Sandstone Acidizing Geochemical Model

Matrix acidizing is among the oldest well stimulation techniques. It is applied to sandstone formations to remove near-wellbore damage, which may have been caused by drilling, completion, production, or workover operations. A routinely used fluid for this purpose is mud acid, which is a mixture of hydrofluoric and hydrochloric acids (HF/HCl) that is capable of dissolving most of the common damaging minerals.Acid treatments do not always improve the well performance. As various minerals dissolve, others may precipitate that can significantly reduce or negate the benefits of acidization. Treatment design becomes a matter of optimization: efficient removal of damaging material balanced against the minimization of secondary precipitation.A number of models provide a theoretical foundation for the design and planning of sandstone acidizing treatments. The two-mineral mode simplifies the reaction chemistry by "lumping" reacting minerals into two groups based on reactivity: fast reacting and slow reacting. This model has been shown to represent well the effluent acid concentrations from short cores at moderate temperature. It does not, however, model precipitation of reaction products. The two-acid three-mineral model have included two additional reactions: the reaction of fluosilicic acid (H₂SiF₆) with aluminosilicates resulting in the precipitation of Si(OH)₄ and the subsequent reaction of the Si(OH)₄ with HF. However, even this two-acid, three-mineral model only considers a small number of reactions compared to the enormous number possible and, in particular, it neglects many important precipitates, such as AlF₃ and K₂SiF₆. So we should establish a new sandstone acidizing models which considers all possible precipitates:The major work are as following:(1) Research the stability of aluminosilicate in hydrochloric acid.(2)In order to understand chemical characteristic of real solution of mud acid, a detail study on the "three reaction" of HF on aluminosilicate during sandstone matrix acidizing has been carried out.(3) Based on the partial local equilibrium assumption (PLEA), establish a new model: geochemical simulator, which allows an arbitrary number of both kinetic and equilibrium reactions involving an arbitrary number of chemical species. Here some chemical reactions are assumed to be in local equilibrium while others are kinetically controlled. Hence, the simulator can account for the effect of flow rates and can be applied to a radial flow system.(4)The traditional models of the permeability response during sandstone acidizing are empirical relationships between permeability and porosity . I presented a permeability model which provides a quantitative connection among bulk physical properties of theinterconnected pore system (e.g., porosity and tortuosity), the statistics of the particle size distribution, and the effects of cementing material on the permeability estimation.