1. Mohr Separations Research, Inc.
DESIGNING SALTWATER DISPOSAL SYSTEMS FOR OPTIMAL OIL RECOVERY AND MINIMUM MAINTENANCE
Kirby Mohr, P.E.
Mohr Separations Research, Inc.
Lewisville, TX
Website: oilandwaterseparator.com oilandwaterseparator.com

2. Introduction - Need for Better Salt Water Treatment
Resource Recovery – can sell any captured oil
Avoid primary plugging of down-hole areas by oil
Avoid secondary plugging by bacterial growth

3. Two Sets of Separation Equipment Required
Primary separation at or near the wellhead
Usually pressurized
May or may not be equipped with sand removal systems
May include heater-treaters
Salt water disposal system for recovering residual oil

4. Wellhead Typical Three Phase Separator

5. Typical Gunbarrel Separator

6. Wellhead Separation Equipment
Three phase separators
Good rough-cut separation system
Gunbarrel separators
Mostly empty tank type system
Both are relatively inexpensive, low-maintenance and simple to operate
Neither are designed to capture small oil droplets and not very efficient

7. Separation by Gravity
Separation governed by Stokes’s Law

8. Stokes’s Law Variables
Variables are
Density of Droplets
Density of the Water
Viscosity of continuous phase (temperature)
Average Droplet size (Squared function)

9. Stokes’s Assumptions Laminar Flow Consistent specific gravity
Spherical Particles
Consistent particle size
Droplets are large enough to avoid Brownian Motion flow regime

10. Information needed for Disposal System Design
Design flow rate
Design inlet oil content and gravity
Design water specific gravity
Design operating temperature range
Oil outlet concentration desired
Design solids content
Design solids type / configuration
Possible variations in the parameters

11. Design Flow Rate
Design flow rate determined on an instantaneous (gpm or equal) basis
BPD if 24 hour operation
30, ,000 BPD is a reasonable large size
For larger flows, use multiple units
Design for maximum flow expected – performance will be better at lower flows

12. Design Inlet oil Content / Specific Gravity
If analyses are available, use highest oil content found.
If no analyses, use 5% as maximum oil content.
If specific gravity is available, use that
If gravity is unknown, use literature value for that field or get a sample tested

13. Design Operating Water Temperature
In general, higher temperature is better up to about 150 F (65 C).
Higher water temperature is better because the viscosity of the water is less at higher temperature
But, at higher temperatures convection and other currents will be worse and may cause separation problems.
Check with the possible water sources for temperatures

14. Design Oil Removal
Can’t get to ZERO ppm oil in effluent, but can get to “non-detect” levels (about 2 ppm)
Better oil removal brings more oil to sell and also reduces operating costs
Can only get down to droplets about micrometers in diameter (Brownian Motion)
Volume of oil in a droplet depends on the cube of the diameter

15. Design Inlet Solids Content
Solid content in the inlet will vary wildly from one truck to the next
Take samples for analysis if possible.
If it is not possible to get samples for analysis, estimate 50 ppm solids.
If the solids content is eventually proven to be more, add solids settling capacity

16. Variations in Parameters
Some parameters are not likely to change substantially:
Oil specific gravity
Removal required
Some parameters will change substantially:
Flow rate
Operating water temperature

17. Design choices Instantaneous flow rate
Surge capacity / solids and oil retention volume
Piping sizes
Flow Scheme and Separations system
Can centrifugal pumps be avoided?

18. Instantaneous flow rate
Treatment systems operate on an instantaneous basis – not a barrels per year basis
This basis should be determined using the maximum flow expected

19. Tank Capacity Inlet tank capacity should be sufficient to contain:
Water to allow for up to two days of operation
Oil content of up to 5% for two days of operation
Solids storage sufficient for 50 mg/l for two days of operation
Total = sum of above

20. Piping Flow Capacity
Make sure the piping system from the inlet of the overall system to the injection pump is large enough for the flow
Use large pipe to avoid pressure drops which cost energy and degrade droplet size distributions
If piping is too small, water will back up in the inlet tankage
Avoid centrifugal pumps if possible

21. Separation System Design
Systems should be designed to remove substantially all of the oil present in the inlet
Coalescing plate separators work well
Really good oil removal will preclude bacterial growth in the system, final filter, and downhole formation.

22. Bacterial growth inhibition
Inefficient oil removal Efficient Oil Removal
Large bacterial growth Minimal bacteria growth

23. Permian Basin Pilot Testing
Inlet and Outlet Samples – two sets

24. Design of Full Scale Unit
Based on 500 barrel Frac Tank
1050 gpm (36,000 bpd) water flow
Capacity:1-7 rows of media
West Texas light crude 0.82 S.G.
Designed for 50 mg/l out with 2000 mg/l inlet concentration with three rows of media
Can add additional rows if necessary for more flow or lower effluent

25. Frac Tank Based Separator
Flow rate approximately 36,000 bpd

26. Frac Tank Based Separator

27. Permian Basin Installation

28. Test Results, Full Scale Unit
Full Scale Unit Operations
Test Results, Full Scale Unit
Inlet Hydrocarbon Concentration
Outlet Hydrocarbon Concentration
90 mg/l
13 mg/l
85 mg/l
14 mg/l
119 mg/l
7 mg/l

29. Coalescing Plate Systems
Gravity operated
High efficiency Predictable oil removal
Design for whatever maximum effluent is allowed
Much smaller than other separators for same flow rate
Plates are not consumed – last years
Recovered oil can be sold

30. How is Maintenance Improved?
Extend periods between filter changes
Reduce filter change cost and labor
Reduce wear and tear on injection pump
Reduce downhole plugging and workover requirements
Reduce plugging due to oil in injection water
Reduce plugging due to bacterial growth

31. Summary and Conclusions
Recover oil that would otherwise be lost
Minimize plugging of final filter – reduce filter changes
Reduce plugging of disposal well by oil
Reduce plugging of well by bacteria
Improve operations and reduce workover and maintenance requirements

32. DESIGNING SALTWATER DISPOSAL SYSTEMS FOR OPTIMAL OIL RECOVERY AND MINIMUM MAINTENANCE
Questions?
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