A Fast and Information-Rich Test Method for Scale Inhibitor Performance

Abstract

Abstract This paper introduces a new scale inhibitor evaluation technique that has beensuccessfully employed in screening scale inhibitor performance for offshorescale control projects and operations. For example, a sudden and unpredictedincrease in barium sulfate scaling in a seawater injected field required rapidselection of a new scale inhibitor that could inhibit both carbonate andsulfate scaling without dispersed particles. Finding the right inhibitorrequired testing of 24 chemicals, determining the minimum effectiveconcentrations at three different water chemistries to satisfy fieldrequirements. The kinetic turbidity method provided fast and efficientscreening of these inhibitors. The technique employs a spectrophotometer withtemperature control (4°C - 97°C), multi-cell capability, each of the 12 cellsequipped with magnetic stirring. Turbidity is measured at 500nm over a two hourtime period. Use of this technique enabled rapid screening of 24 chemicals in2–3 different water chemistries with effective inhibitors further tested underdynamic tube blocking conditions in 3 months. This enabled timely selection ofscale inhibitor for offshore production. This kinetic turbidity technique notonly provides information on scale inhibitor performance, but also richinformation on scale formation kinetics, inhibition mechanism andinhibitor-brine compatibility. The kinetic turbidity plots for differentinhibition mechanisms and examples of inhibitor screening test results will bepresented. This technique has become a standard method for scale inhibitor screeningproviding rapid assessment of scale inhibitor effectiveness and is used as thefirst line of testing for scale inhibitor selection in our laboratories. It isespecially useful when logistics and time constraint problems occur, which areoften found in offshore production. Introduction Scale and its prevention is a major flow assurance issue for most oilproduction at some time in the life of a producing field. Since effective scaleinhibition depends on many factors including field conditions, pressure andtemperature, water chemistry, whether the field is water flooded, changes inconditions over the life of the field, each field requires testing of scaleinhibitor effectiveness to meet the requirements for effective scale control. Two common testing methodologies are the dynamic tube blocking test (Bazin etal. 2005; NACE International Publication 31105) and the static bottle test(NACE TM0197-2010; NACE TM0374-2007). The dynamic tube blocking test measuresthe effectiveness of scale inhibitors in preventing scale build-up in acapillary tube using a flowing system. The static bottle test measures theeffectiveness of scale inhibitors in preventing general scale formation, whether in bulk phase or on the bottle surface. This is both a visualassessment and measurable by following the water chemistry of the sampletested. The most widely used test method for scale inhibitor evaluation in the industryis static bottle test. Static bottle test is a low cost, quick test to evaluateinhibitor's performance on scale formation control in bulk solution. Procedureof static bottle testing involves mixing synthetic cation and anion solutionsbased on the field's water analysis along with scale inhibitor at differentinhibitor concentrations, incubate samples at temperature for a specifiedlength of time, filter and submit the solution for ion analysis. In this test, multiple samples can be run at the same time.