APPLIED GEOPHYSICS, Vol.1, No.2(October 2004)Geophysical exploration technology in the loess plateau Geology and Exploration of
Oil and Gas in the Ordos Basin
Yang Hua*, Fu Suotang*, and Wei Xinshan*
Abstract: The Ordos basin is rich in oil and gas resources. The structures in the basin are generally
rather gentle. Most of the oil and gas pools already found are belong to the types of lithologic, litho-
stratigraphic and paleo-geomorphic with thin rervoirs. The geology of oil and gas and the generation
鲈鱼豆腐汤and distribution of oil and gas resources in the Ordos basin is analyzed in detail in the paper. It is also
pointed out in the paper that what direction should be taken in oil and gas exploration in the basin, and
that the important role of the ismic prospecting technologies in the discovery of large oil and gas
fields in the basin could not be replaced.
Keywords: l itho-stratigraphic pools, loess plateau, ismic prospecting technology, Ordos basin
The Ordos basin is the cond largest
oil-and-gas-bearing basin in China,
located in the central-western part. The
boundary of the basin to the north is
the Huanghe fault, to the south the
Jinhuashan-Qishan mountains, to the
west the Zhuozishan-Luoshan moun-
tains and to the east the Luliang
mountain. The area of the basin is about 25 × 104 km2, across five provinces, i.e. the Shaanxi, Gansu, Ningxia, Inner Mongolia and Shanxi.
The basin is intermittently surrounded by a ries of mountain ranges, with attitude generally about 2000 m above a level. Geographically, the main trend of the ba-sin is high in the west and low in t
he east, with attitude generally about 800-1100 m. Within the basin, taking the Great Wall as a boundary, to the north is the dert and grassland, to the south is the loess plateau. The geology and surface conditions of the loess plateau are very com-plex with crisscross valleys and gullies everywhere.
The weather in the basin is vere and traffic not convenient. The best ason for oil and gas prospecting is the Spring, Summer and Fall. The oil and gas exploration is generally in a low level for a long time due to the com-plicated geology and bad ismic conditions, and the limi-tation of technologies. Along with the development of the exploration technologies and the change of the strategy of the exploration, the situation is getting better and better. Several large oil and gas fields are successively discov-ered with rerve over hundreds of million tons in each. The success has attracted worldwide attention.
Fig.1 Geographic map of the Ordos basin
Manuscript received by the Editor January 22, 2004; revid manuscript received September 23, 2004.
小白菜炖土豆*Changqing Oilfield Company. PetroChina, Changqing Xinglongyuan Block, Xi'an 710021,China.
考试通过的祝福语
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The road of exploration Yang Hua et. al.
new pha for the exploration in the deltaic diments of
the Yanchang ries.
Oil eps known as "Gaolu oil-eps" were discovered along the Qingjianhe River on the loess plateau of the Ordos basin in the history as early as in the E ast Han dynasty. The first oil well on the mainland was drilled on Sep. 6, 1907 in the Qilichun village to the west of the Yanchang county on the loess plateau. From then on, the modern oil and gas exploration was opened up on the loess plateau of the Ordos basin. But from 1907 to 1949 the oil exploration was restricted only in a narrow area along the Yanchang and Weibei counties of the Shaanxi province. All together, 52 shallow wells had been drilled around the oil eps, with depth about 100-200 m. The cumulative oil produced in the 40 more years was only 7054 tons. Since 1950, the oil exploration in the Ordos basin turned over a new page. Generally, it could be divided into 4 stages. Regional exploration stage (1950-1969) In this stage the main task was to investigate the tec-tonic framework of the basin with geologic surveying and gravitational reconnaissance. Oil flow with low produc-tivity was obtained fro
m the Yanchang formation on the Majiatan structure in 1959. The first oil well with indus-trial value was obtained from the Yan'an formation of the Lizhangzi structure. It was the breakthrough in the oil and gas exploratory history of the basin. From then on, the Mafang, Dashuikeng and other oilfields were successively discovered.
Exploring the Jurassic paleo-geomorphic oil pools stage (1970-1979)
In this stage the stress was laid on the exploring the oil pools accumulated in the paleo-geomorphic traps of the Jurassic. After oil was found in localities of Maling, Huachi and Yuancheng, Maling was lected as the main target area to drill. The oil-bearing area of Maling oilfield was quickly delineated, and the first peak of oil rerve increas-ing was come into the basin. After that, oilfields were suc-cessively discovered in the Wuqi and Chenghua areas. Exploring the Triassic deltaic oil pools stage (1980-1988)
The strategy made in 1983 was to explore the deltaic diments toward the east. Oil was discovered in three of the first ries of 4 exploratory wells. E specially, oil daily productivity of 59.86 tons was obtained in the well Sai-1 and it was the discovery well of the large Ansai oilfield with rerve over hundred of million tons. It opened up a Great development in exploring for both oil and gas stage(1989-prent)
The flowing of gas with industrial value in the Ordovi-cian in the well Shanchan-1 in 1989 heralded the discov-ery of large Jingbian gasfield. Since 1996 the stress of exploration was shifted from the lower Paleozoic to the upper Paleozoic, and three large gasfields with rerve over hundreds of billion cu m, the Yulin, Wushenqi and Sulige, were discovered one after another. Up to now, the cumu-lative geologic gas rerve is over one trillion cu m.
At the same time with the discovery of the Changqing gasfield, the exploration for oil in the Mesozoic in the Shanbei area was also obtained great success. With only 4 years, the large Jing'an oilfield with rerve over hundred million tons was efficiently and rapidly delineated. To ex-plore the Ansai area for the cond time in 1996, the proved oil-bearing area was substantially expanded and new proved rerve over hundred million tons obtained. From then on, the exploration for both oil and gas was carried out, and rerves of both oil and gas were incread rapidly, forming the third peak of rerve increa in the basin.
The successive success of oil and gas exploration in the Changqing Oilfields and the discovery of large inte-grated oil and gas fields are cloly related with the ad-vancement and development of exploration technologies, especially in the ismic prospecting.
Geology and exploration of oil and gas Regional geologic background
In the Ordos basin the diments from middle-upper Proterozoic to Meso-Cenozoic were deposited on a crys-talline bament, with maximum thickness up to 6000 m, and volume of 150 × 104 km3. Six tectonic units could be recognized in the basin (Fig.2), i.e. Yimeng uplift, West-ern thrusted zone, Tianhuan sag, Yishan slope, Jinxi flex-ure zone and Weibei uplift. Beside the Yishan slope and the Tianhuan sag, in which the diments are very gentle and structures not clear, in the other four tectonic units the structures are prominent and clear. In the contact relation-ship of the dimentary quences, high-angle unconformity exists on the periphery of the basin. It gradu-ally changed into parallel unconformity or conformity to-ward the center, characterizing the tectonism gradually weakened from the periphery of the basin toward its center.
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Geology and Exploration of Oil and Gas in the Ordos Basin
Fig.2 The tectonic units of the Ordos basin Analyzing the evolution of the basin, it is recognized that the basin has undergone five stages of development, i.e. the aulacogen stage of the middle-late Proterozoic, the shallow marine platform stage of the early Paleozoic, the littoral plain of the late Paleozoic, the hinterland basin of the Mesozoic and the peripheral faulted basin of the Cenozoic. Th
e prent plateau geomorphic feature was formed in the Himalayan orogeny. Four suites of oil-and-gas-bearing-formations were formed in the multi-stage evolution of the basin, showing a distribution framework of gas in the north and oil in the south.
The main targets for oil and gas exploration in the Ordos basin are the lower Paleozoic and the quence above it. All the dimentary quences of the basin are described in the table 1. From Table 1 it can be en that the carbon-ates are deposited in the lower Paleozoic, and the argilla-ceous and arenaceous rocks are in the upper Paleozoic and Meso-Cenozoic. The thickness of various quences is mostly without much change, except for the Yanchang formation and the lower Cretaceous, which are consider-ably changed laterally. The main parallel unconformities, which could be recognized in the quence are tho be-tween the upper and lower Paleozoic, the Jurassic and Triassic, and the Cretaceous and Jurassic. All tho paral-lel unconformities and the Taiyuan formation and Shanxi formation of the upper Paleozoic, and the coal ries in the Yanchang formation and Yan'an formation of the Me-sozoic are very good ismic reflectors which can be traced as markers throughout the basin.中国人寿是国企还是央企
Geology characterized in the
accumulation of oil and gas Geology characterized in the accumulation of oil in the Mesozoic
In the Mesozoic, the Ordos was a hinterland basin, in which the lacustrine oil source rocks were deposited. The main source rocks are in the Yanchang formation, which occupied about 1/3 of the prent basin area. They are mainly distributed in the middle and southern parts of the basin. Under the control of effective source rocks, the oilfields are mainly distributed in the central and southern parts of the basin.
电脑装机配置表In the Yanchang stage, the two main diments sources were come from two directions, the northeastern and south-western of the basin. Through rivers the diments were transported into the lakes, forming a ries of large deltaic sand bodies controlled by the fluvial current. Due to the stacking of sandstone bodies of deltaic front in various stages, very thick (30-50 m) sheet sandstones were formed, which occupies very large area (up to veral thousands sq km). In the process of diagenesis, the condary dis-solved pores were formed, making the sandstones become rervoirs with low porosity and low permeability. The porosity of the sandstones is generally 10-15%, and the permeability 1-5 × 10-3 μm2. As mudstones of deltaic plain appeared in the quence, good matching asm-blages of source, rervoir and cap rocks were formed (Fig.
3). Analyzing from a point of genetics of the traps, it is recognized that the Jianwan mudstone between the sand-stone bodies may constitute a screen at the updip of the formations, the lithologic
and stratigraphic traps may. thus be formed. So far, the large oilfields with rerve over hundreds of million tons, such as the Xifeng, Ansai and Jing'an oilfields are all belong to lithologic traps. It is proved with exploration practice that the geology in form-ing the large integrated oilfields in the Yanchang forma-tion is bad on the large deltaic dimentary system. The delta front is the main facies for the rich accumulation of oil and gas. In the Ordos basin, the main oil-bearing for-mation is the Yanchang formation.
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Yang Hua et. al.
Group Cenozoic
Mesozoic
Lower Paleozoic Stratigraphic System Quarternary Tertiary Cretaceous Jurassic
Triassic
Permian
Carboniferous Ordovician Sequen Series Lower Middle Lower Upper Middle Lower Upper Middle Lower Upper ce Formation Zhidan Anding
Zhiluo
Yan'an
Yanchang Zhifang
Heshanggou Liujiagou Shiqianfeng Upper
Shihezhi Lower Shihezhi
Shanxi
Taiyuan
Benxi (m)
0-280150-1600-128080-150200-400
250-100800-1400210-300
100-130
230-300
260-290130-140140-15080-11025-4010-25500-600
Thickness Lithology
Loess, mild clay, brownish gray sandy conglomerate at the bottom
Reddish brown mild sandy clay and mild clay, pink and brownish gray sandy conglomerate at the bottom occasionally
Interbeds of Brownish red, mid-coar grained sandstone and brownish red and bluish gray argillaceous rocks, locally interbedded with conglomeratic sandstone
Mainly brownish red mudstone, intercalated with silty and fine-grained sandstone in the lower part, and various colored marl in the upper part
Grayish green, fine-grained sandstone, argillaceous sandstone intercalated with grayish green mudstone and arenaceous mudstone in the upper part, gray mudstone, arenaceous mudstone intercalated with gray fine-grained sandstone and argillaceous sandstone in the lower part
Dark gray mudstone and carbonaceous mudstone intercalated with coal ams, and interbedded with grayish, grayish white fine-middle grained sandstone and arenaceous sandstone with different thickness, very thick sandstone at the bottom
Dark gray mudstone and carbonaceous mudstone intercalated with coal am, interbedded with gray fine-grained sandstone and argillaceous sandstone in different thickness locally with coal am
Gray, dark gray and brown mudstone and arenaceous mudstone intercalated with gray and pink fine-middle grained sandstone and arenaceous sandstone with different thickness Purplish red sandy mudstone and sandstone, with grain size coarning downwards, with fine-grained conglomerate locally
Interbeds of brown argillaceous sandstone and siltstone
Brownish red mudstone intercalated with light pink fine-grained sandstone in the upper part, brownish red mudstone intercalated with light gray fine-grained sandstone Thick brown and dark brown mudstone intercalated with light gray fine-grained sandstone
Light gray fine-grained sandstone, grayish white middle-grained sandstone, conglomeratic coar-grained sandstone intercalated with light gray and various colored mudstone Thick dark gray mudstone, grayish black mudstone intercalated with grayish white middle grained sandstone, fine-grained sandstone and thin am of coal
Dark gray and gray limestone intercalated with black mudstone at the top grayish black mudstone, coal am intercalated with gray fine-grained sandstone
Coal am and grayish black carbonaceous mudstone at the top, aluminiferous mudstone at the bottom
Dark gray limestone, gray argillaceous dolomite, muddy dolomite, light gray dolomite,intercalated with evaporate in the lower part
After the deposition of the Yanchang formation, the area was uplifted in the Indo-China movement Within the sags, in which the oil was generating, the diments in the paleo-fluvial system were deposited The fluvial valley cut down as deep as 330 m The eroded surface formed the upward migration route for the oil and gas generated in the Yanchang formation When the oil migrated into the fluvial sandstone bodies, especially in the point-bar sandstones, which possd good physical properties with average porosity over 18-20 %, and average permeability
10 × 10-3 μm 2
, the paleo-geomorphic oilfields with oil pools mostly in small or medium sizes in the middle-lower Jurassic were formed
复韵母ui怎么读
The petroleum geology of the Mesozoic put forward some new requirements for the ismic prospecting, that
106
is the deltaic sandstone bodies should be predicted with ismic, and so the preci form of the eroded surface at the top of Triassic.
Geology characterized in the accumulation of gas in the Paleozoic
Two suites of gas source rocks were deposited in the Ordos basin, i.e. the marine carbonates of the lower Pa-leozoic and the paralic coal ries of the upper Paleozoic.The former generated gas related with oil, and the latter generated gas related with coal. Especially, the source rock of coal ries in the upper Paleozoic is widely distributed,up to 23 × 104 km 2, occupying 92% of the total explor-atory area. It is the main source rock for the gas accumu-lated in both the upper and lower Paleozoic, and it is char-
Table 1 The stratigraphy of the Ordos basin
Geology and Exploration of Oil and Gas in the Ordos Basin
Sandstone Mudstone Pha boundary Oil field
Fig.3 Oil pools forming pattern in the deltaic dimentary system of the Triassic in the Ordos basin自制鲫鱼窝料
acterized with widely gas-generating area. Within an area of 22 × 104 km2 of the basin, gas flow or gas show can be en everywhere. Gas pools with industrial value exist in the 1000 m thick or so quence from the Ordovician to the Shiqianfeng formation of the Permian vertically. Widely generated gas and multi-rervoirs of gas make the gas exploration in the Ordos basin has a very wide range of targets.
Two types of rervoirs, sandstone and carbonates were deposited in the basin. The sandstone rervoirs were mainly deposited in the late Paleozoic, controlled by the deltaic system of shallow water fluvial facies of northern part of the basin. Due to the shallow water, the sandstone bodies of distributary channel were deposited in large areas.In the prent basin area, they extended from north to south, in which lithologic traps of large scale were formed. The source rocks were deposited in the same quence with the sandstone bodies or in their vicinity. The widely dis-tributing gas-bearing sandstone bodies were, then come into being (fig.4). The rervoirs were mainly character-ized with low porosity and low permeability. But rer-voirs with high porosity and high permeability exist due to the influence of various dimentary source, dimen-tary facies, constituents of rocks and diagenesis. Especially, the rervoirs with high permeability exist in the Shan-2 of the Shanxi formation. In the areas the gas producing is very promising. At prent, four large gasfields in the
upper Paleozoic, the Yulin, WuShenqi, Sulige and Mizhi oilfields have been found with rerve of more than hun-dreds of billion cu m in each.
The carbonate rervoir in the lower Ordovician is some kind of carst storage in the weathered crust of the carbonate, which suffered long-time weathering from the Caledonian movement to the Hercynian movement. The original di-mentary facies of the rervoir belonged to the dolomitic plate, which was distributed at the western side of the east salt-lake area in the form of an arc. Various types of dolo-mites in the dolomitic plate facies, such as gypsum dolomite, micritic dolomite, silty dolomite, granular crys-talline dolomite and lime dolomite, suffered weathering and leaching, and multi-stage diagenes in the geologic history. In the process, various forms of dissolved cavities, pores and fractures, such as intergranular, intragranular, moldic, intercrystalline and intracrystalline were formed. So, the carbonate rervoir in the lower Or-dovician is characterized with a texture of stratified net-work of pores, which is formed in the marine carbonate with dolomite as backbone, dissolved pores as connected routes and micro-fractures as the ends.
竖脊肌的锻炼方法Upper Shihezi formation
Lower Shihezi formation
Shanxi-Benxi formation
Majiagou formation
Gas-bearing sandstone Coal am stratigraphic boundary Parallel unconformity
Fig.4 The gas pools forming pattern in the composite lithologic traps in the Upper Paleozoic of the Ordos basin
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