Chemical Removal of Organic Foulants from Produced Water Recycled as Steam (2002)

Chemical Removal of Organic Foulants from Produced Water Recycled as Steam Paul R. Hart Paul R. Hart Baker Petrolite Co. Search for other works by this author on: This Site Google Scholar Paper presented at the SPE International Thermal Operations and Heavy Oil Symposium and International Horizontal Well Technology Conference, Calgary, Alberta, Canada, November 2002. Paper Number: SPE-78966-MS https://doi.org/10.2118/78966-MS Published: November 04 2002 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Get Permissions Search Site Citation Hart, Paul R. "Chemical Removal of Organic Foulants from Produced Water Recycled as Steam." Paper presented at the SPE International Thermal Operations and Heavy Oil Symposium and International Horizontal Well Technology Conference, Calgary, Alberta, Canada, November 2002. doi: https://doi.org/10.2118/78966-MS Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAll ProceedingsSociety of Petroleum Engineers (SPE)SPE International Thermal Operations and Heavy Oil Symposium Search Advanced Search AbstractA limitation on the use of produced water as steam to assist oil recovery by gravity drainage (SAGD) from oilsands is the presence in the water of boiler foulants. Ordinary water clarification treatments were found to leave behind certain classes of organics that shorten boiler cycle times. Using molecular probes to compare produced water from SAGD processes having different rates of boiler fouling, an unstable class of organic colloid was identified, and a new chemical treatment developed to remove it.IntroductionThe Steam Assisted Gravity Drainage (SAGD) process recovers bitumen from underground oilsands in the Athabasca region of Alberta, Canada. Steam injected into the oilsand formation liberates oil (bitumen) and condenses into an oil rich, reverse (oil-in-water) emulsion. The emulsion is withdrawn and the bitumen and water separated. The produced water is then reheated back to steam and reinjected into the producing zone to continue the process. The blowdown from the steam generator has been put to disposal wells, but to protect the environment, future discharge must be minimized.Reducing the disposal of produced water necessitates increasing its recycle. This concentrates the dissolved salts and facilitates their precipitation by evaporation of the remaining water. The recycle also, however, increases the water's organic content, both dissolved and suspended. The increased levels of organics accelerate organic fouling of the steam generators and crystallizer (evaporator) residue. Dealing with this fouling is troublesome and expensive in terms of money, labor, and lost production.This study compares the incidence of boiler fouling to boiler feed composition at two SAGD facilities, one substantially recycling its boiler blowdown, the other recycling none. The boiler feed water and the production and process waters leading up to it were characterized by their responsiveness to a set of chemical reagents designed to measure the stability of suspended organic matter.Theory and DefinitionsOrganics in produced water can be divided into two classes: dissolved or soluble and suspended or emulsified. Molecules that are individually surrounded by water molecules are truly dissolved. Large groups of molecules individually surrounded by each other but as a group surrounded by water molecules are clearly emulsified. Small groups of molecules, though technically emulsified, behave in some ways like solutions and are often given the special status of colloidal solutions or microemulsions. Molecular aggregates smaller than 1 µm are generally considered colloidal though they might contain a billion molecules. For example, 100 million cetane molecules create a 0.2 µm (200 nm) diameter particle, smaller than the wavelength of visible light and therefore nonreflective, invisible even at high concentration.Organic compounds which are truly water soluble (WSOs) at a given temperature are generally even more soluble at higher temperatures. Exceptions include unchelated Fe and Ca salts of carboxylates, which have poor solubility and tend instead to be colloidal. Colloids and emulsions in general are typically destabilized and precipitated by higher temperatures, as well as by lower temperatures.Emulsion Properties.Whereas truly dissolved organics must be desolubilized stoichiometrically (eg by reaction or adsorption) in order to be removed, suspended organics can be flocculated en masse. This is a far more efficient intervention, as it involves interacting only with the surface of the particles. Only 1 out of every 3000 or so molecules of cetane would be on the surface of a 100 µm droplet. Thus, 3000 ppm of such oil particles can be removed with a mere 1 ppm of the right surface active flocculant. That is the magic of water clarification, how so little can do so much. But as the particle size drops, the surface area of a given volume increases proportionally. So 1 m droplets of the same 3000 ppm oil would require 100 ppm flocculant and 0.1 µm droplets would require 1000 ppm flocculant.Emulsion Properties.Whereas truly dissolved organics must be desolubilized stoichiometrically (eg by reaction or adsorption) in order to be removed, suspended organics can be flocculated en masse. This is a far more efficient intervention, as it involves interacting only with the surface of the particles. Only 1 out of every 3000 or so molecules of cetane would be on the surface of a 100 µm droplet. Thus, 3000 ppm of such oil particles can be removed with a mere 1 ppm of the right surface active flocculant. That is the magic of water clarification, how so little can do so much. But as the particle size drops, the surface area of a given volume increases proportionally. So 1 m droplets of the same 3000 ppm oil would require 100 ppm flocculant and 0.1 µm droplets would require 1000 ppm flocculant. Keywords: polymer, bitumen, boiler blowdown, fraction, ppm active, deposit, flocculant, emulsion, clarifier, blowdown Subjects: Improved and Enhanced Recovery, Unconventional and Complex Reservoirs, Environment, Oil sand, oil shale, bitumen, Water use, produced water discharge and disposal This content is only available via PDF. 2002. SPE/PS-CIM/CHOA International Thermal Operations and Heavy Oil Symposium and International Horizontal Well Technology Conference You can access this article if you purchase or spend a download.