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Collaborating Authors
Martin, Benjamin
Abstract Asphaltenes deposition is associated with several detrimental effects on oil production, paramount among these being production deferment and integrity issues. The current paper presents an investigation of asphaltenes risk assessment and mitigation strategies using a dynamic flow test method. It includes a study of the key parameters that influence observation of asphaltenes deposition in the laboratory and how laboratory testing methodologies can be designed to match more closely the processes occurring in the field. In these dynamic tests, dead crude oil is co-injected with n-heptane through a capillary and an inline filter, allowing assessment of both deposition and precipitation in a single test. The method is able to assess deposition tendency and rank asphaltenes inhibitor chemicals under flowing conditions and at more field-representative temperature and pressure, and with much lower volume fractions of n-heptane than required for conventional asphaltenes laboratory tests. Fluid dynamics is recognised to play a key role in the extent of asphaltenes deposition and is often most severe under low-shear conditions because erosive forces can reduce or eliminate deposition at higher shear. Using the dynamic flow test method with capillaries of differing internal diameter, we investigate the factors that either promote or suppress deposition, and determine certain boundary conditions where deposition is inhibited under the influence of increasing shear. The dynamic method is also used to evaluate the effectiveness of asphaltenes inhibitor chemicals against both precipitation and deposition, thus demonstrating that this approach provides much more relevant chemical-performance data than conventional test approaches, and may even elucidate why chemicals selected using non-dynamic methods often perform indifferently in the field or sometimes fail to perform completely. Introduction Background It is estimated that approximately 5 – 10% of the world's crude oils are susceptible to asphaltenes issues, which can cause flow restrictions, compromised integrity including malfunction of control and monitoring equipment, loss of well access for interventions, enhanced emulsion stability and internal under-deposit corrosion. Despite this, currently used methods to assess asphaltenes deposition risk and evaluate the laboratory performance of asphaltenes inhibitors are non-optimal because the conditions used are so far from those prevailing in the field. This can lead to inadequate assessment of risk, erroneous ranking of candidate inhibitors and even selection of chemicals that may not be beneficial in the field at all.
- North America > United States (0.46)
- Asia > Middle East > Israel > Mediterranean Sea (0.24)
Abstract Methods currently used to evaluate laboratory performance of asphaltenes inhibitors are non-optimal because the conditions used are so far from those prevailing in the field, leading to incorrect assessment of dose rates or even selection of chemicals that may not be beneficial at all. We present a dynamic flow test method for asphaltenes risk assessment and inhibitor qualification that uses field-representative temperature, pressure and fluid dynamics to enable successful correlation with field behaviour. This paper discusses the most commonly used laboratory test methods for asphaltenes testing and proposes a new dynamic flow method that offers a significant improvement over other widely-used techniques. Reconditioned dead crude oil is co-injected with n-heptane through a steel capillary and an inline filter. Differential pressures are recorded to monitor the extent of asphaltenes precipitation and deposition. We highlight key parameters that should be optimised to ensure that chemical performance is tested against the actual functionality required in the field and under conditions that are as representative as practicable. We present a case study describing the use of the dynamic flow test equipment to assess asphaltenes deposition risk and to qualify asphaltenes inhibitors for field application. We demonstrate that the method is able to rank chemicals for performance at inhibiting deposition under flowing conditions and at more field-representative temperature and pressure, with much lower percentages of n-heptane than required for conventional dispersancy testing. We discuss the effect of critical parameters affecting the extent of asphaltenes deposition. Fluid dynamics are recognised to play a key role in asphaltenes deposition in the field, not least, because at higher wall velocities the erosive force acting on field deposits is high enough to limit further growth and steady state can be reached. Flowing tests were conducted under a number of fluid-dynamic regimes in which asphaltenic crude oil was destabilised by addition of n-heptane. The effects of wall shear stress, wall velocity, residence time, and other factors were evaluated upon asphaltenes deposition in a steel capillary and upon bulk precipitation by subsequent filtration. The results obtained from laboratory tests correlate well with field observations and demonstrate that flow regimes in laboratory tests can approach those occurring in the field. This paper presents the development of a new laboratory test method utilising dead crude both for asphaltenes risk assessment and inhibitor qualification that offers significantly improved correlation with field behaviour over conventional dispersancy testing, yet remains much more cost effective than labour-intensive autoclave testing utilising live fluids. When considering asphaltenes risk analysis the approach also allows for deposition vs. precipitation to be examined under field realistic conditions, and we demonstrate how this can be of significant importance when, for example, introducing gas lift into asphaltenic crudes.
- Africa > Middle East > Algeria > Ouargla Province > Hassi Messaoud > Oued Mya Basin > Hassi Messaoud Field (0.99)
- Africa > Middle East > Algeria > Ouargla Province > Hassi Messaoud > Berkine Basin (Trias/Ghadames Basin) > Hassi Messaoud Field (0.99)