Abstract Asphaltene plugging is one of the most frequent causes of production depletion in medium and light crude oil reservoirs, especially when the pressure declines due to its exploitation. Other physicochemical phenomena, like intrinsic instability of the produced crude oil, incompatibility between "commingled" produced oils, between streams entering the flow stations, as well as inadequate stimulation procedure, can be responsible for asphaltene deposition during crude oil production and transportation, going from the reservoir to surface facilities.
Asphaltenes precipitation is one of the major operational problems affecting production in the Höflein field northwest Vienna. The deposits were responsible for plugging the coalescing filters, which are designed to dehydrate down to 5 ppm of suspended water. Asphaltene deposition is also blamed for prolonging the annual summer stopover, which is proposed for general maintenance on Korneuburg facilities.
The purpose of this work is to show the application of a systematic technique for detecting the onset of asphaltene flocculation under various pressure and temperature conditions as well as for selection and evaluation of chemical inhibitors in the field Höflein. The results allowed defining the asphaltene deposition envelope (ADE) as well as selecting the best inhibitor evaluated under production facility conditions. In addition, the characteristics of this phenomenon as well as the problems associated with it have been highlighted.
Introduction Heavy organic deposition "especially asphaltenes" during production and processing is a very serious problem in many areas through out the world. Examples, like the Prinos field in North Aegean Sea, some wells would completely cease flowing in a matter of a few days. Similar observations were made in Venezuela after stimulation treatment by acid. In Hassi Messaoud field, Algeria, deposition of asphaltenes in the tubing has been a very serious production problem. In the North Sea and Gulf of Mexico oil fields, asphaltenes deposition in several subseas pipelines lead to economic loss of oil production. Economic implications of this problem were tremendous considering the fact that the workover cost of a problem well could get as high as a quarter of a million dollars.
For nearly six decades, researchers throughout the world have conducted research on heavy organics and mechanisms of heavy organic deposition. They focused on the agglomeration process, solvents and precipitants. A very important characteristic of asphaltenes is that flocculated and/or precipitated asphaltenes can be dissolved by aromatic solvents and repeptized by the addition of resin-like compounds. This fact has enabled the development of remedial techniques in which the uses of chemicals (aromatics &additives) allow for the removal of deposited asphaltenes. Thus, the classification of asphaltenes is based on the solution properties of petroleum in various solvents. Asphaltenes are defined to be soluble in benzene and insoluble in low molecular weight n-alkynes and can be derived from petroleum, coal or shale oil. It has been found that the amount of asphaltenes in petroleum varies with source, depth of burial, API gravity of the crude oil. The particular paraffin used to precipitate them from the crude oil can classify Asphaltenes, and it has been proven that various solvents precipitate different amounts of asphaltenes as shown in Fig.1. The amounts precipitated with n-heptane and heavier n-alkynes show very little difference indicating that n-heptane and heavier solvents precipitate the most insoluble materials. This is the primary reason for selecting n-heptane as the most logical solvent for obtaining the asphaltene content in the crude oil. However, this will be discussed in details in the following sections.