Coupled Adsorption/Precipitation Experiments: 1. Static Results

Abstract

The mechanism of retention of scale inhibitors (SI) within the reservoir formation is central to a squeeze treatment having a long lifetime. Scale inhibitors are retained within porous media by the two main mechanisms of adsorption (Γ) and precipitation (∏). There is not complete agreement in the literature about when we should use one mechanistic description or another, and indeed both can occur together as coupled adsorption/precipitation (Γ/∏). Previously a general model of coupled (equilibrium) adsorption/precipitation has been derived and the agreement between the model and experiment was very good (Kahrwad et al., 2008). This model was subsequently extended to derive a consistent dynamic coupled Γ/∏ flow model for simulating non-equilibrium (kinetic) coupled processes of any type (Sorbie, 2010). This latter model has not yet been fully validated, but the work in this paper and its companion paper (Paper 2: Ibrahim et al, 2010) provides the type of data required in order to do this. In this paper (Paper 1), new static experimental adsorption/precipitation measurements are presented for two phosphonate inhibitors, DETPMP (a penta-phosphonate) and OMTHP (a hexa-phosphonate) using sand, kaolinite and siderite as the mineral phases. These experiments were carried out at a range of adsorbent mass (m)/ fluid volume (V)/ ratios and it is the "apparent adsorption", Γapp vs. the final scale inhibitor concentration, cf, which is measured and plotted. By observing how the Γapp vs. Cf, curves vary for different values of the (m/V) ratio, this indicates whether we are in the purely adsorbing (Γ) or in the coupled adsorption/precipitation (Γ/∏) regime (Kahrwad et al., 2008). For these static apparent adsorption tests, m = 10g, 20g and 30g samples of each mineral were used (with a fixed volume of SI solution, V = 80ml) to analyse the apparent adsorption behaviour. In addition, related pure precipitation/compatibility tests were carried out in the absence of any minerals in the bulk solutions. The experimental results for both phosphonate scale inhibitors show good agreement with the theory in different regions of pure adsorption and coupled adsorption/precipitation. These results show clearly how such laboratory measurements should be carried out to determine both the levels of SI retention and the precise retention mechanism. This paper characterizes the systems used in subsequent dynamic adsorption/ precipitation sand pack floods which are reported in a related paper (Ibrahim et al., 2012) and which will be used in future to validate fully dynamic coupled Γ/∏ flow models (Sorbie, 2010).

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

“…These calculations illustrate the various model predictions for given assumptions and input data. (Sorbie, 2010).…”

“…The actual governing equation for SI transport with dynamic coupled adsorption/precipitation are presented in Paper I (Sorbie, 2010). Numerically, the solution of the transport equation with the adsorption/precipitation model is achieved via the application of a sequential non-iterative technique (SNIA), sometimes referred to as the operator splitting or time splitting approach.…”

“…The adsorption/precipitation of SI and SI_Ca n complex, under equilibrium or kinetic conditions, is solved once per time step per grid block, after calculating the transport of SI and Ca by advection. A fuller description of the SI transport equations can be found elsewhere (Hong and Shuler, 1988;Sorbie et al, 1992;Malandrino, et al, 1995;Vazquez, et al, 2006;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. In this paper, the static and kinetic coupled model is then further developed by incorporating it into a radial coordinate system, which allows us to explore the effects of coupled adsorption/precipitation of a SI_Ca n complex in field applications.…”

An experimental and modeling study of barite deposition in one-dimensional tubes

“…Sorbie presented a generalized kinetic coupled adsorption/precipitation model (Sorbie 2010(Sorbie , 2012) that is fully dynamic and consistent. This model was validated by experimental work (Ibrahim, 2012). Woods et al (2003) described a mathematical model for one-dimensional flow of injected and formation water in porous media, including mass balance equations for barium cations, sulfate anions and barium sulfate salt molecules.…”