This paper is Part B of a two-part series. Part A includes an introduction, background chemistry of iron and iron oxides in produced water, the origins of iron in shale produced water, measurement of iron in produced water, and field observations of iron in shale produced water.
Part B covers facilities problems caused by iron, injectivity problems caused by iron, and the mitigation of colloidal iron-related problems. Part A’s abstract is included, and the Conclusions section of Part B addresses both papers.
This paper reviews the properties of iron compounds (such as iron oxides, iron hydroxides, and iron sulfides) and their impact in shale produced water treatment with an emphasis on the colloidal form of these compounds (small particle size, high surface charge). A wide range of problems is associated with these compounds in produced water including emulsion stabilization, oil-coated solids, pad formation in separators, pipeline solids, and plugging of water disposal formations. In conventional oil and gas production, the role that iron plays and the mitigation strategies for these problems are reasonably well known.
In the burgeoning shale industry, the situation is quite different. Not only are iron concentrations significantly higher than in conventional produced water, but the colloidal properties of iron compounds are only recognized by a handful of specialists. In addition, other colloidal particles such as clays and silts are also present at high concentrations in the produced water. Produced water treatment to remove solids in Permian shale produced water is rather hit or miss.
We were brought to this realization a couple years ago when testing formation plugging in Permian disposal wells. This was our first foray into produced water characteristics in the Permian. We measured produced water quality for about a dozen fields that had experienced declining injectivity. In nine of these fields the produced water contained high concentrations of small particles, tough biofilm in separators, and low-permeability filter cake formation according to the Barkman-Davidson test. It took almost a year to verify the iron-related mechanisms because data and knowledge of produced water characteristics in the Permian are scarce. This paper attempts to rectify the situation by pulling together knowledge of colloidal iron in produced water. Ultimately it is hoped that this work will help in the development of new cost-effective treatment strategies for produced water reuse and/or injection for disposal.
Facilities Problems Caused by Iron
In general, one of the most effective ways to eliminate problems related to suspended iron particles is to eliminate air intrusion in the facilities. By eliminating oxygen, the dissolved iron will remain dissolved in the produced water and will not cause plugging and other problems. This strategy is used extensively in conventional hydrocarbon facilities.
For example, the Chevron Kern River Facility in…