Formation mechanisms and distribution of weathered volcanic reservoirs: A case study of the carboniferous volcanic rocks in Northwest Junggar Basin, China

Abstract

In view of the complex reservoir heterogeneities within weathered volcanic rocks, taking the Carboniferous volcanic weathered profile reservoir of the northwest Junggar Basin as an example, this study aims to characterize weathered volcanic rocks by the core, thin slice, log interpretation, and experimental test. The Carboniferous volcanic rocks are mainly composed of volcanic lava, volcanic breccia, and tuff, etc, which formed in a volcanic arc environment. As a result of the weathering and denudation, the weathered profile can be divided into four layers: weathered clay layer, intensive weathered zone, weak weathered zone, and unweathered compacted zone. The preserved void space mainly includes primary porosity (both vesicular and fractures), secondary pores, and fractures enhanced by weathering and structural processes. Among them, the volcanic facies control the first‐order properties of the reservoir. The degree of weathering‐leaching controls the thickness of the weathered part of the reservoir. The faults and fractures control the seepage/permeability capacity of weathered volcanic reservoir. On the plane, the weathered volcanic reservoirs mainly distributed along the fault zone, tectonic zone, and favorable lithofacies zone. On the longitudinal direction, they are always within the weathered profile toward the top of a certain depth range (20‐240 m).

Pore structure and fractal characteristics of the marine shale of the longmaxi formation in the changning area, Southern Sichuan Basin, China

“…Kerogen as the centre extends radially along the surface of the mineral particles and is considered the main transportation channel for the lateral migration of oil and gas. Hydrocarbon expulsion contraction fractures are mainly developed from the interior of organic matter to the edge of organic matter and mineral particles (Gao, 2019;Fan et al, 2020c;Li, 2022). For long-axis organic matter, contraction fractures divide it into multiple sections, most of which are arc-shaped, and the width of the fracture is up to 20 μm in the middle of the fracture arc (Figure 2K).…”

Fine Logging Evaluation of Fractures in Continental Tight Oil Sandstone Reservoirs of Yanchang Formation in the Ordos Basin

“…Fractures always act as the migration channels and accumulation sites of underground fluids, and the migration and accumulation of fluids may lead to the precipitation of radioactive substances and then lead to radioactivity enhancement. However, the increase in the natural gamma value is generally weak, and it usually appears as a relative increase on a background of relatively low values of the natural gamma curves (Fan et al, 2020c;Fan et al, 2019).…”

Hydrocarbon accumulation model influenced by “three elements (source-storage-preservation)” in lacustrine shale reservoir-A case study of Chang 7 shale in Yan’an area, Ordos Basin

“…Organic-rich shale is widely developed in China, and the shale gas resource potential is huge (Ji et al, 2012;Zhao et al, 2016;Fan et al, 2020;Zheng et al, 2020). According to the sedimentary geological conditions, it is divided into marine shale, continental shale and marine-continental transitional shale (Lama and Vutukuri, 1978;Wu and Yu, 2007;Yang et al, 2016;Hong et al, 2020;Mahmud et al, 2020;Katz et al, 2021;Lan et al, 2021;Qie et al, 2021).…”