At GAMS, we think that geochemical models can be summarized in a limited number of categories. Our products fall into one of the two listed below; following these categories are more detailed model descriptions.

Geochemical Aqueous Equilibrium Models

Equilibrium models calculate static conditions in an aqueous solution. The models estimate the concentrations and activities of all the important aqueous species in a specific water, and calculate the saturation indices for various minerals. These programs have considerable flexibility of input, allowing various corrections to be made for poor or incomplete water analyses, modification of the water chemistry as a result of a user-defined reaction path, or allowing constraints such as gas partial pressure or the presence of a solid phase to control the water chemistry. The strength of these models is based upon their rigorous treatment of the aqueous phase and their ability to modify the fluid composition based on a user-defined process. 

Solmineq.88 pc/shell is this type of program and its capabilities is described at the end of this page.

Geochemical Reaction Path Models

Reaction path models are dynamic mass transfer models for calculating reactions between a fluid and a rock. As the "initial" or "reactant" solids in the rock dissolve into water, the water composition changes and "secondary" or "product" solids may precipitate from or re-dissolve into the liquid. The amount of product solids changes as a function of time until the solid assemblage is in equilibrium with the aqueous phase. The process is monitored as a function of time based on the rate laws assumed for the solids.

GAMSPath is this type of program, and is described next. 


Many geological and industrial processes can be modeled as the result of an isothermal isobaric reaction between an aqueous fluid and solid phases. The reactions are driven by the disequilibrium between the solid phases and fluid, and will continue until equilibrium has been reached. This process redistributes mass in the system among the fluid and solid phases, which may result in the formation of new phases and the complete dissolution of existing phases. GAMSPath makes this type of calculation.

Before mass transfer calculations are initiated, GAMSPath makes a distribution of species calculation. Then GAMSPath simulates the reaction of the fluid with phases not in equilibrium with the fluid. In effect, small amounts of reactant phases are titrated into or from the fluid and the effect on the molality/ activity/ activity coefficient of all the aqueous species determined. GAMSPath also tracks the amount of solvent (water), its activity, the saturation state of minerals and the fugacity of gases. Existing minerals in equilibrium with the solution may precipitate or dissolve, and new minerals may form during this process.

This software is priced $1500 per copy with qualified educational institute pricing of $800.

SOLMINEQ.88 pc/shell





SOLMINEQ.88 pc/shell is a general equilibrium geochemical model, based on SOLMINEQ.88 It was written for DOS but runs under a command prompt in Windows XP and Windows 7, 32 bit versions. PC/SHELL includes a user-friendly interface for program data input and for rapid examination of program output. SOLMINEQ.88 PC/SHELL has many useful options to modify or correct water analyses. Options include boiling, fluid mixing, ion exchange, and a limited mass transfer function. Oil companies, who form the largest group of users, typically use SOLMINEQ.88 PC/SHELL to examine deep formation waters and production waters.

This software is priced $500 per copy with qualified educational institute pricing of $250.