Shiyou shiyan dizhi (Sep 2023)
Basis of petroleum geological theory and exploration direction for ultra-deep exploration of 10 000-meter depth
Abstract
Oil and gas resources are of important strategic importance for China's economic development. After more than 50 years of mining in main oil fields, the water cut of oil fields in China has exceeded 90%. China's external dependence on oil and natural gas has increased from 58.9% and 29.2% in 2013 to 71.2% and 40.2% in 2022 respectively, reaching the oil security warning line and impeding national security. In order to find more replacement reserves, oil and gas exploration has been promoted to the "deeper and more complicated" ultra-deep exploration area of 10 000-meter depth. Recently, domestic oil companies have successively implemented the "Deep Sea No. 1" and "Deep Earth No. 1" oil and gas exploration plans, which have explored and practiced new technologies of intelligent drilling and promoted the implementation of the 10 000-meter exploration plans, and reservoirs have been encountered by wells over 9 000 m deep. Based on recent exploration practice, this paper demonstrates the basis of petroleum geological theory for exploration of 10 000-meter depth from the aspects of ultra-deep hydrocarbon generation, storage and accumulation mechanisms, and it suggests that multi-source hydrocarbon generation can be identified in ultra-deep strata and the hydrocarbon generation threshold has exceeded 120-160 ℃. The "three-element controlling reservoir" theory points out that deep and ultra-deep reservoirs can be developed at depths greater than 4 500 meters and multi-phase hydrocarbon accumulation and preservation constitute a favorable condition for the development of ultra-deep large-scale oil and gas reservoirs. The Sichuan Basin has the total resources of about 15.22×1012 m3 in deep marine strata, wherein the Sinian system on the margin of Mianyang-Changning taphrogenic trough, the Longwangmiao Formation on the margin of central Sichuan palaeo-uplift, the Longwangmiao Formation in Micang Mountain-Daba Mountain areas to the east of Chengkou oceanic trough, and the Upper Paleozoic in western Sichuan have a resource potential of more than hundreds of billions of cubic meters. The Tarim Basin has about 15.262×109 tons of equivalent oil in deep marine strata, wherein the Middle-Lower Ordovician karst area in the Tabei uplift, Tazhong uplift and Maigaiti slope, the Middle-Lower Cambrian platform marginal zone on the western margin of Manjiaer Sag, and the Middle and Lower Cambrian intraplatform shoal of Awat-Shuntuoguole are all oil potential areas of hundreds of millions of tons. There are important oil and gas discovery in the Middle Neoproterozoic in the southwest edge of Ordos Basin. Additionally, the field of clastic rocks such as the deep strata in the central deep depression zone in Junggar Basin and the Kuqa Depression in Tarim Basin are also important areas of exploration of 10 000-meter depth.
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