Oil-water must be separated with some type of gun barrel tank or physical means. Adding chemical cocktails to remove or bind up the oil, iron and scaling ions (with varying degrees of cost and effectiveness) and the use of a biocide or chemical oxidant to manage or kill bacteria.
Throughout the fluid lifecycle, oxidation of the iron (whether natural or catalyzed by other man-initiated reactions) can impede or negatively impact other processes. For example, oxidized iron is known to stimulate growth of certain nutrients for bacteria, reducing the effectiveness of the biocide and driving up biocide costs. Oxidized iron might also form a solid residue that can deposit on pipe walls and restrict production rates.
During the conventional process of treating bacteria with an oxidizing biocide, “collateral” oxidation processes can wreak havoc with pH balances of the fluid, scaling tendencies, bacteria management, and other essential oilfield processes. In addition, the more powerful oxidants can be corrosive in nature, and if handled improperly, raise the risk of toxicity and flammability. Therefore, operators generally prefer to confine their use of oxidants to immediately prior to the frac and use more benign processes where possible to manage bacterial growth prior to the frac.
CarboNet™ water treatment is in the business of helping forward-thinking oil and gas operators and midstream water treatment companies treat produced water for reuse in innovative ways that promote sustainability, reliability and efficiency.
Recycling produced water for future frac jobs helps lower much of the risk, cost and complexity of disposal. But the process creates some new challenges.
One major challenge is how to effectively remove the myriad constituents that can cause major process problems when the recycled water is introduced back downhole. The most vexing culprits include:
Suspended oil droplets not removed from the produced water stream represent lost production revenue for the operation. If iron in solution (Fe2+) comes into contact with oxygen, it is oxidized to form insoluble iron compounds that can build up to clog piping and the reservoir downhole.
So-called hard water containing higher concentrations of calcium, barium and strontium may generate insoluble mineral scales.
Some bacterial strains that feed off the iron can form a brown slimy residue that further impedes production flow and may increase underdeposit corrosion risks.