Control of Paraffin Deposition in Production Operations

Abstract

Abstract Significant operating costs are incurred from treatments designed to remove waxy deposits from production tubing or squeeze treatments designed to inhibit wax deposition. The costs are further increased by formation damage and loss of production that may result from these treatments. Our studies show that paraffin deposition can be prevented or greatly retarded by using chemical surfactants known as dispersants. Two specific surfactants were selected that proved to be very effective paraffin dispersants. One is oil soluble and the other is water soluble. These dispersants can be continuously injected into the well or they can be added in larger quantities in a "batch treatment" at specific time intervals. The choice of whether to use batch or continuous treatment is governed by the type and number of wells requiring treatment. Introduction PARAFFIN DEPOSITION PARAFFIN DEPOSITION The mechanism of paraffin deposition and the fact that paraffin wax does come out of solution at the cloud point of the paraffin wax does come out of solution at the cloud point of the wax when present in paraffin base crude oil is well documented. It is also known that the precipitate may or may not adhere to an exposed surface and result in a deposit. Deposits can range from almost pure white paraffin wax to a totally asphaltic material. Most deposits, however, fall somewhere between these two extremes and are composed of a mixture of asphaltic material; solid hydrocarbon waxes; and varying amounts of retained oil, water, sand, silt, metal oxides, sulfates, and carbonates. PROBLEMS CAUSED BY PARAFFIN DEPOSITION PROBLEMS CAUSED BY PARAFFIN DEPOSITION Paraffin deposits collect in well bores, production tubing, Paraffin deposits collect in well bores, production tubing, and flow lines. Under certain conditions paraffin deposition may also occur in the producing formation. The problem caused by these deposits are all related to restricted flow which leads to increased flow line pressure, decreased production, and mechanical problems. These and other problems are also well documented in problems. These and other problems are also well documented in the literature as described by Shock et al., EnDean, Newberry, and Sifferman. METHODS USED TO TREAT PARAFFIN PROBLEMS There are numerous methods used to handle paraffin deposition. These can be divided into the following four categories: a. Mechanical b. Thermal c. Chemical d. Combinations of the above. Mechanical The method of running a scraper which mechanically cuts the deposit from the tubing has been widely utilized. Wire lining tubing and "pigging" flow lines are two examples. Thermal This treatment method normally consists of minimizing radiation heat losses and the addition of external heat to the system. Insulation of flow lines and maintaining a higher pressure in the flow lines which minimize cooling through dissolved gas expansion are two examples of minimizing radiation heat losses. Such procedures as steaming the flow lines, installing bottom-hole heaters, and circulation of hot oil or hot water are examples of the application of heat in an effort to melt or increase the solubility of the deposit. Chemical Control Chemical control, which this paper is based on, falls into the following classes: those in which a solvent is used to dissolve the deposit once it has formed, and those which inhibit wax crystal growth or inhibits its adherence to the tubing wall. 1. Solvents Solvents used for dissolving paraffin deposits generally have a high aromatic content. A variety of solvents, including crude oils, are heated when used. 2. Wax Crystal Modifiers These are polymers which inhibit or alterwax crystal growth.