Scale Formation During Alkaline Flooding

Abstract

Summary Alkaline chemicals in enhanced recovery operations are used (1) as preflush agents, (2) with polymers and surfactants, and (3) as a principal recovery agent. In these chemical flooding techniques, the precipitation reactions of multivalent hardness ions with alkalis are of particular concern. These reactions may be prevented at the injection wells through adequate preflushing and/or the use of good-quality softened water; filtration can remove any precipitates that form at the surface. In the formation, precipitates that form at the surface. In the formation, many reactions occur that alter the injected slug significantly. Those include dissolution, mixing, neutralization, and ion exchange. Such reactions may lead to beneficial fluid diversion as precipitates form and block high-flow channels. At the producing wells, however, precipitation and deposition phenomena are undesirable because scales may form that restrict production and foul well equipment. With the current higher production and foul well equipment. With the current higher concentrations of alkali being used in the field, the development of well scaling has become noticeable and difficult to control by previously accepted practices. This paper describes the progress and experience gained at the Long Beach Unit, Wilmington, CA, alkaline pilot dealing with scales formed in producing wells. These scales have been made up variously of calcium carbonate, magnesium silicate, and amorphous silica. In particular, the reservoir characteristics and chemical conditions leading to the scale formation are discussed in detail, showing what, how, and why the scale forms. For the Wilmington alkaline pilot, the cause appears to be the mixing of very hard waters from one subzone with moderately alkaline water from other subzones. This mixing and the dissolution of formation solids by the alkali have led to scale formation in the producers closest to the injectors. producers closest to the injectors. A few general scale inhibitor formulations, useful for both formation squeeze treatments and continuous sidestream annular injection, have been effective in controlling the carbonate scale under laboratory and field conditions. However, the physical environment and mechanical limitations in the field have resulted in a new deposit, consisting mainly of amorphous silica, against which the current inhibitor systems am ineffective. We suggest field procedures for dealing with such a situation. It is anticipated that the use of appropriate chemicals and methods can lead to cost-effective scale control. Introduction Them is a large body of literature on alkaline flooding and its variations. However, few authors consider associated scale phenomena at the production wells or in laboratory studies, although it is well known that alkaline chemicals react with reservoir rock and fluids to produce precipitates. Mungan mentions briefly that produce precipitates. Mungan mentions briefly that plugging and scaling were noted in some field-test plugging and scaling were noted in some field-test production wells but gives no details. Raimondi et al. production wells but gives no details. Raimondi et al. describing a sodium hydroxide pilot in the North Ward-Estes field, observed increased gypsum scale formation in producers. This reservoir has a high gypsum content. However, no treatment was discussed. The authors also noted an increase in silica content at the producers but did not detect an accompanying increase in pH value or decrease in hardness levels in the produced fluids. The alkaline slug was believed to have been completely consumed by inaction with gypsum. In a field test at the Trekhozernoye deposit in Russia, fluid-flow diversion was reported because of swelling and migrating clays and precipitation of calcium and magnesium carbonates. The produced fluids showed a decrease in Ca++ ion with subsequent increases in HCO3 - ion. In laboratory tests evaluating alkaline flooding for an Alberta reservoir, Novosad and McCaffrey reported a white precipitate in the coreflood effluents that added to the alkali consumption. They also noted that silicates are more effective at precipitation divalent metal ions. Sydansk observed the formation of new, highly hydrated alumina-silicate precipitates in alkaline com tests; these have lower silica/alumina ratios than the original formation clays. Carbonate minerals in the core dissolved first, leading to accelerated alkaline consumption. Significant amounts of silica were dissolved from the rock matrix at elevated temperatures. A number of other studies show that alkalis react strongly with the various reservoir-rock constituents. These inactions can produce very complex ionic effluents downstream in both laboratory com tests and field production wells. Ehrlich and Wygal studied the caustic consumption of a number of clays and minerals in an attempt to quantify the contribution of each to the overall consumption. More recently, this quantification has been extended by Mohnot et al. Holm and Robertson studied the effect of various preflush agents, including alkaline silicates on divalent ion exchange in surfactant flooding. JPT P. 1466

Application of nanofluid to control fines migration to improve the performance of low salinity water flooding and alkaline flooding

“…In this technique alkali can be utilized (1) as a pre-flush slug (2) in conjunction with polymer and surfactants (3) as a major recovery agent. Injection of an alkaline pre-flush agent can lead to precipitate hardness ions and in turn, precondition the reservoir to accept the surfactant; therefore, the surfactant can be protected from precipitation which in turn improves the efficiency of the surfactant flooding (French and Burchfield, 1990;Holm and Robertson, 1981;Krumrine et al, 1985). Furthermore, the alkali utilized in alkaline/polymer (AP) injection and alkaline/surfactant/polymer (ASP) flood can enhance the efficiency of polymer flooding projects.…”

“…In an alkaline flood the pH of the reservoir environment can be significantly altered ranging from 13.5 to near 7.0 (Krumrine et al, 1985). This high-pH environment can alter the charge density of the medium surface toward more negative values; consequently, in-situ soaps can be formed due to reaction of alkali with naphthenic acids in crude oil (Ehrlich and Wygal, 1977;Kazempour et al, 2012;Liu et al, 2008).…”

“…Very high alkaline environment may result to form intractable scales or precipitates which can block the pore throats and in turn decline the productivity index (Krumrine et al, 1985). Alkaline chemicals can also disturb the interactions existing between clays and the medium surface resulting fines migration and/or clay swelling which in turn result in severe permeability impairment (Krumrine et al, 1985;Somerton and Radke, 1983).…”

“…Alkaline chemicals can also disturb the interactions existing between clays and the medium surface resulting fines migration and/or clay swelling which in turn result in severe permeability impairment (Krumrine et al, 1985;Somerton and Radke, 1983). It is worth mentioning that the resultant surface forces between a negatively charged fine particle and the medium surface at the pH values greater than point of zero charge (PZC) seems to be dominantly repulsive resulting particles detachment and migration.…”

Synthesis of didodecylmethyl hydroxyl sulfobetaine and its evaluation for alkali-free flooding

“…Strong alkali such as NaOH and NaSiO 4 could cause permeability reduction and formation damage (Bagci et al 2000). Scaling formation is another disadvantage of flood using the conventional alkalis, which often leads to the shortening of pump detection period (Krumrine et al 1985;Cheng et al 2008). A new alkali, sodium metaborate, was reported that no scaling formed, but it could decrease the viscosity of polymer (Flaaten et al2010;Hou et al 2005), and was not a good option for brines with high bicarbonate and sulfate concentrations (Gupta et al 2009).…”