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.

Pete Simms, CFO

SEF Energy

Pete Simms serves as the Chief Financial Officer of SEF Energy. Prior to SEF, Pete worked as the Director of Finance and Corporate Development at Seventy Seven Energy and Chesapeake Oilfield Services. In addition, Pete served in various capacities in the energy procurement and trading division of Pacific Gas & Electric, a publicly traded power and gas utility. Pete served in the US Army for 10 years as Special Forces and Infantry officer.  Pete holds a BS in Economics from the United States Academy at West Point and an MBA from the Tuck School of Business at Dartmouth.

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.

Jason Kays, President of Downhole Tools

OSO Perforating

Jason Kays serves as the President of Downhole Tools for SEF Energy, which is comprised of OSO Perforating.  Prior to SEF, Jason served as Operating Executive for Stratford Private Equity, as CEO for Winnercomm and Personnel Concepts and as Vice President for The Dallas Morning News. Jason holds a BS in Economics from Oklahoma State University and an MBA from Harvard Business School.

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 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 15 patents and has co-authored several publications.

Learn more about our companies.