China’s sweeping anticorruption investigation into oil executives and government officials has targeted several people who worked in the late 1980s at the Shengli Field, a major production site located primarily in the country’s eastern Shandong province.

Shengli was discovered in the 1950s and its control was transferred to China Petrochemical Corp., or Sinopec Group, the country’s largest refining company, after Sinopec was established in 2000. Shengli is now China’s second-largest field by oil output and accounted for 13% of domestic oil production last year, according to an energy newsletter affiliated with the official Xinhua news agency.

Oil and gas production is the bread and butter of CNPC and its listed unit PetroChina Co.601857.SH +0.38%, and it’s not uncommon for top executives to cut their teeth running a major oil field (in Chinese). At least three of PetroChina’s current executives — vice president Sun Longde, chief engineer Lin Aiguo and supervisory committee head Wang Lixin — held key positions at Shengli in the 1990s. Mr. Wang is also chief of discipline and inspection at CNPC.

Wang Fucheng, a vice president at CNPC, was a senior executive at Shengli between 1986 and 1992. None of these executives has been linked to any wrongdoing.

But three of the people detained so far have ties to the country’s former security chief, Zhou Yongkang, who ran the field from August 1989 to June 1990. Mr. Zhou is oil industry veteran who once headed CNPC and then rose to become one of China’s most powerful men — a member of the central leadership and the chief of internal security for five years until his retirement in November.

Mr. Zhou hasn’t been accused of any wrongdoing, but Jiang Jiemin, who is now head of the State-owned Assets Supervision and Administration Commission and the highest-ranking official to be named in the probe, rose through the ranks of the oil industry at Shengli under Mr. Zhou. Mr. Jiang was considered a protégé of Mr. Zhou’s and rose to become head of CNPC and PetroChina after Mr. Zhou left the companies for higher office, according to some analysts and industry insiders.

One of the detained executives, Li Hualin, head of PetroChina’s natural-gas distribution unit Kunlun Energy Co., served as a personal aide to Mr. Zhou in the late 1980s while Mr. Zhou ran Shengli, according to two people who knew Mr. Li personally and asked not to be named.

State media reported in June that Chinese authorities were investigating Guo Yongxiang, a former vice governor of Sichuan and, according to his official biography, a veteran of the Shengli oil field who was also there at the same time as Mr. Zhou.

“Petroleum politicians with the closest ties are probably those from CNPC who worked at the Shengli oil field before it was transferred to Sinopec,” according to a Erica Downs, an expert on Chinese national oil companies at the Brookings Institution. “A ‘rule of thumb’ is that anyone above the director level at CNPC who worked at Shengli was promoted by Zhou,” Ms. Downs wrote in a 2010 paper, citing an unnamed industry insider.