# Workshop 4, Theme 2, Session 3 A Water Chemistry Perspective on Flowback Reuse with Several Case



# Studies 30 March 2011 Keith Minnich, Water Sustainability Advisor2 

### Frac Flowback Reuse/Disposal – Early Shale Work In the beginning, near fresh quality water was the standard for frac fluid preparation and flowback was disposed in deep wells. Deep well disposal is widely practiced. Approximately 3 billion cubic meters are injected in the USA annually from conventional energy production.
Injection Well and Tank Battery at Commercial Disposal Facility in Texas from DOE Award DOE Award No.: FWP 49462 – Argonne Labs • Source water not a constraint and frac makeup was typically fresh water • Some believed at the time that near fresh quality water was necessary for the frac ingredients to perform as intended • Deepwell disposal was available for flowback. Frac flowback injection is small fraction of the total.3 

### Frac Flowback Reuse/Disposal – Dealing with Constraints Disposal constraints in new plays provided the motivation to reuse flowback by treating it to near fresh quality by removing dissolved solids (TDS) • High Total Dissolved Solids (TDS) flowback water and the presence of organics present treatment challenges • Very difficult application for Reverse Osmosis due to organics and clay • Only proven option is evaporation technology Range of Flowback TDS4 

### Frac Flowback Reuse/Disposal – Dealing with Constraints Application of water treatment technologies to create near fresh quality water from flowback

• Creating near fresh quality is feasible • High capital and operating costs • Evaporation does not allow 100% reuse of flow back Pre-treatment Evaporation Plant

Fountain Quail, Texas5 

### Frac Flowback Reuse/Disposal – Optimizing Constraints Experience and testing shows that near fresh quality water is not always a requirement for fracking • Options exist for saline tolerant chemical additives • 100% Reuse has been demonstrated and practiced Fountain Quail, Texas

Friction Reducer Source: Schlumberger Water Services

Good Enough for Fracking in some Cases6 

## Two Perceived Obstacles to Flowback Reuse are Suspended Solids and Scaling Constituents • Case Study 1; Removing Suspended Solids from Flowback, Is Filtration Necessary ? • Case Study 2; Managing Metals and Hardness • Logistics of Transporting and Storing Flowback
− Any discussion on reuse must emphasize the differences between the North American (Western Canada, Eastern Canada, Eastern USA, and Southern USA) shale gas formations and the differences between different locations in the same formation. Reuse decisions and logistics will be site specific.7 Data Collection to Support Reuse Water Management – Case Study 1; Removing Suspended Solids from Flowback Is Filtration Necessary ?

Filtration Recommended by Water Treatment Companies Stokes Law Analysis Indicates Filter Not Necessary8 Case Study 1; Flowback Filtration Necessary or Not? Particle Size Distribution after Settling in Flowback Storage

Suspended Solids Profile after Surge Tanks Total Suspended Solids ~ 1,500 mg/l9 Case Study 1; Flowback Filtration Necessary or Not? Particle Size Distribution after Settling in Flowback Storage

Suspended Solids Profile after Holding Tanks Total Suspended Solids ~ 100 mg/l10 Case Study 1; Flowback Filtration Necessary or Not? Particle Size Distribution after Settling in Flowback Storage11 Case Study 1; Flowback Filtration Necessary or Not? Particle Composition after Settling in Flowback Storage

XRD Analysis shows Suspended Solids after settling consist primarily of Barite12 

### Case Study 1; Scheme for Removing Suspended Solids

Surge Tanks Arranged in Parallel Surge Tanks Arrange in Parallel Inlet and Outlet at Opposite Ends Arrangement of Surge and Storage Tanks to Achieve < 50 mg/l of SS > 30 microns13 Case Study 1 Summary; Removing Suspended Solids from Flowback 

### • Attempts to filter flowback resulted in filter blockage with fines, creating an obstacle to reuse of flowback. • Settling in surge and storage tanks reduces suspended solids to < 50 mg/l of particles with a size range of 30 microns to 100 microns. • The amount of suspended in the flowback has not had any noticeable impact on well performance. No long term studies have been made. • Talisman has not observed biomass suspended solids which do not settle. • Settled solids are removed from tanks by vacuum trucks and disposed in licensed landfills.14 Case Study 2; Managing Metals and Hardness for Scale Control
Ionic balance shows closure within 8.5%, which is acceptable15 Case Study 2; Managing Metals and Hardness for Scale Control Ions of Concern for Scaling Low concentrations of scale forming anions Very high concentrations of scale forming cations Enough iron to have a concern16 Case Study 2; Managing Metals and Hardness for Scale Control Potential Scaling Compounds BaSO4 is at its saturation concentration with large amounts of excess Ba to precipitate with SO4 from fresh blend makeup or formation water There is some potential for CaCO3 or SrCO3 precipitation with large amounts of excess Ca and Sr There is some potential for ferrous carbonate or other iron scale precipitation17 Case Study 2; Managing Metals and Hardness for Scale Control Ionic Strength Increases BaSO4 Solubility, but not to a Significant Degree Compared to Ba Availability

Source: – Solubility of Barium Sulfate in Sodium Chloride Solutions from 25 C to 90 C, Charles Templeton, Journal of Chemical and Engineering Data, October 196018 Case Study 2; Managing Metals and Hardness for Scale Control Typical Recommendations for Scale Control and Alternative 

### • Scaling Potential
− BaSO4 is at saturation point with large amounts of excess Ba
− Large amounts of excess Ca and Sr are present to drive CaCO3 or SrCO3 precipitation
− Soluble iron is present to form FeCO3 precipitate
− SO4 and alkalinity from fresh makeup increase potential for precipitation 

### • The traditional recommended approach is to remove Ba, Sr, Ca and Mg from flowback using Na2SO4 and Na2CO3 and CaO which requires large amounts of chemicals and also trucking:
− 1.5 tons of Na2SO4 for every 500 bbl of flowback
− 3.5 tons of NaCO3 for every 500 bbl of flowback
− Trucking chemicals and flowback to and from treatment facility
− Solids generated by treatment must be landfilled19 Case Study 2; Managing Metals and Hardness for Scale Control Typical Recommendations for Scale Control and Alternative 

### • Alternative is to take advantage of formation water chemistry in above ground blending of flow flowback and source water to reduce scaling potential

− The constituents in flowback will react with the constituents in source water to reduce the scaling potential of the blend20 Case Study 2; Managing Metals and Hardness for Scale Control Using Natural Barite Seed Crystals for Scale Control

Source: – Solubility of Barium Sulfate in Sodium Chloride Solutions from 25 C to 90 C, Charles Templeton, Journal of Chemical and Engineering Data, October 1960 625 mg/l of barite de-supersaturates Flowback after settling has 250 mg/l of primarily barite SS Co-precipitation of scaling salts is known from other applications – this has not been studied for flowback21 Case Study 2; Managing Metals and Hardness for Scale Control Typical Chemistry after Blending Flowback and Fresh Water

• Talisman has reused flowback with only settling • No chemical addition for precipitating metals and hardness • Blend TDS of approximately 50,000 mg/l • No apparent negative impact on the formation or gas production22 Case Study 2 Summary; Managing Metals and Hardness for Scale Control Blending of Flowback and Fresh Water for Scale Control • Talisman has reused flowback with only settling, and no chemical addition for metals and hardness reduction, for blend TDS of approximately 50,000 mg/l • Why might blending of flowback and fresh water reduce scaling potential?
− Iron is likely oxidized and precipitated as Fe(OH)3 in surface tanks
− Reduction in ionic strength reduces BaSO4 solubility by 50%. SO4 from surface water reacts with excess Ba and likely precipitates on seeds
− Some CaCO3 and SrCO3 precipitation will occur. However, at this time scale control is indicated because of inverse solubility with respect to temperature and lack of definite information on co- precipitation • What about formation compatibility?
− The presence of barite “seeds” should reduce down hole and formation scaling due to preferential precipitation on the seeds
− Caution is recommended for formations with soluble sulfate. However, barite “seeds” might be useful in such situations
− In principle, fewer salts should be solubilized from the formation with higher TDS frac fluid
− The impact of increased frac fluid density has not been investigated23 

### Importance of Logistics for Managing Flowback Reuse

• Number of wells per pad – Flowback reuse on Multi -Well pads reduces movement of flowback off the pad • Timing - storage required to deal with when flowback is available and 

### when it is required • Variations in the amount of flowback. The range is 10% to 50% of the injected frac fluid • Location of fresh makeup • Contiguousness of leases The logistics of transporting and handling flowback to minimize environmental and public health risks must take the following into consideration:24 Flowback Logistics – Multi -Well Pads Reduce Truck Traffic when Flowback is Reused Multi -Well Pads (6 to 24 per pad)

Source: Statoil Reuse of flowback significantly reduces the amount of flowback removed from the pad versus no reuse of flowback25 

### Flowback Logistics for < 20% Flowback

Flowback Storage Portable tanks are suitable for smaller volumes of flowback26 

### Flowback Storage for > 40% Flowback Source Water

Flowback Storage Portable tanks are less suitable for smaller volumes of flowback and field erected tanks are more practical27 Logistics for Managing Flowback Reuse Pipelines versus Trucks 

### • Trucks

− Justified when flowback volumes are small
− Truck traffic reduced substantially by multi -well pads 

### • Pipelines

− Justified when flowback volumes are large
− Reduces truck traffic
− More land disturbance than trucks 

### • There is no specific rule for one versus the other28 

### Shale Gas Flowback Water Reuse Summary • Water chemistry considerations indicated that flowback does not require extensive treatment in all cases before it is reused • Talisman Energy has successfully reused flowback with only settling of suspended solids for TDS of approximately 50,000 mg/l • From a scale control perspective it might be advantageous not to remove metals and hardness before blending
− Takes advantage of the de-supersaturation capability of naturally occurring barite seed crystals. Co- precipitation of other scaling salts might be a benefit.
− The seed crystals might reduced down hole and formation scaling 

### • Reuse reduces truck traffic when disposal wells are not available • Due to variations between locations, the flowback reuse and logistics issues are site specific