Water Recovery via Thermal Evaporative Processes For High Saline Frac Water Flowback

Transcription

1 Water Recovery via Thermal Evaporative Processes For High Saline Frac Water Flowback JOSEPH TINTO, ROBERT SOLOMON, GE Water & Process Technologies, Bellevue, WA (IWC-10-XXXX) KEYWORDS: Frac Water Treatment, Thermal Evaporative Treatment, Frac Water Recovery To avoid the water related limitations and further the development of the nation s shale gas resources an economical process to recover and reuse water from hydrofracturing operations is required. Currently, most frac water is trucked off-site for disposal by deep-well injection. This water returns as flowback and produced water having a high TDS level (>100,000 ppm). A study examining thermal processes for water recovery and beneficial use of salt waste was conducted. The contribution to the U.S. energy supply from unconventional natural gas sources such as tight shale formations is increasing dramatically. To release natural gas from a shale deposit, 1-5 million gallons of water plus hydrofracturing chemicals are pumped under high pressure down a shale gas well. This water (12-60%) returns as flowback water (TDS ranging from 40,000 mg/l to 150,000 mg/l) and produced water having a TDS level (>100,000 ppm) and high hardness (>10,000 ppm as CaCO 3 ), including significant levels of barium. Currently, most frac water is either trucked off-site for disposal by deepwell injection or is processed for reuse in further frac operations by means of metals removal and suspended solids removal treatments. The handling and processing of both the flowback produced waters is a major cost issue for Gas Producers. The disposition of these waters are a major focal point of many environmental groups across the nation as well as a point of regulatory focus for many state environmental protection agencies. In some shale gas plays the availability of source water for frac operations is at times limited adding to the focus of recovery on these waters. To avoid the water related limitations and further the development of the nation s shale gas resources an economical process to recover and reuse water from hydrofracturing operations is required. An indepth study of water recovery involving thermal processes of evaporation combined with salt production by crystallization was undertaken. Studies of the reuse of the distillate and the beneficial use of salt products, meeting TCLP & ASTM standards as well as State regulations were conducted. The results of the simulations and pilot testing are discussed in this paper. 1

2 Full treatment systems ranging in capacity from a 50-gpm mobile treatment system to fixed plants of 200,000 GPD to 1.0 MGD have been developed and are presented. the flowback and produced waters from the Southwestern area of Pennsylvania, however the results can be applied across most shale plays upon evaluation of the specific water characteristics. Introduction The frac water, as presented from wells sampled in the Marcellus Shale in Southwestern Pennsylvania, can be treated to recover approximately 82% of the water in a Pretreatment, Evaporation & Crystallization plant. The residual salts from crystallization can be used as feedstock for saleable salt products such as road deicing salt or for industrial softener processes. The pretreatment process was developed by GE Water & Process Technologies in our Thermal Products lab utilizing our in depth database of Marcellus Shale frac water samples. The results of the pre-treatment were applied across the samples with consistent results. The frac water samples show various high TDS levels, ranging from 110,000 mg/l to 150,000 mg/l. The GE Water & Process Technologies treatability study did create a 134,000 mg/l TDS blended solution for the test as a reference flow equalized feed from a wide gas well feedwater source. The flow equalized feed will result from the flowback and produced waters of many wells across a given geography having various elapsed time periods from the date of the well fracture. All shale plays are different in terms of the water characteristics of the flowback and produced waters returned from the gas well fracturing and production operations. In fact, the characteristics of these waters has been observed to vary considerably within a specific shale play. The study presented here is focused on the results of an evaluation of 2 GE Water & Process Technologies Bellevue, Washington office has been conducting analyses and performing tests on frac flowback water and produced waters from several natural gas wells in the Marcellus Shale zone in SW Pennsylvania to determine the most effective method of treating the water via a thermal evaporative process. The results of this effort has lead to the development of a thermal Zero Liquid Discharge (ZLD) discharge system for treating natural gas drilling wastewater, known as both frac and produced water. The project s primary objective is to treat the frac water, produce dried solids suitable for recycle or disposal, and recover water for reuse in the gas well frac business. Because this is the first of its kind ZLD treatment system for frac water, an extensive laboratory test program was developed to generate the required process design data. The laboratory test program consisted of bench scale evaporator & crystallizer testing. The specific objectives of the laboratory test program include the following:

3 Develop process design basis Evaluate feed pretreatment requirements Identify optimum evaporator design parameters o Maximum concentration factor (CF) o Boiling point rise (BPR) o Foaming, fouling, and scaling tendencies o Distillate composition Evaluate Crystallizer Designs & Performance o Boiling point rise (BPR) o Foaming, fouling and purge stream potential o Salt purification / separation A baseline feed chemistry for the ZLD system was established. Several frac water samples were collected, blended, and analyzed. Based on these analyses the frac water composition range listed in Table 1 was established for the ZLD system process design basis. Frac water contains a high concentration of total dissolved solids (TDS). The TDS is mainly sodium chloride and calcium chloride. High barium and strontium levels were identified in the wastewater. High amounts of iron, magnesium, and potassium were detected. Overall, the frac water chemical composition depends on the contributing frac wells and their associated age post frac. The frac water feed contains very high total suspended solids (TSS); therefore, the feed will most likely require pretreatment prior to entering the ZLD system. A Baseline Test of the Raw Water Feed to the Heat Exchanger & Evaporator glassware simulators was conducted to evaluate pretreatment requirements. TABLE 1: ANALYTE Baseline Feed Chemistry Raw Water mg/l ph, standard 20 C 6.3 Conductivity, µmhos/cm 115,000 Turbidity, NTU 8 Total Suspended Solids 13 Total Dissolved Solids (105 C) 134,000 Total Dissolved Solids (180 C) 130,000 Fixed Solids (550 C) Density, g/ml Total Solids (105 C), % w/w Acid Insoluble Matter, % w/w Loss-On-Ignition (550 C), % w/w Sodium 31,800 Calcium 8,790 Magnesium 770 Potassium 130 Silica by colorimetry Silica by ICP 25 Total Sulfur < 20 Sulfate Sulfide Chloride 75,560 Fluoride < 2 p-alkalinity (as CaCO3) 0 t-alkalinity (as CaCO3) 59.6 Total Inorganic Carbon Ammonia Nitrogen 89 Total Organic Carbon Oil & Grease (HEM) Total Phosphorus < 3 Barium 3,060 Iron 71 Manganese 4.2 Strontium 2,430 1 Results are given in mg/l on a filtrate basis. Three primary options are available for pretreatment either a combination of aeration and filtration, the use of chemical oxidizers or the use of precipitation agents. The method of pretreatment was established by testing the methods on sample frac water. 3

4 Objectives Based on our experience with fracture water and produced waters from various shale plays we developed a series of analysis and tests to gather information to answer six key questions: 1.1 What is the composition of the water and how does if vary with age of the well (post-frac)? Develop Frac Water Blends using flow based well data. 1.2 What types of pretreatment are appropriate to deal with the high mineral content, suspended solids, and total organic carbon? 1.3 What is the chemical consumption for the process? 1.4 What is the scaling potential and how will it be dealt with for the: Heat exchanger Evaporator 1.5 What is the recovery rate and the chemistry of the concentrated brine? 1.6 What is the analysis of the waste brine and the recovered salt properties? Test Methods To address each of the questions, the following methods were employed: Question 1. What is the composition of the water and what is a representative sample? 2. What type of pretreatment is appropriate? 3. Will scaling be a problem with the brine and are scale inhibitors a solution? 4. What dosages and total amounts of chemicals will be used? 5. What are the water recovery factors? 6. What is the composition of the Waste Brine and recovered salt? Test Method Water chemistry analysis for daily samples + well production logs Simulation of: Aeration Filtration Precipitation Simulation of: Heat exchanger Evaporator Record results of chemical usage for: Pretreatment Scale inhibitor usage Evaporator simulation Record results of: Distillate recovery (from evaporator simulation) Saturation indices Compound salts and scaling Chemistry analysis of evaporator simulator sump and crystallizer solids. 4

5 Water Chemistry Analysis Table 2.1 Sample Sample ANALYTE SX-23 SX-13 4-Feb 4-Feb mg/l mg/l ph, standard 20 C Conductivity, µmhos/cm 121, ,000 Turbidity, NTU Total Suspended Solids Total Dissolved Solids (105 C) 147, ,000 Total Dissolved Solids (180 C) 146, ,000 Fixed Solids (550 C) Density, g/ml Total Solids (105 C), % w/w Acid Insoluble Matter, % w/w Loss-On-Ignition (550 C), % w/w Sodium 36,400 42,700 Calcium 11,300 14,600 Magnesium 1,460 1,590 Potassium Silica by colorimetry Silica by ICP Total Sulfur 30 < 10 Sulfate x Sulfide Chloride 84, ,000 Fluoride < 2 < 2 p-alkalinity (as CaCO3) t-alkalinity (as CaCO3) 0 0 Total Inorganic Carbon < 10 < 10 Ammonia Nitrogen Nitrite Nitrogen Nitrate Nitrogen Cyanide Thiocyanate Total Organic Carbon x Oil & Grease (HEM) Total Phosphorus < 5 < 5 Aluminum Arsenic Barium 8.9 3,780 Boron Cadmium Chromium Copper Iron Lead Lithium Manganese Molybdenum Nickel Selenium Silver 5

6 Water Chemistry Analysis Table 2.2 Sample Sample Sample Sample ANALYTE M-9 PW-A RH-1 K-3 4-Feb 4-Feb 4-Feb 4-Feb mg/l mg/l mg/l mg/l ph, standard 20 C Conductivity, µmhos/cm 129,000 73,000 40, ,000 Turbidity, NTU Total Suspended Solids Total Dissolved Solids (105 C) 162,000 67,400 32, ,000 Total Dissolved Solids (180 C) 158,000 66,000 31, ,000 Fixed Solids (550 C) Density, g/ml Total Solids (105 C), % w/w Acid Insoluble Matter, % w/w Loss-On-Ignition (550 C), % w/w Sodium 40,200 17,400 8,330 57,700 Calcium 9,940 4,040 2,070 17,100 Magnesium ,420 Potassium 1, ,160 Silica by colorimetry Silica by ICP Total Sulfur < < 20 Sulfate x Sulfide Chloride 89,900 37,600 17, ,000 Fluoride p-alkalinity (as CaCO3) t-alkalinity (as CaCO3) Total Inorganic Carbon Ammonia Nitrogen Nitrite Nitrogen Nitrate Nitrogen Cyanide Thiocyanate Total Organic Carbon x Oil & Grease (HEM) Total Phosphorus < 5 < 5 < 5 < 5 Aluminum Arsenic Barium ,060 Boron Cadmium Chromium Copper Iron Lead Lithium Manganese Molybdenum Nickel Selenium Silver Strontium 2, ,630 Zinc 1 Results are given in mg/l on a filtrate basis. 6

7 Baseline Testing & Evaluation The frac water composite blend (134,000 mg/l TDS) will be run through the Heat Exchanger & Evaporator Simulations with and without the use of scale inhibitors and prior to any other pre-treatment methods. This procedure will develop a baseline for the thermal evaporative system performance. Pre-Treatment Methods and Analysis Aeration This test determines how quickly oxidation occurs to exhaust the soluble iron and magnesium. The speed and effectiveness of oxidation was used to determine the residence time for the influent during pretreatment (if applicable). Filtration The aerated water was then filtered to simulate media filtration. Filtration will remove the suspended particles such as insoluble iron and magnesium. The efficacy of filtration will be determined by the time required to filter the samples. Chemical Oxidation This test determines how quickly oxidation occurs to exhaust the soluble iron and magnesium. The speed and effectiveness of oxidation was used to determine the residence time for the influent during pretreatment (if applicable). Chemically assisted oxidation methods were used to evaluate alternatives to aeration and filtration. Strong oxidizers followed by filtration have been found to successfully treat the high iron and TSS content feed where aeration has not been successful. It was shown that chemical pre-treatment is more effective in the Marcellus region while aeration/filtration is more effective in other shale plays. Precipitation Chemically assisted precipitation methods were used to evaluate alternatives to aeration and filtration, as well as chemically assisted oxidation. Chelating agents used in the well frac operations can bind the dissolved iron resisting oxidation attempts. It was shown that chemically assisted precipitation may overcome the chelating agents and allow the removal of dissolved iron. Simulation of Equipment with Scale Building Tendency and Effectiveness of Scale Inhibitors Laboratory glassware apparatus was used to simulate equipment with scaling potential - the heat exchanger and the evaporator. Two types of solution were evaluated a high salinity composite (blend) of the frac water samples - with and without the use of a scale inhibitor. Heat Exchanger To simulate the heat exchanger a threemouth flask was utilized with a titanium coupon suspended via a glass rod, as shown in figures 1 and 2 below. The titanium coupon was submerged in the brine solution. Distillate vapor was returned to the closed system via a cold-water condenser. The sample was refluxed at 206 F for 20 hours (to ensure that chemical equilibrium was reached) and then the coupon and solution was examined to determine if scaling occurred on the coupon or whether there was any turbidity in the solution. 7

8 Figure 1 - Heat Exchanger Simulation Figure 2 Close-up of Heat Exchanger Simulation Figure 3 Bench Scale Evaporator Test Apparatus 8

9 Evaporator To simulate the evaporator a three-mouth flask was utilized with a titanium coupon suspended via a glass rod. The titanium coupon was submerged in the brine solution. A pump was used to replace brine lost in the distillation process to maintain a constant level in the sump. The distillate was cooled via a cold-water condenser and captured for analysis. The procedure was carried out until a terminal TDS value of ~300,000 mg/l is achieved (approximately a concentration factor of 2.1 to 2.35). After reaching the desired concentration factor, the coupon, condenser, and solution were examined to determine if scaling occurred on the coupon or condenser and whether there was any brine foaming potential in the solution (and how it was treated). Figure 5 Iron (Fe) buildup on operating evaporation simulator wall Figure 4 Evaporator simulation glassware test Careful monitoring of the sump and condenser surfaces provides an indication of fouling potential. Visual observations regarding brine foaming potential was reported, and if necessary, treated using commercial antifoams widely with the approaches studied for pretreatment. Figure 6 Iron (Fe) scale shown on evaporation simulator wall 9

10 Chemical Dosage and Consumption Estimates The chemical dosage/consumption varied Pre-Treatment Any chemicals used as part of the pretreatment simulation were documented to provide a basis for a scaled up process. and settled for retention times ranging between 30 and 60 minutes. The results provided virtual complete removal of the dissolved iron. It was observed that a majority of the TSS and TOC along with the magnesium precipitated as well. Scale Inhibitor Due to the very high iron content there were concerns whether pre-treatment via aeration and filtration would be sufficient. Therefore, a scale inhibitor was analyzed to determine if chemical treatment alone would be sufficient and negate the need for aeration and filtration. The use of scale inhibitors appeared to be negligible in affecting system performance. This could be explained by the presence of residual inhibitors from the well frac operation. Chemical Oxidizing Agents Due to the very high iron content and the scaling tendencies demonstrated in the baseline testing, Chemical Oxidizing agents (Sodium Hypochlorite and Hydrogen Peroxide) were tested. Sodium Hypochlorite at dosages ranging from ppm was attempted with minimal effect on dissolved iron reduction. Hydrogen Peroxide at dosages ranging from ppm was attempted with minimal effect on dissolved iron reduction. In both cases aeration was attempted in conjunction with the chemical oxidation agent however severe foaming was observed. Figure 8 - Iron (Fe) sludge precipitation in sedimentation vessel Below is a brief summary of the centrifuge studies for the high Salinity Composite Frac Water Blend, and the sludge settling characteristics are shown in the attachment. Centrifugations were done at 2,500 rpm (corresponding to about 1,400G) with 100 ml samples and varying spin duration (see below): Precipitation Agents Agent was added to the frac water composite blend raising the ph of the fluid 10

11 High Salinity Agent treated slurry ph 10.4 Total wet solids from 1.0 L (from filtration study) g Centrifugation at 2,500 rpm (1,400G): 10 min pellet 2.7% V/V 2 min pellet 5.0% V/V 1 min pellet 6.0% V/V 0.5 min pellet 7.0% V/V The resulting supernatants were all visibly crystal clear, with turbidity measurements indicating only small amounts of fines (especially after 0.5 minute spin time). Turbidities were as follows: 0.5 min NTU, 1 min NTU, 2 min - < 0.2 NTU, 10 min - < 0.2 NTU. Figure 9 - Iron (Fe) sludge centrifuge test Heat Exchanger Operation The pre-treated frac water composite blend was run for 24 hours through the heat exchanger simulator operating at 205 degrees F. The pellets were light orange, and the liquidsolid boundary was very sharp. Despite this, no pellet was firm enough to support the weight of a small stirring rod. On the other hand, the supernatant brines could be decanted without disturbing the pellets in all cases, except for the 0.5 min spin time. Based on the visual observations, it is estimated that the centrifuge solids would pass the "Paint Filter Test," possibly with the exception of the shortest spin duration. Figure 12 Heat Exchanger Simulation on Frac Water Composite Blend with Iron, TSS & TOC removed 11

12 boiling point. Small retention samples of distillate and sump concentrate were taken at the designated concentrations, and these were used to determine the TDS. Figure 13 Close up of Heat Exchanger simulation on Frac Water composite blend with Iron, TSS & TOC removed Data points were taken at designated time intervals. The volume, ph, and conductivity, were recorded for the heated composite blend along with the temperature. Visual observations regarding the heated frac water composite blend turbidity and/or precipitation were made at each datum point. The analytical results for precipitate and scaling tendencies were recorded. Figure 14 Evaporator Simulation on Pretreated Frac Water Composite Blend at CF of 2.1 Evaporator Operation On reaching the final concentration ( CF), the sump was refluxed to ensure that chemical equilibrium between dissolved and precipitated species is reached. The final brine was analyzed. Data points were taken at designated concentration. The volume, ph, and conductivity, were recorded for the distillate along with the sump concentrate ph and Figure 15 Close up of Evaporator Simulation 12

13 Visual observations regarding sump turbidity and/or precipitation were made at each datum point. The analytical results for chloride were also used to assess and verify concentration factors. Individual Well Sample Analysis The individual well samples, supplied from wells throughout Southwestern PA, were Tested as separate sole feed streams to detect any potential effects on the pretreatment method. The results of the individual well samples were consistent with the High Salinity Frac Water Composite Blend that was tested. The results of the individual sample pretreatment settling results are shown below Water Recovery, Concentrated Brine Analysis of the Modeled System Phase 1: Pretreatment The pretreatment involves the removal of iron, manganese, TSS, TOC, and a reduction in magnesium. The iron sludge solids removed in this process comprise roughly 5 % of the initial volume with 65 % moisture content. The flow out of the pretreatment process is projected as 631 gpm. For a modeled total system feed of 665 gpm, the total water recovery, from the evaporation and crystallization process is predicted at 92% equal to 612 gpm. Phase 2: Evaporation The water recovery in phase 1 the evaporation system, has been demonstrated to be 60% of the evaporator feed equal to 379 gpm. Phase 3: Crystallization The water recovery in phase 2 the crystallization system, has been predicted to be 92 % of the crystallizer feed equal to 233 gpm. The salt solids account for the remaining flow to the crystallizer. Concentrated Brine Analysis Figure 16 Pre-treated samples from Individual wells The concentrated brine generated from the evaporation process (Phase 2) is envisioned being sent to the crystallization process (Phase 3) for the production of beneficial use salt products. Alternatively, the concentrated brine, projected at 252 gpm, could be hauled via tanker truck or rail tanker to approved & contracted disposal wells. This disposal 13

14 option could be employed if investment in the crystallization plant (Phase 3) was not desired, however the amount of trucks required and the cost of the transportation and ultimate deep well disposal would seem to make this approach prohibitively expensive. Solids Production and Disposal Options Pretreatment Specific pretreatment of the concentrated brine, prior to introduction to the crystallization plant, is not anticipated at this time Initial treatability study of the concentrated brine taken to crystallization shows the potential production of feeder material suitable for refinement into saleable salts for uses such as road de-icing or industrial softener salt. The production of acceptable feeder material for either road grade de-icing salts or industrial softener salts does not guarantee the availability of purchase contracts for the salt. Weather and seasonal conditions may require large storage facilities for the salt products while awaiting contracts and shipments. The salt production of primary feeder material, from the modeled facility, for road salt production is anticipated to be over 300 tons per day. Full Treatment Systems Based upon the results of the study on evaporative treatment of frac water flowback and produced waters, several full scale plant applications were developed. A system for treating 1.0 MGD of frac water flowback and produced waters, illustrated above, can provide a treatment cost to the producers of less than $5.00/bbl of water brought to the facility. The facility operator is envisioned to be independent of the natural gas producers, though the operator would contract with the producers for specific treatment volumes. 14

15 The treatment costs for various size operations with daily plant throughput ranging from 1.0 MGD down to 0.25 MGD would be affected by the ratio of the CAPEX and OPEX costs against the plant s throughput. The projected costs for full evaporation & crystallization treatment based upon the previously noted plant throughputs range from $5.00/bbl to $6.80/bbl. Fixed facilities can be placed on sites of 2 4 acres, dependent upon truck access and site water storage requirements. Mobile Evaporator Systems Trailerized, truly mobile evaporator systems can handle up to 50 gpm of frac water flowback and produced waters for volume reduction at remote well sites. The disposal of the reduced volumes of concentrated brine is still required. Treatment cost for mobile evaporator only operations are projected at less than $6.50/bbl of water brought to the system. 15