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Initiation mechanisms of radial drilling-fracturing considering shale hydration and reservoir dip
Energy Science & Engineering ( IF 3.8 ) Pub Date : 2021-09-07 , DOI: 10.1002/ese3.969
Yuxin Chen 1 , Yunhong Ding 1 , Chong Liang 1 , Dawei Zhu 1 , Yu Bai 1 , Chunmei Zou 1
Affiliation  

Radial drilling-fracturing is an innovative fracturing technology that achieves superior stimulation effects. This paper develops a model for radial drilling-fracturing in shale reservoirs, which can predict fracture initiation pressure and failure mode of shale. Compared with published models, this model additionally considers shale hydration and inclinations of boreholes and reservoir. Then, the influences of 7 factors are studied and main conclusions are as follows. First, with the angle between radial borehole and formation strike increasing, matrix failure pressure declines only around 90° and 270°. Bedding tensile failure pressure ascends and then falls back. Bedding shear failure pressure rapidly descends, then reaches a plateau, and finally rebounds. A small or large angle is favorable for bedding tensile failure. Shale tends to crack with bedding shear failure under a moderate angle and with matrix failure only at 90° and 270°. Second, with the enlargement of azimuth difference between the radial borehole and main wellbore, matrix failure pressure periodically fluctuates, forming an inverted W-shape curve. Bedding tensile failure pressure and bedding shear failure pressure both ascend, then slide downward, and finally rise again. Besides, a small azimuth difference inclines shale to bedding shear failure, and the other failure modes tend to occur when azimuth difference is around 90°. Third, pressures required for all failure modes descend as the dip of shale formation increases. However, the difference in descending rate leads to that the increase of dip angle can incline shale to bedding shear failure. Besides, pressures required for bedding tensile failure and matrix failure decline linearly with the increasing reservoir temperature. Temperature has no impact on bedding shear failure. Hence, matrix failure and bedding tensile failure are more prone to occur in the high-temperature reservoir. The research provides a reference for field applications of radial drilling-fracturing in the shale reservoir.

中文翻译:

考虑页岩水化和储层倾角的径向钻压起爆机理

径向钻压是一种创新的压裂技术,增产效果显着。本文建立了页岩储层径向钻井-压裂模型,可以预测页岩的起裂压力和破坏模式。与已发表的模型相比,该模型还额外考虑了页岩水化以及钻孔和储层的倾斜度。然后,对7个因素的影响进行了研究,主要结论如下。首先,随着径向钻孔与地层走向之间的夹角增加,基质破坏压力仅下降 90° 和 270° 左右。层理拉伸破坏压力先上升后回落。层理剪切破坏压力迅速下降,然后达到平台,最后反弹。小角度或大角度有利于层理拉伸破坏。页岩倾向于在中等角度下随着层理剪切破坏而破裂,并且仅在 90° 和 270° 处发生基质破坏。其次,随着径向井眼与主井眼方位差的增大,基质破坏压力周期性波动,形成倒W型曲线。层理拉伸破坏压力和层理剪切破坏压力均先上升,然后向下滑动,最后再次上升。此外,较小的方位差使页岩向层理剪切破坏倾斜,而当方位差在 90°左右时容易发生其他破坏模式。第三,所有破坏模式所需的压力随着页岩地层倾角的增加而下降。然而,下降速率的差异导致倾角的增加使页岩向层理剪切破坏倾斜。除了,层理拉伸破坏和基质破坏所需的压力随着储层温度的升高而线性下降。温度对层理剪切破坏没有影响。因此,高温储层更容易发生基质破坏和层理拉伸破坏。该研究为页岩油藏径向钻井压裂的现场应用提供了参考。
更新日期:2021-11-02
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