Natural fractures at depth in shale reservoirs: new insights from the southern Sichuan Basin marine shales

IF 1.9 4区地球科学 Q3 GEOSCIENCES, MULTIDISCIPLINARY

Petroleum Geoscience Pub Date : 2024-01-04 DOI:10.1144/petgeo2023-071

Tao Nian, Yuhan Tan, Fengsheng Zhang, Heng Wu, Chengqian Tan, Pengbao Zhang

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引用次数: 0

Abstract

Natural fractures are pervasive in southern Sichuan Basin marine shales, China, and provide a desired opportunity to understand subsurface fracture network in shale reservoirs. Based on cores and electrical imaging logs from vertical and horizontal petroleum wells in southern Sichuan Basin, four types of natural fractures are identified in terms of orientation, size, filling properties, and spatial distribution. The uncemented bed-parallel shear fracture is developed at or in the vicinity of the mechanical interfaces and inclined to present in shale layers with dip angles greater than 12°. The cemented bed-parallel fracture is characterized with crack-seal texture marked by multiple bands of fibrous cement, and its intensity decreases upwards and shows a positive relation with the TOC values. The uncemented bed-oblique fracture is barely developed, and bears limited open space. The cemented bed-oblique/perpendicular fracture is the most developed fracture type and distributed on a regional scale with a pattern of two systematic sets. The results imply that these shale fractures could be formed sequentially by local and regional tectonic deformation, and by abnormally high-pressure. Most natural fractures cannot contribute to reservoir storage or efficiently enhance its permeability yet can act as planes of weakness and be potentially reactivated during hydraulic fracture treatments.

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页岩储层深部的天然裂缝：四川盆地南部海相页岩的新发现

天然裂缝普遍存在于中国四川盆地南部海相页岩中，为了解页岩储层地下裂缝网络提供了一个理想的机会。根据四川盆地南部垂直和水平油井的岩心和电成像测井记录，从方向、尺寸、充填性质和空间分布等方面确定了四种类型的天然裂缝。非胶结床面平行剪切裂缝发育于力学界面或其附近，倾向于出现在倾角大于12°的页岩层中。胶结的床面平行断裂具有裂缝密封纹理，以多条纤维状胶结物带为特征，其强度向上递减，并与总有机碳值呈正相关。未胶结的岩床斜向断裂几乎不发育，具有有限的开放空间。胶结床斜/垂直断裂是最发育的断裂类型，在区域范围内分布有两组系统模式。研究结果表明，这些页岩裂缝可能是由局部和区域构造变形以及异常高压先后形成的。大多数天然裂缝不能促进储层储量或有效提高储层渗透率，但可以作为薄弱平面，在水力压裂处理过程中可能被重新激活。

本文章由计算机程序翻译，如有差异，请以英文原文为准。

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来源期刊

Petroleum Geoscience 地学-地球科学综合

CiteScore

4.80

自引率

11.80%

发文量

审稿时长

>12 weeks

期刊介绍： Petroleum Geoscience is the international journal of geoenergy and applied earth science, and is co-owned by the Geological Society of London and the European Association of Geoscientists and Engineers (EAGE). Petroleum Geoscience transcends disciplinary boundaries and publishes a balanced mix of articles covering exploration, exploitation, appraisal, development and enhancement of sub-surface hydrocarbon resources and carbon repositories. The integration of disciplines in an applied context, whether for fluid production, carbon storage or related geoenergy applications, is a particular strength of the journal. Articles on enhancing exploration efficiency, lowering technological and environmental risk, and improving hydrocarbon recovery communicate the latest developments in sub-surface geoscience to a wide readership. Petroleum Geoscience provides a multidisciplinary forum for those engaged in the science and technology of the rock-related sub-surface disciplines. The journal reaches some 8000 individual subscribers, and a further 1100 institutional subscriptions provide global access to readers including geologists, geophysicists, petroleum and reservoir engineers, petrophysicists and geochemists in both academia and industry. The journal aims to share knowledge of reservoir geoscience and to reflect the international nature of its development.