Formation Mineralogy Affects Scale-Inhibitor Squeeze Designs

Abstract

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 113261, "Formation Mineralogy Impacts Scale-Inhibitor Squeeze Designs," by Rick Gdanski, SPE, Halliburton, originally prepared for the 2008 SPE Europec/EAGE Conference and Exhibition, Rome, 9-12 June. The paper has not been peer reviewed. Scale-inhibitor squeeze designs often are developed using short-core laboratory flow tests for estimating treatment life and fluid/rock compatibility. Laboratory tests provide a relatively high level of successful squeeze designs. However, occasionally, squeeze treatments cause unexpected production loss and have a short squeeze life. The full-length paper discusses how formation mineralogy can improve successful designs of squeeze treatments even before laboratory tests are conducted. A radial model was used to demonstrate key principles of optimizing treatments. Introduction Prevention of formation damage and plugged perforations caused by scaling brines is a common challenge for producing wells. The consequences of uncontrolled scale can be particularly costly in offshore subsea installations. Deposits that can occur in the formation near the wellbore and in the tubulars often are mitigated with scale inhibitors by squeezing them into the formation. It might be expected that there would be an optimum "normalized" squeeze design that would be applicable for nearly all formations. However, this is not the case because of the variation in formation mineralogy. Squeeze designs that work very efficiently at preventing scale in one area may not provide the same performance in another area. Unfortunately, squeeze treatments that show no damaging effects in one formation may show extensive production loss in another. The work described in the full-length paper was conducted to demonstrate a systematic approach to designing scale-inhibitor squeeze treatments on the basis of formation mineralogy, porosity, water-production rate, and minimum inhibitor concentration (MIC). Formation Mineralogy Often, it is tempting simply to consider a sandstone formation as having a generic composition, consisting mostly of quartz with some feldspars, clays, and perhaps some carbonate. However, the specific compositions of the nonquartz mineral groups can be very important in understanding fluid/rock interactions, acidizing challenges, and scale-inhibitor adsorption and desorption. Smectite. Some formations respond poorly to weak brines because of clay swelling. Smectite often exists as a separate mineral. However, it is more often found in the form of mixed-layer (ML) illite-smectite clay. Not all ML clays are swellable, and so a number often is included to indicate the percentage of swellable smectitic layers. As such, ML(35) indicates an ML illite-smectite clay having 35% swellable layers. In general, smectitic clays will begin to swell when the sodium chloride (NaCl) concentration falls below approximately 6%.