The effect of attack angle of borehole failure related to bedding plane

What is it about?

Attack angle (aat) is the angle between the wellbore and the bedding plane, it’s normally taken as acute angle. The array of bedding plane, borehole position and the dip/strike angle of formation are important parameters if anyone want to apply the in-situ stresses equations for determining failure criterion, rock strength and want to develop models of wellbore failure. Azimuth, position of wellbore, fracture angle, failure Plane and attack angle are considered confusing to determine at a time. The assessment of in-situ stress and analysis of borehole failure due to instability and the relation of attack angle with inclination borehole represent one of the most critical factors when evaluating borehole stability that causes borehole failure. A lot of scientists and engineers specially Aadnoy and Chenevert [2,3] showed that at a certain angle rock failed at very low load condition. This paper focused, analyzed and used the data from the Aadnoy et.al [3] models to address the existing problem on this matter. According to this research, attack angle had been changed with different azimuth although inclination was same. So it’s important for testing the bedding exposed with different azimuth with constant inclination. It found that attack angle was the lowest value on the down dip position and the highest value on the up dip Position. Aadnoy et.al. [3] paper did not address about the effect of attack angle and azimuth. This Paper and my research confirmed that attack angle is affected the azimuth angle definitely which ultimately will affect the result of bedding exposed position. Attack angle depends on the relative position of bedding plane and a plane that contain horizontal stress. So it has to be confirmed what are the dip angle and azimuth before taking the drilling action in to a formation. This paper analyzed the 3D effect of attack angle with changing azimuth for a constant inclination on bedding plane. Interestingly paper got that bedding exposed is not only depends on inclination but also depends on dip of the formation, attack angle and azimuth [1]. Keywords: Drilling, Borehole Stability, In-Situ Stress, Attack angle, Bedding Plane

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Why is it important?

Im[ortance Rock mechanics for directional drilling

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