The oldest oil accumulation in China: Meso-proterozoic Xiamaling Formation bituminous sandstone reservoirs

PETROLEUM EXPLORATION AND DEVELOPMENT Volume 38, Issue 4, August 2011 Online English edition of the Chinese language journal Cite this article as: PETROL. EXPLOR. DEVELOP., 2011, 38(4): 503–512.

RESEARCH PAPER

The oldest oil accumulation in China: Meso-proterozoic Xiamaling Formation bituminous sandstone reservoirs Liu Yan1,2,3,*, Zhong Ningning1, Tian Yongjing4, Qi Wen5, Mu Guoyan1 1. State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Beijing 102249, China; 2. Working Station for Postdoctoral Scientific Research, PetroChina Dagang Oilfield, Tianjin 300280, China; 3. Exploration and Development Research Institute, PetroChina Dagang Oilfield, Tianjin 300280, China; 4. Exploration and Development Institute, Sinopec EastChina Branch, Nanjing 210036, China; 5. Northwest Branch of PetroChina Research Institute of Petroleum Exploration and Development, Lanzhou 737002, China

Abstract: Based on analysis on the coexistent relationship between igneous rock intrusion and bituminous sandstone of the Xiamaling Formation in northern Hebei (Qnx), the accumulation time of the Xiamaling Formation bituminous sandstone reservoir is defined by the methods of organic petrology and isotope chronology. According to field investigation, observation of thin-section and the shallow drilling show, and based on the previous results of oil seepages and bitumen spots in the Qnx base sandstone, thirty-one new oil seepages (bitumen spots), including twenty-one visible black bitumen spots, were discovered in the Qnx. The distribution of paleo-reservoirs in the Qnx bituminous sandstone was identified, and 4 paleo-reservoirs, i.e. Shuangdong paleo-reservoir in Pingquan, Longtangou paleo-reservoir in Lingyuan, Lujiazhuang paleo-reservoir and Tashan paleo-reservoir in Kuancheng, have been named. The reserves of the paleo-reservoirs are 0.7-1.0 billion tons, which are calculated by the volume method with the solid bitumen content. Organic petrology analysis shows that two kinds of solid bitumen with diferent reflectivity characteristics were developed. Class structure of natural coke is discovered in solid bitumen, which is the first direct evidence to prove that severe thermal alteration occurs in the Qnx base sandstone bitumen. The age of Qnx gabbro-diabase baddeleyite by SHRIMP U-Pb dating is 1 327 Ma±2 Ma, which indicates that the accumulation time of the Xiamaling Formation bituminous sandstone is 1 400 Ma to 1 327 Ma. So, it is the oldest oil accumulation in China. Key words: bituminous sandstone; Mesoproterozoic-Neoproterozoic; Xiamaling Formation; igneous rock; oldest reservoir; accumulation time; Yanshan

Introduction Yanshan is one of the areas with most Meso-Neoproterozoic strata in China. On the standard cross-section of the Jixian County, the Meso-Neoproterozoic layers reach a total thickness of 9 553 m[1]. The Meso-Neoproterozoic hydrocarbon source rocks are developed in the Yanshan area[1−4], with a very low geothermal gradient currently[1], and a moderate thermal evolution of organic matter[5−7]. Generally speaking, it is still in the status of “liquid window”, and is one of best prospects in China for pre-Cambrian survey[6,8,9]. There is abundant oil seepage and bitumen in the Jibei depression to the east of this area, which shows that oil and gas generation and charging happened in large scale in this area, and have formed an oil reservoir with certain scale. Researchers have common views on the thermal evolution of hydrocarbon source rock and the originality of oil and gas in this area[1,6−8,10], while they show different opinions on the oil/gas

accumulation time and the effect of the later modification. For example, some of them think that the oil/gas accumulation time is 763 Ma, while others think that it is around 980 Ma, or the Permo-Carboniferous period, or the Triassic-Jurassic period[1,7,11]. Multiple tectonic movements had happened during the geological history of over 1 000 Ma for the Meso-Neoproterozoic areas, which made the tracing of the thermal evolution history of the organic matter and oil/gas accumulation history very difficult. It is meaningful both theoretically and practically to further study the oil/gas accumulation time in this area, either for the purpose of correctly understanding the oil/gas accumulation history or developing new oil/gas survey area in China, or improving the Pre-Cambrian oil/gas accumulation theory of China.

1

Geological setting of the study area The Yanshan Meso-Neoproterozoic rift basin is mainly lo-

Received date: 17 Nov. 2010; Revised date: 20 May 2011. * Corresponding author. E-mail: [email protected] Foundation item: China National Key Basic Research Development Planning (973) Program (2006CB202303); Sinopec Marine Prospecting Program (YPH08028). Copyright © 2011, Research Institute of Petroleum Exploration and Development, PetroChina. Published by Elsevier BV. All rights reserved.

Liu Yan et al. / Petroleum Exploration and Development, 2011, 38(4): 503–512

Fig. 1

Range of study area and distribution of oil seepage and bitumen

cated in the northern areas of North China and the west of the Liaoning province, with an area of 8×104 km2. It is comprised of 7 structural units in a pattern of five depressions and two uplifts (Figure 1). The study area is located in the Jibei depression, to the east of the Yanshan mountain, neighboring the Liaoxi depression in the east, Mihuai uplift in the west, Shanhaiguan uplift in the south, and the earth axis of Inner Mongolia in the north. It is 120 km long from East to West, and 60 km from South to North, with a total area of 8 730 km2. Yanshan is one of the areas with the best Meso- Neoproterozoic development and reservation. It experienced different stages of structural evolution, including the Mesoproterozoic avlakogene, the Neoproterozoic-Palaeozoic cratonic cover, and the Mesozoic-Cenozoic inland orogenesis[12.13]. After the Lüliang Movement at the end of the Palaeoproterozoic Era, many rift basins were formed in and at the edges of the craton in North China. Particularly, the Meso-Neoproterozoic strata are developed well in the Yanliao rift trough and are regarded as the

product of Columbia supercontinent’s breaking apart and its further evolution[14]. The Meso-Neoproterozoic strata are divided into 12 groups in 3 series from bottom to top, and contact the underlying the Archean in angle unconformity, with the top covered by the Lower Cambrian (see Figure 2). Since the 1970s, oil seepage/bitumen has been discovered in this area, which attracts the attention of some scholars and proves the originality of the oil seepage[1,7,11]. The North China Oilfield Company drilled Well Shuang-1 and Hua-1 in the Shuangdong anticline zone and the Huapi structure of the Jibei depression, in which oil show was found but there was no industrial oil flow. In recent years, with the study on marine strata progressing and driven by the high world oil price, the research of oil/gas geology in this area is highlighted again. By the end of 2009, 223 oil seepage/bitumen spots in the Yanshan rift belt had been discovered. Among the 115 oil seepage/bitumen spots in the Jibei depression, 98 spots were found with the Meso-Neoproterozoic oil seepages, mainly as

Liu Yan et al. / Petroleum Exploration and Development, 2011, 38(4): 503–512

Fig. 2

Histogram of Meso-Neoproterozoic strata in Yanshan area, North China (modified from reference[15])

liquid oil seepage. There are diversified views on the oil/gas accumulation time. Wang Tieguan, according to the alteration characteristics of the bituminous sandstones in Longtangou and their contact with diabase bed, holds that the accumulation time of the old oil accumulation in bituminous sandstone of the Xiamaling Formation, Longtangou, Lingyuan, should not be later than the intrusion time of the diabases, i.e. around 763.40 Ma±8.61 Ma[11]. Hao Shisheng et al tried to rebuild the evolution history of the Meso-Neoproterozoic by combining

estimation of earth thermal flow value and simple analysis of old mature oil generation threshold, and presented that the original oil gas accumulation time in the Yanshan shall fall between the Triassic-Jurassic[1]. Qin Jianzhong et al rebuilt the hydrocarbon generation history with the method of basin simulation, based on the organic mature extent of the Meso-Neoproterozoic in the Jibei depression, and presented the view of twice hydrocarbon generations in the Meso- Neoproterozoic in the Jibei depression, stating that the first hy-

Liu Yan et al. / Petroleum Exploration and Development, 2011, 38(4): 503–512

drocarbon generation started from the Permo-Carboniferous period and ended at the end of the Triassic; the second hydrocarbon generation happened at the end of the Jurassic period[7]. Based on many field investigations, the authors discovered that the sandstone at the Xiamaling formation contains stable bitumen layers, and the intrusive bodies in the igneous rocks in the Xiamaling Formation have obvious and broad coexistent relationship with oil seepages. Previous scholars also noticed that the partial maturity of the sedimentary organic matter in the Xiamaling Formation is obviously higher than the maturity of underlying and overlying layers, and they concluded a certain genesis relationship[1,7,11]. Up to now, neither field observation nor shallow drilling reveal any signs of direct contact between sill and bituminous sandstone or erosion of the bituminous sandstone, and no direct evidence can prove that the emplacement of magma affects the hydrocarbons in the bottom sandstones of the Xiamaling Formation. With respect to the coexistent relationship between the bituminous sandstone and the igneous rocks intrusion in the Xiamaling Formation, this article intends to correctly define the accumulation time of the Xiamaling Formation bituminous sandstone with the methods of organic petrology and isotope chronology, so as to provide basis for a correct understanding of the history and laws of oil/gas accumulation in this area.

2 Distribution of oil accumulation in bituminous sandstone in the Xiamaling Formation 2.1 Distribution and types of old oil accumulation in bituminous sandstone in the Xiamaling Formation According to field investigation, observation of thin-section and the shallow drilling show, and based on the previous results of oil seepages and bitumen spots in the Qnx base sandstone, 31 new oil seepages (bitumen spots) were discovered in the Qnx, including 21 visible black bitumen spots and 10 sandstone spots with lower bitumen but distinguished microscopically (see Figure 3). The plane distribution laws and minimum scope of the oil accumulation in bituminous sandstone in the Xiamaling Formation were ascertained basically (see Figure 3). According to the distribution characteristics of the oil seepage/bitumen spots, 4 paleo-reservoirs are named: the Shuangdong paleo-reservoir in the Pingquan area, the Longtangou paleo-reservoir in the Lingyuan area, the Lujiazhuang paleo-reservoir and the Tashan paleo-reservoir in the Kuancheng area (see Figure 3). The Shuangdong paleo-reservoir in the Pingquan area is located in the Shuangdong anticlinal structure of the Shuangdongzi Village, to the southeast of the Pingquan city (see Figure 3a and Figure 4a). The oldest outcropping terrain at the

Fig. 3 Distribution of igneous rocks and oil seepage/bitumen spot in the Xiamaling Formation, Jibei depression (see Figure 1 for Area A, B and C)

Liu Yan et al. / Petroleum Exploration and Development, 2011, 38(4): 503–512

Fig. 4 Cross-sections of the Shuangdong paleo-reservoir in Pingquan and the Longtangou paleo-reservoir in Lingyuan, Jibei depression (see Figure 3)

core of the Shuangdong anticline is the Wumishan Formation, and the Hongshuizhuang Formation, Tieling Formation, Xiamaling Formation and Palaeozoic are at the wings. The anticlinal area is around 50 km2. The bituminous sandstones are distributed in the bottom sandstones of the Xiamaling Formation at the perimeter of the anticlinal in loop stripes (Figure 3a). The bottom bituminous sandstone of the lower Xiamaling Formation is well developed and outcropped in the south of Dashanqian, Sidaogou, and Xishan and Dongshan of Shuangdong Liudui. The Longtangou paleo-reservoir in Lingyuan is located in the Dahebei County, Lingyuan, and is a monoclinal old oil accumulation (see Figure 3b), with the strata declining towards northwest (see Figure 4b). Based on the existing sandstone spots in Longtangou, and through further exploring the sandstone at the bottom of the Xiamaling Formation, 9 sandstone spots were found at the bottom of the Xiamaling Formation, with the bitumen content declining towards northeast and southwest from Longtangou as the center. The distribution range of the paleo-reservoir has been defined. The Tasan and Lujiazhuang paleo-reservoirs are located in the southwest of the Kuanxian County, with bituminous sandstone at the bottom of the Xiamaling Formation exposed at the outcrop of the Xiamaling Formation (see Figure 3c). The bitumen content in sandstone at the bottom of the Xiamaling Formation in Dongbingyao and its east is lower, but solid bitumen can be seen under the microscope. 2.2 Scale of the Xiamaling Formation bituminous sandstone reservoir According to the result of field investigation, the distribu-

tion laws of the bituminous sandstone in the Xiamaling Formation is as follows: it’s thicker in Shuangdong in Pingquan and Longtangou in Lingyuan, with the cross-section of Sidaogou of Pingquan 4.4 m thick and the cross-section of Longtangou of Lingyuan 3.8 m thick; it is thicker in Kuancheng, with the bottom sandstone of the cross-section of top of Dongshan, Lujiazhuang, Kuancheng 4.4 m thick, and the bituminous sandstone 1.97 m thick, and 2–3 m thick at the Cuizhangzi village of Tashan. It can be concluded that the thickness of the bituminous sandstone at the bottom of the Xiamaling Formation is stable, mostly over 2 m. The bitumen layers in the bottom sandstone of the Xiamaling Formation in the Jibei depression is stable, and bituminous sandstones exist from Tashan at the southwest of the Dangba syncline, along the synclinal axis, towards the same tectonic layers in the Shuangdong and Longtangou structures in the northeast. The bituminous sandstone is distributed stably and broadly. The Xiamaling Formation bituminous sandstone mainly is distributed in the Pingquan anticlinal zone and Dangba synclinal zone, with the total area of 5 000 km2. The Jibei (or Northern Hebei) area experienced not only large scale oil and gas generation, but also large scale gas and oil accumulation. The Xiamaling Formation paleo-reservoir discovered recently at different tectonic layers should be the product of regional oil/gas accumulation event. In order to obtain bituminous sandstone samples less influenced by the surface weathering, many exploratory trenches were dug in the Longtangou and Lujiazhuang areas (see Figure 5a). According to the result of the exploration, at the core of the paleo-reservoir, the bituminous sandstones of the Xiamaling Formation are quite loose (see Figure 5b). The obser-

Liu Yan et al. / Petroleum Exploration and Development, 2011, 38(4): 503–512

Fig. 5

Xiamaling bituminous sandstone in the Jibei depression

vation under the microscope indicates that the quartz particles are point-contacted or line-contacted (see Figure 5c, 5d), the gap between particles are much developed with the plane porosity falling to 8%–20%, and the pores are filled with solid bitumen (see Figure 5c, 5d). This indicates that when oil and gas charged to the bottom sandstone of the Xiamaling Formation, the sandstone had not begun to freeze into rocks or was in the early stage of diagenesis. The primary pores are developed in the sandstone, and the charging of oil and gas curbed the diagenesis. The Xiamaling Formation bituminous sandstone is generally developed in the Jibei depression. Taking into account the non-uniform distribution, to calculate in a conservative method by taking 80% of the Pingquan anticlinal zone and Dangba synclinal zone, the bituminous sandstone reservoirs of the Xiamaling Formation can reach 4 000 km2, or according to 60% of the total area, the figure even amounts to 3 000 km2. According to the measurement of the cross-section, and taking into the variation of plane distribution account the thickness of the old oil layer can reach 2 m. Since the diagenesis of the reservoir is weak, its porosity should be over 15%, with the oil density of 0.86 g/cm3. Calculated by this way, the primary scale of the bituminous sandstone reservoir in the Xiamaling Formation is 7.6×108−10×108 t, it is thus an old reservoir with a quite large scale.

3 Relationship between Xiamaling bituminous sandstone reservoir and igneous rocks 3.1 Lithology and special distribution characteristics of igneous rock intrusion The outcropped parts of the igneous rock intrusion in the

Xiamaling Formation are strongly weathered with the characteristics of spheroidal weathering. The lithology of the intrusion is gabbro diabase. The stones are reflected in diabase and blocked structures, and mainly composed of plagioclase, potassium, common pyroxene and quartz. The plagioclase is distributed in automorphous stripes and frames, with the zonal structure obscurely seen and prehnitization. The pyroxenes are in the shape of automorphous particles and columns, uniformly distributed among the plagioclases, with the size of 0.4−2.0 mm. Parts of them are metasomated by the chlorites and biotites, and other parts show a false image, with the plagioclase embedded in its rims or the middle. The potassiums and quartz are in micrographic co-existing body. The contained minerals are as follows: plagioclase 45%−60%; pyroxene 45%; potassium and quartz, less than 5%. The diabases of the Xiamaling Formation are widely distributed in this area. Diabases can be seen in each outcropped part of the Xiamaling Formation (see Figures 1 and 3). In the Jibei depression, the Xiamaling diabases are mainly exposed in the Pingquan Shuangdong tectonic belt, the Lingyuan Longtangou tectonic belt, Kuancheng Huapi tectonic belt and Xinglong Lishugou area. Vertically, 2-3 layers of gabbro diabase sill are developed in the Xiamaling Formation, or even 4 layers in some parts such as Chengde Dishui Rock, and the thickness of a single layer of sill is 13−143 m, with the accumulated thickness for the diabase sill reaching 87.7−312.3 m[2]. The fringe rocks of the top and bottom of diabase layers show different degrees of hornfelsization, silicification, and fading. The fringe rock alteration belt is around 0−30 m wide, closely related to the sill thickness, with the top alteration belt thicker than the bottom alteration belt.[2].

Liu Yan et al. / Petroleum Exploration and Development, 2011, 38(4): 503–512

3.2 Relationship between igneous rock intrusion and reservoir Compared with the evolutionary process of the whole basin, magma movements are extremely short. However, since the temperature of the intrusion is much higher than that of the fringe rock[16], even much higher than the temperature range of the oil/gas accumulation (mostly lower than 200 ºC)[17], the volcanic movements may exert significant influences on the evolution of the temperature field of the basin and each step of the whole oil/gas accumulation process, such as speeding the maturity and hydrocarbon production process of sedimentary organic matter, altering the porosity of the fringe rock, making intrusion as the oil/gas reservoir and cover form special trap, and enhancing the transportation and accumulation of oil/gas[18−21]. The Xiamaling Formation intrusion is developed widely in the Jibei depression with quite thick sills. The degree of ther-

Fig. 6

mal alteration caused by magma movements can be expressed with vitrinite reflectance[21]. According to the reflectance of the samples taken from the cross-section of 4 bases of the Jibei depression, the reflectance of the Xiamaling Formation samples is obviously higher than the underlying and overlying terrains (see Figure 6), which suggests that the intrusion of diabases significantly influenced the thermal evolution history of this formation. The previous scholars have also pointed out the contribution of the heating effect of gabbro diabase sills to this phenomenon[1,7,11]. Due to the absence of evidence of direct contact between the diabase and bituminous sandstone, there has been no primary evidence to prove that the magma emplacement has influenced the hydrocarbons in the basal sandstones of the Xiamaling Formation. There have been doubts on whether the solid bitumen in the basal sandstone of the Xiamaling Formation is the product of thermal alteration of the primary oil accumulation caused by the diabases. Wang

Cross-section of thermal evolution of organic matters in Jibei depression

Liu Yan et al. / Petroleum Exploration and Development, 2011, 38(4): 503–512

Tieguan et al contended that the intrusion of the gabbro diabases is the main cause for the alteration of bituminous sandstone reservoir in the Xiamaling Formation, but he also admitted the possibility of other influencing factors such as the post oxidation and degration[11]. The natural coke produced by the magma movements in the surrounding rock was regarded as an important evidence of the thermal alteration of sedimentary organic matter[22,23]. There are two kinds of bitumen which is different in attribute and optical properties in the pores of the Xiamaling bituminous sandstone of Lingyuan Longtangou (see Table 1): (1) Table 1

Solid bitumen is gray, distributing along the fractures and closely contacting vertically or in curved interface with the mineral particles, embedded as particles or in uniformly blocks, with a high bitumen reflectance (see Figure 7a and Figure 7b). The optical structure of natural coke was also discovered. For example, such solid bitumen was discovered in the pores of the Xiamaling bituminous sandstone of Lingyuan Longtangou (see Figure 7c and Figure 7d); (2) The solid bitumen is gray, distributing along the fissure or inside the fissure, in uniform blocks with low reflectance (see Figure 7a, Figure 7b). The discovery of the quasi-structure of natural

Measured bitumen reflectance of the sandstone and shale at the bottom of the Xiamaling Formation, Neoproterozoic, Jibei de-

pression Sample No.

Equivalent vitrinite reflectance/%

Number of measuring spots

Sampling location

Sampling place

L2

Tuzishan, Longtangou

1.8 m from top shale

L1

Tuzishan, Longtangou

2.9 m from top shale

LY-LT-17

Front beam of north ditch, Longtangou

0.5 m from top shale

LY-LT-16

Front beam of north ditch, Longtangou

2.0 m from top shale

2.22

35

2.61

35

0.95

6

2.48

15

1.65

3

2.38

11

1.98

7

LY-LT-15

Front beam of north ditch, Longtangou

0.2 m from bottom limestone

LY2-7

Front beam of north ditch, Hezhangzi

Shale contacting the sandstone

LY2-1

Front beam of north ditch, Hezhangzi

0.2 m from top shale

Fig. 7

2.52

16

0.81

35

1.68

17

1.01

17

2.39

30

Anisotropic

Quasi-structure of natural coke in solid bitumen in pores of bottom sandstone of the Xiamaling Formation

Yes No Yes No

Yes No Yes No Yes No

Liu Yan et al. / Petroleum Exploration and Development, 2011, 38(4): 503–512

coke directly proves for the first time that the first type of solid bitumen is the product of strong heating received by the primary oil accumulation, which directly reflects the alteration effect of the intrusion against the oil accumulation. 3.3

Intrusion time of igneous rocks

Due to the genetic relation between diabase and bituminous sandstone in the Xiamaling Formation, the intrusion time of diabase becomes the key geological event for deciding the first accumulation of bituminous sandstone. The previous scholars got the age of the deep layer βμ1 gabbro diabase sill as 763 Ma with the K-Ar method[11], and 980 Ma with the Rb-Sr method[24]. As the limited technology and method, these results are not so reliable. In recent years, since the more reliable zircon SHRIMP U-Pb age-detecting method was adopted, more reliable gabbro diabase sill age values were reported: 1 368 Ma±12 Ma[25], 1 370 Ma±11 Ma[26], 1 366 Ma±9 Ma[26], 1 379 Ma±12 Ma[27], 1 380 Ma±36 Ma[27] and 1 320 Ma±6 Ma[14]. These precise age value reports indicate that the Xiamaling Formation started to sediment before 1 380 Ma, which not only caused controversy on terrain columns of the Mesoproterozoic Erathem in the Yanshan area and their tectonic environment, and the difficulty for global comparison[14], and also caused confusion in understanding the oil/gas accumulation history in this area. This article chooses samples from Well Jiqian 2 and the βμ1 gabbro and diabase closest to the bituminous sandstone in the Shuangdong area, Pingquan, for SHRIMP U-Pb isotope age testing analysis. The sorting of zircon and baddeleyite was conducted at the lab of the Langfang Regional Geological Survey Institute of Hebei Province, and the baddeleyite dating was done with the isotope Dilution Thermal Ionization Mass Spectrometry (ID-TIMS) method on the sensitive high resolution ion microprobe (SHRIMP II) in Beijing Ion Needle Center. The tested samples are baddeleyites. For details of analyzing process and data processing methods, please see literature [28−30]. The data obtained is 1 327.0 Ma±2.3 Ma and 1 327.5 Ma±2.4 Ma, with an average value of 1 327 Ma±2 Ma, which fits well into the latest Meso-Neoproterozoic Erathem. The previous scholars reported the gabbro diabase age of the Xiamaling Formation in Kuancheng, Huapiliuzi, Huangjiazhuang as 1 320 Ma±6 Ma[14], which proves the reliability of the test result in this article. The conclusion that gabbro and diabase intrusion of the Xiamaling Formation happened in 1 327 Ma is reliable. According to the latest dating data, it is generally believed that the Xiamaling sedimentation started in 1 400 Ma[14]. The Xiamaling bituminous sandstone oil accumulation time can not be earlier than the year in which the Xiamaling Formation itself began to sedimentate, nor shall it be later than the intrusion age of gabbro diabase (1 327 Ma). That is to say, the bituminous sandstone of the Xiamaling Formation was formed between 1 400−1 327 Ma. It can be concluded that the bituminous sandstone reservoir of the Xiamaling Formation is the oldest reservoir in China up to now and is also one of the oldest reservoirs in the world.

4

Conclusion

A great deal of genetic oil seepage/bitumen exists in the Meso-Neoproterozoic of the Jibei depression, Yanshan area. Based on field investigation and sampling analysis, the scope of the old oil accumulation is defined, and four paleo-reservoirs are named according to their distribution characteristics: Pingquan Shuangdong, Lingyuan Longtangou, Kuancheng Tashan and Lujiazhuang. The scale of the bituminous sandstone reservoir of the Xiamaling Formation with the volume method is 7×108−10 ×108 t. The micro structure of class natural coke discovered in the solid bitumen directly proves for the first time that the bituminous sandstone of the Xiamaling Formation is the product of thermal alteration of primary oil accumulation. The dating result for gabbro diabase in zircon SHRIMP U-Pb method is 1 327 Ma, which indicates that the bituminous sandstone reservoir of the Xiamaling Formation was formed between 1 400−1 327 Ma, and it is the oldest reservoir ever found in China up to now.

Acknowledgement Academician Wang Tieguan, Professor Huang Zhilong, Professor Zhang Zhihuan and Professor Zhao Fenghua contributed to this study with aids and assistance. Academician Dai Jinxing gave thorough guidance in completing this article. They are sincerely appreciated!

References [1]

Hao Shisheng, Gao Yaobin, Zhang Youcheng, et al. Neoproterozoic-Mesoproterozoic petroleum geology in north china. Dongying: Petroleum University Press, 1990.

[2]

Chen Jianfa, Sun Shengli. Preliminary study of geochemical characteristics and formation of organic matter rich stratigraphy of Xiamaling formation of later Proterozoic in north China. Natural Gas Geoscience, 2004, 15(2): 110−114.

[3]

Wang Jie, Chen Jianfa, Dou Qilong. The study of depositional environment and hydrocarbon potential of source rocks of Neo-Mesoproterozoic in North China. Natural Gas Geoscience, 2001, 12(3): 27−33.

[4]

[5]

[6]

[7] [8]

Wang Chunjiang, Wang Tieguan, Wang Guangli, et al. Neo-Mesoproterozoic source rock, source and resource potential in Yanshan area . Beijing: Sinopec, 2009. Wang Tieguan, Zhong Ningning, Zhu Shixing, et al. The study of oil-bearing and predicting the prospecting area in lower assemblage of North China Platform. Beijing: Sinopec, 2009. Liu Baoquan, Liang Digang, Fang Jie, et al. Organic matter maturity and oil-gas prospect in Middle-Upper Proterozoic and Lower Paleozoic carbonate rocks in Northern China. Geochimica, 1985, 14(2): 150−162. Qin Jianzhong. Source rocks in China. Beijing: Science Press, 2005. Wang Tieguan, Zhao Chenglin, Guan Defan, et al. The good prospects for primary reservoir of Sinian Suberathem in Yanshan area. Zhuoxian: Petrochemical Industry Petroleum Geology Earthquake Science Conference in East China, 1988:

Liu Yan et al. / Petroleum Exploration and Development, 2011, 38(4): 503–512

42. Huang Xinghan, Zhang Yiwei. Petroliferous property of Sinian Suberathem and Lower Palaeozoic Erathem in the west part of Yanshan. Journal of the College of Petroleum, East China, 1979(1): 103−114. [10] Wang Tieguan. Indigenous characteristics of oil seeps in Sinian Suberathem in Yanshan region and its petroleum geological meanings. Petroleum Exploration and Development, 1980, 7(2): 34−52. [11] Wang Tieguan, Huang Guanghui, Xu Zhongyi. A fossil oil pool on the basement of the Xiamaling formation of the upper Proterozoic in Longtangou, west Liaoning. Oil & Gas Geology, 1988, 9(3): 278−287. [12] Chen Jinbiao, Wu Tieshan. Multiple classification and correlation of the stratigraphy of China (10): Regional stratigraphy of North China. Wuhan: China University of Geosciences Press, [9]

1997: 20−26. [13] Cui Shengqin, Li Jinrong, Sun Jiashu, et al. The sequence of tectonic movement and the regional tectonic pattern in the northern margin of North China Block. Beijing: Geological Publishing House, 2000: 100−116. [14] Li Huaikun, Lu Songnian, Li Huimin, et al. Zircon and beddeleyite U-Pb precision dating of basic rock sills intruding Xiamaling Formation, North China. Geological Bulletin of China, 2009, 28(10): 1396−1404. [15] Zhu Shixing, Sun Shufen. Paleontology of Mesoproterozoic carbonate in Yanshan Aera. Beijing: Sinopec, 2009. [16] He Tongxing, Lu Liangzhao, Li Shuxun, et al. Lithology of

conditions forming oil and gas accumulation. Northwest Geoscience, 1997, 18(1): 59−65. [20] Chen Rongshu, He Sheng, Wang Qingling, et al. A preliminary discussion of magma activity on the maturation of organic matter: taking Geyucheng -Wenan area of Hebei province as an example. Petroleum Exploration and Development, 1989, 16(1): 29−38. [21] Dow W G. Kerogen studies and geological interpretation. Geochem Explor, 1997, 7(2): 79−99. [22] Stach E, Mackowsky M T H, Teichmuller M, et al. Stach’s textbook of coal petrology. Berlin: Gebruder Borntraeger, 1982: 177−197. [23] Yang Qi. The coal metamorphism in China. Beijing: Coal Industry Press, 1996. [24] Wang Chengwen. 1︰50000 reports on regional geology of Guozhangzi and Yangshuling. Beijing: China Geological Survey, 1999. [25] Gao Linzhi, Zhang Chuanheng, Shi Xiaoying, et al. Zircon SHRIMP U-Pb dating of the tuff bed in the Xiamaling Formation of the Qingbaikouan System in North China. Geological Bulletin of China, 2007, 26(3): 249−255. [26] Gao Linzhi, Zhang Chuanheng, Yin Chongyu, et al. SHRIMP Zircon Ages: Basis for refining the chronostratigraphic classification of the Meso-and Neoproterozoic strata in North China Old Land. Acta Geoscientica Sinica, 2008, 29(3): 366−376. [27] Su W B, Zhang S H, Huff W D, et al. SHRIMP U-Pb ages of K-bentonite beds in the Xiamaling Formation: Implications for revised subdivision of the Meso-to Neoproterozoic history

metamorphic rock. Beijing: Geological Publishing House, 1988.

of the North China Craton. Gondwana Research, 2008, 14(3): 543−553.

[17] Waples D W. The kinetics of in-reservoir oil destruction and gas formation: constraints from experimental and empirical data, and from thermodynamics. Org Geochem, 2000, 31(6): 553−575. [18] Pepper A, Dodd T. Simple kinetic models of petroleum formation: Part II: oil-gas cracking. Marine and Petroleum Geology, 1995, 12(3): 321−340. [19] Feng Qiao, Tang Xiyuan. The magma activity’s influence on

[28] Song Biao, Zhang Yuhai, Wan Yusheng. Mount making and procedure of the SHRIMP dating. Geological Review, 2002, 48(Supp.): 26−30. [29] Ludwig K R. SQUID ver.1.02: A user’s manual. Berkeley Geochronology Center Special Publication, 2001(2): 1−19. [30] Ludwig K R. User’s manual for Isoplot/Ex version 3.00: A geochronological toolkit for Microsoft Excel. Berkeley Geochronology Center Special Publication, 2003(4): 1−70.