Coupled Adsorption/Precipitation of Scale Inhibitors: Experimental Results and Modeling

Abstract

Summary In this paper, results are presented on the general mechanisms by which scale inhibitors (SIs) are retained within porous media. There is a generally accepted view that the main two mechanisms of SI retention are "adsorption" and "precipitation," and these are described by different but related modeling approaches in the literature. These approaches have been used quite successfully to model field squeeze treatments. To analyze in a detailed and unambiguous manner where a given retention mechanism (e.g., pure adsorption) or mechanisms (e.g., coupled adsorption and precipitation) are operating requires that we carry out careful laboratory experiments under "field relevant" conditions. In this work, we study adsorption vs. adsorption/ precipitation by performing a series of experiments where we know that the system exhibits either (a) adsorption only or (b) coupled adsorption/precipitation. Experimentally, it is straightforward to determine which regime the system is in. We present the theory describing the coupled adsorption/precipitation process. In addition, an extensive series of experimental adsorption/precipitation measurements is presented for various mineral separates including sand, chlorite, siderite, muscovite, kaolinite, and feldspar. The coupled adsorption/precipitation model is in very good agreement with the experiment.

A General Coupled Kinetic Adsorption/Precipitation Transport Model for Scale Inhibitor Retention in Porous Media: II. Sensitivity Calculations and Field Predictions

“…The possibility that very low concentration levels of [SI] in the return curves are governed by precipitation alone seems very unlikely from these calculations (and this is supported by the experimental results reported elsewhere, Kahrwad et al, 2009);…”

“…The calculations presented here also clarify the roles of adsorption and precipitation mechanisms and how they affect field squeeze return curves. These results (and related experimental work, Kahrwad et al, 2009) show that precipitation is a more important process at higher SI concentrations going over to pure adsorption at lower concentrations. These modeling results indicate how we may then exploit the roles of each of these different mechanisms in the high SI and low SI regimes.…”

“…This process may be described by a solubility product (K sp ) or some other related model and is denoted  in this work (see Paper I; Sorbie 2010). Finally, coupled adsorption/precipitation  refers to when both mechanisms act simultaneously in the SI retention process (Kahrwad et al, 2009 The main purpose of this paper is to describe a range of sensitivity calculations which illustrate both the laboratory and field SI return predictions for coupled adsorption/precipitation processes. A preliminary static equilibrium model was presented previously by Karhwad et al (200) and Part I of this paper (Sorbie, 2010) described how to extend this coupled equilibrium model to a kinetic coupled adsorption/precipitation () model and this is incorporated into a transport code.…”

Mechanistic Investigation of Adsorption Behavior of Two Scale Inhibitors on Carbonate Formations for Application in Squeeze Treatments

“…As a corollary, such results can be used to show directly when we are in the pure adsorption (Γ) and the coupled adsorption/ precipitation (Γ/Π) retention mechanism regimes. 29 Most previous experimental scale inhibitor/mineral adsorption work has studied retention of SIs in sandstone formations, with far less work focusing on retention in carbonate substrates. However, there are an increasing number of field and laboratory studies examining these minerals, such as calcite, limestone, and dolomite, despite the challenges presented by their greater chemical reactivity.…”

Analytical Solutions for a 1D Scale Inhibitor Transport Model with Coupled Adsorption and Precipitation

“…The well is then shut in for a period of time to allow the SI/rock interaction in the pore spaces to reach equilibrium. The SI chemical is retained in the rock formation mainly through two mechanisms: adsorption (denoted Γ ; Trogus et al 1977;Ramirez et al 1980;Sorbie et al 1991Sorbie et al , 1992 and precipitation (denoted Π ; Kahrwad et al 2009;Sorbie 2010Sorbie , 2012Vazquez et al 2010;Zhang et al 2000). Once production is re-started following the shut-in, the SI chemical then desorbs or dissolves into the formation brine at a concentration which is sufficient to prevent the formation of scale crystals.…”