Pet.Sci.(2010)7:355-361 355 DOI 10.1007/s12182-010-0077-x

Oil accumulation related to migration of source kitchens in the Lukeqin structural belt, - Basin,

Liu Bo1, Huang Zhilong1 , Tu Xiaoxian2, Sang Tingyi2 and Chen Xuan2 1 State Key Laboratory of Petroleum Resource and Prospecting, China University of Petroleum, Beijing 102249, China 2 PetroChina Turpan-Hami Oilfi eld Company, Hami, 839009, China

© China University of Petroleum (Beijing) and Springer-Verlag Berlin Heidelberg 2010

Abstract: The Lukeqin structural belt is the main heavy oil accumulation zone in the Turpan-Hami Basin. The recent discovery of light oil in the Triassic indicates that there may be multiple source kitchens contributing to the oil accumulation. According to oil geochemical analysis and oil-source correlation, the oil in deep and shallow reservoirs of the Lukeqin Oilfi eld presents different physical and saturated hydrocarbon mass spectrum characteristics. The Triassic heavy oil is from the northern Upper Permian lacustrine source rocks, and the light oil represented by the Yudong-9 Well is from the northwestern Lower Jurassic coal-measure source rocks. The timing of oil charging was determined by K/Ar isotope dating, reservoir fl uid inclusion analysis and the evolution history of different source rocks. In summary, the accumulation process consists of two stages. From the end of Triassic to early Jurassic, the northern Permian source kitchen generated a considerable amount of oil, which was fi nally degraded to heavy oil, migrated to the south and then accumulated. The northwestern Jurassic coal-measure source kitchen began to generate oil at the end of Cretaceous, while the northern source kitchen could only generate a little hydrocarbon. The heavy oil and the light oil have different source rock locations, migration directions and accumulation times. The migration of hydrocarbon source kitchens affects the distribution of heavy oil and light oil reservoirs at the present time.

Key words: Source kitchen, light oil, oil-source correlation, timing of oil charging, Turpan-Hami Basin

1 Introduction dipping nose shaped structure in the area since the end of Triassic, we can infer that the oil in the Lukeqin structural The Lukeqin structural belt located in the western part of belt may have come from the Taodonggou Group in the the Tainan Sag is a heavy oil enriched zone (Yin, 1997). A Taibei Sag dipping to the northwest. The palaeotemperature heavy oil show was discovered in the Aican-1 Well in 1995, of the Permian source rocks in the Taibei Sag reached 80-100 and commercial heavy oil was discovered in the Triassic °C, which means that the oil and gas generated in the Permian Formation in Yudong-1 and Yu-1 wells. Previous might have migrated and accumulated in the early Jurassic. studies have shown that the Lukeqin structure is in the area Since the large scale uplifting of the Huoyanshan fault- where the source rock of the Permian Taodonggou Group (P2) anticline belt occurred in the late Cretaceous to Tertiary, the was deposited (Zhao et al, 1998; Li et al, 2004). However, hydrocarbon originating from the Permian in the Taibei Sag due to the continuous uplifting since the end of the Triassic, migrated updip from north to south and reached the Lukeqin the Permian and its overlying strata in the Lukeqin structural heavy oil belt before the uplifting (Yang et al, 2005; Li et al, belt are of low maturity and much thinner than those in the 2006). Taibei Sag (Tu et al, 1998; Li et al, 2000; Jin et al, 2006). With the increase of exploration in recent years, the Exploration wells drilled through the Permian did not discovery of light oil in Triassic reservoirs breaks the encounter oil and gas shows, so the Permian should not be the traditional concept about hydrocarbon migration and major source rocks of heavy oil in the Lukeqin structural belt accumulation, and indicates that there may have been more (Wang et al, 2007). Based on the oil/water contact dipping than one hydrocarbon source kitchen in this area. A clear from south to north and from east to west, and the northwest- understanding of the relationship between oil and sources, the distribution of source kitchens, migration pathways, and timing of hydrocarbon accumulation may lead to new *Corresponding author. email: [email protected] discoveries (Rangel et al, 2003). Received November 19, 2008 356 Pet.Sci.(2010)7:355-361

2 Geological setting the intersection of faults in the main parts of the structure. The The Lukeqin structural belt, located in the Tainan Sag NW-trending faults control the strike of the structural belt, on the south of the Turpan Depression in the Turpan-Hami and the NE-trending faults cut the structural belt, forming a (Tuha) Basin, is the only pre-Jurassic heavy oil enriched zone grid-shaped fracture framework. At present, the discovered discovered in the basin. So far nearly 100 million tonnes of oil traps are fault blocks in such a structural setting. Two oil reserves have been discovered. The overall structure is a oil-bearing intervals are developed in the Middle-Upper large-scale nose shaped uplift gradually dipping from east to Triassic Karamay Formation (T2k) and Middle Jurassic (J2), west. The Lukeqin area is mainly controlled by faults, with respectively (Fig. 1).

Formation catalog 0 2000 4000 m Taibei Lianmuqin Well record Well thickness

Stratigraphic contact relationship Erathem Formation Series System Huoyanshan structural belt Sag structural belt Q Quaternary

N2p Luxi N E -N t Yuxi-2 Cenozoic 3 1 Yu-1 (K -E)sh Upper 2 Yu-2 K l Lukeqin Yudong-5 1 K1sh Lower

Cretaceous Tertiary K s Uplift structuralYudong-201 belt 1 Tainan Lu-10 Lu-8 J3k

Legend Upper J q Yudong-9Lu-4 Ying-8 3 Sag J q Aican-1 2 UpliftStructural belt Sag J2s 67-135 Middle

Mesozoic J x 71-245 Jurassic 2 Well Secondary structure boundary M J1s J b 0-222

Lower 1 M N

T2k Middle 238-525

Q-K Triassic T s 1 0-109 T1j J -J q Lower 3 2 P2e 0-68 J s P w 0-118 J x 2 2 2 P q 0-224 T2 2 T

1 Upper P-C P2td 0-363 Permian

Palaeozoic 0-433 P2y Lower Lukeqin Huoyanshan C d structural belt structural belt 2 76 Middle Carboniferous

Fig. 1 Regional geological map and strata section of the Lukeqin structural belt

3 Characteristics of crude oil and analysis of spectrogram of lacustrine source rocks of the Taodonggou Group of the Aican-1 Well is similar to that of m/z=123 of oil sources the Yudong-1 Well (Fig. 3). Based on the evolution of source The Triassic heavy oil in the Lukeqin structural belt is rocks and the structural evolution of this area, we think that characterized by a relatively low carbon isotope value. this type of crude oil mainly comes from the lacustrine source The δ13C value of oil is from -30.22‰ to -30.01‰, which rocks of the Upper Permian Taodonggou Group. indicates a typical sapropel organic facies (Wang et al, 2003; The main characteristics of light oil from the Chen et al, 2004). The GC–MS characteristics are high Yudong-9 Well are a specific content of tetracyclic abundance of n-alkanes with a post-peak pattern, a high terpane, a low content of tricyclic terpane and content of β-carotane, a relatively high content of tricyclic gammacerane in the mass spectrograms of m/z=191, and terpane and gammacerane, a specific content of pregnane ααα20RC27>ααα20RC29>ααα20RC28 of regular sterane, and homopregnane, a low content of diasteranes, and showing “L” shape. The Tm/Ts value is large, and the

ααα20RC27<ααα20RC28<ααα20RC29 of regular sterane, pristane/phytane ratio is 3.27. These characteristics showing “/” shape in the mass spectrogram of m/z=217, indicate that the crude oil has a high degree of maturity indicating a high degree of maturity (Fig. 2). The light oil and was generated from coal-measure source rocks (Chen et has a lighter carbon isotope ratio. By comparing several al, 1999). Owing to ααα20RC27<ααα20RC29 of coal-measure mass spectrograms of saturated hydrocarbons from oil generated in the Taibei Sag (Zhang and Sun, 2008), this mudstone samples, we find that the characteristic mass kind of light oil may be generated by the Lower Jurassic coal- Pet.Sci.(2010)7:355-361 357

m/z=191 m/z=191

m/z=217 m/z=217

Yuxi-1 Well, 3521-3550m, T2k, oil Lu-8 Well, 2628-2665m, T2k, oil

Fig. 2 Mass spectrograms of m/z=191, 217 of T3, T2k, J1 thickened crude oil and oil sand asphalt

C30

m/z=123 m/z=123

C29 C31

C27

Yudong-1 Well, 2700-2721m, T2-3k, oil Aican-1 Well, 3165.49m, P2td, source rock

Fig. 3 Mass spectrograms of m/z=123 of Yudong-1 crude oil and saturated hydrocarbon from Aican-1 P2td source rocks

measure source rocks in the Tainan Sag (Fig. 4). Qiketai Formation heavy oil reservoir (J2q) is 94.6 Ma. This illustrates that the accumulation periods of the Machang 4 Analysis of timing of oil charging structure and the Lukeqin structure are consistent, both in the Early Jurassic. The accumulation period of shallow heavy oil K/Ar isotope dating confirms that the isotopic age in the Qiketai Formation is Late Cretaceous. The heavy oil of authigenic illite from the Triassic heavy oil reservoir migrated upwards due to the faulting in the Late Cretaceous sandstones is 113.4-199.8 Ma, mainly in the range of 179.3- and accumulated again in the upper Qiketai Formation. 199.8 Ma. This means that the main formation period of The fl uid inclusions of the second stage in the lower part Triassic heavy oil accumulations is Early Jurassic. of the sandstone heavy oil reservoir are likely to refl ect late According to the reservoir diagenetic sequence, fluid light oil charging. inclusion distribution and freezing point, the fl uid inclusions According to the evolution history of source rocks in the of Triassic heavy oil reservoirs can be divided into two Yuxi-2 Well in the northwest of the Tainan Sag, we can fi nd stages (Fig. 5). The homogenization temperatures of the two that the Lower Jurassic source rocks became mature relatively stages are mainly in the range of 60-70 °C and 90-100 °C, late (Fig. 7). They did not enter the mature stage to generate respectively. This refl ects that there are at least two stages of hydrocarbon until the end of the Cretaceous. At present, they oil charging for the Triassic heavy oil reservoirs. The early have entered a highly mature stage and can generate abundant stage, which is dominant, is from the end of Triassic to Early oil and gas. Since the uplifting of the Huoyanshan structure Jurassic and the late stage is from the end of Early Tertiary to in the Lukeqin structural belt from the end of the Cretaceous Neocene (Fig. 6). to the Early Tertiary, the oil and gas in northern sag could The test results of two heavy oil sands of the Ma-1 Well not migrate to the south. The coal-measure oil in the Lukeqin in the Machang structure to the east of the Lukeqin structural structural belt formed from the Early Tertiary to the Neocene belt show that the geologic age of authigenic illite of Upper could only come from the down-dipping coal-measure source Permian heavy oil reservoir is 175.8 Ma, and that of the rocks which lie northwest of the Tainan Sag. 358 Pet.Sci.(2010)7:355-361

m/z=191 m/z=217

2 Yudong-9 Well, 2219-2224m, T2k , oil

m/z=191 m/z=217

2 Yudong-9 Well, 2252-2255m, T2k , oil

m/z=191 m/z=217

Le-10 Well, 1540-1547m, J2s, oil

Fig. 4 Comparison of the characteristics of sterane and terpane between coal-measure light oil in Yudong-9 Well and light oil in the Taibei Sag

35 belt entered the peak of generating and expelling hydrocarbon 30 in the Early Jurassic. The hydrocarbon migrated and

25 accumulated in the southern Lukeqin structural belt (Fig. 8). 20 However, in the Early Jurassic, most parts of the southern 15 Lukeqin structural belt were still being uplifting and denuded,

10 and the accumulated oil was biodegraded and became heavy Frequency, % Frequency, 5 oil (Ma et al, 2005; Ni et al, 2005). In the late Early Jurassic, 0 the Lukeqin structural belt underwent deposition of coarse 50-60 60-70 70-80 80-90 90-100 100-110 110-120 120-130 clastics and was still in shallow water oxidizing environment. Homogenization temperature, °C Oil was also biodegraded and accumulations were further Fig. 5 Homogenization temperature of fl uid inclusions destroyed. The fluid inclusions record the charging process in the Yudong-2 Well of hydrocarbon from Late Triassic to Early Jurassic and show that the aqueous phase had a low salinity (the salinity of brine 5 Relationships between migration of inclusion is 3.5%-5.2% NaCl). The reservoir is in a relatively hydrocarbon source kitchens and oil open environment. During the deposition of the Middle Jurassic Xishanyao Formation, the Lukeqin structural belt accumulation received deposits gradually. The degradation, water washing There are two hydrocarbon source kitchens in the Lukeqin and destruction of Triassic reservoirs weakened gradually, structural belt. Their strata, locations, time of hydrocarbon and the reservoirs entered the preservation stage in the Middle generation and migration pathways control the migration of Jurassic (Zeng and Zuo, 2002; Su, 2004). oil accumulations. In the Late Cretaceous, the Carboniferous and Permian The study of tectonic evolution shows that the northern source rocks in the Lukeqin structural belt could also generate Taibei Sag and Lukeqin area were united prior to the Early and expel hydrocarbon that migrated vertically through faults Yanshan movement and this was favorable for the southward and accumulated in Triassic heavy oil reservoirs. Because migration of Permian lacustrine oil. The Permian hydrocarbon of the low rate of hydrocarbon generation and expulsion, source kitchen in the northern part of the Lukeqin structural less oil and gas was charged. The fl uid inclusions record this Pet.Sci.(2010)7:355-361 359

T JKPalNFormation 0 Q

N p 50°C 2 60°C

70°C E3-N1t 1000

K2-E2sh Depth, m 80°C

Ks1

2000 80°C 90°C J2q-J3q 90°C J s Early hydrocarbon charging 2 J2x J b Late hydrocarbon charging 1 T2-3k

3000 250 200 150 100 50 0 t=0 Age, Ma

Fig. 6 Relationship between burial history and Triassic oil charging in the Yudong-2 Well

Dev CPermT JKPalNFormation 0

N2p-Q

1000 E3-N1t

K2-E2sh

2000 K1s

J2q-J3q

3000 J2s J2x Depth, m J1b

T2-3 4000 Early mature (oil)

0.5 to 0.7 (%Ro) Mid mature (oil) C-P

0.7 to 1.0 (%Ro) 5000 Late mature (oil)

1.0 to 1.3 (%Ro) Main gas generation

1.3 to 2.6 (%Ro) 6000 t=0 400 300 200 100 0 Age, Ma

Fig. 7 Burial history and evolution history of source rocks of the Yuxi-2 Well in the northwest of the Tainan Sag charging process and show that the aqueous phase had a high oil generated by the mature Lower Jurassic coal-measure salinity (the salinity of brine inclusion is 11.0%-21.4% NaCl). source rocks in the northwestern Tainan Sag entered the The reservoir is in a viscous flow environment, favorable Triassic sandstones through unconformities at the top of the for hydrocarbon preservation. The original heavy oil was Triassic and faults, forming light oil accumulations (Yudong-9 diluted owing to late oil and gas charging. The saturated Well, light oil reservoir at the top of Triassic). We can infer hydrocarbons in crude oil are also related with hydrocarbon that the oil generated by the coal-measure source rocks could charging. also migrate along Jurassic sandstones to the updipping From the end of the Cretaceous to the Early Tertiary, the Lukeqin structural belt (Fig. 9). 360 Pet.Sci.(2010)7:355-361

South Lu-2Lu-8 Yuxi-1 North A A’

J1

T2

T1-P3 P Unconformity surface Formation boundary Fault 2 P1 Heavy oil accumulation Migration direction C

Fig. 8 Model of heavy oil migration and accumulation in the Lukeqin structural belt from the end of Triassic to the Early Jurassic

West East A Yudong-9 Lu-8 Lu-10 A’

Q-K

J3

J2q

J2s

J2x

J1 2 T2k Ư 2 T2k ư

T1-C

Coal-measure oil accumulation Unconformity surface Formation boundary

Carboniferous accumulation Migration direction Fault

Fig. 9 Model of light oil migration and accumulation in the Lukeqin structural belt (Northwest-southeast section)

As a result, there exist differences between the location of source kitchen. Its main oil generation occurred in the Late source rocks, the migration direction, and the accumulation Triassic-Early Jurassic. time of heavy oil and those of light oil in the Lukeqin The Lower Jurassic coal-measure hydrocarbon source structural belt. The migration and evolution of hydrocarbon kitchen in the northwest of Tainan Sag controls the formation source kitchens control the formation and distribution of and distribution of coal-measure oil, which was generated at heavy and light oil accumulations (Fig. 10). the end of the Cretaceous to Tertiary. The favorable area for 6 Conclusions coal-measure oil may be in the high positions in the southeast. In the Lukeqin structural belt, there are two kinds of oil Acknowledgements with different sources. Analysis of accumulation processes shows that the distribution of heavy oil and light oil reservoirs This paper is supported by the Basic Research in the Lukeqin structure is mainly controlled by two Development Program of China “Accumulation hydrocarbon source kitchens of different periods. mechanisms and distribution patterns of hydrocarbon in The formation and distribution of heavy oil in the Lukeqin typical superimposed basins of west China” (973 Program, structure is controlled by the northern Permian hydrocarbon No.2006CB202303). Pet.Sci.(2010)7:355-361 361

0 3000 6000 m

Lian-2

Taibei Sag

Luxi Yuxi-2 Yu-1

Yu-2 Yudong-5

Uplift Yudong-201 Lu-8 Lu-10 Ma-1 Tainan Sag Ying-8 Yudong-9 Lu-4 Legend Aican-1

Heavy oil accumulation Light oil accumulation Lunan-3 sourced from Permian sourced from Jurassic

Permian Jurassic coal- source kitchen measure kitchen

Fig. 10 Distribution map of hydrocarbon source kitchens and oil accumulations in the Lukeqin structural belt

References structural belt of the Tuha Basin. Special Oil and Gas Reservoirs. 2004. 11(2): 3-5 (in Chinese) Che n J P, Deng C P, Liang D G, et al. Quantifi cation of mixed oil derived Tu X X, Liang H and Huang W D. Oil/gas reservoir formation condition from multiple source rocks: a typical case study of the Cainan in the Lukeqin arc-like belt, Turpan-Hami Basin. Xinjiang Petroleum Oilfi eld in the east , Northwest China. Acta Geologica Geology. 1998. 19(6): 458-461 (in Chinese) Sinica. 2004. 78(2): 279-288 (in Chinese) Wan g C G, Wang T G, Chen J P, et al. Recognition of crude oil types Chen J P, Huang D F, Li J C, et al. Main source rocks of petroleum from in the Jurassic reservoirs of Cainan Oilfield, east Junggar Basin. Jurassic coal-bearing strata in the Turpan-Hami Basin, Northwest Petroleum Geology & Experiment. 2003. 25(2): 183-189 (in China. Acta Geologica Sinica. 1999. 73(2): 140-152 (in Chinese) Chinese) Jin A M, Lou Z H, Zhu R, et al. Formation mechanism of heavy oil Wang Z Y, Du H Y, Jin Z J, et al. Discussion on the origin of heavy oil reservoirs in the Lukeqin structure belt, Turpan-Hami Basin. Journal and reservoir formation in Permian system of Turpan-Hami Basin. of Zhejiang University (Science Edition). 2006. 33(4): 464-468 (in Acta Sedimentologica Sinica. 2007. 25(5): 787-794 (in Chinese) Chinese) Yan g Z X, Kang Y S, Jiao L X, et al. Differential hydrocarbon Li C M, Su C G, Chen X H, et al. Analyses of reservoir forming accumulation of the Triassic in the Taibei and Tainan sags, Tuha characteristics and exploration prospects for Lukeqin heavy oil belt. Basin. Xinjiang Petroleum Geology. 2005. 26(4): 397-400 (in Tuha Oil & Gas. 2004. 9(4): 323-326 (in Chinese) Chinese) Li W, Liang S J, Jiang J W, et al. Special migration and accumulation Yin Z H. Reservoir geological characteristics and hydrocarbon of heavy oil reservoirs in the Lukeqin area of the Turpan Depression. accumulation regularity in the Lukeqin structural belt. Tuha Oil & Acta Petrolei Sinica. 2006. 27(6): 14-18 (in Chinese) Gas. 1997. 3(2): 27-34 (in Chinese) Li Z J, Li B and Chen H. Tectonic evolution and pool-forming regularity Zeng J H and Zuo S J. Fluid geochemistry, dynamics and hydrocarbon in the Tainan Sag. Oil &Gas Geology. 2000. 21(1): 53-56 (in Chinese) migration and accumulation in the Lukeqin structure, Turpan-Hami Ma A L, Zhang S C, Zhang D J, et al. Advances in the geochemistry of Basin. Petroleum Exploration and Development. 2002. 29(1): 72-75 the biodegraded oil. Advances in Earth Sciences. 2005. 20(4): 449- (in Chinese) 454 (in Chinese) Zha ng R and Sun X G. FTIR study on the hydrocarbon-generation Ni C H, Bao J P, Wang P H, et al. Novel progress in source correlation mode of Jurassic coals from the Turpan-Hami Basin, Xinjiang. of biodegraded crude oil. Xinjiang Petroleum Geology. 2005. 26(6): Spectroscopy and Spectral Analysis. 2008. 28(1): 61-66 (in Chinese) 711-714 (in Chinese) Zha o W Z, Li W and Zhang Y. A preliminary study of the forming Ran gel A, Katz B, Ramirez V, et al. Alternative interpretations as to the process of the Lukeqin heavy oil pool and its exploration signifi cance origin of the hydrocarbons of the Guajira Basin, Colombia. Marine to the Turpan-Hami Basin. Petroleum Exploration and Development. and Petroleum Geology. 2003. 20(2): 129-139 1998. 25(2): 1-3 (in Chinese) Su C G. Heavy oil degradation and densification in the Lukeqin (Edited by Hao Jie)