Our Team

Our leadership team has over 75 years of proven industry experience. Their hands-on leadership style, vision, and strategic capital allocation with manufacturing investments have resulted in robust growth and enduring success for our Oklahoma-based companies.

Zac Graves, CEO

SEF Energy

Zac Graves serves as the Chief Executive Officer of SEF Energy.  Prior to SEF, Zac served as President of several entities within Chesapeake Oilfield Services, the predecessor company to Seventy Seven Energy.  Before joining Chesapeake, Zac held the positions of Chief Financial Officer and Executive Vice President of Operations for Bronco Drilling Company, a publicly traded company listed on the Nasdaq.  In addition, Zac worked in various capacities in both public and private energy-focused companies controlled by Wexford Capital LP.  Zac graduated from the University of Oklahoma with a BBA in Accounting.

Brian Wiesner, President of Surface Systems


Brian Wiesner serves as the President of Surface Systems at SEF Energy, which is comprised of the Downing brand. Brian joined SEF in 2015 after 20 years in various technical, management, and international positions at Baker Hughes, FMC Technologies, and GE Oil & Gas.  Brian holds a BS in Engineering from the Colorado School of Mines and an MBA from both Cornell University and Queen’s University.  Brian has authored 4 United States patents.

Tim Marvel, VP Business Development and Technology

SEF Energy

Tim Marvel serves as the Vice President of Business Development and Technology. Prior to SEF, Tim was Managing Director for Alcoa Oil & Gas before joining Dover Energy Automation as Vice President / General Manager of Production Optimization. Tim began his career at Baker Hughes, working in a variety of roles including Global Product Manager, Director of Product Development and Engineering, Director of Technology, and Director of Business Development and Marketing. Tim holds a bachelor’s degree in Mechanical Engineering from Colorado School of Mines and is a licensed professional engineer in the state of Texas. He holds 20 patents and has co-authored several publications.

Learn more about our companies.