Abstract
The characteristics of laminae in lamellar shale oil reservoirs have important influences on reservoir parameters, especially permeability. In order to explore the influence of lamina density and occurrence on the permeability of lamellar shale after hydration, we studied the lamellar shale in the Chang 7 member of the Yanchang Formation of Triassic in Ordos Basin. By comparing the permeability of bedding shale and lamellar shale with different densities of laminae, it was found that the permeability anisotropy of lamellar shale was stronger. In the direction parallel to the lamina, the permeability increased approximately linearly with an increase in lamina density. The effect of hydration on rock micropore structure and permeability was studied by soaking shale in different fluids. Most of the microfracture in the lamellar shale was parallel to the lamina direction, and hydration led to a widening of the microfracture, which led to the most obvious increase in permeability parallel to the lamina. Collectively, the research results proved that lamina density, occurrence, and hydration have a significant influence on the permeability anisotropy of lamellar shale.
Highlights
Shale permeability is an important parameter for productivity evaluation and economic development of shale reservoirs [1,2]
When the 50 × 25 mm cylinder samples were drilled at the sam densities of lamin (Figure 6) showed that shale permeability increased with an increase in the full diameter core, the lamina density in 45° and 90° samples was simila in lamina density, whether in water or drilling fluid
The permeability of lamellar shale had a larger variation range than that of bedding shale, which proved that the existence of laminae increased the influence of hydration on rock permeability
Summary
Shale permeability is an important parameter for productivity evaluation and economic development of shale reservoirs [1,2]. While a shale reservoir is usually dense, with low matrix permeability and high clay content, its permeability is greatly affected by bedding occurrence and hydration of rock [3,4,5]. Shale anisotropy is related to the development of weak plane structure, which is an important factor affecting the physical and mechanical properties of rock [8,9,10]. The clay content of continental shale is high, and the changes of rock structure and properties caused by clay hydration and expansion are the key points related to the study of shale [11,12]. Water absorption parallel to the bedding plane will enhance the influence of anisotropy on the geological mechanical behavior of shale [15]
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