Mud cleaners are equally effective for both weighted and unweighted drilling fluids and effectively lower both drilling fluid expenses and disposal costs.
The question frequently arises, ‘‘Would it be cheaper to simply jet drilling fluid from the system instead of using solids-control equipment?’’
To answer this question, examine the discard rates in Table 2 and compare them with the volume of drilling fluid that must be discarded to eliminate the same volume of drilled solids. Cost of drilling-fluid ingredients vary from company to company and from contract to contract.
Rather than actually calculate a cost, the comparison will be made between using the mud cleaner and pumping drilling fluid to eliminate the same quantity of low-gravity solids from the system using the measurements in the preceding tables.
An 11-ppg drilling fluid with 13%vol total solids would contain 6.4%vol low-gravity solids and 6.6%vol barite. With the first circulation and 60 psig manifold pressure, 1317 lb/hr of drilled solids and 484 lb/hr of barite are discarded. Since the solids in the drilling fluid are presented in terms of volumes instead of weights, the mass flow rate needs to be translated into volumes.
With a SG of 4.2, the density of barite would be 4.2 times the density of water (8.345 lb/gal), or 35.05 lb/gal. With a SG of 2.6, the density of low-gravity solids is 2.6 times the density of water, or 21.7 lb/gal. The volume flow rate of solids would be the mass flow rate divided by the density. The volume flow rate of barite would be (484 lb/hr)/(35.5 lb/gal), or 13.6 gal/hr, and the volume flow rate of low-gravity solids would be (1317 lb/hr)/(21.7 lb/gal), or 60.7 gal/hr.
In this drilling fluid there is 6.4%vol drilled solids. If the discarded low-gravity solids are 6.4% of the mud volume and 60.7 gal/hr of drilled solids are discarded, the total volume discarded to contain that amount of solids would be:
VLG discarded = 6.4%(volume of 11-ppg drilling fluid)
or, 60.7 gal/hr = (0.064)(volume of 11-ppg drilling fluid). The volume of
11-ppg drilling fluid discarded is 948 gal/hr.
This quantity of drilling fluid contains 6.6%vol barite, or (0.066) (948 gal/hr) ¼ 62.6 gal/hr of barite. Converting barite volume to barite weight, (62.6 gal/hr)(35.05 lb/gal), means that 2194 lb/hr of barite would be lost to eliminate the 1317 lb/hr of low-gravity solids. Compare this with the measured loss of only 484 lb/hr of barite loss from the mud cleaner screen. In addition to the cost of the excess barite, the pit levels would decrease by 948 gal/hr. This is equivalent to losing (948 gal/hr) (24 hr)/(42 gal/bbl), or 541.7 bbl of drilling fluid daily.
Clearly, concentrating the low-gravity solids with equipment is preferable
to dumping drilling fluid to eliminate drilled solids (Table 1).
Table 1 Eight 4-inch Hydrocyclones Above an API 150 Screen
Cyclone Manifold Pressure(psi) | Manifold Head (ft) | Screen Discharge (sec/qt) | Discharge density (ppg) | Volume % Solids | Drilled Solids Removed (lb/hr) | Barite Discarded (lb/hr) |
First circulation: Bottoms up after TIH with new bit | ||||||
38 | 66.4 | 16 | 16.8 | 58 | 108 | |
52 | 90.9 | 7 | 17.7 | 58 | 1275 | 552 |
60 | 104.9 | 7 | 17.5 | 58 | 1317 | 484 |
78 | 136.4 | 6 | 17 | 58 | 1659 | 368 |
Second circulation | ||||||
40 | 69.9 | 25 | 16.4 | 50 | 308 | 132 |
50 | 87.4 | 19 | 16.7 | 58 | 547 | 79 |
60 | 104.9 | 9 | 17.6 | 58 | 1008 | 403 |
70 | 122.4 | 5 | 17.5 | 58 | 1844 | 678 |
Third Circulation | ||||||
42 | 73.4 | 40 | 16.6 | 58 | 263 | 32 |
55 | 96.2 | 20 | 17.1 | 57 | 471 | 138 |
60 | 104.9 | 10 | 17.3 | 58 | 951 | 292 |
74 | 129.4 | 9 | 17.3 | 58 | 1057 | 324 |