Petrological characteristics, reservoir property and oil-bearing potential of intrusive rocks in well Shaduo 1, Qintong Sag, Subei Basin

Abstract

Igneous rock oil and gas reservoir has gradually become an important type of oil and gas reservoir, but the igneous rock reservoir is highly heterogeneous, the reservoir property varies greatly, and the study of reservoir genetic mechanism is unsubstantial, which has become the main bottleneck of igneous rock reservoir evaluation. Taking the intrusive rocks in the second member of Paleogene Funing Formation in the Qintong Sag, Subei Basin as the research object, through systematic core observation, thin section identification, electron probe analysis and testing and logging interpretation, the lithologic and lithofacies characteristics, reservoir characteristics and main controlling factors of reservoir development of the intrusive rocks in the second member of Funing Formation in well Shaduo 1 in the Qintong Sag were analyzed. The results show that the lithology of the intrusive rocks varies remarkably longitudinally, and the intrusive rock body is composed of multiphase intrusive rock, with diabase on the top, pyroxene monzonite in the middle and olivine gabbro at the bottom. The development of porosity varies, with diabase and pyroxene monzonite exhibiting low porosity, while olivine gabbro showing relatively higher porosity. Due to the superimposition of multiple intrusions and hydrothermal alteration, good reservoir spaces are formed, with predominant pore types being dissolution pores and structural fractures, accompanied by the development of shrinkage fractures. The main factors affecting the reservoir physical properties are lithology and hydrothermal fluid activity. Among them, dark minerals such as pyroxene in olivine gabbro are most easily altered, so dissolution pores are highly developed. Additionally, regional fault structures generate numerous structural fractures in many dense igneous rocks, effectively connecting the pore-fracture system of intrusive rock reservoir and providing channels through which magmatic hydrothermal fluids flow in the subsequent dissolution processes. Generally, the overall oil-bearing potential of the intrusive rocks encountered in well Shaduo 1 is poor. Sporadic fluorescence is observed in the lower intrusive rock layers, while the upper intrusive rock layers are essentially devoid of oil.

Keywords

• intrusive rock reservoir
• oil-bearing potential
• second member of funing formation
• qintong sag
• subei basin