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Home , Northern Shaanxi, Shale, Shale oil, Shizuishan, Yanan Formation, Yijun County

Geological Characteristics and Resource potentials of in Ordos Basin, Center BAIYun-lai, ZHAO-Yingcheng,MA Long, Wu –jun,MA Yu-hu （Northwest Branch Institute of Research Institute of Exploration and Development, PetroChina. ,730020 ,, China） Abstract It has been shown that not only there are abundant oil, gas, , coal- gas, groundwater and giant deposits but also there are abundant oil shale resources in Ordos basin.The main oil shale layers (abbre.OSL) occurred at , respectively, the Shanxizu Formation (early ),the upper of the lower bench of Yanchangzu Formation(middle –late ), the Wayaobaozu Formation (late Triassic),the Yananzu Formation(early stage of middle ) and the Andingzu Formation (late stage of mddle Jurassic).Oil shale were ,usually, in formations buried at the basin. Both Yanchangzu Formation and Yananzu Formation were the two main formation of beaing oil shales. Oil shale in early Permian was formed in paralic offshore, and in middle –late Triassic was formed in terrestrial (batho and half -batho lacustrine), and in late Triassic and early middle Jurassic was formed in terrestrial facies lake delta and lake bog. And it was paragenesized together with coal layers (abbre.CL).But oil shale in late middle Jurassic was, merely, confined in half batho lacustrine. It has been shown also that the thickness of oil shale is ,usually, 4-36m, oil yield 1.5%-13.7%, caloric value 1.66～20.98MJ/kg, apparent density 1.55-2.46 by dissecting the oil shale in northern – of , China and Tanshan of of , northwest-China. The resource amount of oil shale with burial depth less than 2000 m is over 2000×108t (334).Within it, confirmed reserve is about 1×108t（121）,which displays a giant resource future. The bury depth of oil shale in both southeastern and western parts of the basin is shallow; part of it has been verified to be high quality. With excellent road conditions connecting to outside the basin, it is not only huge economic benefit to develop the oil shale in time, but also precious experience in developping oil shale may be obtained in Ordos basin.

Key words: Oil shale; Geological characteristics; Resources, Ordos basin, Center-western China About the first author: BAI Yun-lai ,male, born 1957,doctor and senior engineer, has long engaged in the study of regional tectonic, and metallogenesis and now mainly undertakes basin analysis and oil shale resource research; E-mail: [email protected]

Ordos basin is one of the largest oil and gas basins (OGB) in China. The area of antetype of 2[1] Ordos basin is nearly 400,000km in middle-late Triassic( T2-3). It has been proved that not only huge hydrocarbon resources exists but also abundant coal, coal-seam-gas and groundwater resource present in Ordos basin [2]. Especially, the sand -type uranium deposits which can be in-situ leaching were discovered in the northeastern basin in 2001[3]. All these indicate Ordos basin is a treasure-house in which many kinds of resources were accumulated. In addition to what mentioned above, according to our field investigation and combining to previous data,writers think that Ordos basin has giant oil shale resource. Only “shale oil” (“shale oil” is come from a distillation of oil shale, amounts to crude oil) resources amount exceeds 500×108t in Chang-7 Oil-Formation which is apart of Yanchangzu Formation. The resources amount is 34% of the nationwide total [4,5], which is the largest in China. In Ordos basin, the oil shale occurs in many formations of different geologic age(early Permain, middle-late Triassic，late Triassic and middle Jurassic ) and several different type of facies (offshore facies, delta facies in which oil shale associated with coal, and deep and semi deep lacus).and oil shale has a fairly uniform lateral extension, with vast areal distribution, high oil yield, and simply geologic structure. The setting of the oil shale deposits is suitable for the opencast production similar to those of Shaanxi Tongchuan Bawangzhuang oil shale but also part of the deposits is suitable for the underground production similar to the Shaanxi county coal

1 field in which oil shale associated with coal layers. It is a very important to study the characteristics of oil shale which may be formed in different geologic periods, including occurrence regularities, resource extension, developing and utilization conditions. This paper is a summary in oil shale study in Ordos basin in the past few years by PetroChina and by PetroChina Changqing Oil field Company. It has huge economic benefit to continue to study oil shale and accumulate related data and techniques once the oil price goes much higher. This is because although new oil and gas fields continue to be found, but the demand for oil and gas is even faster than the new fields are found, and the disparity between the deliverables and the demand would be much greater after 20-30 years.[6] But, the technology for processing oil shale is relatively proven, and oil shale has been conveniently extracted , widely used, and had the long utilized history [4,7-13]. It is highly probable that oil shale would be a new resource that may substitute petroleum partly. Therefore, it is very important to investigate oil shale future and to study conditions of both developing and utilizations in Ordos basin.

1 The distributed characteristics of oil shale in time and space in Ordos basin

It has been proved that there were many suites of oil shale layers in Ordos basin [14-16].Oil shale was controlled by structural cycles and palaeo-climate changes. They occured in early Permain (Shanxizu Formation ),middle-late Triassic (Yanchangzu Formation), late Triassic( Wayaobaozu Formation) and early-stage of middle Jurassic (Yananzu Formation), later-stage of middle Jurassic( Andingzu Formation )in Ordos basin（Table 1）.They occur in layerings buried deep at the basin and occur at shallow depths around the edges of the basin. It also exposed in incised valley and some bore holes. Oil shale in Shanxizu Formation (P1), mainly occurred at the bordering part of the basin in Baode and Hongdong counties in province, and Shizuishan and counties in the Ningxia province where Oil shales are usually co-existing with coal layers.Often the coal layer is at the bottom with a thickness of 0.5m and rich in oil yield. The oil yield is higher than any other places. Because of the deep buried depth of oil shale which exceeds 600m in the eastern parts, and reaches 2200m in the western parts, organic substance may be transformed into natural gas, which may be the origin of the gas fields in the interior basin of province. For this reason,those Oil shales will not be discussed in details in this paper. Oil shale of both Yanchangzu Formation (T2-3) and Wayaobozu Formation(T3) occur in the form of an asymmetric syncline, upwarping and cropping out in the eastern part of the basin, slightly dipping westward in the middle eastern part, is deepest in the Huachi and Huanxian counties of Gansu province. It is gradually uplifted by the graben and dips eastward and the upper part were eroded. Outcrops of oil shale were mainly distributed in the eastern and southern parts of the basin forming an arc crossing , Tongchuan city, Yaoqu town, Binxian county of the northern Shaanxi province. This is shown in (Fig.1). Oil shale of Yananzu Formation (early J2) crops out to the surface mainly in the western part of the basin across Tanshan town of Guanyuan city in southern Ningxia, and Huating county in the eastern Gansu. The distribution in the western basin is in concordance with the distribution of the coal layers, and the distribution in the eastern basin is in concordance with the lake deposits (Fig.2) . Oil shale of Andingzu Formation (late J2) occurs in the lake range of the basin and lied deep in the center of the basin. Outcrops may be seen in the incised valley(Fig.3).

2 The geologic characteristics of oil shale

2.1 The geologic characteristics of oil shale in middle-late Triassic（taking oil shale

2 of northern Tongchuan as an example）

Table 1The middle-upper Triassic and Jurassic sequences and their controlling factors and the accumulation of various energy resources in Ordos basin(modified by literature [1,2,5,14-21])

2.1.1 Stratigrphic position of oil shale

The stratigraphic position of oil shale in northern -Tongchuan in Ordos area is the second section of Yanchangzu Formation(Ty2). Yanchangzu Formation is, fundamentally, composed of grey-green, grey-yellow-green, light red arcose ,and being interbed with deep grey- green shale and coal strings, pertaining to a terrestrial origin [16]. The lower part of the Yanchangzu Formation is interbed with dark shale and the middle-upper part is oil bearing. From the dark colour, Yanchangzu Formation may easily be differentiated of the upper formation and the lower formation, and conformable contacted with the lower and the upper formation. The lack of crimson in Ermayingzu Formation(T2)marks the base of the Yanchangzu Formation. In the upper, the show of an interbedding of coal beds and a sandy mudstone marks the base of the Wayaobozu Formation of deltaic facies. There is another oil shale layers in Wayaobozu Formation, which will be discussed late .The oil shale and the oil layer (see table 2)are superposed in space.

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Shaaxi

Fig.1 The map showing the distribution outcrops of middle-late Triassic strata (upper) and the cross section(below) of Ordos basin (upper map after literature[16]; lower map after PetroChina,Changqing Oilfield company，2002) 1-Trassic System;2- System and Permian System;3- reservoir;4-Oil shale;5-Carbonate rock ;6-;7-；Q -Quaternary System; N -Neogene System; E- Paleogene System; K - System; J-Jurassic System ;T -Triassic System;C-P Carboniferous System and Permian System; ∈-O - System and System; Pt2-3 - Middle – Upper Proterozoic; Ar-Archean

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Fig.3 Lithofacies and palaeogeographic in Fig.2 The map showing distribution of coal bed in Anding Formation in later-stage of middle Yan′an Formation in early-stage of middle Jurassic Jurassic in Ordos basin (Oil shale distrubuted in (Oil shale intercalated in coal bed in the distributed relatively abyss, after literature [2，18] ). area of coal, and lacustrine facies oil shale 1-Ablation area ； 2-Fluvial facies ； 3-Fluvial and distributed in no-coal area (0 contour line) in Ordos lacustrine facies ； 4-Shallow lacustrine facies ； basin，after literature [2，18] ). 5-Shorelake area;6-Relatively abyss ； 7-Border of 1-Ablation area；2-Border of stratum save；3- Thickness stratum save；8-Thickness contour of stratum contour of coal bed

In Fig.4, a key section (253-266 layers) of oil shale had already been listed. The main characteristics of oil shale may be easily found by Fig.4; the lower part compr ised silt, fi ne-grained sandstone, interbedded oil shale layers which is generally thinner than Fig.4 The architectural characteristics of oil shale in key position in southeast Ordos basin the others, 1-Sandstone；2-；3- Argillaceous sandstone；4-Shale；5-Oil shale(Column showing lithology about 0.5-2m, only denotes lithological assembled, but not denotes true thickness,which had shown in thickness and oil shales column )

5 in the middle part is the main oil shale layers, the thickness is generally greater than others, about 20-36m. There are not much of interbedding of the sandstone and shale but with more stable areal distribution; the upper part is interbedded silt, shale, and mudstone. The main oil shale layers in the middle part has generally high commercial value and is the main exploratory target.

Table2 The relationship between the stratum system ,oil layers and marker beds in Yanchang Formation

STRATA SYSTEM MARKER BED OIL GEOGRAPHICAL LAYERAS SYSTEM SERIES FORMATION SECTION AREA MARKER BED INDICATOR ASSEMBLY BED WAYAOBAO COAL WAYAOBAOZU UPPER Ty5 CHANG SERIES STRATA ( Tw) 1,2 （ASSIST） YONGPING 4 Ty CHANG3 SANDSTONE SECTION （ASSIST） FISHING NECK U CHANG4+5 MUDSTONE TRIASSIC SECTION（ASSIST） 3 MIDDLE YANCHANGZU Ty 1～2 CHANG6 -UPPER ( Ty) 3～4 CHANG 6 THIN B ED 1＋2 CHANG 7 TUFFACEOUS SANDSTONE ZHANGJIATAN CHANG 3 7 SHALE,OIL SHALE DTy1,2 CHANG 8，9 LIJIABAN SH ALE

2.1.2 The characteristics of structure in the distributed area of oil shale

Fig.5 shows the distribution characteristics of oil shale in space in the northern Tongchuan which is situated in the southern Ordos basin. Hejiafang-Qianlieqiao section shows a large , the core of which is located in Hejiafang-Qianlieqiao section. The strata at the core of the anticline belongs to the lower part of the first bench of Yanchangzu Formation（Ty1）,and the upper strata, include the oil shale have all been eroded. The strata of both flanks of the anticline dip gently. Because of the effect of a downthrown fault, the west wing of the anticline was preserved without being eroded. The Huashihe-Donggoukou section shows a west gentle-dipping monocline and the oil shale plunges gradually toward the west. Qianlieqiao-Fengjiaqu section shows a southern plunging monoclinal structure. Bawangzhuanghouliang- Fengjiaqugoukou section shows a relatively flat structure. In summary, the structure character of the Northern-Tongchuan oil shale is a domal structure with small size. The core is located in Hejiafang. The west and south parts of the dome have a tendency to plunge westward and southward. It may be called “Hejiafang Dome Structure”. It controls the distribution of the oil shale in Northern-Tongchuan.

2.1.3 The thickness of oil shale

According to the outcrop and well loggings, the thickness of the main oil shale is in general about 25～36m. The thickest section is located in Tangnihe-Mazhuang and becomes thinner toward southward and south-westward

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Fig.5 The fence diagram showing structure of oil shale in northern –Tongchuan 1-Holocene series, alluvium-diluvium；2-Loess layer；3-Third layer of third segment of Yanchang Formation： celadon shale, sandstone；4- Second layer of third segment ofYanchang Formation：celadon thick sandstone with thin bed；5- First layer of third segment of Yanchang Formation：celadon-french grey shale；6- Fifth layer of second segment of Yanchang Formation：celadon –olivine shale, upper thick sandstone；7-Four layer of second segment of Yanchang Formation：oil shale with oil sand；8- Third layer of second segment of Yanchang Formation：celadon shale, arenaceous shale； 9-Second layer of second segment of Yanchang Formation：celadon intermediated-thick sandstone；10- First layer of second segment of Yanchang Formation：celadon thick sandstone.Red line and red arrowhead show faults and their movement direction

2.1.4 T he macrofeature and the substance component

In northern Tongchuang ,the oil shale shows dark, greasy luster, and appears red in the basal surface(photo 1).Oil shale appears flaky, banding and bedded structure with uneven -conchoidal

7 fracture , and soft with light brown streak and prominent greasy luster. In general the oil shale is ,mainly, made up of mineral by unaided eye. The bedding plane is showing glossy luster, and becomes a little coarser when containing sands. This may be the characteristics which is different from oil shale elsewhere. Depositional environment of oil shale was a deep lacus to semi-deep lacus and anaerobic but near-source. This is because the clastic was detected and slabby feldspar debris can be seen by microscope（photo 2）. Under microscope, both blastopelitic texture and planar structure can be seen in oil shale. The main components are clay, silt and ferrum. Clay is aphanocrystalline, and silt scrip is and plagioclase. The pattern of minerals are directional and forms planar structure. Microaphanitic clay has been partially sericitized. Ferrum and aphanocrystalline components filled up in the clay. Silt appears angular, subangular and rounded with granul diameter 0.03～0.06mm. Some reach 0.15mm of sand size. Platy cleavage is well developed. Clay and silt accumulated and segregated into alternating bedding. Mineral composition is: Clay 92％，silt 3％and ferrum 5％.Chemical composition of oil shale（×10-2） is:

SiO2 52.02（56.14～47.89）、Al2O313.42（12.22～14.61）、TFe2O37.03(8.62～5.44)、MgO1.12(1.28～ 0.95)、CaO0. 78(0.67～0.68)、 Na2O 1.66(1.79～1.53) 、K2O 2.96(3.19～2.72)； within it, the sum -2 of SiO2 and Al2O3 is 65.44×10 and it shows that the main chemical composition in oil shale is SiO2 [22] and Al2O3.The oil shale falls into moderate ash content range .Other components are minor, -2 -2 -2 -2 and belongs to siliceous ash in which SiO2 is 40×10 ～70×10 、Al2O38×10 ～30×10 、 -2 -2 [22] Fe2O3<20×10 、CaO<20×10 ） ；Both SiO2 and Al2O3 are relatively less than the oil shale in , in which

Photogram 2 The characteristics of Bawangzhuang Photogram1 Oil hale in Bawangzhuang, under microscopic(remaining argillaceous texture， Tongchuan（ Scale 1：4） slab structure. The rock composed of cryptocrystalline clay, ferrum and silt quartz scrap. The rock has been lightly sericized. It has also been dyed by ferrum. Cross ×4)

8 -2 -2 [23] -2 -2 SiO261.59×10 、Al2O323.36×10 .Organic is 14×10 and total carbon is 16.28×10 . 2.1.5 Quality of oil shale Both oil yield and caloric generation value are the top index mark for evaluating the oil shale. Based on these criteria and data from previous investigators, oil shale in Ordos is considered as above fair quality. Its oil yield is generally 1.8 ～ 13.7%，mean value 7. 70%（table 3），and caloric generation is 1.66～11.45 MJ/Kg（authors detect)，and type of is I-II1，capability of producing hydrocarbon is 400Kg/t [24].Density of oil shale in Ordos is generally 1.41～2.59（ARD）， average 1.72. Moreover, Both Lu Jincai and Liuzhaojun [5]②obtained oil yield in oil shale of Chang 7 oil layer to be 5%～10%. In 1950s，Shannxi Petroleum Industry Bureau proved oil yield in Qianlieqiao oil shale to be 7%， in Tangnihe5%, in Hejiafang9.25%. For comparison, oil yield is 5%～10%, known reserve is 41×108t in Fushun of Liaoning, China ,and oil yield 6%～8% （mean），highest 13.66%, caloric value 3900～6200 J/kg ,thickest is 49 m, and known reserve is 55.15×108 t. These may help to compare with others. Putting all the parameter mentioned above together, the reserves is 7000×104t at northern Tongchuan. Comparing TOC and other index mark of oil shale in Ordos to others, one may conclude that oil shale in Ordos belongs to good quality (table 4).

Table 3 The oil yield of oil shale in southeast Ordos basin Gray-King LOW TEMPERATURE DISTILLATION TOTAL SPECIMEN NAME No SEMI-COKE YIELD MOISTURE COKE (SITE OF SAMPLING) oil yield （％） （％） YIELD TYPE （％） Black flaky oil shale V-1 13.7 77.9 2.5 B (Lieqiaocaozigou） Black slip oil shale t68 11.0 80.8 1.6 B (Jiaquhe) grey-black flaky oil shale VII-2 10.6 80.2 4.0 B (Jiaopingzan) Black flaky oil shale VI-1 （present grey red after ） 10.2 77.4 4.6 B （Hejiafang） Black flaky oil shale IV-1 9.6 78.6 7.0 B （Tangnihe） Black flaky oil shale t74 8.9 78.5 6.0 B (Wushimut） Black flaky oil shale t61 （ present ashen after weathering ） 8.6 76.2 5.0 B （Liushutai） Black flaky oil shale t21 7.0 82.6 3.3 B （Fengjiaqu） Black flaky oil shale t94 6.4 83.9 4.1 B （Maquan） Black flaky oil shale t69 （ present white after weathering ） 5.2 78.6 8.8 B （Niejiahe） t86 Grey black flaky oil shale（Fudi） 5.2 89.4 3.4 B Black flaky oil shale（ present grey -yellow II-1 3.6 86.2 3.0 B after weathering）（Bawangzhaung） Black flaky oil shale （ present white after t28 2.5 90.0 4.8 B weathering ）（Banjiegou） present minium after weathering） TC-1-1 1.8 92.8 4.2 B （ Bawangzhaung ） Notes：Specimens were collecting by Bai Yunlai (2008)，who is a professor in Northwest geological institute of PetroChina. Specimens were analysed by Liu Bingyuan (2008)， who is a engineer in Gansu coal quality supervision examine station. The test procedure mean is Gray-King LOW TEMPERATURE DISTILLATION and the test criterion is GB-T1341-2007

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Table 4 The correlation table of organic material abundance between shale in southeast Ordos basin and land facies oil source rock in China ITEM LITHOFACIES LITHOLOGY C% ‘A’%CHLO H C ×10-6 H C⁄ （ORGANO C） ROFORM (TOTAL C% HYDROCARBON） GOOD OIL Half batho-batho Grey black ﹥1.0 ﹥0.10 ﹥500 ﹥4 SOURCES lacustrine mudstone ROCK SUB-GOOD OIL Shallow half Greymudstone 0.6～1.0 0.051～0.1 200-500 2-4 SOURCES ROCK batho lacustrine (dominate) RELATIVELY NOT Shore lacustrine Mudstone 0.051～0.1 0.01～0.05 100-200 1-2 GOOD OIL –shallow SOURCE ROCKS lacustrine NO OIL SOURCES Fluvial facies Grey ﹤0.4 ﹤0.05 ﹤100 ﹤1 ROCK greenmudstone(do minate) YAOJIE OIL Shallow half Black oil shale 10.55 0.28 2108 2.19 SHALE batho lacustrine ORDOS OIL Shallow -batho Black oil shale 19.3 0.4-1 1.92-5 SHALE lacustrine .77 Notes：Both the abundance and evaluate index of OM of land facies oil sources rock of China were on the grounds of Huang Difan1998[4].Yaojie oil shale data comed from northwest geological institute of petroChina(1992④)

2.1.6 Genesis of oil shale in northern Tongchuan At the moment ,oil shale may generally be classified into three types [4,5,23]：First type is black, light brown oil shale formed in marine facies plateau on Passive continental deposits, and it is very rare and associated with carbonatite, silicalite, and phosphatic series. Oil shale of this kind is very thin, and thickness does not exceed 2-3 meters. The thickness which attained 10m is very rare, but oil yield is high and can attain 20％. The second type is also black in color, formed in batho-half batho-lacustrine facies. The thickness of oil shale of this kind can reach several hundred meters but oil yield percentage is low and generally less than10%. This type is the product of periodic change of water -organisms and chemical environment in lake, which was directly controlled by seasonal climate cycle and is lacustrine origin. The third type is associated with coal layer, including those formed in paralic and paludal facies ,in which oil shale, generally, distributed in the upper, bottom of coal beds or between coal beds. But majority is distributed at the bottom of coal bed, and high oil yield is its feature but the thickness is relatively thiner. Oil shale of northern Tongchuan belongs to the type which formed in large half batho-batho inland lacus.

2.2 The geologic characteristics of oil shale in middle Jurassic（taking oil shale of Tanshan as a example）

2.2.1 The areal geology generalization and the position of oil shale

Oil shale in Tanshan of Guyuan city of Ningxia province of northwest China, is situated in west Ordos basin [26]、east of -Guanyuan discordogenic fault. It is the remnant after the west part of the basin gone through folding and erosion of the Himalayan orogeny. Oil shale occurs in [26] Yanan Formation (J2) ,which was made up of sandstone and shale mingled with coal beds, oil shale and . Its thickness attained 300 m，and has anglur uncomformity to the substratum

（Fig.6）.Another Formation is Anding Formation(late J2) in oil shale district, and the composition is mainly quartz sandstone with shale, and is disconformably to the substratum. 2.2.2 The structure of the oil shale district

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The oil shale district is situated in the west Ordos, which is a fold-thrust zone. The structure is developed and chiefly composed of a series of folds with different orientations and fault types in the fold-thrust zone. Most of the exploration area is located in the east wing of the Qinjiayao main anticline (Fig. 7),which is made up by four sub-folds of moderate tight structure, namely; Qijiayao anticline, Huaichaliang syncline, Caozi anticline and Xiaoxiwan syncline. The fold axial trend: is basically NWW(ichnography is omited) but slightly showing “S” shape in the southern II line . The main anticline generally plunges to the north and tilt in the sout.The two limbs are relatively symmetry in the southern III line, and the angle of strata is generally 20° ～ 30°. The location of the axis of Qinjiayao anticline is already determined by boreholes and by two flanks and outcrops , but is poorly known between the north of F5 fault and the south of F8 fault, and mostly is by deducing. There are 9 major faults in the area. According to the relationships between faults and folds, these faults may Fig.6The synthesis histogram of Tanshan oil shale deposit be classified roughly into 4 groups ， namely;longitudinal faults

11 （NNW），transversal faults(NEE) ; oblique NE faults and NW faults. These fault have major determining factor in the distribution of oil shale layers and coal beds (no tautology).

W E

0 40 km

Fig.7 The exploration line profile of Tanshan oil shale deposit.

2.2.3 The characteristics of oil shale

（1） The characteristics of the occurrence of oil shale As mentioned previously, oil shale of Tanshan occurred in Yanan Formation(J2), and similarly for the coal layers. the distribution of oil shale was fully controlled by the Yanan Formation and its tectonics. In these areas, there are 8 sets of oil shale, and the total thickness is about 14.39m. The oil shale is mainly distributed in the first and the 1-2 second coal-bearing section of Yanan Formation( J2y ) and is closely related to coal layers which is clearly shown in Figure 6 (the area synthesize histogram). Photogram 3 Oil shale in Tansham Combining from a regional distribution of view and relations to coal layers(CL)14,16, and 19, the oil shale layer(OSL)3,4,5, and 6 have a fairly uniform lateral distribution and the thicknesses are greater than elsewhere. OSL 3 ,4 are located at the upper part of CL14 and 16, respectively. OSL5 is located at the upper part of CL19 and OSL 6 is located at the lower part of CL19. The thickness of OSL 3,4,5,6 is 2,2,4,0.95 m, respectively. The distribution of OSL is very closely related to the folds and fractures mentioned above (as OSL2, 4). It is worthy mentioning here that the CL19 has very high sililceous content(﹥40%), but its oil yield reaches up to 7%. It has only been used for oil refining so far, but can be considered as oil shale. Its reserves are about 7284×104tons. Convert to pure shale oil, it amounts to 510×104tons at least. （2） The macro characteristics, chemical composition and oil yield Oil shale in Tanshan shows black color in naked eye, slightly greasy luster, flaky, layered structure, with uneven-conchoidal fracture. The hardness is soft, its streak is shining brown. It mainly comprises clay minerals.The surface is smooth and slightly greasy. (Photo 3). The analysis shows (Table 5)：oil yield is ,commonly, 2.0%～11%， high heat generation 4.36 ~ 20.98MJ / kg; low heat generation 3.91 ~ 19.38MJ/kg; this is close to or higher than the calorific requirement value of oil shale(4.18 MJ / kg). The oil yield of the oil shale samples are all met with

12 the industry demand in the mining area but slightly lower in the outer circle of the mining area. -2 The chemical constituents of oil shale are (× 10 ); SiO2 :20.44, TiO2 :0.32, Al2O3 :7.12, Fe2O3 +: :6.36, FeO :1.50, MnO :0.013, MgO:0.83, CaO: 0.27, Na2O :0.27, K2O :1.12, P2O5 :0.050, H2O -: -2 1.90, H2O 3.39; LOI:61.73. The sum of SiO2 and Al2O3 is 27.44 × 10 , which is far less than the 83 × 10-2 ,which is the upper limit of siliceous content of oil shale by ZHAO( ZHAO Longye [22] ,1995). If the siliceous content is higher than this value, it would be called oil-bearing shale. These contents show that the chemical compositions of oil shale in Tanshan is mainly composed of SiO2 and Al2O3, which is much lower than the ones in Fushun and other places, in which SiO2 is -2 -2 [23] 61.59 × 10 , Al2O3 is 23.36 × 10 （see Jianqi 1979) . (3) The size of oil shale in Tanshan: according to oil-bearing rate , distribution range and related criteria , estimated the reserves of shale is about oil 3718× 10-2t [26] in Tanshan

Table 5 Oil- yield rate of Tanshan oil shale Gray-King LOW TEMPERATURE DISTILLATION

SEMI-COKE TOTAL LOSS (%) CCOKE SERIAL SPECIMEN SITE OF NAME OF YIELD (%) MOIST TTYPE NUMBER NUMBER SAMPLING SPECIMEN OIL URE YIELD(%) YIELD( %) 1 ts-1 Dquanwangou(oute Black flaky 2.0 82.2 10.0 5.8 A r ring) oil shale 2 ts-2 Drilling No Z902 Black flaky 2.7 88.9 5.0 3.4 bore depth oil shale 100m(outer ring) 3 ts-3 Drilling No3 Black oil 4.6 76.1 9.0 10.3 A （OSL3） shale 4 ts-4 Drilling No2 Black oil 5.4 82.7 8.0 3.9 A （OSL 4） shale 5 ts-5 Drilling No Black flaky 11．6 75.0 0.5 4.7 A 3( OSL 5） oil shale

Notes：Specimens collecting ,analysis , test procedure mean and the test criterion is the same as Table 3

2.2.4 The genesis of Tanshan oil shale Because it is associated with coal seams, occurs either at the top or at the bottom of coal layers, or within a coal bed , the Tanshan oil shale was formed in the marsh environments.

3 The resource assessment for oil shale in the Ordos basin

Summing up all the descriptions before, there are 4 main oil shale formation. They were formed in middle to late Triassic; late Triassic ; early middle Jurassic; and late middle Jurassic 1 2 (T2-3, T3 , J2 , J2 ). Figure 8 shows the distribution of middle late Triassic Yanchang extension Formation(T2-3) and late Triassic Wayaobao Formation(T3) . Oil shale occurred in Yanchangzu Formation was formed in batho and half batho lacustrine environment. The thickness is generally 13 - 36 m, oil yield is 5% -10 %.The oil shale occurred in Wayaobaozu Formation was formed in paludal facies, associated with coal. The thickness is 8 - 12 m, oil yield 6% -14% [20] . 1 The distribution of oil shale in Yan'anzu Formation(J2 ) is the same as the coal layer in the western part of the basin. In the eastern part of the basin, the distribution of oil shale is the same as half batho lacustrine deposits but without coal. (Figure 2). The thickness of lacustrine oil shale is 4-10 m, oil yield 1.50%-12%. Those oil shale with oil yield less than 3.5% were not accounted in the calculation of resources [21] The oil shale of Anding Formation was deposited in a half deep lacustrine environment in late

13 2 stage of middle Jurassic(J2 ).(Figture 3) .During this geological period, neither coal or oil shale can be deposited in deltas Due to hot dry climate [21], and can only be formed in deep lake emvironments. The estimates of oil shale resources basin-wide is listed in Table 6. 4 Conclusion There are massive resources of oil ,natural gas, coal and coal seam gas, groundwater , uranium ,and oil shale in the Ordos located at central-west China. The major formations of oil shale are ,respectively ,the Shanxizu Formation (Early Permain), the upper part of lower Yanchangzu Formation(middle –late Triassic), the Wayaobaozu Formation (late Triassic), the Yananzu Formation(early stage of middle Jurassic) and the Andingzu Formation (late stage of middle Jurassic).Oil shale occurs

usually in laminations and buried deep in the Fig.8 The areal map of oil shale in Yanchang center part of the basin. But it can be seen at Formation in Ordos the edge of the basin in shallow incised 1-Thickness isoline of oil shale;2-burial depthof oil shale valleys and bore holes. The major oil shale

Table 6 Assessment for the amount of resources of oil shale in Ordos basin EPOCH AND AREA(km2) THICKNESS DENSITY OIL SHALE OILYIELD SHALE OIL POSITION OF OIL （m） RESOURCES （ MEAN） RESOURCES SHALE （MEAN） AMOUNT AMOUNT （×108t） （×108t） ANDINGZU 8200 8.00-14.00（11） 2.46 2218.92 4.00-5.00（4.5） FORMATION (LATE-J2) 99.85 YANANZU 113660 4.00-6.00（5） 1.55 8808.65 1.50-12.00(6.75 FORMATION(EARLY ） J2)( PALUDAL FACIES) 594.58 YANANZU 17541 5.00-10.00（7.5） 2.46 3236.31 3.00-5.6（4.3） FORMATION(EARLY J2)( PALUDAL FACIES,LACUS FACIES ) 139.16 WAYAOBAOZU 800 8.00-12.00（10） 2.45 1960 6.00-14.00（10） FORMATION (LATE T3) 196 YANZHANGZU 29400 20.00-36.00 1.72 14159.04 1.80- 13.70(7.7) FORMATING(T2-3) （28） 1090.24 SUM 30382.92 2119.83 NOTE：The area of oil shale distribution of Yanchangzu Formation is base on data of Yanchang Oil Field Co.The area of oil shale distribution of Yananzu Formation(paludal facies part) is base on data of Zhang Hong [21] 1 producing formations are Yanchangzu Formation(T2-3) and Yananzu Formation(J2 ). Oil shale in early Permian was formed in paralic offshore; oil shale in middle –late Triassic was formed in terrestrial facies(batho and half -batho lacustrine); oil shale in late Triassic and early stage of middle Jurassic was formed in terrestrial facies lake delta and lake bog(paragenesis together with coal layer), and oil shale in late middle Jurassic was, merely, confined in half batho lacustrine. The thickness of oil shale is ,usually, 4-36m,oil c yield 1.5%-13.7% . (those of less than 3.5% were not accounted in the assessment of resources ). Just the shale oil with the burial depth shallower than 2000

14 meter(334) is over 2000×108tons. Confirmed reserve is（121）1×108t. This demonstrates giant future of oil shale in the Ordos basin. To sum up, Not only the quantity of oil shale of Ordors is huge but also there are confirmed reserve that can be produced in the near future. The structure associated with oil shale is simple as well as its hydrologic geology conditions. The thicknesses of oil shale layers are thick and all information are well verified with high degree of confidence. With good road conditions connecting the areas outside of the basin, coupled with reasonable production methods and good environmental sense in mind, it is very doable to developed the oil shalein the Ordos basin. If adopting the good experience of “Small furnace refining” in Huadian mine of northeast China, the exploitation of oil shale in Ordos basin can have economic benefit but also the experience of developing of oil shale is previous.

Acknowledgement

We want to thank Dr. James Tung of Rowland heights, California for editing parts of the English script.

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