53rd U.S. Rock Mechanics/Geomechanics Symposium,
New York City, New York
2019. American Rock Mechanics Association
1 in the last 30 days
34 since 2007
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ABSTRACT: Zubair Formation is one of the richest petroleum systems in Southern Iraq. This formation is composed mainly of sandstones interbedded with shale sequences, with minor streaks of limestone and siltstone. Borehole collapse is one of the most critical challenges that continuously appear in drilling and production operations. Problems associated with borehole collapse, such as tight hole while tripping, stuck pipe and logging tools, hole enlargement, poor log quality, and poor primary cement jobs, are the cause of the majority of the nonproductive time (NPT) in the Zubair reservoir developments. Several studies released models predicting the onset of borehole collapse and the amount of enlargement of the wellbore cross-section. However, assumptions involved in these models have limited their applications to very specific scenarios. In this study, an analytical solution for determination of the volume of collapse during drilling is presented based on changes in the geometry of boreholes. The approach can be used in conjunction with different failure criteria to estimate the collapse onset in the presence of formation strengths and principal stresses. The study highlighted how the integration of information from different sources and disciplines were able to estimate the shear failure induced on the borehole wall during drilling.
During the drilling development in the Zubair Formation, shear failure (collapse) is the main instability problems. Historically, over 90% of wellbore problems in the Zubair Formation occur due to borehole collapse . These borehole collapse problems, such as tight hole while tripping, stuck logging tools, and subsequent fishing, stuck pipe, and sidetracking are time-consuming and expensive. Many times, due to a severe stuck pipe problem and unsuccessful fishing operations, the well has to be drilled with more than one sidetrack or, in the worst case, the wellbore has to be abandoned . Another difficult scenario is when the higher operational costs that are caused by lower drilling performance or more complex operations are taken into consideration. Unfortunately, this has placed constraints on field development plans .
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