Natural fractures in tight-oil sandstones: A case study of the Upper Triassic Yanchang Formation in the southwestern Ordos Basin, China

Lyu, Wenya; Zeng, Lianbo; Zhou, Sibin; Du, Xiaosheng; Xia, Dongling; Liu, Shuai; Li, Jian; Weng, Jianqiao

doi:10.1306/0130191608617115

Cited by 28 publications

(27 citation statements)

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“…horizontal compressive stress is 60-70 • . The value of present in situ stress has a good linear relationship with buried depth, and the stress gradients of the maximum, intermediate, and minimum principal stresses are 0.0301, 0.0212, and 0.0165 MPa•m −1 , respectively (Zeng and Li, 2009;Lyu et al, 2019).…”

Section: In Situ Stressmentioning

confidence: 87%

“…This system significantly improves the seepage capacity and effectiveness of storage space in tight sandstone reservoirs, showing that the cumulative oil production of the wells drilled fracture zone is much greater than that of wells not drilled into fracture zones. There is a positive correlation between the density of meso-and small-scale fractures and initial production (R 2 = 0.838) (Lyu et al, 2019). As the density of meso-and small-scale fractures increases, the initial production of wells increases.…”

Section: Influence Of Different Scale Fractures On Oil Productionmentioning

confidence: 96%

“…The porosity and permeability of fractures can characterize the migration and storage capacity of fluids (Gong et al, 2021). According to the calculation results of porosity and permeability, small-scale fractures can increase the permeability of tight sandstone reservoirs by 1-2 orders of magnitude, and their porosity is similar to the reservoir matrix (Lyu et al, 2019). This means that the small-scale fractures mainly improve the reservoir permeability and secondly serve as the reservoir storage space.…”

Section: Influence Of Different Scale Fractures On Oil Productionmentioning

confidence: 98%

“…Based on the above methods, the maximum and minimum principal stresses are in the horizontal direction, and the intermediate principal stress is vertical in the southwest of Ordos Basin. The dominant direction of the maximum FIGURE 1 | Location map of the Ordos Basin, study area, wells, and fault systems (modified from Zeng and Li, 2009;Lyu et al, 2016;Lyu et al, 2017aLyu et al, , 2019. horizontal compressive stress is 60-70 • .…”

Section: In Situ Stressmentioning

confidence: 99%

“…The fracture development is controlled by lithology, rock mechanical units, sedimentary microfacies, diagenetic facies, and reservoir heterogeneity (Zeng et al, 2008;Gong et al, 2019). Besides, the contribution of natural fractures to reservoir permeability and their influence on oil and gas development are also discussed (Lyu et al, 2019). However, there is a lack of research and understanding of fracture scales and the differences in the effects of multi-scale fractures on reservoirs.…”

Section: Introductionmentioning

confidence: 99%

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The Effect of Multi-Scale Faults and Fractures on Oil Enrichment and Production in Tight Sandstone Reservoirs: A Case Study in the Southwestern Ordos Basin, China

et al. 2021

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The Chang 8 Member of the Upper Triassic Yanchang Formation in the southwestern Ordos Basin is a typical tight sandstone reservoir and has an average porosity of 8.60% and air permeability 0.20 mD. Multi-scale faults and fractures are widely developed in these reservoirs. In this study, three-dimensional seismic data, outcrops, cores, imaging logs, and thin sections were used to classify faults and fractures at multiple scales. Combined with the oil production data, the influence of multi-scale faults and fractures on the oil enrichment and production was analyzed. The results show multi-scale faults and fractures can be divided into six levels: type-I faults, type-II faults, large-scale fractures, mesoscale fractures, small-scale fractures, and micro-scale fractures. As the scale decreases, the number of fractures increases in a power function. Type-I faults cut the caprocks and are not conducive to the preservation of oil. Type-II faults connect the source rocks and reservoirs and are migration channels of the oil source. Large-scale fractures cut the mudstone interlayer and are the seepage channel inside the reservoir. Mesoscale fractures are controlled by thick interlayers, and small-scale fractures are restricted by thin interlayers or layer interfaces. These fractures are the main seepage channels and effective storage spaces. Micro-scale fractures serve as important storage spaces for these reservoirs. The case study of oil reservoir development proves that type-I faults have the greatest impact on fluid flow, while wells drilled into the type-II faults zone have a higher oil production capacity. The oil production changes with the development degree of fractures in different scales, strikes, and positions of faults. Meso- and small-scale fractures are the key to influencing the early single-well production, and micro-scale fractures are conducive to the stable production of single wells. Consequently, multi-scale faults and fractures have significantly different effects on the oil enrichment and production of tight sandstone reservoirs, and the research conclusions can guide to the exploration and development of such similar reservoirs.

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Section: In Situ Stressmentioning

confidence: 87%

Section: Influence Of Different Scale Fractures On Oil Productionmentioning

confidence: 96%