Abstract

Deformation bands are widely formed and distributed in Triassic high-porous rocks as a result of multistage tectonic movement. In this research, core observation, the rock thin section (fluorescence and casting thin section), FIB-SEM, X-ray diffraction, Raman laser, and thermometry of fluid inclusions were employed to describe the macro- and micro characteristics of deformation bands and their associated relationship with microfractures. Results indicate that the main types of deformation bands formed in the Lunnan Triassic high-porosity sandstone during the Yanshanian and Himalayan periods under different temperature and pressure conditions are compaction shear bands, and their quantity increases evidently with the distance of thrust faults. The density of deformation bands near the fault is about 15/m; porosity and permeability decrease sharply compared with those of the host rock. Microscopically, two obtained fluid-inclusion planes (FIPs) can be distinguished as 51 samples collected from 12 wells by the cutting relationship and mechanical characteristics. The homogenization temperature of associated aqueous inclusion is generally characterized by two peaks, mainly 70–80°C and 110–120°C, which were formed in the Late Yanshanian and Late Himalayan periods. The formation period of deformation bands induced by the intragranular microfractures improved the reservoir seepage capacity. In the later stage, as the interlayer and barrier with low porosity and low permeability affects the distribution of oil and gas, which is an important factor in this study of the local fluid dynamic field and high-quality reservoir evolution distribution.

Highlights

  • Fault zone structures with different lithology properties caused by various tectonic movements are significantly different (Fossen et al, 2007; Fossen et al, 2018)

  • Deformation band is a kind of brittle-ductile sub-seismic deformation structure that develops in consolidated or semi-consolidated high-porosity rocks, which is the intuitive response of the host rock to the velocities and displacements imposed by tectonic movements, and the direction, distribution, and types of deformation bands developed by specific boundary conditions and tectonic structures have certain regularity (Fossen et al, 2007; Philit et al, 2018)

  • It can be divided into dilatation band, shear band, and compaction band according to the type of stress; the most common type is the compaction shear band (CSB) formed by both shear and compaction (Fossen et al, 2018)

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Summary

Introduction

Fault zone structures with different lithology properties caused by various tectonic movements are significantly different (Fossen et al, 2007; Fossen et al, 2018). Fossen classified deformation bands into disaggregation band, phyllosilicate band, cataclastic band, and solution-cementation band according to the combining mineralogical characteristics, cementation degree, porosity, and stress state of deformation bands (Exner et al, 2013; Soliva et al, 2013; Pei et al, 2015; Bossennec et al, 2018; Fossen et al, 2018). The variability of its inherent physical properties affects the migration and preservation of hydrocarbons to a certain extent, and its distribution rules and relevant characteristics are influential scientific issues for reservoir inhomogeneity and exploration prediction in petroliferous basins

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