Abstract

This article attempts to summarize measures that are required to be adopted in order to have safe drilling practices mainly in unstable shale formation and have a smooth landing section in target reservoir below the shale. For the last three years in North Kuwait, the number of geo-steering jobs increased significantly and some encountered problems while drilling Wara shale that may end up in losing tools and eventually the hole itself. This paper focuses on information regarding problems encountered in geo-steering jobs and the best practices followed to achieve goals. Stratigraphically, Wara shale lies underlying Tuba and overlying Mauddud carbonates. It has thickness variation in between 80 to 110 feet TVD. Wara shale in North Kuwait is generally unstable and very sensitive to mud properties and creates instability of the wellbore. A wide range of drilling data from well placement jobs were documented and analyzed in order to get an idea of the behavior of shale section, how to drill safely across this layer and mitigate possible risks that may harm the well as well as the tool. Detailed scrutiny was done to compare the drilling parameters, log responses, inclination and trajectory direction between stable and unstable wells. The results were integrated with regional tectonic regime in the area. The methodology and learning curve continuously improved with assimilation of new drilling data and information. Integrated study on all aspects in drilling that involving geo-steering engineers, drilling team, geologists and field engineers on-site has enhanced the ability to understand the situation in the hole and ultimately able to provide faster decision. It was observed that there is strong relationship of building inclination, direction of the well and mud weight in some wells when crossing Wara shale. Wells that have East - West or Northwest - Southeast direction tend to be unstable when compared to wells in North - South or Northeast - Southwest direction. Low incident angle (high inclination) will mostly cause more problems in drilling than high incident angle due to longer section of exposure as well as overburden. Compressional tectonic regime of the area dictate the recommendation of well trajectory should go towards maximum horizontal stress. Recommended to cross it with low inclination and consequently approaching the target reservoir with high dogleg severity tool was to maintain the stability of the wellbore. These findings will help service provider and client to make proper planning, adopt best practice, take proper decision and thereby successfully execute well operations. Indeed saving rig and delivery time that fulfill business objectives as planned.

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