Coupling Relationship Between the Reservoir Densification Process and Hydrocarbon Charging Process in the Ahe Formation in the Dibei Area of the Kuqa Depression

doi:10.19657/j.geoscience.1000-8527.2024.072

Abstract

Abstract:

The Lower Jurassic Ahe Formation is a key target for tight oil and gas exploration in the Dibei area. In recent years, industrial oil and gas flows have been obtained from Wells Dibei 2 and Dibei 5, demonstrating favorable exploration prospects in the area, which also serves as a critical replacement zone for oil and gas exploration in the Kuqa Depression. Previous studies have systematically investigated hydrocarbon sources and accumulation conditions in the Dibei area, but research on the quantitative characterization of porosity evolution remains limited, and controversies persist regarding whether hydrocarbon charging occurred in two or three stages.In this study, sandstone samples from Wells Dibei 5 and Ditan 2 were analyzed using casting thin sections, scanning electron microscopy (SEM), cathodoluminescence, and fluid inclusion thermometry. These methods helped identify diagenetic types, clarify the diagenetic evolution sequence, quantitatively characterize the reservoir porosity evolution history using the inversion backstripping principle, and elaborate on the coupling relationship between reservoir densification and hydrocarbon charging.The results indicate that the Ahe Formation in the Dibei area underwent diagenetic processes including compaction, dissolution, and cementation, with intense compaction being the primary cause of underdeveloped primary pores. The diagenetic sequence is as follows: mechanical compaction→early calcite cementation→quartz overgrowth→feldspar dissolution→crude oil charging→late calcite and ferrocalcite cementation→calcite dissolution and natural gas charging→tectonic compression, featuring multi-stage dissolution and cementation.The Ahe Formation reservoir has undergone two stages of hydrocarbon charging. The early-stage crude oil charging occurred in the early-middle Kangcun Formation (14.1-12.3 Ma), when the reservoir was not yet densified, though the crude oil charging was on a small scale. The late-stage natural gas charging took place in the middle-late Kangcun Formation (10.2-8.1 Ma), by which time the reservoir had already been densified (with the densification time at approximately 11 Ma). At this stage, the Triassic source rocks were in the mature to high-maturity stage, and inclusions were well-developed, indicating a high intensity of natural gas charging.Thus, the coupling relationship between reservoir densification and hydrocarbon accumulation in the Ahe Formation is characterized by “densification prior to accumulation”. These findings help clarify hydrocarbon enrichment patterns in the Ahe Formation and provide a basis for well placement.

Key words: Kuqa Depression, Dibei Area, hydrocarbon accumulation, reservoir densification, diagenetic evolution

CLC Number:

P618.1

JING Taotao, LI Wenhao, DONG Wei, CHEN Yifan, WANG Longwei, YANG Yifang. Coupling Relationship Between the Reservoir Densification Process and Hydrocarbon Charging Process in the Ahe Formation in the Dibei Area of the Kuqa Depression[J]. Geoscience, 2025, 39(04): 1156-1168.

Figures/Tables 12

Fig.1 Structure location map of Kuqa Depression and composite columnar section of Dibei area (Fig.(b) modified according to reference [34])

Fig.2 Triangle diagram of tight sandstone rock types of the Ahe Formation in Dibei area(unit: %)

Fig.3 Reservoir space types of tight sandstones in the Ahe Formation, Dibei area

Fig.4 Frequency distribution histogram of physical properties of the Ahe Formation in Dibei area

Fig.5 Characteristics of hydrocarbon inclusions in the Ahe Formation of Well Dibei 5, Dibei area

Fig.6 Hydrocarbon charging periods of the Ahe Formation in Dibei area

Fig.7 Diagenesis characteristics of the Ahe Formation in Dibei area

Fig.8 Diagenetic evolution sequence of tight sandstones in the Ahe Formation, Dibei area

Table 1 Timing and paleoburial depth of key diagenetic events in the Ahe Formation, Dibei area

关键成岩作用阶段	时间(Ma)	古埋深(m)
压实作用始	201.3	0
早期方解石、石英次生加大始	174.0	1012
长石溶蚀始	140.0	2209
晚期方解石、铁方解石胶结始	12.3	4795
晚期方解石、铁方解石溶蚀始	10.2	5084
构造挤压始	5.0	5740

Fig.9 Relationship between surface porosity and porosity of the Ahe Formation in Dibei area

Fig.10 Porosity evolution history of the Ahe Formation in Dibei area

Fig.11 Relationship between reservoir densification process and hydrocarbon charging in the Ahe Formation, Dibei area

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