Mineralogical Controls on Inhibitor Adsorption/Desorption in Brent Group Sandstone and Their Importance in Predicting and Extending Field Squeeze Lifetimes

Abstract

The problem of downhole mineral scale formation is most commonly remedied by carrying out scale inhibitor "squeeze" treatments. The success of this process depends on there being an appropriate level of interaction between the scale inhibitor species and the rock formation. This interaction is described by an adsorption isotherm, F(C), in adsorption/desorption type squeeze treatments and the nature of this isotherm governs the dynamics of the inhibitor return profile. The isotherm depends on the factors relating to (i) the chemical species itself e.g. acid phosphonate, phosphinocarboxylic acid, polymer etc.; (ii) the conditions in the fluid e.g. [Ca2+], pH, iron content, temperature etc.; and (iii) the nature of the adsorbing surface i.e. mineralogy, surface charge, wettability etc. In reservoir formations, all of these factors may be important in determining the inhibitor/rock interaction and,, hence, the squeeze lifetime which is defined as the "time" - in days or in terms of produced fluid - that the squeeze lasts before the scale inhibitor concentration falls below the "threshold concentration", Ct, required to inhibit scale in that particular case. In this paper, we focus on the effects of the reservoir mineralogy and surface conditioning of the rock on the squeeze lifetime. Commercial barium sulphate scale inhibitors (acid phosphonate and poly phosphinocarboxylic acid) were tested in core flooding experiments using oil-reconditioned Brent Group Sandstones (North Sea) in order to evaluate their performance prior to field squeeze application. Representative results are presented from an extensive series of phosphonate and poly phosphinocarboxylic acid (PPCA) scale inhibitor core flooding experiments using sandstone cores from different formations within the Brent Group as the adsorbing substrate. In order to isolate the mineralogical effects, results from comparative floods using identically oil-conditioned, clean (highly quartzitic) outcrop sandstone cores are presented. The mineralogy of these cores is described and is found to be significant when inhibitors are being selected for field application. From the experimental work presented, the presence of clay minerals (principally kaolinite) is particularly important because of their influence on the adsorption of inhibitor species. Variation in mineralogy between individual formations within a single reservoir must be addressed prior to inhibitor and core selection so that more appropriate experiments that can support the modelling of field squeeze treatments can be carried out. The results from this experimental work are then used in the computer modelling of the data in order to develop the "Field Squeeze Strategy". An example of this is presented for a field case from the North Sea where the computer predictions were used to design an improved squeeze strategy. These recommendations were implemented by the operator and the subsequent field observations are compared with the design predictions. We find that this experimental/modelling approach can result in extended lifetimes of field squeeze treatments.

Carbon Nanotubes: A New Methodology for Enhanced Squeeze Lifetime CNTs

“…However, it was demonstrated that presence of Ca 2+ plays an important role in adsorption of SI on rock [79]. In addition, kaolinite has been shown to facilitate adsorption of inhibitors onto the rock [80]. It is concluded that PPCA does not have a tendency to react with silica in DW, but on the other hand it has a propensity to bond with CNTs.…”

“…The entire NAST procedure was applied step by step, and results are compared with baseline corefloods using a current standard procedure [80] in which no CNTs were used. Figure 12 illustrates the SI concentration at outlet of cores for standard and NAST coreflood tests.…”

Effect of Produced Sand Particles and Fines on Scale Inhibitor: A Review

“…It has been reported that in adsorption/desorption squeeze treatment applications, the nature of the isotherm depicts the behavior of the inhibitor return profile [75]. Reports have depicted that the nature of adsorption isotherm is influenced by (i) inhibitor species itself, (ii) the formation brine composition and pH, (iii) application pH and temperature, and (iv) the nature of adsorbing surface, i.e., surface charge, reservoir mineralogy, and wettability [62,75]. Bassioni [76] maintained that electrostatic interaction by means of ionpair formation, ion exchange, hydrogen bonding, or complex formation on the surface of formation rock with saturated adsorption plateau gives rise to adsorption.…”

Effect of Produced Sand Particles and Fines on Scale Inhibitor: A Review

“…At equilibrium, the concentration of the solute or adsorbate in the bulk liquid to the concentration of the adsorbate on the solid phase defines the adsorption isotherm (Salvaraju and Pushpavanam, 2009). It has been reported that in adsorption/desorption squeeze treatment applications, the nature of the isotherm depicts the behaviour of the inhibitor return profile (Jordan et al, 1994). Reports have depicted that the nature of adsorption isotherm is influenced by (i) inhibitor species itself, (ii) the formation brine composition and pH, (iii) application pH and temperature and (iv) the nature of adsorbing surface i.e.…”

“…Reports have depicted that the nature of adsorption isotherm is influenced by (i) inhibitor species itself, (ii) the formation brine composition and pH, (iii) application pH and temperature and (iv) the nature of adsorbing surface i.e. surface charge, reservoir mineralogy and wettability (Jordan et al, 1994;Vazquez et al, 2011). Bassioni (2010) maintained that electrostatic interaction by means of ion-pair formation, ion exchange, hydrogen bonding or complex formation on the surface of formation rock with saturated adsorption plateau gives rise to adsorption.…”