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Frontiers of Earth Science

ISSN 2095-0195

ISSN 2095-0209(Online)

CN 11-5982/P

Postal Subscription Code 80-963

2018 Impact Factor: 1.205

Front. Earth Sci.    2019, Vol. 13 Issue (3) : 575-587    https://doi.org/10.1007/s11707-019-0756-x
RESEARCH ARTICLE
Accumulation of unconventional petroleum resources and their coexistence characteristics in Chang7 shale formations of Ordos Basin in central China
Jingwei CUI1,2(), Rukai ZHU1, Zhiguo MAO1, Shixiang LI3
1. Research Institute of Petroleum Exploration and Development, PetroChina, Beijing 100083, China
2. Shandong Provincial Key Laboratory of Depositional Mineralization & Sedimentary Mineral, Shandong University of Science and Technology, Qingdao 266590, China
3. Changqing Oilfield Research Institute of Petroleum Exploration and Development, CNPC, Xi’an 710018, China
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Abstract

The Ordos Basin is the largest oil and gas producing basin in China, where tight oil, shale gas, oil shale, and other unconventional oil and gas resources have been found in the Chang7 subsection of the Triassic Yanchang Formation. However, the mechanism of formation and the distribution of unconventional oil and gas resources in the shale layers have not been systematically investigated until now. According to the type of unconventional oil and gas resources, main controlling factors, and the maturity, depth and abundance of organic matters, the shale oil and gas resources from Chang7 region are divided into five zones that include an outcrop-shallow oil shale zone, a middle-matured and medium-burial shale oil zone, a medium-matured and medium-burial in situ conversion process (ICP) shale oil zone, a high-maturity and deep-burial shale gas zone, and an adjacent-interbedded tight sandstone oil zone. By the distribution of resources, orderly evolution of oil and gas resources and coexistences in lacustrine shale formations have been put forward, and also a strategy of integrated exploration and development of resources in the shale formations is proposed. Overall, the outcome of this study may guide on the effective utilization of unconventional oil and gas resources in other shale formations.

Keywords shale formation      oil and gas resources      orderly accumulation and coexistence      integrated exploration and development     
Corresponding Author(s): Jingwei CUI   
Just Accepted Date: 12 July 2019   Online First Date: 12 August 2019    Issue Date: 15 October 2019
 Cite this article:   
Jingwei CUI,Rukai ZHU,Zhiguo MAO, et al. Accumulation of unconventional petroleum resources and their coexistence characteristics in Chang7 shale formations of Ordos Basin in central China[J]. Front. Earth Sci., 2019, 13(3): 575-587.
 URL:  
https://academic.hep.com.cn/fesci/EN/10.1007/s11707-019-0756-x
https://academic.hep.com.cn/fesci/EN/Y2019/V13/I3/575
Fig.1  The setting and tectonic units of the Ordos Basin
Fig.2  Histogram of total organic carbon (TOC), hydrocarbon potential, bitumen “A” (extracted using chloroform), and total hydrocarbons (amounts of saturated and aromatic composition in bitumen “A”.
Fig.3  Organic maceral Composition of Shale in Chang7 subsection.
Fig.4  Frequency distribution of Ro (a) and Tmax (b) in Chang7 shale.
Well
No.
Depth/m Oil Saturation/% Water Saturation/% Gas porosity/% Porosity/% Oil amount
/(mg·g1)
S1
/(mg·g1)
TOC/%
1 3066.80 50.29 47.6 2.1 5.05 8.27 5.81 3.82
2 3057.20 52.29 42.3 5.4 4.64 7.83 4.83 3.01
3 2995.50 51.83 43.5 4.7 4.68 8.03 6.50 4.01
4 2989.80 53.98 43.4 2.6 4.11 7.32 5.79 3.64
5 2988.80 46.51 48.8 4.7 4.33 6.56 4.23 2.61
6 2980.80 49.11 45.0 5.9 4.60 7.60 6.84 3.94
7 2979.40 53.25 41.4 5.4 4.48 7.61 4.93 3.42
8 2976.30 34.12 45.4 20.5 5.37 5.74 2.93 1.39
9 2213.60 46.46 49.0 4.5 5.30 8.31 5.38 3.80
10 2489.60 12.90 69.9 17.2 4.23 2.16 2.54 16.12
Tab.1  Comparison of typical Chang7 shale SPR Dean-star method with pyrolysis value
Fig.5  S1 versus TOC correlation. (a) S1 per rock samples; (b) S1 per TOC.
Fig.6  The category, characteristics, occurrence and development technology of petroleum resources.
Fig.7  Orderly accumulation and coexistence of oil and gas resources in shale formations in Chang7 subsection, Ordos Basin.
Fig.8  Specific technology for petroleum resources in shale formations.
Fig.9  Orderly evolution of unconventional petroleum resources in shale formations.
Fig.10  Spatial coexistence of unconventional petroleum resources in shale formations.
Resource type Forming conditions and main controlling factors Accumulation mechanism Sweet spot Specific technology
Oil shale Oil shale formed in high- productivity lake bay, deep lake or uplifting shelf where it’s an oxic and deep burial and thermal anomaly didn’t occur, and controlled by high productivity, reducing environment and low maturity Shale with high organic matter and low maturity; in-situ resource. Zones with low maturity,
shallow burial,
high organic matter and high oil content
Semi-subsurface production
Open-pit mining and heating with Cyclotron furnace
Fractured shale oil Shale oil formed in fracture development zone in mature shales; and controlled by structure, stress releasing zone and mature source rock. Fractures constitute main reservoir space. Shale oil accumulates adjacent to source rocks The zone with structural fractures in mature shale Fracture forecast technology
FMI
Geostress analysis
Shale oil Tight layers are adjacent to source rock. The quality of shale oil is controlled by migration distance and maturity. Maturity, TOC and porosity are controlling factors Pores in minerals and organic matter. Shale oil is residual in source rocks Moderate-maturity shale thick and with high brittle minerals Hydraulic fracturing for dark shale and ICP for the shale with high TOC
Tight oil Tight layers with relatively developed fractures and high porosity and permeability are near source rocks during oil generation.
Porosity and source-reservoir matching relationship are controlling factories
Intergranular, intragranular and solution pore sand fractures in inorganic minerals; near-source-rock accumulation The zone with relatively high porosity and permeability, large thickness and high brittle mineral content Horizontal wells, volume fracturing and water free fracturing
Shale gas Pores in minerals coexist with pores in organic matters, and micro-fractures are developed in the shale with high organic matter.
High organic abundance, porosity and mineral composition are controlling factors.
Organic pores, intergranular, intragranular and solution pores and fractures in inorganic minerals; near-source-rock accumulation The zone with relatively high porosity and permeability, large thickness and high brittle mineral content Horizontal wells, volume fracturing and water free fracturing
Tight gas Tight layers with relatively developed fractures and high porosity and permeability are near source rocks during oil generation.
Porosity and source-reservoir matching relationship are controlling factories
Intergranular, intragranular and solution pores and fractures in inorganic minerals; near-source-rock accumulation The zone with relatively high porosity and permeability, large thickness and high brittle mineral content Horizontal wells, volume fracturing and water free fracturing
Tab.2  Forming conditions and sweet spots of petroleum resources in shale formations
Fig.11  Schematic of integrated exploration of unconventional petroleum resources in shale formations.
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