Sains Malaysiana 53(7)(2024): 1545-1558

http://doi.org/10.17576/jsm-2024-5307-06

Characteristics of Oil and Gas Distribution and Controlling Factors of Hydrocarbon Accumulations in the Eocene Pinghu Formation of the Xihu Depression, East China Sea

(Ciri Pengagihan Minyak dan Gas serta Faktor Pengawalan Pengumpulan Hidrokarbon dalam Formasi Pinghu Eosen di Kelekukan Xihu, Laut China Timur)

LIAO KAIFEI¹, ZHONG KAI¹, LU YI¹, GOH THIAN LAI^2,* & LEE KHAI ERN³

¹State Key Laboratory of Marine Geology, Tongji University, Shanghai 200092, China

²Department of Earth Sciences and Environment, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor, Malaysia

³Institute for Environment and Development (LESTARI), Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor, Malaysia

Received: 3 April 2024/Accepted: 6 June 2024

Abstract

The Xihu Depression at the shelf of the East China Sea is a petroliferous basin with excellent exploration potential. The Eocene Pinghu Formation has become a recent oil and gas exploration target and as the critical hydrocarbon-bearing stratigraphic layer in the basin. However, studies specifically examining the characteristics of hydrocarbon distribution and the controlling factors of reservoirs in the Kongqueting area remain limited. The lack of in-depth hydrocarbon accumulation model research restricts subsequent exploration. In this paper, based on data from drilling, 3D seismic, well test, and geochemical analysis, we found that coal bed-related hydrocarbon source rocks were widely occurred in the Pinghu Formation in the Kongqueting area. The source rocks provide good hydrocarbon supply of near-source and distant-source to reservoir. The river sands were connected laterally and stacked vertically, forming a pattern characterized by ‘lateral succession and vertical superposition’ indicative of good quality of reservoir. During the deposition period of the Pinghu Formation, two large sets of regional cap rock (P3 and P7) were excellent sealing rock. The sand reservoir was interbedded with shale layers, forming a Mille-feuille type of reservoir-seal pair. Faults formed at the early stage of the formation of basin serve as conduits for hydrocarbon migration, governing both the spatial distribution of hydrocarbon-bearing strata and the types of hydrocarbon accumulations. These faults were instrumental in facilitating the formation of extensive oil and gas accumulations. This paper establishes a hydrocarbon accumulation model in the Kongqueting area, characterized as ‘dual hydrocarbon supply from source, upper oil, and lower gas, good reservoir-seal pair, hydrocarbon migration through fault conduit’.

Keywords: Controlling factors on hydrocarbon accumulation; hydrocarbon accumulation model; Kongqueting area; oil and gas distribution; Xihu Depression

Abstrak

Kelekukan Xihu di pelantar Laut China Timur ialah satu lembangan berpetroleum dengan potensi penjelajahan yang sangat baik. Formasi Pinghu Eosen telah menjadi sasaran penjelajahan minyak dan gas yang terkini dan sebagai lapisan stratigrafi galas hidrokarbon kritikal dalam lembangan. Akan tetapi, kajian khusus meneliti ciri taburan hidrokarbon dan faktor kawalan reservoir di kawasan Kongqueting masih terhad. Kekurangan penyelidikan model pengumpulan hidrokarbon yang mendalam menghalang penjelajahan seterusnya. Dalam kertas ini, berdasarkan data daripada penggerudian, seismos 3D, ujian telaga dan analisis geokimia, kami mendapati bahawa batuan sumber hidrokarbon yang berkaitan dengan dasar batu arang adalah terwujud secara meluas dalam Formasi Pinghu di kawasan Kongqueting. Batuan sumber membekalkan bekalan hidrokarbon yang baik sebagai sumber dekat dan sumber jauh untuk reservoir. Pasir sungai yang bersambungan secara sisi dan disusun secara menegak, membentuk corak yang dicirikan sebagai ‘succession sisi dan superposisi menegak’ yang menunjukkan kualiti reservoir yang baik. Semasa pemendapan Formasi Pinghu, dua set batuan tukup serantau yang besar (P3 dan P7) merupakan batuan pengedap yang sangat baik. Reservoir pasir adalah saling lapisan dengan lapisan syal, membentuk satu pasangan reservoir-kedap jenis Mille-feuille. Sesar yang terbentuk pada awal pembentukan lembangan berfungsi sebagai saluran untuk penghijrahan hidrokarbon yang mengawal kedua-dua taburan ruang strata yang mengandungi hidrokarbon dan penumpukan hidrokarbon. Sesar ini memainkan peranan penting dalam memudahkan pembentukan penumpukan minyak dan gas yang meluas. Kertas kerja ini mewujudkan model penumpukan hidrokarbon di kawasan Kongqueting, dicirikan sebagai ‘bekalan hidrokarbon dwi daripada sumber, minyak atas, dan gas bawah, pasangan reservoir-kedap yang baik, penghijrahan hidrokarbon melalui saluran sesar’.

Kata kunci: Faktor kawalan pengumpulan hidrokarbon; kawasan Kongqueting; lekukan Xihu; model penumpukan hidrokarbon; pengagihan minyak dan gas

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*Corresponding author; email: gdsbgoh@gmail.com