Stability Analysis of Highly Deviated Boreholes to Minimize Drilling Risks and Nonproductive Time

Abstract

The Lower Cretaceous Zubair Formation is a regionally extended gas- and oil-producing sandstone sequence in Southern Iraq. Due to the weak nature of the Zubair Formation, the lack of wellbore stability is one of the most critical challenges that continuously appears during the drilling development operations. Problems associated with lack of wellbore stability, such as the tight hole, shale caving, stuck pipe, and sidetracking, are both time-consuming and expensive. This study aimed to construct a geotechnical model based on offset well data, including rock mechanical properties, in situ stresses, and formation pore pressure, coupled with suitable rock failure criteria. Mohr–Coulomb and Mogi–Coulomb failure criteria were used to predict the potential rock failure around the wellbore. The effect of the inclination and azimuth of the deviated wells on the shear failure and tensile failure mud weights was investigated to optimize the wellbore trajectory. The results show that the best orientation to drill highly deviated wells (i.e., inclinations higher than 60 deg) is along to the minimum horizontal stress (140 deg). The recommended mud weight for this selected well trajectory ranges from 1.45 to 1.5 g/cc. This study emphasizes that a wellbore stability analysis can be applied as a cost-effective tool to guide future highly deviated boreholes for better drilling performance by reducing the nonproductive time.

Geomechanical assessment of the Lower Turonian AR-F limestone Member, Abu Gharadig Field, Egypt: Implications for unconventional resource development

“…In deviated wells, in situ stresses should be transformed into a new Cartesian coordinate system (x, y, z) associated with well orientation. For a well with inclination "i" drilled in a direction of "θ" with respect to the regional S hmax azimuth, the in situ stresses in (x, y, z) space are defined as (Abbas et al, 2019):…”

“…These are resolved by Kirsch's equations. At the borehole wall, these are transformed as (Abbas et al, 2019):…”

“…where MP is the drilling mud pressure. Considering zero shear stresses, the effective principal stresses, therefore, can be written as (Abbas et al, 2019):…”

The complex system of climate change security and the ripple effect of water–food–socioeconomic nexus

“…In 2019, floods arose due to heavy rainfall in Iraq (Yadollahie, 2019). Moreover, the temperature increase and rapid population growth will complicate environmental challenges severely; the population is expected to reach 50 million by 2030 (United Nations, 2019), placing great pressure on urban areas in the absence of an integrated water management strategy (Abbas et al, 2019). The rise in temperature, along with changes in precipitation patterns, will shift the ice in the mountains of southern Turkey, which will likely diminish water quality, particularly through sea-level rises and saltwater intrusion into aquifers and rivers (Al-Marashi and Causevic, 2020;Yaseen et al, 2016).…”

Comparison of Predicted Failure Area Around the Boreholes in the Strike-Slip Faulting Stress Regime With Hoek-Brown and Fairhurst Generalized Criteria

“…A borehole with radius a in an elastic, homogeneous and isotropic environment under non-isotropic stresses of s H , s h is considered (Figure 1). The stresses around the borehole according to the Kirsch relations are obtained as follows (Jaeger et al, 2009;Abbas et al, 2019):…”