Accumulation characteristics and exploration potential of tight limestone gas in the Taiyuan Formation of the Ordos Basin

doi:10.13745/j.esf.sf.2022.8.24

Abstract

Abstract:

In 2021, a high-yield daily output of more than 5.0×10⁵ m³ industrial gas was obtained in well Yutan*H, signifying a major breakthrough in natural gas exploration in the limestone reservoir of Taiyuan Formation, Ordos Basin. Now, more than 700 exploratory wells have good gas shows in the reservoir, showing excellent exploration potential, which is of great significance for further studying the geological characteristics of the limestone of Taiyuan Formation. Based on comprehensive analysis of the source rock characteristics, sedimentary environment, reservoir characteristics and hydrocarbon accumulation assemblage in the area, we show that: (1) The limestone of Taiyuan Formation is an epicontinental carbonate deposit, in which favorable sedimentary facies belt composed of bioclastic beach and biological mound is developed, and the widespread bioclastic silty limestone and algal-rich limestone can form favorable reservoirs after short-term leaching by atmospheric freshwater in penecontemporaneous period. (2) The limestone of Taiyuan Formation develops several types of reservoir space, where solution pores, submicron to nano intergranular micropores and microfractures superimpose to form a three-dimensional reservoir space; meanwhile across the region, 4-10 m thick bioclastic silty limestone reservoir develops in the Hengshan-Jingbian-Zhidan area, and 2-6 m thick algal-rich limestone reservoir develops in the Jiaxian-Zizhou-Qingjian area. (3) The hydrocarbon accumulation mode has a “sandwich-like” structure, where the limestone reservoir is sandwiched between main coaly source rocks, and the generated natural gas enters limestone reservoir through faults and fractures to accumulate and form a lithologic gas reservoir. With a combined area of 1.5×10⁴ km², the bioclastic beach in Hengshan-Jingbian area and the biological mound in Zizhou-Qingjian area are the favorable exploration targets for the limestone of Taiyuan Formation, which is expected to bring the increase of natural gas reserve and production.

Key words: Ordos Basin, Taiyuan formation, limestone, bioclastic silty limestone, algal-rich limestone, hydrocarbon accumulation mode, tight limestone gas in source

CLC Number:

TE13

FU Jinhua. Accumulation characteristics and exploration potential of tight limestone gas in the Taiyuan Formation of the Ordos Basin[J]. Earth Science Frontiers, 2023, 30(1): 20-29.

Figures/Tables 14

Fig.1 Distribution map of limestone of Taiyuan formation in Ordos Basin

Fig.2 Stratigraphic histogram of the Permian Taiyuan formation in Ordos Basin

Fig.3 Distribution map of limestone of Taiyuan formation in Ordos Basin

Fig.4 Sedimentary microfacies map of Taiyuan formation in Ordos Basin

Fig.5 (a) Sedimentary histogram of well jin26; (b) Sedimentary histogram of well ZT1H

Fig.6 limestone reservoir characteristics of Taiyuan formation in Ordos Basin

Fig.7 Porosity histogram of limestone reservoir of Taiyuan formation in Ordos Basin

Fig.8 Permeability histogram of limestone reservoir of Taiyuan formation in Ordos Basin

Fig.9 Characteristics of mercury intrusion curve in limestone reservoir of Taiyuan formation

Fig.10 Typical karst breccia in limestone of Taiyuan formation, Ordos Basin

Fig.11 Microscopic characteristics of organic matter in limestone of Taiyuan Formation in the basin

Fig.12 Macro and micro characteristics of limestone fracture system of Taiyuan formation in Ordos Basin

Fig.13 Natural gas accumulation model map of Taiyuan limestone in Ordos Basin

Fig.14 Production curve of Zhou * well in Taiyuan limestone

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