The Impact of Hole Geometry on the Near-wellbore Stress Around a Damage Wellbore

Abstract

In petroleum drilling, it has been observed that the actual wellbore is always deteriorated from ideal circular geometry. It is widely known that the standard stress calculation method is limited to a wellbore with a circular cross-section, and hence can no longer be used. In many practical oilfield operations, such as post-drill open hole stability assessment and hydraulic fracturing,  information regarding the near-wellbore stress state after the wellbore has been drilled may still be required. Recently, Setiawan and Zimmerman (2020) proposed a semi-analytical method for the calculation of the stresses around a wellbore having an essentially arbitrary cross-sectional shape. To examine the significance of hole geometry on the near-wellbore stress, an actual wellbore has been reconstructed from an ultrasonic log. The in-plane near-wellbore stress is computed from the known hole geometry in a given in situ stress to identify zones of high-stress concentration attributed to the local irregularities around the wellbore. It is found that irregularity of the hole geometry has a significant impact on the near-wellbore stress. The stress concentration around such an irregular cross-sectional wellbore could be up to 50% higher than that of the standard  computation. The impact of such under-estimation could be significant in various operations such as hydraulic fracturing, cementing, completion and perforation, where knowledge about the near-wellbore stress is crucial. Hence, the current method provides accurate near-wellbore stress without taking any assumption regarding the wellbore geometry.