These energy firms are trading at their financial-crisis lows

Energy stocks have had a trying year, and there’s no sign of relief in sight.

The S&P 500 energy sector is the worst performing this year, up just 0.2%, versus the S&P 500 index’s SPX, +0.06% 16.7% gain. A confluence of trade tensions, global growth concerns and a slump in oil prices that began in April have weighed on the sector, while concerns about future demand for fossil fuels has clouded the long-term outlook.

Few companies have felt the brunt of these trends like oil services firms Schlumberger Ltd. SLB,...