Possible effects of carbonate content in source rocks on fluid composition and chemical reaction - A preliminary result of simulation

摘要

Simulations of the interaction between formation water,source rocks and reservoir rocks suggest that the carbonate content of the source rock not only influences the chemical reactions in the system,but also affects the overall porosity and permeability of the reservoir rock itself.A great deal of organic acid is produced during the interaction of formation water with the source rocks,but if the source rock contains high amounts of carbonate,that organic acid will first react with the carbonate.This initial and primary interaction results in the consumption of a great deal of the acid;the end results of this consumptive process area a),a significant decrease in the overall amount of organic acid in the source rock's fluid content and b),a corresponding(past-saturation)increase in the detectable quantities of Ca and Sr.When those same depleted fluids are expelled from the source rocks into the reservoir rock,the small and residual amounts of organic acid will have little or no impact in their new environment;the diluted acid content is simply not strong enough to promote the dissolution of aluminosilicate and carbonate.Moreover,Ca and Sr precipitate as carbonate because of the high content of Ca and Sr in the fluid;this also serves to decrease the porosity and permeability of the reservoir rock.