Mixing technology contains circulating the drilling fluid throgh jet nozzles(mud gun) or impellers(agiatator),are becoming less satisfactory in achieving the desired properties for polmer-based drilling mud. The mixing technique used today are required to better disperse the chemical additives, but be gentle enough to perserve their long polymer chains and chemical structure.The mixing process and apparatus needs to be easily utilized at both on shore fluid mixing plants and at the rig-site. Both process and equipment must be economical,safe and environmentally resposible.
Multifarious chemical process and mechanical engineering evaluations have allowed the effects of high-shear mixing on water-,oil- and synthetic-based drilling fluid system to be determined.
Most mud tanks and pits are equiped with jet nozzles and/or agitators for mixing. Chemicals are added through hoppers that often supply addtional mixing capabilities, Furthermore,drilling fluid fluids are subjected to additional blending during pumping and other handling activities.
Land rigs that drilling with a simple mix of clay and water are quickly becoming history in favor of more efficient advanced fluid chemical compositions with improved chemical and physical properties and optimized performance. The input of mechanical work, such as:shearing,agitation, and heat, helps the chemistry to perform as designed. These chemical advances required advanced mixing processes and machiner to facilitate innovative technologies for feilling fluid mixing.
Considerations For Drilling Fluid Mixing
Several methods of shearing fluids currently exist. Anozzle and low-pressure pump operated at 50 to 80 psi can achieve shear rates on the order of 3000 to 5000s. A nozzle and high-pressure pump, capable of delivering 700 – 800 psi can achieve shear rates of from 30,000 to 50,000 s. It is recognized that the highest level of shear is achieved when fluid is passing thought the bit while drilling, where a small oriface, high temperature and high pressure all contribute to creat a combined effect. In term of shear reates, shear through a drill bit nozzle and high-pressure triplex pump can achieve rates 30,000 to 80,000s.Rotor-stator mixers provide the capability to meet or exceed the highest shear rate levels provide by the drill bit nozzle and triplex pump combination. The lowest shear rates produced by high shear mixers are 10,000s, and the highest are 100,000s.
High Shear Mixer
A mechanical solution for the preparation of drilling fluids that would improve the required properties.Reviewing existing practices to find undeveloped potentials with jets, mud agitators and some impeller-based mixing devices proved pointless.None of these techniques were deemed sufficient to impart enough energy and meet the solution criteria, whcih primarily focus on safe,easy, efficient and economical operation.The rotor-stator high-shear mixer was identified as being capable of providing shear efficient to enhance fluid properties.
|Table 1 -Rheology Data for Freshly Prepared WBM Sheared One Pass From The Mixing Tanks on a Liquid Mud Plant|
|/||Base||Single-stage Unit||Multi-stage Unit||Base||Single-stage Uint||Multi-stage Unit||Base||Single-stage Uint||Multi-stage Unit|
|API FL, mL||6.6||4.6||6.8||6.0||4.0||6.0||6.0||4.4||6.4|
|600-rpm dia reading||55||57||57||55||57||57||55||57||58|
|300-rpm dial reading||37||41||42||37||41||42||37||41||42|
|100-rpm dial reading||23||25||21||23||25||21||23||25||21|
|6-rpm dial reading||11||11||11||11||11||11||12||11||11|
|3-rpm dial reading||10||10||10||10||10||10||11||10||10|
|Yeild Point, lb/100ft||19||25||27||19||25||27||25||25||26|
|10-sec gel strength, lb/100ft||9||10||12||9||10||12||8||10||12|
|10-min gel strength, lb/100ft||12||16||18||12||16||18||13||16||18|