ABSTRACT:

Radial drilling-fracturing, combining radial drilling and hydraulic fracturing, is an innovative approach to develop unconventional oil and gas reservoirs. In this study, we developed an analytical model to investigate the influences of pre-existing weakness plane on fracture initiation, when the plane is drilled through by the radial borehole. This model is based on the stress superposition induced by the excavation of main wellbore and radial borehole, and the tensile failure criterion is adopted. Then, we analyzed the effects of weakness plane distance (distance of intersection point of the weakness plane and radial lateral axis to the main wellbore axis) and occurrence under different u stress regimes (normal fault, strike slip and reverse fault). Results show that the influence of weakness plane distance from main wellbore is significant for all of three u stress regimes. Under the u stress regime of normal fault, fracture may initiates from the weakness plane when the plane is near the main wellbore. In contrast, under the u stress regime of strike slip and reverse fault, fracture may initiates from the weakness plane when the plane is far from the main wellbore. The influence of weakness plane occurrence on fracture initiation is significant when the u stress regime is strike slip or reverse fault and the weakness plane is far from the main wellbore. This study could provide critical insights to into understanding radial drilling-fracturing initiation mechanisms.

1. INTRODUCTION

Radial drilling-fracturing, combining radial drilling and hydraulic fracturing, is an innovative approach to develop unconventional oil and gas reservoirs (Liu et al., 2017a). As shown in

Fig. 1

, several radial lateral boreholes are drilled from the main wellbore; then, fracturing fluid is injected through the radial boreholes to the formation; and multiple fractures are created (Liu et al., 2017b). It has been proved that this technology could decrease fracture initiation pressure (Liu et al., 2018a) and guide the fracture propagation along the radial borehole (Guo et al., 2016). There have been several practical applications in low permeability (Li et al., 2000), aged (Cinelli and Kamel, 2013) and coalbed methane reservoir (Megorden et al., 2013), with good stimulation effectiveness.

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