</sup>], temperature, rock mineralogy etc, affect the adsorption level and the shape of the adsorption isotherm. However, these same factors may also lead to deleterious effects in terms of both formation damage and inhibitor solution effectiveness; the latter effect is referred to in this work as `fluid damage'. In this paper, results and discussion are presented on the potential for formation damage and inhibitor fluid damage when acid phosphonates are applied in clastic reservoir formations. Results are presented from an extensive series of phosphonate (DETPMP) scale inhibitor core flooding experiments using Brent Group (North Sea) sandstone cores as the adsorbing substrate. Careful effluent analysis along with detailed petrography and permeability measurement before and after core flooding are shown to be invaluable in assessing the degree of formation damage (and `fluid damage') arising due to several factors. Most of the points raised here are quite general and they are illustrated by the specific field results. This work therefore contributes to the development of safer field applications of scale inhibitor squeeze treatments in the light of individual reservoir petrography.