China's Tarim Basin is considered to be the last large onshore basin where giant oil and gas deposits remain to be discovered and developed. In 1977, the discovery well, Ke No. 1, located in what is now the Kekeya oil and gas field on the southwest margin of the basin, produced oil and gas at high flow rates. The initial rates were 1600 m3 (10,000 bbl) of oil and 270,000 m3 (9.5 mmcf) of gas per day. In the northern part of the basin, on the Shaya uplift, another discovery well, the Shacan No. 2, produced oil and gas from Ordovician dolostone at initial rates of 1000 m3 (6290 bbl) of oil and 2 million m3 (70 mmcf) of gas per day in 1984. Recently there have been still other discoveries of substantial volumes of oil and gas in various formations. The ages of the producing zones vary over a wide range—Cretaceous, Jurassic, Triassic, Carboniferous, and Ordovician. Especially encouraging was the Central No. 1 discovery well in the Central No. 1 structure, which yielded 576 m3 (3620 bbl) of oil and 340,000 m3 (12 mmcf) of gas per day in 1989. All these discoveries indicate that Tarim Basin is promising.
The Tarim Basin, with an area of 560,000 km2, was a huge platform during the Paleozoic. Later, in the Mesozoic-Cenozoic, the platform subsided and became a basin. There were two major cycles of marine transgression and regression that resulted in thick sediments containing two marine facies favorable for oil generation— one in the Sinian-Devonian, and the second, after a hiatus, in the Carboniferous-Permian. In addition, the Triassic-Jurassic section contains good continental facies source rocks.
In two oil fields of the Tarim Basin—the Yiqikelike field in the Kuche depression and the Kelatuo field in the Southwest depression—the crude oils were derived primarily from Jurassic and Triassic sediments and have geochemical characteristics of the Jurassic continental coal measure strata. However, some production of Miocene oil and gas of the Kekeya field might be derived from Carboniferous-Permian source rocks. Most of the oil and gas in the four fields/blocks on the Shaya uplift was generated from Paleozoic marine source rocks, but part of it is from Triassic-Jurassic continental source rocks, resulting in an oil and gas accumulation from cosources. Separate oil and gas accumulations from Paleozoic marine facies and Mesozoic continental facies also have been found there. The oil and gas of the Central No. 1 structure may have been derived from Paleozoic source rocks.
In the Tarim Basin, the areas considered to have optimal conditions for giant oil and gas fields are the Shaya uplift, the Central uplift, and the southwest margin of the Southwest depression.
Figures & Tables
The success of Memoir 14 and the worldwide interest shown for data on giant fields prompted AAPG to schedule a symposium on giant fields at the end of each subsequent decade. The 1968-78 symposium was held in Houston, Texas, April 1-4, 1979, and the papers were published in AAPG Memoir 30, December 1980.
The Stavanger Conference "Giant Oil and Gas Fields of the Decade: 1978-1988" was held in Stavanger, Norway, September 9-12, 1990, and is a continuation of the Giants of the Decade series.
Scientific studies and projections of future world energy demand indicate that although alternative-energy fuel sources must be actively pursued and developed, there also must be adequate petroleum supplies to bridge the gap. For the international petroleum industry, the years covered by this conference, 1978-88, were complex. They were years of boom and bust. The world's energy consciousness was boosted sharply by the effects of the 1979 Iranian revolution and the resulting embargo, which sent world oil prices to record heights. Global petroleum exploration soon surged, leading to the industry's all-time drilling high in 1981. Then came the oil price collapse in 1985, and the following years were characterized by falling oil prices and drastic budget cuts for exploration and development.
Although exploration dropped sharply during the latter part of the decade, there was a steady flow of giant oil and gas field discoveries. Using the giant field designation criteria of 500 million bbl of oil recoverable for fields in Asiatic Russia, North Africa, and the Middle East,