The project goal is to further develop a proprietary, high-temperature nanofiltration (NF) technology (DurafluxTM) to remove salt and other dissolved solids from produced water originating from domestic oil and gas production. Treated water can be re-used in the extraction process without cooling/re-heating costs or can be recycled as an acceptable supply of source water. Project objectives are to (1) scale-up the fabrication process to create full-length tubular membranes; (2) perform long-term tests on processed water samples to demonstrate salt rejection, stability after multiple cleaning cycles, and stability under harsh temperature/dissolved solid exposure; and (3) develop a membrane filter plant reference design model and cost structure.
Eltron Research and Development Inc., Boulder, CO
Methods of produced water treatment vary by location in chemical makeup, volume, regulatory requirements, soil characteristics, and access to off-site disposal or deep well injection. Treatment costs are a combined sum of costs broken down into primary treatment, secondary treatment, pre- and post-treatment requirements, operating costs, and byproduct disposal (oil and grease, brine, and solids). Primary treatment of produced water from traditional oil and gas production typically uses a variety of physical separation methods to strip gas, volatiles, suspended oil, grease, and solids from the water. Secondary treatment often requires pretreatment steps such as reducing water temperature; removing dissolved organics, fine particulate, and precipitated iron oxides; adding antiscalants or water softeners; and adjusting pH and calcium to protect secondary treatment systems.
The recovery of oil and natural gas in the United States, especially from unconventional sources, is often limited by economic and environmental impacts of water co-produced during the extraction process. Innovative and cost-effective produced water treatment methods—particularly for removing salts and organic contaminants to meet regulatory quality standards for surface discharge—are needed to improve the economic viability of unconventional reserves.
The fastest growing source of produced water originates from capture of hydrocarbons from coalbed methane and shale gas reserves. Economic and environmentally responsible treatment methods will increase gas yields and provide freshwater resources for beneficial uses in arid regions while reducing environmental impacts in others. Cost-effective recycling of boiler feed water used for steam injection will reduce freshwater consumption and disposal costs. Duraflux™ technology is also capable of treating produced water at high temperature, thus reducing the energy required to re-heat it.
The composite membranes have showed consistent 60–67 percent magnesium sulfate (MgSO4) rejection. Membranes were also tested at higher temperatures and showed only slightly lower rejection than at lower temperatures. The membranes showed only slightly lower performance when exposed to organics. These membranes could be utilized in applications to separate salt (NaCl) solution containing organic solvents and at high temperature and pressure. The project setbacks created by supplier issues has resulted in an improved membrane synthesis process with attention to many factors that can affect performance.
Eltron received new samples from their supplier to replace the discontinued reagents used for membrane fabrication. Polymer deposition was completed in August 2012 and membranes were tested at high temperatures and pressures for use in the Duraflux™ process to treat produced water. Initial results showed that the membranes created with the new reagents did not perform as well as previous membranes. The researchers employed a test matrix for further polymer deposition experiments in order to achieve improved membrane performance.
Phase II membranes have reached >60 percent MgSO4 rejection in reproducible trials. The membranes are now being optimized for NaCl rejection. Scale-up to full membranes will begin once MgSO4 rejection is >80 percent and NaCl rejection is near 50 percent.
Membranes were delivered to AQWATEC for high temperature and pressure testing. The membranes were tested with a 2000 ppm MgSO4 feed solution at three different temperatures and pressures. Two membranes showed higher MgSO4 rejection and less change in performance after high temperature exposure. Membranes were prepared on the ceramic substrate and MgSO4 rejection ranged from 14 to 64 percent.
Membranes were deposited using the polymer formulation from Phase I studies, and MgSO4 rejection averaged 20 percent. Optimizing the polymer deposition conditions resulted in membranes with MgSO4 rejection of up to 60 percent.
Eight polymer coated tubes were tested for permeation flux and salt rejection. Salt rejection for these membranes ranged from 3 to 5 percent whereas Phase I membranes achieved 30 percent rejection. Flat membranes were tested using SEM and FTIR and results showed that the plates may not be sufficiently coated.
Eltron completed research on February 28, 2013, and has prepared a final report.