A $1.6-million grant from the U.S. Department of Energy is funding a three-year project of a University of Texas professor that could help minimize the environmental footprint of hydraulic fracturing as well as reduce costs.
Hydraulic fracturing is the practice of injecting water, sand, and chemicals under high pressure into deep shale deposits to allow trapped oil and gas to flow to the surface. Critics express concern about health issues and the environmental impact, such as the amount of water used and water contamination.
The grant is one of several awarded by the Department of Energy for multi-year research projects to promote environmentally sensible development of oil and natural gas resources.
The funding will allow a team led by Dr. Mukul Sharma, professor in the Department of Petroleum and Geosystems Engineering at UT’s Cockrell School of Engineering, to build and test a diagnostic downhole tool that can be used to determine where sand or other proppant [the solid material used to keep the fracture open] pumped into a fracture is going.
“There is a real benefit knowing where the sand is going because you can place it more accurately,” Sharma says. “If you don’t know precisely where the sand is going, you tend to over-treat things. You tend to use too much sand, too much water, too much fluid whereas if you have a decent idea of where things are, you may be able to optimize, use less water or sand.”
Dr. Mukul Sharma, University of Texas Cockrell School of Engineering. Image: UT PGE
Despite the importance of determining where the proppant is going in the fracture, “we have no way of actually measuring that today,” says Sharma. Common practice is to do microseismic monitoring, which identifies shear failure occurring all around the main crack, he explained. “What [we] aim to do is not look at the ‘side show’ which are all the shear failure events [around the main fracture] but to look at the main event. Where is the sand going? Because that’s what ultimately will allow the fluids to flow back,” he adds.
This will be accomplished by using an electrically conductive proppant pumped into the fracture. Then, the plan is that a very low-frequency electromagnetic logging tool that his team will build will be able to measure where the fracture is, its length, height, orientation, and the distribution of the sand in the fracture. “This is the ultimate goal,” he says.
Having completed some preliminary modeling work that shows the feasibility of the project, the team will first build models for simulating the process. “It’s quite involved,” Sharma says. “Then we intend to test some of the electrically conducted proppants in our lab and build a prototype for the tool that we can put in the well. Finally, we would like to do the inverse problem. Rather than specifying the fracture geometry and computing the response at the receivers, [we would] do the opposite problem.” In other words, by measuring at the receivers, can the location of the proppant be inferred, he says.
The biggest challenge, he says, is coming up with the appropriate design for the transmitters and receivers that will “allow us to look deep into the formation. By deep, I mean several hundred feet.”
The team is building models in order to reduce electromagnetic coupling between the transmitter and receivers that are being run in a well. This transmitter will send out an electrical and magnetic field into the rock and the presence of the fracture will then modify what’s measured at the receivers, he says. The team must also actually build the special transmitters and receivers. “There is nothing we can buy off the shelf,” says Sharma, who has been researching hydraulic fracturing for more than 25 years. “I wish we could.”
The plan is that the modeling and tool design will be completed in the first two years and testing in the well with a prototype can be done during the third year of the project. “The expectation is that once we run this and show the feasibility of the idea and have a prototype tool, it will be ready for commercialization,” says Sharma. Once turned over to industry, the design can be used as a prototype and, if needed, could be modified or improved.
This is just one of several areas that Dr. Sharma and his team is working on to reduce the environmental footprint of hydraulic fracturing. Others include safe water disposal, recycling of the water used for fracturing, and using fluids other than water.
Nancy S. Giges is an independent writer.
Learn more at the ASME Hydraulic Fracturing Conference 2015
If you don’t know precisely where the sand is going, you tend to over-treat things.
Dr. Mukul Sharma, Cockrell School of Engineering, University of Texas