ABSTRACT:

Radial drilling-fracturing, the integration of radial drilling and hydraulic fracturing, is an innovative approach to develop low permeability, thin target layer and naturally fractured reservoirs, etc. Investigating fracture initiation process is essential for the successful design and operation of radial drilling-fracturing. We developed an analytical model for determining the fracture initiation pressure (P), location of rock failure zones, and initial fracture direction from radial lateral borehole. Then, we analyze effects of in-situ stress regime, lateral orientation and pre-existing weakness plane. Results show that in-situ stress regime, lateral orientation and weakness plane greatly influence P, location of rock failure zones, and initial fracture direction. For a given combination of in-situ stress regime and lateral orientation, when fracture initiates longitudinally, P enlarges moderately with lateral orientation increasing; rock failure zones consist of two symmetric wings at the base of radial borehole on its top and bottom sides. When fracture initiates horizontally, P declines moderately with lateral orientation increasing; rock failure zones consist of two symmetric wings on the remote region of radial borehole on its two lateral sides. Fracture will firstly initiate from the weakness plane, if its tensile or shear failure pressure is less than that P from rock matrix.

1. INTRODUCTION
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