Asphaltene deposition is a major problem in the petroleum industry. Deposition problems occur in onshore and offshore fields around the world. The occurrence of asphaltene deposition depends on the production system design, conditions therein, and the chemistry of the specific crude oils. For most production systems, the crude oil chemistry is the dominant factor controlling the inherent stability of the asphaltenes and corresponding deposition potential. For some production systems, the actual production operations can create problems. For example, carbon dioxide flooding operations almost universally cause asphaltene deposition.
The proper identification and control of asphaltene deposition is necessary for the economic benefit of all assets. For onshore production, remediation operations can be performed relatively easily. For offshore production though, it is a much different situation. The high capital costs of deepwater subsea production systems make asphaltene deposition an extremely serious issue. The potential for immense production losses and the difficulties and expense in remediating deposition in subsea systems make it imperative that deepwater fields are evaluated for asphaltene concerns. If concerns exist, effective prevention treatments must be designed for the success of the deepwater field.
Therefore, having effective asphaltene inhibitor treatment programs and better methods to evaluate inhibitor performance is extremely valuable for operators. The understanding of asphaltene-related problems and screening methods has been evolving over the last 40 years. This paper will review a selection of asphaltene inhibitor screening methods, as well as, present a new simple, high-throughput dead-crude oil asphaltene stability analysis method.
Asphaltene–ACSA is a new asphaltene stability analysis method that was recently developed and introduced to the petroleum industry. The method uses an analytical centrifuge to evaluate the stability of asphaltenes in crude oils which have been simultaneously subjected to a solvent that destabilizes asphaltenes and centrifugal force. The method can be used for field-monitoring programs and for evaluating the relative performance of asphaltene inhibitors. The destabilizing solvent procedure used in the Asphaltene–ACSA method has been selected to work with much higher crude oil concentrations and to destabilize a much smaller fraction of the asphaltene distribution (in comparison to some other dead-crude oil methods) to move test conditions closer to actual field conditions.
The combination of the altered destabilizing procedure and the simultaneous application of centrifugal force has been found to provide better differentiation in evaluating asphaltene stability and differentiating asphaltene inhibitor performance than methods like ASTM D7601-04. In general, the Asphaltene–ACSA method has been found to offer relatively quick and reproducible results. Results from testing using different crude oils, destabilizing solvents, and asphaltene inhibitors will be presented to illustrate capabilities of the method. Special focus will be given to comparing various asphaltene screening methods and highlighting example Asphaltene–ACSA test results for evaluating asphaltene inhibitors.