Evaluating Formation Damage Owing to Mineral Precipitation/Dissolution Mechanisms

R. S. Schechter, C. Novak, L. W. Lake

Certain waters are incompatible with the formation rock; that is, precipitates may form owing to rock/fluid interactions. The formation of precipitates may very well lead to formation damage and must, therefore, be avoided if at all possible.

Two distinct mechanisms exist by which the interaction may take place. Ion exchange or ion adsorption may change the injected water composition in such a way that precipitates form. Secondly, the injected fluid may dissolve a mineral that is originally present in the formation with the consequent precipitation of others not originally present.

In this paper, a new mathematical theory describes the precipitation and dissolution process for the cases in which local equilibrium is a valid assumption. The solution of the mathematical problem is shown to predict the existence of well-defined chemical waves, which originate at the well bore and which propagate into the formation as fluid injection is continued.

A new method of solution, which includes a heuristically guided search, is described and several examples relating directly to formation damage are cited. Complex problems involving changes in pH or Eh can be considered and these variables are important, as is the composition of both the fluid and the formation.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.