Microscale Evaluation of Asphaltene Deposition to Comprehend its Instability Mechanism

Abstract Changing thermodynamic and compositional conditions of producing fields can cause decreased asphaltene stability and initiate aggregation, subsequent precipitation, and eventual deposition within flowlines. Usage of asphaltene inhibitors that prevent aggregation and tackle the problem right at the inception is widely preferred. However, such chemistries were observed to be counter-productive and led to higher asphaltene deposition in many cases. Thus, raising the question of what approach works best for assessing asphaltene stability: Dispersion or Deposition? This study used a microfluidic device with both high permeability (high-perm) and low permeability (low-perm) regions within the same microchip. The two regions have the same porosity but different permeabilities to mimic heterogeneous formation. Microfluidic systems are easy, fast, and visual tools that can be used to investigate flow processes through porous media. A series of microfluidic experiments were conducted at room temperature using produced oil from deep-water Gulf of Mexico region and asphaltene precipitant (n-heptane) being co-injected through a T-junction to destabilize the asphaltene clusters. Precipitation and deposition of asphaltenes on the microchannels were recorded with a high-speed camera. Asphaltene coverage was measured using image processing software. A high sensitivity pressure transducer was also used to monitor the in-situ pressure drop across the microfluidic device. Effect of four distinct asphaltene inhibitor chemistries were evaluated at two dosages using the same process. It was observed that the dispersants impacted asphaltene deposition rates and amounts as well as the deposit morphology. The deposits formed by smaller aggregates, resulting from the dispersant stabilization of the asphaltenes in solution, exhibited higher overall deposition rates. This may be due to the reduced hydrodynamic erosion and highlights the importance of considering both static and dynamic flow conditions. Additional validation of the microfluidic experiments was carried out by correlating the results with thermoelectric, and dynamic deposition loop test methods. Thermoelectric method describes the aggregation state of asphaltenes within native crude oil. Flow loop setup assesses total mass deposited when the oil and precipitant mixture is flown through capillary tubes. 85% match was observed between microfluidic and thermoelectric test method results. The key role of asphaltene cluster size as a bridge relating the dispersion and deposition-based test method is revealed in this paper. Therefore, it is imperative that the asphaltene inhibitor development philosophy must include test screening methods focusing on each instability stage (precipitation, aggregation, and deposition) individually and combine the learnings to come up with the best recommendation.