Poland’s biggest oil company said a writedown on domestic shale gas activities reduced second-quarter earnings by almost a fourth, sending its shares down by the most in 2015.

PKN Orlen SA posted net income of 1.37 billion zloty ($364 million), compared with a loss of 5.2 billion zloty a year earlier when it wrote down the value of its refineries in the region. The company missed the 1.84 billion-zloty estimate of eight analysts surveyed by Bloomberg after taking a 421 million zloty hit on its Lublin shale project.

The Lublin area in eastern Poland, earlier tipped to be “promising,” won’t allow for wider production, Orlen said in an e-mailed statement on Thursday. It also said it will limit shale gas exploration there, focusing on conventional and tight gas. Its shares slumped 5.3 percent, the biggest decline since December 2014, to 74.47 zloty at 10:02 a.m. in Warsaw.

State-controlled Orlen, following its bigger international competitors, is changing its view on the country’s shale gas project, which Poland hoped would grant it more autonomy from Russia gas supplies. Since the government granted more than 100 exploration licenses earlier this decade, almost all foreign investors, including ConocoPhillips, Marathon Oil Corp. and Chevron Corp., have withdrawn having failed to find commercially interesting deposits of gas trapped in shale rock.