A new fracturing sand slurry mixing system has been designed. High sandconcentration slurries using a high viscosity non-newtonian gel can be mixed atlow or high rates. A full size mixing system was built and tested withfracturing gel and sand. This system includes automatic agitation control, newbaffle and agitator design excepts, and new methods for rapid material wetting.The new mixing system has been utilized on new stimulation blendingequipment.
Mixing sand slurries to essentially homogeneous uniformity for fracturing is aproblem in the oil service industry. Problems typically encountered when mixinghigh concentration slurries at high rates are air entrainment in the fluid, inadequate solids wetting, and dispersion of solids. Various mixing methodshave been tried by service companies with varying degrees of success. As a partof the development of new fracturing equipment new sand slurry mixing systemhas been designed. High sand concentration slurries using a high viscositynon-newtonian gel can be mixed at low or high rates. Conventional agitatordesigns typically will not perform the mixing job at high sand concentrations, because as the sand concentration increases the slurry becomes more viscous.Sand concentration in the oil service industry is defined as the mass of solidsper unit volume of fluid.
The specific objectives of this research (1) were to obtain the informationnecessary for the design of a full scale fracturing sand slurry mixing systemand (2) to design a mixing system to produce a homogeneous, high sandconcentration slurry.
Mixer performance is typically expressed in terms of fluid velocity generated, total pumping capacity of the impeller, total flow in the tank or in terms ofan evaluated criterion. If the application is relatively simple and easilyanalyzed, a detailed examination of complicated fluid mechanics in a mixingtank will be unnecessary. When the process is complex, a thorough examinationof shear rates and tank turbulence may be required. Sometimes it is possible toexpress a complex mixing process in terms of bulk velocity and pumping-capacityrelationships.1 Significant progress has been made in organizing andpresenting mixing design concepts and procedures.2,3,4,5 Theseprocedures and techniques were utilized in this work to make preliminaryestimates of mixing system specifications.
Mixing fracturing sand slurries can be define as: the mixing of solids andliquids into a pseudo-homogeneous mass that is more or less stable. A wellmixed slurry using fracturing gel should have some life before noticeable sandsettling occurs. These fracturing gels are normally very viscous andnon-newtonian in nature. They are shear thinning fluids, a property which makesthe design of the mixing tank and agitator system extremely critical.
The mixing task to be performed is to mix fracturing sand and gel into auniform suspension. Agitation within the tank must be intense enough to createthe required fluid turbulence to complete the mixing job in the requiredtime.