Simple water line planning techniques keep complex projects in hand
Planning, developing, and executing an efficient and profitable water plan, whether for a two-well pad or a multiple-well mega pad can be a challenge to anyone in the oil and gas industry. In this article, we will consider how thoughtful planning and a supply chain management approach can improve efficiency and ensure profitability.
There are many variables that go into proper planning and execution of a project and even more variables that go into changing a plan once it starts. It is important to understand the definition of a water management plan for well completions and its elements.
We often refer to a water manager’s tasking of this plan as “liquid logistics.” The term logistics refers to activities that generally occur within the boundaries of a single organization. In larger completions a better definition would be “water supply chain management.”
A supply chain refers to a network of companies, divisions within a company, or to organizations that work together to coordinate their actions to deliver a certain product to the market, or in this case water to a completions location.
The difference between these two definitions is that logistics traditionally focused on activities such as procurement, distribution, maintenance, and inventory management of water. Supply chain management acknowledges all the traditional logistics functions, but it also includes activities such as marketing of water products, customer service, project financing, and change orders in response to water requirements in a completions program.
Whether we call it liquid logistics or water supply chain management, these plans are about getting the right amount of water to the right end user in the right quantity and condition delivered to the right pad at the right rate during the right time for the right cost (the “R” depended equation). With some planning we can solve this “R” equation in order to make any completion program more profitable.
All the Water, All the Time
Whether it is for a very large operator, a mid-size water midstream company, or a water resource engineer, a completions program plan must consider some fundamental planning equations to be successful.
The place to start is a solid water balance plan or equation. Technically, a water balance plan looks to fulfill the continuity equation,
This simple equation is the fundamental starting point for proper water balance of a system; it is sometimes called the supply and demand relationship. These types of equations can easily be solved for in a spreadsheet where the daily supply (Inflow), is followed by the daily demand from the completions team (Outflow). Other columns would include daily additions of extra water in the system or where water is taken out during the completions project, and if elaboration is needed, columns added for evaporation, multiple storages, recycled water inflow and so on.
Adding visual aids to the spread sheet helps to see how storage volumes empty or grow, providing the team member or client visual cues for how water is being managed in a system. Drilling down into this fundamental equation and understanding its primary functions allow for system optimization which leads to an increase in profitability.
Hydraulics Drive Profitability
Developing a water plan using water supply chain management can drive profitability for a project. To achieve that goal, an understanding of hydraulics is vital.
Water is heavy (8.34 lbs/gal) and it is incompressible. An objective of hydraulic analysis in water balancing is to optimize pump placement and minimize the number of pumps while maximizing the efficiency and the daily deliverable flow rates at any point in a water balance table.
In the example above, three separate completion locations can be shown moving water to multiple well pad locations. In this case, the inflows indicate water supply moving from storage to frac pad locations from each fresh water transfer and produced water line.
The aerial image below shows a site in the south-central portion of Martin County, Texas. For reference, the area in the map measures approximately 5 miles by 3 miles. There are 2 lines shown in the figure: a fresh water line in green and the aboveground storage tank facility to produced water line in red.
Both lines feed the frac location that features multiple wells on each pad. When planning this location, Google Earth® was used for location and route planning of each water line. In this way, routes and lines can easily be manipulated and shared among different groups, from the land team to operations, to help ensure that final routes are feasible and acceptable to all links in the water supply chain.
Pump Placement Analysis
A comprehensive water plan includes a hydraulic grade line (HGL) analysis for each proposed route. An HGL analysis can be performed using formulas like Hazen-Williams and Darcy-Weisbach. These are equations which build relationships for the flow of water in pipe or hose with the physical properties of the system, the pressure drops caused by friction and elevation in a system, the pumping head and available horsepower.
Mapping software and a simple spreadsheet allow for quick testing of simulated pump locations.
Using these formulas, we can create a pump placement design in series to maintain a necessary flow rate range of 50 to 100 BPM. This also allows the system to be optimized with minimal pump quantities and maximum distance between pumps while maintaining the lowest line pressures throughout the system.
By taking this approach, safe working conditions are provided at the completions site, flow rate deliverability is maintained, and pump horsepower expenses are minimized.
In the case noted above, the green line was designed to deliver 50 BPM of fresh water from a storage pit to the location and the red line was moving produced water from a central AST facility to a separate completions location. For many mega-pad completions, the produced water and fresh water lines deliver to the same completion locations.
To determine vertical control along the pumping line, elevation profiles are generated using information contained in the high-precision ground surface elevation data from the National Elevation Dataset (NED). At 10-meter resolution, this is the same accuracy as the datasets used by Google Earth to generate aerial images. Maintained by the U.S. Geological Survey, the NED datasets are found online and available for free.
With this information, each water line can then be designed at the desired flow rate by determining the head loss and pressure inputs needed to maintain each set of deliveries needed on location. Pumps can then be located at the points in the HGL where pressure inputs are needed.
When we run a series of optimization scenarios combined with an iterative analysis, pump locations can be verified as to their proper placement. These conditions can then be reevaluated for different hose or pipe configurations to come up with various scenarios optimized for the project. Finally, keep in mind that route optimization can aid in pumping system efficiencies, but temporary water line routes frequently depend on lease roads and property boundaries and not the elevation contours.
Lay Flat Scenarios
After multiple iterations of the proposed water plan shown above, the results indicated the use of 12-inch lay flat hose allows for the best transfer of water while minimizing horsepower and achieving the 50 BPM pit-to-pit flow rate criteria for the green line.
In the figure below, we can see an HGL analysis for three different flowrate scenarios. In all three scenarios, 12-inch lay flat was used to determine the optimized flow rate and pump combination with locations and mile marker demarcation for other team members consideration.
The 12-inch line scenario above can easily be compared to a 10-inch line scenario to determine optimization of pump quantity and pressures. This allows for comparison to determine the most reliable flow rates for achieving a minimum of 50 BPM with a safety factor if higher demand is needed.
In the 12-inch scenario, the system under consideration would require one 600 horsepower pump to reach the discharge pressures needed for the flow rate criteria. The 10-inch lay flat hose scenario shown below provides an HGL analysis for three different flow rate scenarios. Here, the line needs inline pumps to create enough head to move the water to the end of the line at the desired rate. As a result, operating costs would increase.
In order to achieve 50 BPM, the analysis of a 10-inch line scenario shows this system will require at least two 325 HP pumps. However, the two pumps would be maxed out at 100 psi and have no safety margin if higher delivery rates are needed.
In this case, it might be necessary to add the extra flexibilty of three 325HP pumps (orange line) to achieve the flow rate needed for this project. Naturally, the additional pump would increase costs compared to a single, larger pump as in the 12-inch case.
Using free mapping software like Google Earth and a simple spreadsheet is helpful during line planning because it allows for quick testing of simulated pump locations. As a result, adjustments can be easily made before the operations or land groups are involved in the process. This can help save time and money for all involved.
In our examples, we found the distance in feet where each pump should be located. Using elevation profiles in Google Earth and locating the pump according to the HGL analysis, we can also consider other factors such as existing roads, operator safety, and maintenance. As indicated by the red arrow in the image above, we have chosen a pump location that allows for people to fuel, operate and maintain the pumps safely and out of traffic.
Layers of Complexity
The image below shows a more complex system that required several months of planning to accommodate a 6MM bbl completions program on a four-pad system with water from four separate pressure pumping companies going down hole every day at different rates.
For this very large project, a 500M bbl storage pit was used for staging. Access to another 6MM bbl of aggregate storage was available at other nearby locations and required multiple pit-to-pit lines. The project included more than 12,000 HP pumping capacity to supply water to the staging pit with a flow rate of more than 350M BWPD. The lines and pad schematic for this project are shown below.
During completion operations, there was another 7,200 HP of pumps supplying water at 300M BWPD at a rate of more than 100 BPM to each of the four pads. Water transfer alone consumed more than gal/day of diesel fuel during downhole completions.
Although the massive effort described above was completed in thirty days, the prefill for the project took much longer to plan, arrange and complete. Since this job in 2017, permanent pipelines were installed to allow for higher pressure and more efficient transfers of larger volumes. Using the techniques of water supply chain management, we have worked on multiple mega-pads like the one described above that were completed at or near the same time.
Using water supply chain management techniques, we completed multiple mega-pads at or near the same time.
Ready for the Challenges
Completions programs in many shale plays are becoming more and more efficient and water management companies must look to optimization to help drive margins. System automation, more sophisticated water supply chain management and new technology will help support better margins on larger and larger projects. In the project described above, pump placement optimization and horsepower reduction saved more than $100,000 in fuel costs alone.
As the oil and gas industry moves increasingly to a standardized well manufacturing model that highlights large, complex multi-well pads, supply chain management of water and other completion materials will present companies with ever-increasing challenges. In the meantime, E&P companies must deal with constant demands to increase profitability which puts pressure on service companies to control costs. As its record proves, this industry will tackle these challenges head on as it continues to lead the world in energy development.
Authored by Chris Harich