The experimental and theoretical study of fines migration in porous media under particle-rock repulsion and attraction.

Abstract

This is a PhD thesis by publication. The essence of the research performed has been published in one book chapter, five journal papers and four SPE papers. The thesis contains laboratory study of deep bed filtration in porous media accounting for particle migration, mobilization and straining for two particular cases: straining-dominant particle capture and filtering under high flow velocities. Advanced challenge core flood test methodology to determine pore throat size distribution under unfavorable particle retention conditions is designed and developed in the thesis. It includes significant advance in design of the laboratory set-up if compared with previous version, development of the test procedures to provide the particle-rock repulsion and measure the post-mortem retention profile, analysis of accuracy and uncertainties of the experiments. In more details, the improvements of the laboratory set-up and procedures include sieving of glass beads in the ultrasonic bath with consequent reduction of the sieving time and more reproducible grain size distribution, application of the dual syringe pump system with continuous injection of suspension and pulseless delivery of particles in the porous medium, measurements of the retention profile after the test by cutting up the porous column in 4-6 pieces and dispersing the material in water. The above methods are applicable to continuous as well as to a pulse type particle injection. Latex particle have been injected into packed glass beads or borosilicate filters at different concentrations, velocities, pH, and salinities. However, main varying parameters are size distributions of injected latex particles and compacted glass beads. The tests show that the pore throat size distributions can be recovered from the challenge tests. Another development of the thesis includes deep bed filtration investigation under high flow velocities under favorable particle retention conditions. It includes the design of laboratory set-up, development of the experimental methodology to reveal the hysteretic phenomena of the particle attachment and detachment under high velocities, treatment of the data using the Forchheimer law of high velocity flow in rocks and formulating the modified Forchheimer law under the conditions of formation damage, development of the methodology for estimates of the accuracy and uncertainties of the performed laboratory high-velocity tests. In more details, high velocity suspension flow in engineered porous medium was studied at various volumetric flow rates and conditions favorable for particle attachment under the occurrence of the phenomena of particle deposition, mobilization, migration and entrainment. The maximum retention function (the critical particle retention concentration) derived is a quadratic function of flow velocity. A strong particle surface attraction as indicated by calculation of DLVO energy potential, translates to almost a quarter of filter surface coverage by the attached particles. The particles can’t be removed by an increase of solution velocity only due to strong particle-matrix attraction. The removal of approximately 17.5 % of the attached particles was achieved only after the reduction of salinity and increase in pH of solution at maximum velocity. The work includes the development of the Forchheimer model for the case of particle retention, i.e. the advanced formula for inertial coefficient versus retained concentration is proposed. Application of the Forchheimer law to the laboratory data results in the formation damage coefficient dependency of the critical retained concentration and the inverse dimensionless function of velocity. The inertial coefficient showed similar behavior at low velocities, although it remained almost constant at low surface coverage. Partial formation of the external cake on the inlet surface of the filter was observed by a post-experimental examination using an optical microscope and via an abrupt increase in the formation damage and inertial coefficients during particle deposition at lower velocities. The partial cake coverage is the indication of the continuation of deep bed filtration even at high surface coverage which is supported by high filtration coefficient values at lower velocities. Results from the theoretical micro scale model based on the torque balance exerted on attached fine particles agree well with the experimental critical retention concentration data within combined standard uncertainties in the entire range of velocities. It allows proposing the model with modified Forchheimer flow equation and micro scale based maximum retention function for high velocity colloidal flows in porous media.