Hydrocarbon accumulation in the northwest Chaluhe Fault Depression, Yitong Basin, North China

Abstract

The Yitong Basin is a strike-slip fault basin, which tectonically belongs to the northern section of the Tanlu Fault Zone. Exploration has demonstrated that the northwest Yitong Basin is a hydrocarbon enrichment zone. However, the complex geological conditions and a poor understanding of the accumulation models and hydrocarbon enrichment factors have impeded petroleum exploration in the basin. This paper focuses on the hydrocarbon accumulation processes in the strike-slip fault zone in the northwest Yitong Basin. We proposed the reservoir critical porosity concept for reservoir dynamic evaluation. A mathematical model for sandstone porosity evolution in the northwest Chaluhe Fault Depression is established to reconstruct the sandstone porosity over geological time. A fault critical burial depth is proposed to evaluate the present fault-sealing property. The critical condition for oil charge into sandstone was also simulated using an oil-charge simulation experiment. The results indicate that the reservoir critical porosity of the Shuangyang Formation in the northwest Chaluhe Fault Depression was 11% during the accumulation. The present tight sandstone reservoirs in the northwest Yitong Basin were conventional reservoirs during the hydrocarbon accumulation with relatively high porosity and permeability, beneficial for hydrocarbon accumulation at the time. The critical burial depth of faults in the middle–deep layers is 2050 m in the northwest Chaluhe Fault Depression. The hydrocarbons can be effectively sealed when the burial depth of the fault is greater than the critical burial depth. The critical hydrocarbon accumulation threshold for a sandstone reservoir depends on the coupling of reservoir critical porosity and critical injection pressure during hydrocarbon accumulation. We put forward three hydrocarbon accumulation plays for the northwest Chaluhe Fault Depression: (1) extensional fault block play, which is close to the source rock and experienced two stages of hydrocarbon accumulations; (2) flower structure play, which is far away from the source rock and is characterised by a late hydrocarbon charge and accumulation; and (3) fault-lithological play, which is far away from the source rock and experienced a late hydrocarbon accumulation. For the Yitong Basin, reservoir properties and faulting appear to be the main controlling factors for hydrocarbon accumulations.

伊通盆地是一个走滑断层盆地，构造上属于郯庐断裂带北段。勘探表明，伊通盆地西北部是一个油气富集区。然而，复杂的地质条件和对成藏模式和油气富集因素缺乏了解阻碍了盆地石油勘探。本文侧重于西北伊通盆地的走滑断裂带油气成藏过程。我们针对油藏动态评价提出了储层孔隙度的关键概念。为了重建地质时期中砂岩空隙度，我们建立了Chaluhe断层地陷。我们提出断层关键埋藏深度来评价现有断层密封特性。我们使用油充入模拟实验来模拟油充入砂岩的临界条件。结果表明，Chaluhe断陷西北部的双阳组的储层临界孔隙度为11％。伊通盆地西北现有的致密砂​​岩油气藏油气累积过程中的传统储蓄层，具有较高的孔隙度和渗透率，有利于当时的油气成藏。在Chaluhe断陷西北部，中等深度断层的临界埋深是2050米。在断层埋藏深度大于临界埋藏深度条件下，油气可被有效地密封。砂岩储层的油气藏临界点取决于油气成藏过程中储层临界孔隙度和临界注入压力的耦合。我们提出Chaluhe断陷西北部的三种油气成藏显示（1）伸展断块显示，它接近源岩和经历过两次油气藏; （2）花型结构显示，它远离源岩，其特征是晚期油气充入和成藏; （3）断层岩性显示，它远离源岩，经历了晚期油气成藏。对于伊通盆地，储层特性和断层作用似乎是油气成藏的主控因素。

KEY WORDS:

• Yitong Basin
• Chaluhe Fault Depression
• porosity evolution process
• reservoir critical property
• fault critical sealing property
• hydrocarbon accumulation model

ACKNOWLEDGEMENTS

This study was supported by the State Key Project of Oil and Gas (2011ZX05001). Grateful acknowledgements are made to CNPC Jilin Company Ltd and individuals, which contributed cores and geological data for this work. The Laboratory of Com-Rich Petroleum Engineering Technology Co. Ltd (Beijing) provided assistance for our sample analyses. Our heartfelt gratitude also goes to the reviewers for their scientific and linguistic revisions of the manuscript.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Editorial handling: Keyu Liu