Chemical divide pathway models have been shown to be useful for delineating the evolution of formation waters and the rock-water interactions of reservoir systems. The physical and chemical processes which formation fluids undergo during production can be modeled by pathway methodology. Since these processes may result in scale formation and formation damage they are of interest to production engineers and geologists. We have developed a pathway of critical divides for the processes involved in the formation of scale minerals accompanying production from sulfate mineral bearing clastic reservoirs.

The critical divides characterizing these processes involve the following: 1) the presence or absence of sulfate bearing minerals within the production fluid contacted volume; 2) the presence of sulfur-rich petroleum; 3) the presence of iron within the formation and production line; 4) the ratio of the concentration of bicarbonate to hydrogen sulfide; 5) the mixing or dilution of the formation waters; 6) the introduction of sulfate-reducing bacteria and 7) the magnitude of pressure and temperature reduction during production. The model qualitatively predicts the liklihood of: sulfate, sulfide and carbonate mineral precipitation and dissolution within the production tubing or the formation. The prediction is based upon the pathway of interactions between production fluids and the reservoir material as well as the insitu geochemical conditions.

This pathway model has been developed from the production histories for Weber sandstone fields and has been applied to anticipated scale problems within the Tensleep and Minnelusa Formations of Wyoming during CO2 treatments. The model indicates that problems of scale formation will potentially be the greatest in the Minnelusa and that scale formation and formation damage due to CO2 injection in the Tensleep will be minimal.

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