Numerical Simulation of Coupled Adsorption/Precipitation of DETPMP in Carbonate Porous Media

Inorganic scale precipitation is one of the main problems in the industry when incompatible fluids containing ions mix and form solids in the production system. This problem may also occur within the formation causing permeability impairment. Therefore, preventing scale formation, often through the application of scale inhibitors (SI), is very important.

SIs are usually phosphonate or polymeric compounds that have some affinity with the ions that are engaged in scale formation. For example, phosphonates may interact with divalent cations such as Ca2+ and Mg2+, forming complexes. These SI/M2+ complexes are moderately soluble but in higher SI or divalent concentrations they may also precipitate in the formation. This is not necessarily a problem, as this effect has been used in “precipitation squeeze” treatments. Many successful applications of this type have been reported in the literature.

In precipitation squeeze treatments, the retention of SI in the formation is a complex process that is controlled by coupled precipitation(□) and adsorption(□) action of SI molecules in the formation. Previous transport modeling approaches have mostly considered only SI adsorption in the formation although some simulations have been carried out using simple solubility models to describe the precipitation process. Simple solubility functions are not a very reliable or well- validated approach to modeled coupled adsorption/precipitation processes, especially in reactive formations like carbonates.

In this work, an advection/diffusion/reaction transport model is coupled with the DETPMP-brine-carbonate formation, where the full multi-component set of chemical species is included in the reaction and transport model. The full coupled adsorption/precipitation process is also included in the chemical description of the entire process. This complete advection/diffusion transport model is developed for both linear and radial systems based on the finite difference approach. This is coupled with the reaction system that has been reported previously by the authors. The reaction model considers all the reactions occurring in the SI-Brine-Carbonate system including the speciation of SI, complexation of SI with divalent cations, dissolution and precipitation of carbonate, and carbonic system reactions. Also, the equilibrium reaction model considers the adsorption and precipitation in the equilibrium system based on a coupled G/P model which has been presented previously. Finally, the developed model was used to run a sensitivity study on the effect of the adsorption and precipitation of the design and implications of squeeze treatments. Several previously unsuspected results have come of this modeling work which provide a rationale for several of our previously unexplained experimental observations.