Produced or fresh water being treated may have suspended solids, such as formation sand, rust from piping and vessels, and scale particles, or dissolved solids (various chemical ions). For most uses or disposal methods, these solids may need to be removed. It may be necessary to remove these solids to prevent wear in high-velocity areas, prevent solids from filling up vessels and piping and interfering with instruments, and comply with discharge restrictions on oil-coated solids. This equation applies strictly to creeping flow regimes in which the Reynolds number is less than unity; this is mainly concerned with spheres of very small diameter surrounded by a liquid. For very small particles, the inertial forces are much less than the viscous forces because of the low particle mass, and the particle does not enter into a turbulent settling regime. Most sedimentation basins are rectangular flumes with length-to-width ratios of 4:1 or greater to limit crossflow. The width of the flow channel can be determined by setting the time required for a particle to settle from the top of the flume to the bottom equal to that required for the water to traverse from the inlet of the flume to the outlet, as shown in Figure 1.
Produced water typically enters the water-treatment system from either a two or three phase separator, a free water knockout, a gun barrel, a heater treater, or other primary separation unit process. It probably includes small amounts of free or dissolved hydrocarbons and solids that must be removed before the water can be re-used, injected or discharged. The level of removal (particularly for hydrocarbons) and disposal options are typically specified by state, province, or national regulations. This article discusses techniques for the removal of free and dissolved hydrocarbons. See Removing solids from water for information on solids removal. In applying these concepts, one must keep in mind the dispersion of large oil droplets to smaller ones and the coalescence of small droplets into larger ones, which takes place if energy is added to the system. The amount of energy added per unit time and the way in which it is added will determine whether dispersion or coalescence will take place. Stokes' law, shown in Eq. 1, is valid for the buoyant rise velocity of an oil droplet in a water-continuous phase. Several immediate conclusions can be drawn from this equation.
Solids are almost always present in an oil, gas, and water-producing stream. Unfortunately, the solids are usually ignored until the problems caused by the solids become so onerous that action is required. This article discusses the impact of suspended solids in produced water. In some cases, the reservoir sands are known to be unconsolidated, and sand control is part of the project development. However, even if sand control is successful, fine solids will still be produced and end up in the produced water system.
Water management can significantly add to the cost and environmental footprint of oil production and innovations in water management can provide significant economic and environmental gains. New treatment technologies make recycling of water for hydraulic fracturing possible. Methods for recycling fracking water include anaerobic and aerobic biologic treatment; clarification; filtration; electrocoagulation; blending (directly diluting wastewater with freshwater); and evaporation. Generally, anaerobic treatments on wastewater are implemented on concentrated wastewater. Anaerobic sludge contains a variety of microorganisms that cooperate to convert organic material to biogas via hydrolysis and acidification.
In this study, a pilot plant with a capacity of 50 m3/d was used to conduct flotation, filtration, and adsorption trials for produced-water treatment at a crude-oil gathering facility. The number of offshore facilities employing waterflooding with desalination continues to grow. Currently, more than 50 sulfate removal units are in operation offshore with a total capacity of approximately 8 million BWPD.
Water treatment systems in the North Sea differ from those in the deepwater Gulf of Mexico (GOM). This paper provides a detailed understanding of these differences and provides insight into the design of water-treatment systems in general. In this study, a pilot plant with a capacity of 50 m3/d was used to conduct flotation, filtration, and adsorption trials for produced-water treatment at a crude-oil gathering facility. A recent webinar covered the varieties of current technology for flotation equipment and provided an in-depth look into flotation technology and the options surrounding offshore applications. The author reviews advances in produced water treatment, particularly offshore, since the 1960s.
Water treatment systems in the North Sea differ from those in the deepwater Gulf of Mexico (GOM). This paper provides a detailed understanding of these differences and provides insight into the design of water-treatment systems in general. A recent webinar focused on hydrocyclones and their application for offshore oil and water separation. The discussion includes fundamental science, practical considerations, implementation and field experience. The author reviews advances in produced water treatment, particularly offshore, since the 1960s.
While storage and logistics are critical elements of the viability of water reuse, if the water chemistry is not fit for gel fracturing formulations, it will not matter how much is stored in centrally located impoundments. This paper reports on performance of an advanced MVR system in north-central Texas. With inconsistent inlet water quality being the rule rather than the exception, sizing and operational considerations of the treatment system components must vary accordingly to make the most economic sense. The demands for the fresh water used in many hydraulic fracturing operations are placing pressure on water sources in some regions of the United States. Because of the high volumes of water needed for fracturing and competing demands availability of fresh water has decreased and costs have grown.
Many oil and gas companies are pursuing fracture-flowback-water and produced-water recycling for subsequent drilling and fracturing operations. Removal of metals is important to success of these processes. This is the third article of a series on water management for hydraulic fracturing in unconventional resources. This month, water treatment technologies are introduced, beginning with the removal of suspended solids by coagulation/flocculation and electrocoagulation for recycling flowback fluids.
Enhanced oil recovery processes, particularly offshore, create challenges for produced water treatment. Higher oil prices has created increased interest in chemical enhanced oil recovery (CEOR) using polymers, surfactants, and alkalis. This technology poses some special challenges, especially around water treatment.