Abstract

Reservoir fluids containing paraffin's and asphaltene's are common in the petroleum industry. The presence of these components causes significant operational problems during the life of the producing wells. The identification of wax and asphaltene precipitation conditions is the first step towards applying any remedial options. There are various procedures applicable in determining the onset of wax and asphaltene precipitation conditions. These techniques are dependent on the oil characteristics. The most important criterion is the colour of the oil. For dark coloured oil, the popular light-scattering technique becomes inadequate. In this case, near-infrared (NIR) light spectrum is necessary to identify any changes in the response due to phase change phenomenon.

An emerging technology, called Acoustic Resonance Technology (ART), has been tested at Hycal Energy Research Laboratories Ltd. to identify the onset conditions of wax and asphaltene precipitation. The system is applicable to any type and colour of oil. The basic principle behind the technique is the transmitting of sound waves through the fluid while it is exposed to wax or asphaltene precipitation conditions by changing pressure, temperature or composition conditions. The acoustic response shows drastic changes during the phase transition (i.e. nucleation of wax or asphaltene) in the fluid. Initial results of the onset of wax and asphaltene precipitation are extremely promising. Comparison of the onset values of wax and asphaltene precipitation using ART showed excellent agreement with that obtained using a light-scattering technique.

Introduction

Acoustic Resonance Technology (ART) is based on measurement of the response of a fluid or fluids, contained in a cylindrical cavity, to acoustic variable stimulation. The most powerful use of ART is to study the state and time evolution of the resonance response of fluids under variable and well controlled conditions of pressure, volume and temperature.1,2,3 In these cases, one can obtain information related to fluid phase behavior or phase transitions and transport properties. ART offers a sensitive, objective method for probing and measuring bulk fluid properties and processes.

Asphaltene's are dark brown to black solid compounds with no definite melting point. They decompose while heating and leave a carbonaceous residue. They are non-crystalline substances or mixtures of relatively high molecular weight fractions4 of bitumen with characteristics of strong aromatic polar substances.5,6 Asphaltene's are defined as the n-heptanes insoluble fraction of crude oil.7,8 They are classified by the particular solvent used to precipitate them.9 They are generally soluble in benzene and insoluble in low molecular weight n-alkenes.10 Asphaltene precipitation can be determined experimentally.

Waxes are defined as normal paraffin's as well as other molecules containing long chain alkyl groups usually ranging from C18 to C60. Solid waxes crystallize or precipitate when cooled below their cloud point temperature. The wax precipitation process is thermodynamically reversible.11 The viscosity of crude oil is increased by the presence of the wax crystals.12 lf the temperature is reduced sufficiently, the crude can become highly viscous and approach its pour point temperature.

Solid (waxes and asphaltenes) precipitation from reservoir fluids causes severe operational problems in the subsurface, surface equipment, wellhead equipment, separators and tanks.13,14 Clean-up costs can be very high in off-shore oil product

This content is only available via PDF.
You can access this article if you purchase or spend a download.