Oxidation, settling and aeration at the heart of simple, efficient program that grows reuse to 60 percent.
Since the days when Roman legions marched across their European empire, military banners have been used to identify unit designation and corps affiliation.
These standards, usually poles topped with signs, symbols or flags, remain an important representation of military organizations. In the U.S. Armed Forces, a guidon (guide on) is considered a rallying point for the troops and is always in the front of a formation.
To establish a culture of comradery and purpose, the name Guidon Energy was chosen in 2016 by the founders of a independent shale-play oil company focused on the Midland Basin.
In three years of operation, Guidon has found success developing an acreage position in Martin County, Texas, northeast of the City of Midland, that includes 28,000 net acres with 1,200 drill-ready locations. The company had three horizontal rigs running in December.
Like other Permian operators, Guidon recognized produced water logistics and disposal would present a challenge.
While initially working with a third-party disposal company as it developed an internal water program, Guidon set a goal of increasing reuse. To achieve that goal, it put out a bid request for help designing a water management system specifically for the levels of bacteria, iron, sulfides, pH and total suspended solids typically found in its produced water. It chose Hydrozonix to help develop a simple, cost effective system.
Founded in 2016 by Jay Still, president and CEO, with the backing of the private-equity investment firm, Blackstone Energy Partners, Guidon’s objective is to develop its leasehold through manufacturing styled horizontal well development.
The company’s experienced leadership intends to capitalize on their operational excellence and track record, and the financial support of Blackstone, to grow Guidon’s acreage position, deliver strong well results and support a culture of health, safety and environmental leadership. Guidon’s mission has led to development of a first-class produced water management program.
Brett Creeser, chief operating officer, relied on his industry experience to build a team from the ground up. In his decades in the industry, including at Mobil Oil, Pioneer Natural Resources, and Laredo Petroleum, Creeser has managed development of cradle-to-grave water management programs. For Guidon, he recruited Chuck Pounds to build and operate the company’s produced water program.
A believer in the concept of “Failure University,” Pounds follows a trial and error approach that allows learning from mistakes and refining your approach until a successful program is developed. Pounds relies on this idea for continued refinement of his systems for improved performance and reduced costs.
One of the company’s first challenges was managing its own disposal well program.
In the Midland Basin, the most popular disposal choice is in the San Andres formation. Unfortunately, this formation is famously pressuring up in areas. There are more than 2,000 shallow San Andres disposal wells in the Midland, about 40 percent of which are commercial wells operated by third parties. As a result, even if a company reduces injection rates to control pressure on its well, nearby commercial wells may operate at high volumes and impact formation pressure for the operator.
The number of commercial disposal wells in Texas has increased by 566 percent since 2010. It is estimated that 4 billion bbl of oilfield water has been injected in these shallow San Andres wells since then.
Beyond the pressure issues, there are safety risks associated with drilling in the San Andres. Among them, hydrogen sulfide (H2S) levels of 20-50 ppm are common with levels of 200-300 ppm reported. Exposure to H2S can cause loss of smell at 100-150 ppm and death after 48 hours of exposure at 100 ppm. As a result, operators now use modified drilling techniques when drilling into the formation.
Estimates show that issues related to formation pressure in the San Andres have increased costs to $13 million for every two square miles of land. These are mostly attributed to increased use of drilling liner, which can run to $600,000 per well. Continued disposal into the San Andres only increases these risks and costs.
The issues with the San Andres have led some operators to look to the Ellenburger Formation which is deeper. The Ellenburger has been widely studied and seen some controversy.
Since 2008, seismicity concerns in the Barnett Shale and a series of minor earthquakes near Azle, Texas, in 2013 and 2014, forced two local E&P companies to defend their disposal wells and the Texas Railroad Commission to tighten up its permitting regulations for disposal wells.
Induced seismicity is generally not a concern for operators in the Midland basin, but the pressuring up of the San Andres limits disposal capacity, increases drilling costs and includes potential safety hazards. These concerns led Guidon to pursue a produced water reuse program from the onset.
DOWN THE PATH
Many start-up operators like Guidon initially rely on third party contractors for disposal of their produced water. Later, the same contractor may help the operator develop a reuse program so the operator can focus on new wells and field development.
Guidon initially partnered with a third party deep-disposal company while building its own water management infrastructure. Once developed, Guidon’s private water infrastructure allowed the company to establish a blending program of 13 percent reuse to 87 percent freshwater for its fracs. Since then, Guidon has stayed on the reuse path while continuing to add to its infrastructure.
The first step in developing a produced water reuse program is developing a company specification for produced water and a standard for reuse.
As more operators develop their own produced water reuse programs, water specs and standards have become more uniform. Guidon’s water treatment goals were based on levels of bacteria, iron, sulfides, pH and total suspended solids in its produced water.
The Guidon water treatment program relies on oxidation for bacteria, iron and sulfide control while a settling or sedimentation process was used for TSS. Once the treatment standard was in place, a treatment strategy was defined and developed. For Guidon, the strategy became oxidation, settling and aeration, a simple and cost-effective strategy.
Simply stated, oxidation is the loss of electrons. When an atom or compound loses one or more electrons, it is referred to as being oxidized. Some elements are said to be easily oxidized when they lose electrons more readily than others. Metals including sodium, magnesium, and iron, are easily oxidized. In the case of produced water, oxidation is used for iron, bacteria and sulfide control.
With iron, ferrous iron is water soluble while ferric iron is insoluble and will drop out with other solids. When ferrous iron is oxidized, it becomes ferric iron and gives water a rust color. This ferric iron rust color can be settled out.
When bacteria lose an electron during oxidation, its cell wall is destabilized and ruptured. This kills the bacteria cell.
Oxidation treatment of sulfides is a two-step process. The first converts sulfides to sulfur. Further oxidation takes sulfur to sulfates which are water soluble. Some oxidizers act quickly and take sulfides directly to sulfates; others act slowly with an intermediate stop at sulfur.
Depending on the operator’s goal, sulfur may be dropped out as a solid. If the goal is not to generate extra solids, full oxidation takes sulfides to sulfate. The down side of full oxidation is that sulfate scaling can develop, but if barium and strontium are not present, scaling may not be an issue.
Common oxidizers used in oilfield water treatment include chlorine dioxide (ClO2 ), hydrogen peroxide (H2 O2 ), sodium hypochlorite (NaOCl) and ozone (O3 ). For its water oxidization needs, Guidon selected a portable ozone system supplied by Hydrozonix.
Ozone has an advantage over chlorinated oxidizers as it does not form chlorinated disinfection byproducts, which are prevalent as a contaminant of concern in groundwater. Byproduct formation is not currently a big concern, but it may limit water reuse options down the road. By selecting ozone for oxidation, Guidon also got control over bacteria, iron and sulfides.
Sedimentation is a basic process in water treatment. It is commonly used and understood throughout the world. As a preliminary step in water treatment, it can:
• Reduce chemical demand:
• Make subsequent processing easier:
• Lower overall cost:
• Decrease the variation in water quality.
There are variety of systems for sedimentation, but the most common are settling basins. For produced water management, sedimentation can be accomplished using clarifiers, oil/water separators, dissolved air flotation systems, and weir tanks.
One of the limitations of these systems is capacity. Most sedimentation systems have a design flowrate estimated to provide enough solids settling to achieve turbidity or TSS goals. For oilfield water management, flowrates can change and typically increase as new wells are developed. Increasing flowrates in these fixed systems can exceed their design criteria and prevent solids from settling.
Settling occurs using gravity. Solids are typically entrained in flowing water as a result of turbulence. Filtration systems are commonly used to remove solids, but pressure and operational costs usually limit them to 10 micron and larger. Solids at this size are more cost effectively settled.
Colloids for example, are particles ranging in size from 0.001 microns to 1 micron. Colloids rely on Brownian motion and the presence of electrostatic forces can prevent colloids from settling. As a result, colloids cannot be easily removed by simple filtration and settling can also be a challenge. However, TSS or turbidity goals can still be met without affecting colloids.
Gravity and Stoke’s Law are the foundation for understanding settling of solids. Stoke’s Law explains the relationship between settling rate and particle diameter. Under specific conditions, the settling rate of a particle is directly proportional to the square of its diameter and inversely proportional to the liquid viscosity.
The settling velocity, defined as the time it takes the particles to settle, enables the calculation of the size of a settling tank. The problem is produced water flowing from different wells is not steady state and the particle size, velocity and viscosity are constantly changing. As a result, settling solids can take place outside of these tank systems and in pits and storage tanks.
Guidon decided to optimize its gathering systems with improved tank batteries and gun barrel systems. This helped reduce overall solids loading and removed oil from the equation.
Use of settling basins makes sense once the limitations of tank systems is understood. For its program, Guidon chose settling basins as its primary pit for treating produced water. This allowed the primary pit to also be used for the oxidation process.
As noted, oxidation can form additional solids, so the primary pit are where treatment is initiated but also where solids can settle like a settling basin. The design of this primary pit features a sloped bottom to collect solids and a suction line to remove the settled solids. This eliminated the need for surface tanks for settling solids, but also sidestepped the design limitation of surface tank systems. The primary pit has enough capacity for changes in flowrate, viscosity or solids particle size. If an upset results in oil moving to the primary pit, the surface can be skimmed.
The storage pit has an aggressive aeration design to maintain treated water quality after oxidation. This simplified approach uses oxidation and settling in a primary pit and aeration in a larger storage pit. As a result, costs are reduced while established water treatment reuse objectives are achieved.
Guidon operated an ozone oxidation system under a service contract with Hydrozonix. It then made the decision to purchase two fully automated ozone systems to further reduce its water treatment costs. Following a competitive bid process, the company selected Hydrozonix as its supplier.
Determining produced water volumes and choosing the right oxidation system to meet its needs became apparent for Guidon after several months of operating the Hydrozonix system. With an option to purchase, the company saved money by operating a system it owned in much the same way it saved by developing and operating its own SWD.
For operators of ozone systems, the advantage over liquid oxidizers is that ozone systems use ambient air as the raw material to make ozone rather than relying on the supplier of a commodity. The electricity to power an ozone system is in the range of $0.002 - $0.005 bbl for grid-supplied power.
Onsite production of ozone and the lack of required storage space gives the operator a lower operating expense than liquid chemical oxidation. Also, without having to handle potentially hazardous materials, the operator’s health and safety risks are lowered. Finally, stored chemicals can also degrade in sunlight losing their efficacy, a disadvantage not included with onsite ozone generation.
The storage pit has an aggressive aeration design to maintain treated water quality after oxidation.
The success Guidon has attained with its unique approach to pit design and its purchase option for the automated ozone system allowed it to significantly increase reuse of treated produced water at a low cost. An indication of its success was seen when it reached an agreement to accept produced water from a neighboring operator and reuse it.
Today, Guidon uses up to 60 percent recycled water in its completion operations. As more produced water becomes available, this percentage will increase. In a region where traditional produced water disposal has become more difficult and expensive, Guidon’s water management program has reduced its dependence on SWD and reduced its overall cost.
Authored by Mark Patton