University and School
5. Discusión y conclusiones
Given: Suction Tank, 9 ft L x 7 ft W x 9 ft H 18 ppg mud
1. Vt = (9 x 7 x 9) x 7.481 = 4242 gal 2. Recommended TOR, from Table 1: 75 sec 3. Impeller Displacement Rate:
D = (60) (4242)/75 = 3394 gpm
4. Since tank depth > 5 ft, a canted-blade impeller is selected.
From Table 2, nearest D = 3764 gpm, Impeller Diameter = 32 in.
5. From Fig. 6, for 32 in. diameter and 18 ppg mud, required agitator horsepower = 5 HP (MA5).
6. From Table 3, for model MA5 agitator and 9 ft tank depth, shaft length reduction = 10 in.
Total Shaft Length = 9 ft x 12 in./ft - 10 in. = 98 in.
7. Impeller location above tank bottom = 0.75 x 32 = 24 in.
8. Total Agitator Weight = 98/12 x 15.1 lbs/ft + 580 lbs + 50 lbs = 753 lbs.
Table 2 Impeller Displacement Rates Canted-Blade Flat-Blade
Impeller Displacement Rate GPM at 48 rpm (50Hz) Canted-Blade Flat-Blade
12 11 213 246 177 205
16 15 484 560 404 467
20 19 909 1051 760 877
24 21 1645 1941 1373 1620
28 38 2468 2839 2060 2370
32 50 3764 4365 3142 3644
36 61 5402 6273 4510 5237
40 74 7284 8411 6081 7023
44 101 9928 11300 8288 9435
48 118 12512 14401 10445 12024
52 126 16100 18630 13440 15552
* D = AB x V x 7.481 gal/ft3, where AB = projected blade area, ft3, V = impeller velocity, ft/min Canted-blade area based on 60× angle
Brandt data
Table 3 Physical Specifications for Mechanical Mixers
Model HP Shaft
MA7.5 7.5 2-3/8 32 15.1 1200 22-1/2 12
MA10 10.0 3 32 24.0 1224 22-1/2 12
MA15 15.0 3 36 24.0 1830 26-5/8 13-1/8
MA20 20.0 3-1/4 40 28.1 1898 27 13-1/2
MA25 25.0 3-1/2 40 32.7 3130 33 13-1/2
* Bottom shaft stabilizer required at 6 ft, all others require bottom stabilizer at 8 ft.
** Shaft Length = Distance from tank bottom to top of agitator support beams - shaft length reduction.
Brandt data
9 Summary
· Addition/mixing systems must be correctly designed to minimize material consumption and ensure complete and even mixing.
· The two most common mixing hoppers are the venturi type and the Sidewinder hopper. Laboratory tests conducted with bentonite showed little difference between the two devices in both capacity and mixing capability. The Sidewinder does not entrain air like the venturi hopper, but dust can be a problem when adding some materials.
· Bulk systems are economical for storing and distributing material required in large quantities. There is less waste and trash compared to sacked material. Bulk systems are also becoming popular for the accurate metering of dry material and chemicals in low dosages.
· Mixing polymers such as PHPA present additional problems such as polymer fish-eyes, extensive mixing times, and shaker screen blinding.
Polymers with a higher fraction of high molecular weight polymer will be harder to dissolve and generate higher viscosities. Higher shear rates produce lower molecular weights, but below a certain molecular weight, the inhibitive characteristics of PHPA are lost.
· A mixing and shearing system consisting of a perforated-wafer type of jet shear mixer, coupled with a SECO Homogenizer, was found to provide improved polymer mixing. Guidelines for building concentrated premix volumes are provided.
· Premix systems are highly recommended for the numerous advantages they provide:
A. Improved hydration
B. Better control over active system mud properties C. Less material consumption
D. Easier to monitor dilution rates E. Less manpower requirements
· All dilution water streams should be metered to monitor solids removal efficiency. Water should be added at the flowline to reduce viscosity and improve shaker performance. Any water used on the rig will contribute to the total liquid waste volume. No leaks should be tolerated.
Use low volume nozzles on the wash water lines. Recycle water where possible.
· Mechanical (paddle type) agitators are recommended in the solids removal section of the active system. Mud guns are acceptable in the addition/suction compartments only. A procedure is provided to correctly size mechanical stirrers.
Tank Design and Equipment Arrangements
1 Tank Design... 1 1.1 Compartment Equalization... 2 1.2 Sand Trap... 3 1.3 Slug Tank ... 3 1.4 Equipment Arrangement... 4 1.5 General Guidelines for Surface System Arrangements... 5
2 Equipment Arrangements... 6 2.1 Unweighted Mud - Centrifuge Processing Active System... 6 2.2 Unweighted Mud - Centrifuge Processing Hydrocyclone Underflow ... 8 2.3 Unweighted Mud - Centrifuge Processing Mud Cleaner Underflow ... 10 2.4 Weighted Water-Based Mud - Single-Stage Centrifuging (Barite Recovery) ... 12 2.5 Weighted Mud - Two-Stage Centrifuging ... 14 2.6 Complete System Layout For Both Weighted and Unweighted Mud ... 16
3 Summary... 18 FIGURES
Fig. 1. Unweighted mud - centrifuge processing active system. ... 7 Fig. 2. Unweighted mud - centrifuge processing hydrocyclone underflow... 9 Fig. 3. Unweighted mud - centrifuge processing mud cleaner underflow. ... 11 Fig. 4. Weighted water-based mud - single-stage centrifuging (Barite recovery) ... 13 Fig. 5. Weighted mud - two stage centrifuging. ... 15 Fig. 6. Generic - complete system. ... 17
1 Tank Design
The surface pits that comprise the active circulating system should be designed to contain enough usable mud to maintain mud properties and to fill the hole during a wet trip at the rig’s maximum rated depth. Usable mud is defined as the mud volume which can be pumped before suction is lost. For example, a typical 10,000 ft well will normally require a minimum active system tank volume of 500 bbls.
The active surface system can be divided into two sections: Solids Removal and Addition-Suction. All solids removal equipment and degassing occurs in the Solids Removal section. The Addition-Suction section is used to add fresh mud to the circulating system and provide sufficient residence time for proper mixing to occur before being pumped downhole. A slug tank is usually available to pump small “pills” such as LCM or barite slugs for tripping.
Each section must be further divided into enough compartments to efficiently carry out its designed function. The number of compartments needed will depend upon the amount and type of solids removal equipment, system size and circulation rate. Each compartment must have enough surface area to allow entrained air to break out of the mud. A rule of thumb for the minimum surface area is calculated by:
Area (sq ft) = Maximum Circulating Rate (GPM)/40
To maximize solids suspension and usable volume, the best tank shape is round with a conical bottom. Next best is a square or rectangular shape with a V-bottom. The least-preferred shape is the square or rectangular box with a flat bottom. The ideal tank depth is equal to the width or diameter of the tank. This design provides sufficient pump suction head and is best for complete stirring.