Prior to 1958 gas production was limited to associated gas from oil wells in western Turkmenistan. In 1958, the first gas wells were drilled at Serhetabat (then Kushky) and at Derweze. Oil and gas fields were discovered in the Central Karakum Desert between 1959 and 1965.  In addition to Derweze, these include Takyr, Shyh, Chaljulba, Topjulba, Chemmerli, Atabay, Sakarchage, Atasary, Mydar, Goyun, and Zakli. These fields are located in Jurassic and Cretaceous sediments. The Turkmen gas industry got underway with the opening of the Ojak gas field in 1966. To put this in perspective, associated gas production in Turkmenistan was only 1.157 billion cubic meters in 1965, but by 1970 natural gas production reached 13 billion cubic meters, and by 1989, 90 billion cubic meters. The USSR exported much of this gas to western Europe. Following independence, natural gas extraction fell as Turkmenistan sought export markets but was limited to existing delivery infrastructure under Russian control: Turkmenistan-Russia in two lines (3087 km, originating at Ojak, and another of 2259 km, also originating at Ojak); the Gumdag line (2530 km); and the Shatlyk line (2644 km) to Russia, Ukraine, and the Caucasus.  On 1 January 2016, Russia halted natural gas purchases from Turkmenistan after reducing them step by step for the previous years.  Russia's Gazprom announced resumption of purchases in April 2019, but reported volumes remained low compared to previous delivery levels.