Drilling fluid is an important part of oil and gas extraction. The fluid performs several function, among which are extraction of debris from the well, prevention of well collapsing, lubrication of drilling instruments etc.
There are many formulas for drilling fluid production, but the most common are water and hydrocarbon based fluids. Water, salt solutions and hydrogels, polymer, polymer clay and clay solutions are used in the former case. The latter involves inverse emulsions and lime-bitumen solutions. Standard components may not always ensure the required performance of the fluid; therefore, special additives are used to modify the structure and rheological qualities of the product.
Drilling fluid production usually involves various mixers, blenders, dispersers etc.
Main Types of Mixers and Dispersers Used in Drilling Fluid Production
Let’s take a look at the various mixers and disperser’s used for the production of drilling fluids. Drilling extension wells in remote locations makes use of the hydraulic method, when solid particles of clay in drilling fluids are destroyed exclusively by the kinetic energy of the flow. Devices based on this principle are known as hydraulic mixers.
Centrifugal mixing is used in final stages of drilling fluid preparation. It involves agitators with vanes which disperse clay particles.
Static mixers are designed an inset in a tube where drilling fluid is flows. These inset’s can vary in length, diameter and shape, making it possible to mix many components with different chemical origin, viscosity and density. The main purpose of a static mixer is homogenization of the material, even distribution of viscosity gradient, protection from air bubbles and increased turbulence of the flow.
In practice, the final mixing of components occurs only when the solution is run through all mixers and dispersers in several processing cycles. With the above in mind, and also considering mechanical agitators involved, the process takes much time and consumes much electricity. Also, quality is not not always guaranteed. Therefore, development of new systems to reduce the time and power costs of quality drilling fluid preparation is important.
Application of Vortex Layer Generators in Preparation of Drilling Fluid
The vortex layer device consists of a chamber, located inside an inducer coil which generates a rotating electromagnetic field (figure 1).
Ferromagnetic vortex layer device:
1 – Non-magnetic stainless steel chamber inset;
2 – induction coil generating a rotating EM field;
3 – induction coil housing;
4 – Non-magnetic stainless steel chamber;
5 – ferromagnetic elements
The chamber contains ferromagnetic elements, i.e. cylinders with 1-5 mm diameter and 1-50 mm length (specific dimensions depend on process requirements). The amount of the elements is several dozens to several thousands (0.05-5 kg), with the precise amount depending on the critical element mass coefficient. The main feature of this device is simultaneous running of various physical and chemical processes in the chamber.
Due to the special geometry of the chamber and magnetic induction of 0.11 to 0.15T, a vortex layer forms in the chamber, in which the direction of radial velocity vector direction is equiprobable, and the tangential component is directed mostly in the direction of field motion, which causes circular motion of the entire layer. Besides, when the ferromagnetic elements collide with one another and with the walls of the chamber, and under the influence of the flow, the elements are subject to the longitudinal velocity component along the unit’s axis. The ferromagnetic elements move around the chamber. Each separate element is a dipole magnet; the elements vibrate due to magnetic polarity reversal and collide with other elements. The frequency of collisions is proportional to the length to diameter ratio. Maximum collisions are observed at l/d=9….13. Some of the most important processes inside the chamber which facilitate intensive mixing are:
- electromagnetic field influence;
- physical influence of the ferromagnetic particles on the processed material;
- hydrodynamic influence (high shear forces in the liquid, pressure and flow velocity pulses);
- hydroacoustic influence (intensive cavitation and shockwaves);
The energy of the rotating electromagnetic field excites the internal energy of the processed medium (surface layer activation).
The combined effects of the various forces inside the unit, which facilitates simultaneous dispersion and mixing, as well as the relatively low power required to create the EM field, make the vortex layer devices promising in drilling fluid production.
For practical research we used a hydrocarbon-based drilling fluid formula. The fluid prevent the well from collapsing. It contained diesel fuel (835 kg/m3), water, emulsifier (20 l/m3), lime (20 kg/m3), organophilic clay(12 kg/m3) and halite (90 kg/m3).
The research of drilling fluid preparation efficiency was performed using an AVS-100 vortex layer device made by GlobeCore (figure 2), and steel ferromagnetic elements, 2 mm in diameter and 20 mm in length. To minimize accumulation of metal filings in the solution, the elements were made from high strength ball bearing steel.
After emulsion preparation, such parameters as filtration ability, plastic viscosity, density and voltage stability were measured. The results are listed in Table 1.
The measurements illustrate the high quality of the drilling fluid made by the AVS-100 device.
The results of the experiments indicate the following.
1) The multiple physical and chemical processes in the vortex layer device facilitate simultaneous dispersion and mixing of the drilling fluid in a single device. This allows to simplify production equipment by eliminated other mixers and dispersers;
2) The quality of the fluid made by the AVS-100 in one stage is not inferior to that of the drilling fluid made in several processing cycles in mechanical agitators and dispersers;
3) Replacing mechanical agitators with vortex layer device allows to half the electric energy required per one cubic meter of the drilling fluid;
4) Vortex layer processing reduced the time of drilling fluid production several-fold compared to similar parameters of mechanical equipment.
Processing capacity of the AVS-100 unit is 1-1.5 m3/hour with power consumption of 3.5-4 kWh; the AVS-150 unit operates at the rate of 2-2.5 m3/hour with power consumption of 9.5 kWh.