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December 27, 2010

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Hunting for oil in the desert: Qaidam Basin

UNTOLD treasures lie beneath the deserts of the Qaidam Basin. Tectonic activity in the geologically active Tibetan Plateau has created complex folds that have trapped vast resources of crude oil and natural gas. The exploration and extraction of oil in this barren land has been ongoing for 50 years and the search for black gold continues. Wang Xiaofeng and Chen Xuanhua report.

aidam Basin is a treasure 200 million years in the making. Here dunes of all shapes and sizes rise and fall like waves in a sea of sand. However, this barren land is also a vast treasure trove - deep beneath the surface are precious reserves of oil and gas.

Covering 121,000 square kilometers, the Qaidam Basin in Qinghai Province was formed during the Mesozoic and Cenozoic eras on rock strata that dates back to the Jurassic period.

The sediments accumulated in the basin are around 200 million years old. Of these, the oil-rich Mesozoic and Cenozoic sediments account for 96,000 square kilometers, with a maximum thickness of 17,200 meters.

After 50 years of oil prospecting in the Qaidam Basin, three major production areas have been found: the Mangnai oil and gas zone in the west, where 12 oil and gas fields have been discovered including Gasikule, Huatugou and Youshashan; the northern Qaidam Basin fault belt oil and gas zone, which includes the Lenghu oil fields; and three natural gas zones in the east.

It may seem easy that we could now describe the oil and gas resources in Qaidam Basin in such detail, but this was really the result of the sweat and tears of many geologists and oil prospectors. With its high elevation and harsh environment, the Qaidam Basin presents the toughest challenge for oil exploration in China.

Rows of abandoned houses, their roofs long gone to the wind and rain, adorn the lifeless landscape. This is Lenghu, the first oil town in the Qaidam Basin. Once a bustling hub for oil exploration, it is now a ghost town - a silent testimony to the boom and bust brought by the oil industry.

From boom to bust

In 1955, Sun Dianqing, former director of the Institute of Geomechanics of the Chinese Academy of Geological Sciences, led a team to search for oil reserves in the Qaidam Basin.

Extensive surveys in the northern Qaidam Basin revealed layers of coal in the Jurassic stratum at Iqe and other areas, a sign that the basin was once warm and moist, with abundant vegetation - ideal conditions for the formation of oil.

The exposed strata from the Tertiary period comprised mainly river sediment with plenty of fossils, indicating a potential source of crude oil. Traces of oil and gas were also detected in many places.

Nevertheless, the presence of such oil and gas does not guarantee the existence of oil fields. From exposed Tertiary formations at Lenghu, Sun and his team found the folds were well-developed, and were compressed into a regular pattern that resembled the wringing of a towel.

Under such pressure, the oil trapped in the reservoir layer could escape to the surface through exposed folds or along fault lines. In a dry, windy and sandy place like the Qaidam Basin, the evaporated oil would stick to the sand, forming mounds of oily sands.

That was exactly what Sun later found at the Shuiyazidun area in Lenghu, and he promptly proposed drilling on the anticline where the oil seepage was found.

Sun's efforts led to the discovery of the first oil field in Lenghu. In 1956, a geological team drilling at the Lenghu-4 well hit a shallow oil layer, sending crude oil shooting 20 meters into the air. This was followed by an even more spectacular find at the Lenghu-5 well in September 1958.

Miners hit oil at a depth of 650 meters, and the ensuing blowout continued nonstop for three days and three nights, spewing as much as 800 tons of crude oil in a single day.

This discovery was a major breakthrough in oil exploration in the Qaidam Basin. Lenghu became one of the four major oil production areas in China at the time, alongside Yumen (Gansu Province), Karamay (Xinjiang Uygur Autonomous Region) and Sichuan Province.

However, Lenghu's fortunes started to wane in the 1980s. Its shallow oil deposits were almost depleted and no deeper layers were found. Oil companies and their employees began moving out of Lenghu, abandoning the town that had been their home for over 20 years.

But this may not spell the end of Lenghu's glorious days. New technology has brought new hope for locating oil and gas reserves. Seismic tests and exploratory drilling conducted after 1995 have revealed a Jurassic layer rich in hydrocarbons at the northern edge of the Qaidam Basin, once again hinting at the vast potential that lies beneath the sand.

Flowers in the desert?

However, Lenghu is not the first oil field found in Qinghai, neither is it the most important. Currently, the most productive oil fields in the province are the Gasikule oil field, which produces 1 million tons a year; and Huatugou, with an annual output of over 300,000 tons.

The Gasikule oil field is located to the northeast of Lake Gasikule and south of the Yousha Mountains. Lying to the north of the lake is the Huatugou, which literally means "a gully of flowers."

How could that be true in this barren place? It turns out that the deep gullies cut on the surrounding mountains resemble a "flowery" pattern from afar. The oil workers here thus decided to give this lifeless place a beautiful name: Huatugou.

Many lives were lost in the search for oil in the Qaidam Basin, as a trip to the Lenghu and Huatugou cemeteries would reveal. One of those buried at Huatugou was a legendary figure: Mumainusi Yisha Aji, who passed away in October 1969 at the age of 74.

Aji was the best guide of Qaidam Basin the world had known. In his youth he often traveled around the Qaidam Basin for business, and thus gained an intimate knowledge of the area. He had led the People's Liberation Army to hunt for bandits, found new routes and water supplies for prospecting teams, and guided the siting of farms and the construction of railways.

To many, Aji was a "living map" and a "camel" of the Qaidam. His expert local knowledge was critical to the discovery of the first oil field in Qaidam - the Youquanzi oil field of Mangnai in December 1955.

In 1956, the newly established Qinghai Oil Prospecting Bureau moved its headquarters to Huatugou, turning it into a bustling hub almost overnight.

However, there were no houses built at Huatugou; the entire settlement was a "tent city" comprised of thousands of tents. In 1958, the Huatugou and Qigequan oil fields were discovered in the western Qaidam Basin, and the first batch of crude oil produced from the Qaidam Basin was sent in February the next year.

The eight fairies

The town of Da Qaidam and the neighboring areas of Nanbaxian, Iqe and Mahai are important oil and gas zones along the northern edge of the Qaidam Basin.

The area is rich in Jurassic rock laden with hydrocarbons; near the surface are also abundant deposits of Jurassic coal, making it an important coal production base in the northwestern province.

Nanbaxian is also home to one of the world's largest yardang landscapes. Covering over 1,000 square kilometers, these labyrinthian "devil's cities" are the result of hills and ridges carved into all kinds of extraordinary shapes by the wind.

Treasure hunt

The Qaidam Basin lies in an area of intense geologic activity, where the earth's crust was literally turned upside down in a few places. Soft coal layers formed 200 million years ago were actually found beneath older rock formed 500 million years ago.

This is also part of the reason why further surveys have found new oil and gas reserves at some old wells. For instance, a re-analysis of old well data at Nanbaxian has led to the discovery of more oil and gas layers.

What else lies beneath? Perhaps there are still many more treasures waiting to be discovered in the Qaidam Basin.


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