A Simplified Method to Predict and Prevent Asphaltene Deposition in Oilwell Tubings: Field Case

Abstract

Abstract The natural state of asphaltene in petroleum fluids is described as a colloidal system stabilized to some extent by the resins that act as peptizing agents. Destabilization of colloidal asphaltene appears to happen as a result of changes in temperature, pressure, and composition. This can significantly affect the production efficiency of the reservoir during oil recovery. The phenomena of asphaltene flocculation and deposition in oil well tubing appear to be influenced by two mechanisms, the fluid phase (gas/liquid/solid) separation and well flow regime respectively. The predictions of the onset of asphaltene flocculation determined by fluid phase laboratory studies do not necessarily imply that asphaltene deposition will occur during flow conditions. We believe that the deposition is due to the change in well flow regimes under the effect of reservoir drawdown pressure. This paper presents a method capable of predicting the onset of asphaltene deposition under well flow conditions. This allows us to take preventive actions before asphaltene problems occur by keeping the asphaltene dispersed in the oil phase. A well monitoring technique was conducted in West Kuwait Marrat (Jurassic) deep wells to monitor the behavior of the well flowing pressure using programmable data logger. The data gathered from the logger have predicted the onset of the mechanism that influenced asphaltene deposition in well tubing. The deposition thickness of asphaltene in well tubing was estimated by the data and was found agreeable with the results obtained by the caliper test. Introduction It is generally1–6 accepted that crude oil is considered as a colloidal system constituted of saturates, asphaltenes, resins and aromatics fractions. Asphaltenes fractions defined as the dispersed colloids in the oil phase and stabilized to some extent by the resins molecules, which act as protective bodies for asphaltene particles. Colloidal asphaltene can be naturally or artificially precipitated if the resins protective shield is removed from asphaltene particle surfaces. The details of asphaltene characterization have been reported in numerous references. Asphaltene deposition can occur in deferent parts of the production system including well tubing, surface flow lines and even near the wellbore. Asphaltene precipitation and deposition in oil production systems depend on the changes in the flow conditions such as pressure, temperature and oil composition7–11. The main factor that plays a major role in asphaltene problems under flow conditions is the well flowing pressure behavior. This pressure controls the well flow regime within the production system. In well tubing, as the petroleum fluid moves vertically, flow regime changes take place complicating the multiphase flow and may cause severe asphaltene separation and deposition. This phenomenon decreases reservoir productivity and could increase production costs by requiring frequent chemical treatments for removal of asphaltene deposits. In the Arabian Gulf it has been observed that asphaltene deposition problems in oil well tubing have increased in the past years12. This may be due to the changes in reservoir pressure with time and the increase in gas/oil ratio. The later have shown to be an important factor in asphaltene particles flocculation in production systems. In West Kuwait, asphaltenes depositions within the well tubings have been increasing in deep wells12. This paper will focus on monitoring asphaltene flocculation and deposition in oilwell tubing. The monitoring technique is based on the interpretation of the well flowing pressure data obtained from a programmable data logger.