PREDICTION OF CaCO3 SCALE UNDER DOWNHOLE CONDITIONS

Abstract

Prediction Of CaCO3 Scale Under Downhole Conditions O.J. Vetter; O.J. Vetter Vetter Research Search for other works by this author on: This Site Google Scholar V. Kandarpa V. Kandarpa Vetter Research Search for other works by this author on: This Site Google Scholar Paper presented at the SPE Oilfield and Geothermal Chemistry Symposium, Stanford, California, May 1980. Paper Number: SPE-8991-MS https://doi.org/10.2118/8991-MS Published: May 28 1980 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Get Permissions Search Site Citation Vetter, O.J., and V. Kandarpa. "Prediction Of CaCO3 Scale Under Downhole Conditions." Paper presented at the SPE Oilfield and Geothermal Chemistry Symposium, Stanford, California, May 1980. doi: https://doi.org/10.2118/8991-MS Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex Search nav search search input Search input auto suggest search filter All ContentAll ProceedingsSociety of Petroleum Engineers (SPE)SPE International Conference on Oilfield Chemistry Search Advanced Search AbstractCaCO3 is one of the most common scales in oilfield and geothermal operations. Various thermodynamic models have been reported in the literature to predict the precipitation of CaCO3. Each of these existing models has its limitation when applied to the real situations of the field operations. Some models (e.g., Stiff-Davis method) ignore many conditions leading to CaCO3 precipitation.In the present paper, we describe a model to predict the CaCO3 scale formation at any location predict the CaCO3 scale formation at any location within the field as a function of water composition, temperature and pressure. This model is based on equilibrium thermodynamics, but uses only the experimentally measured parameters. The input data for the model are (1) one water analysis, (2) one pH measurement at any location in the field, (3) the temperature at which the only field pH measurement is made, (4) the CO2 concentration of the gases (if a gas phase exists upstream or at the point where the liquid sample is taken and the pH is measured), and (5) the amount of flash (if a gas phase exists upstream or at the point of sample collection). The model then takes these measured data and calculates the equilibrium brine composition (including pH) in the reservoir.The calculated brine composition data can then be used either to predict the CaCO3 precipitation for any set of prescribed conditions or to predict the CaCO3 precipitation at various locations within an oilfield or geothermal operation. For a set of temperature and pressure, the model goes through a decision to determine whether a single phase or two phase condition exists for the brine. phase condition exists for the brine. For the case of the existence of the single phase brine, the model calculates the amount of CaCO3 precipitate taking into account the pertinent chemical precipitate taking into account the pertinent chemical reactions involving the various carbonate species.For the case of the existence of two phase brine, the model first computes the CO2 emission and its effect on the pertinent reactions involving the various carbonate species and, hence, calculates the amount of CaCO3 precipitate.IntroductionCalcium carbonate scale (CaCO3) is one of the most common and most annoying scales in oilfield and geothermal operations. As opposed to most other types of common scales (e.g., BaSO4, SrSO4, CaSO4), CaCO3 scale formation requires not only the consideration of pressures, temperatures and water compositions, but pressures, temperatures and water compositions, but also the consideration of the chemical reactions within the brine.As shown in a number of publications, pressure and temperature have an effect on the solubility of sparingly soluble salts leading to the formation of scale. In the case of sulfate scales, a simple change of pressure and/or temperature in a given brine may lead to the precipitation of sulfates which, in turn, can lead to the formation of scale at any given location within field operations. Thus, the normal pressure drop encountered across the sandface in a flowing pressure drop encountered across the sandface in a flowing well (see Figure 1) can lead to the formation of scale and, with that, to a critical decrease of the well productivity. productivity. Within limitations, we can calculate the amount of sulfate scale formed by pressure and temperature changes based on fairly simple thermodynamic correlations. A similar situation is encountered in the case of CaCO3 as long as no carbon dioxide (CO2) escapes from the liquid phase. However, if a two or more phase flow is encountered and if the CO2 distribution between the phases changes with the flow conditions (mainly pressure and temperature), a now and more complex situation is created. The CO2 may travel from the brine phase into the gas or oil phase, thus starting a depletion of the CO2 in the brine. This CO2 depletion leads to critical chemical changes within the brine which, in turn, can lead to accelerated CaCO3 precipitations. It is not unusual that these CaCO3 precipitations critically impair the brine flow inside a well or a surface facility within hours or days. For example, geothermal wells in the Westmorland area can cease to flow within a matter of three or four days. The situation shown in Figure 2 was encountered in the brine flow lines in an East Mesa location. The CaCO3 scale shown in Figure 2 was formed in a 10 inch flow line after a production of approximately 200,000 barrels of brine within approximately 100 hours.P. 155 Keywords: wax remediation, wax inhibition, paraffin remediation, Hydrate Remediation, Artificial Intelligence, Production Chemistry, asphaltene remediation, Upstream Oil & Gas, remediation of hydrates, hydrate inhibition Subjects: Production Chemistry, Metallurgy and Biology, Inhibition and remediation of hydrates, scale, paraffin / wax and asphaltene This content is only available via PDF. 1980. Society of Petroleum Engineers You can access this article if you purchase or spend a download.