Abstract

Deposition of asphaltenes in oil wells, pumps, flowlines, pipelines and production facilities can reduce well productivity, damage pumps, restrict or plug flowlines and pipelines and foul production handling facilities. The economic impact of this problem can be very detrimental. Until recently, the conventional way to treat asphaltene deposition was through remediation. Remediation methods include solvent soaks with aromatic solvents and/or aromatic solvents blended with dispersants and physical removal such as wirelining, pigging, hydroblasting, and drilling. These treatment methods attack the problem after it occurs. Until now there has not been an economical method to prevent the deposition of asphaltenes. This paper describes the development of a new asphaltene treatment program that will prevent asphaltene flocculation and deposition onto the near-well bore formation and throughout the production system thus preventing formation damage and system failure.

Introduction

Petroleum asphaltenes are defined as a solubility class of the heavy components in crude oil that are insoluble in a nonpolar solvent such as pentane. They are complex polar macro-cyclic molecules that contain carbon, hydrogen, oxygen and sulfur. Asphaltenes are aromatic and occur in crude oil as stabilized micelles. Resins and maltenes which are the lower molecular weight precursors to asphaltenes, act to stabilize the asphaltene micelles. Here the polar heads of the resins and maltenes surround the asphaltenes while the aliphatic tails extend into the oil. Crudes with high resin and maltene content are more stable. Under stable reservoir conditions the asphaltenes resins, maltenes and the oil are in a thermodynamic equilibrium. When this equilibrium is disturbed and the resins and maltenes are disassociated from the asphaltenes, flocculation of the asphaltenes can occur. The equilibrium can be disturbed when there is a drop in pressure, a temperature change, and/or when the crude is placed under shearing conditions. Chemical factors also can destabilize the equilibrium of asphaltenes in crudes. These chemical factors can come from mixing of incompatible crudes, miscible floods, CO2 floods and acidizing. When flocculation of asphaltenes occurs, the asphaltenes can deposit anywhere in the oil production system. Asphaltenes can deposit in the near-well bore formation, on downhole submersible-pumps, in tubing, in flowlines and in the production handling facility. The most damaging place for asphaltenes to deposit is in the near-well bore area, where the asphaltenes can damage the formation and restrict oil production. Recently a new class of polymeric dispersants was developed that act as asphaltene inhibitors, stabilizing the asphaltenes and preventing flocculation. It is widely believed that these asphaltene inhibitors act in the same manner as the resins and maltenes interacting with the asphaltenes and stabilizing the asphaltene micelles in the crude oil. These asphaltene inhibitors have a stronger association with the asphaltenes than the natural resins and maltenes and are able to stabilize the asphaltenes through greater changes in pressure, temperature, shear and chemical environment. It is important that these asphaltene inhibitors are added to the crude oil before the asphaltenes become destabilized and flocculation occurs.

Conventional asphaltene inhibitor treatment techniques involve continuous treatment by means of a chemical pump at the well head either downhole through a capillary tubing or by a slip-stream. Although these methods are effective at preventing flocculation and deposition of the asphaltenes in the tubing and flowlines, they do nothing to prevent deposition of asphaltenes in the near-well bore area.

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