| Summary: | The onshore exploration realm has been continuously expanded to (ultra-) deep oil and gas recently in China. New comprehension and significant breakthroughs have been made in understanding generation and preservation conditions, reservoirs formation mechanisms, exploration potential, petroleum resources assessments, and exploration engineering technology of deep oil and gas. Deep oil and gas reservoirs include clastic, carbonate and volcanic settings. The temperature of deep oil can be up to 295 °C. Long term shallow burial and rapid deep burial at late stages help preserve the porosity in deep clastic rocks, and dissolution and fracturing effects improve their reservoir properties. Affected by faulting, hydrothermal karst processes, dolomitization and early oil and gas injection, carbonate rocks have good reservoir properties even at depths of 8 000 m. Controlled by tectonism, volcanism, diagenesis and diagenetic reconstruction during supergene and burial stages, primary and secondary weathering types of reservoirs develop deep volcanic reservoirs. Deep oil and gas resources in China are distributed mainly within three main practical areas of carbonate, clastic and volcanic areas. Dominated by gas, some of the more productive areas include the Tarim, Ordos, Sichuan, Junggar, Songliao, Santanghu and Bohai Bay basins. Deep oil and gas exploration in China has entered an age of breakthrough and discovery. Relevant engineering technology, such as ultra deep well drilling and ultra high temperature drilling fluid techniques have facilitated the ability to find (ultra-) deep oil and gas. Key words: deep oil and gas, reservoir formation mechanism, resources potential, exploration engineering technology
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