Deposition of colloidal asphaltene in capillary flow: Experiments and mesoscopic simulations

The aggregation and deposition of colloidal asphaltene in reservoir rock is a significant problem in the oil industry. To obtain a fundamental understanding of this phenomenon, we have studied the deposition and aggregation of colloidal asphaltene in capillary flow by experiment and simulation. For the simulation, we have used the stochastic rotation dynamics (SRD) method, in which the solvent hydrodynamic emerges from the collisions between the solvent particles, while the Brownian motion emerges naturally from the interactions between the colloidal asphaltene particles and the solvent. The asphaltene colloids interact through a screened Coulomb potential. We vary the well depth ecc and the flow rate v to obtain Peflow » 1 (hydrodynamic interactions dominate) and Re « 1 (Stokes flow). In the simulations, we impose a pressure drop over the capillary length and measure the corresponding solvent flow rate. We observe that the transient solvent flow rate decreases when the asphaltene particles become more sticky . For a well depth ecc = 2kBT, a monolayer deposits on the capillary wall. With an increasing well depth, the capillary becomes totally blocked. The clogging is transient for ecc = 5kBT, but appears to be permanent for ecc = 10-20kBT. We compare our simulation results with flow experiments in glass capillaries, where we use extracted asphaltenes in toluene, reprecipitated with n-heptane. In the experiments, the dynamics of asphaltene precipitation and deposition were monitored in a slot capillary using optical microscopy under flow conditions similar to those used in the simulation. Maintaining a constant flow rate of 5 µL min-1, we found that the pressure drop across the capillary first increased slowly, followed by a sharp increase, corresponding to a complete local blockage of the capillary. Doubling the flow rate to 10 µL min-1, we observe that the initial deposition occurs faster but the deposits are subsequently entrained by the flow. We calculate the change in the dimensionless permeability as a function of time for both experiment and simulation. By matching the experimental and simulation results, we obtain information about (1) the interaction potential well depth for the particular asphaltenes used in the experiments and (2) the flow conditions associated with the asphaltene deposition process. © 2008 American Chemical Society

Measurement of the mechanical properties of filtercakes

In order to improve drilling mud design to cater for specific well situations, a more comprehensive knowledge and understanding of filter cake failure is needed. This paper describes experimental techniques aimed at directly probing the mechanical properties of filter cakes, without having to take into account artefacts due to fluid flow in the substrate. The use of rheometers allows us to determine shear yield stress and dynamic shear modulii of cakes grown on filter paper. A new scraping technique measures the strength and moisture profiles of typical filter cakes with a 0.1 mm resolution. This technique also allows us to probe the adhesion between the filter cake and its rock substrate. In addition, œdometer drained consolidation and unloading of a filter cake give us compression parameters useful for Cam Clay modelling. These independent measurements give similar results as to the elastic modulus of different filter cakes, showing an order of magnitude difference between water based and oil based cakes. We find that these standard cakes behave predominantly as purely elastic materials, with a sharp transition into plastic flow, allowing for the determination of a well-defined yield stress. The effect ofsolids loading on a given type of mud is also studied

Recent developments in the deposition of colloidal asphaltene in capillary flow : experiments and mesoscopic simulation

The aggregation and deposition of asphaltenic material in reservoir rock are significant problems in the oil industry and can adversely affect the producibility of a given reservoir. To obtain a fundamental understanding of this phenomenon, we have studied the deposition and aggregation of colloidal asphaltene in capillary flow by experiment and simulation. For the simulation, we have used the stochastic rotation dynamics (SRD) method, in which the solvent hydrodynamics emerge from the collisions between the solvent particles, while the Brownian motion emerges naturally from the interactions between the colloidal asphaltene particles and the solvent. We compare our simulation results with flow experiments in glass capillaries where we use extracted asphaltenes only in toluene, re-precipitated with n-Heptane and also asphaltenes precipitated from the whole oil. In the experiments, the asphaltene precipitation and deposition dynamics were monitored in a slot capillary using optical microscopy under flow conditions similar to those used in the simulation. Maintaining a constant flow rate of 5µL/min, we found that the pressure drop across the capillary first increased slowly, followed by a sharp increase, corresponding to a complete local blockage of the capillary. Subsequently the pressure fell sharply as asphaltenes were re-entrained. This condition was confirmed by the visual observations that showed the slow build-up of asphaltenes deposit followed by the sudden erosion of a channel through the deposit at the time when the pressure suddenly decreased. We calculate the change in the dimensionless permeability as a function of time for both experiment and simulation. By matching the experimental and simulation results, we obtain information about 1) the interaction potential well depth for the particular asphaltenes used in the experiments, and 2) the flow conditions associated with the asphaltene deposition process. The data obtained will also be used as input parameters for a deep-bed filtration model