Crude Oils of Kentucky and Tennessee: Characteristics, Problems, and Solutions

Abstract

Paraffin and asphaltenes can cause many types of problems depending upon the characteristics that they give to a particular crude oil. The problems can range from deposition of paraffin or asphaltenes in the formation or equipment, causing the oil to congeal, oil wetting of the formation, causing emulsions or rigid film emulsions during acid treatments. The analysis of crude oils from wells in Kentucky and Tennessee has been carried out to determine the possible organic problems that will affect the production from these wells. Problems, causes, and solutions will be discussed with case histories presented. Introduction Paraffin and asphaltenes are naturally occurring components of crude oil. Paraffins are composed of carbon and hydrogen atoms with the formulas of C20H42 to > C100H202. Although usually straight chain, they can also contain branched alkyl or cyclic groups.1 Asphaltenes are heterocyclic macromolecules consisting primarily of carbon, hydrogen, and minor components, such as sulfur, nitrogen, and oxygen.1 Both these components of crude oil are in thermodynamic equilibrium at "normal" reservoir conditions. This equilibrium can be disturbed by a number of factors: temperature decrease, decline of reservoir pressure towards the bubblepoint, addition of miscible solvent to the oil from EOR techniques, acidizing, hot oiling or other oilfield operations. Once the equilibrium is disturbed, the opportunity for deposition and subsequent formation damage is created. The primary mechanism for paraffin deposition is thermal with decreasing temperature promoting deposition. The major mechanisms for asphaltene deposition are pressure drops and the addition of incompatible fluids 3,4. Each oil is unique in it's physical properties that the paraffin and asphaltenes impart to it. The types and quantity of paraffins, amount of various solvent components (C1H4 to C19H40) and amount of asphaltenes and resins give each crude a different ability to cause problems. Paraffin Components of Crude The paraffin series of compounds or n-alkanes contain only hydrogen and carbon 8. The number of carbon atoms can range from 1 to >100. The ratio of carbon to hydrogen atoms can be shown by the formula CnH2n+2. This means that for every carbon atom there will be twice as many hydrogen atoms plus two.1,8 The alkanes from C1H4 to C19H40 are the solvents for the longer chain alkanes in the oil and the combinations of all possibilities are what make each oil unique. The oil around the wellbore of each well is unique and then changes as the oil is produced through the system to the stock tank. Differences in drilling, completion, stimulation and production techniques will cause changes in the oil produced and the surrounding formation characteristics.