Abstract

Development, delineation and appraisal wells drilled in high pressured, naturally fractured Jurassic reservoirs of West Kuwait are exposed to the risk of "well kicks" and "mud-losses". The risk becomes greater due to differential reservoir pressures, presence of naturally open fractures, and narrow pressure window between formation- and fracture-pressures. In many instances, "alternate loss & gain scenario" ensues and the well control options become limited, occasionally, further drilling becomes impossible leading to temporary suspension or even termination of the wells. This causes safety issues and large loss of rig time and money.

On the other hand, lack of high formation pressure and absence of open natural fractures can lead to unproductive wells. Therefore, characterization of natural fractures is needed not only for productivity of the well, but also to ensure successful drillability of the well. Conventional fracture characterization using geophysical methods lacks resolution, while petrophysical methods often fail to conclusively identify open fractures in in-situ sub-surface conditions. Other well testing methods such as wire-line formation testing and open-hole drill stem testing are also cumbersome and risky and often not usable in tight fractured reservoirs. In this context, the micro-mud loss detection technique becomes indispensable for both mud loss and kick detection as well as for the natural fracture characterization.

Mud losses data appear to be the only way to detect and characterize the conductive fractures in these reservoirs. In fact, the cores show that almost all the natural fractures are cemented and only a few partially open fractures can be seen. When coring operations are not fully successful, it is difficult to assess if poor recovery was due to the presence of open fractures or to other causes. Furthermore, it is impossible to use image logs in order to individuate potentially producing intervals, as they cannot discriminate between open and closed fractures.

Advance mud flowmeter ensures safe drilling by early detection of minor well kicks and mud-losses occurring in subsurface. It remains the only source of Real-Time information on the presence of open fractures while drilling. The sensor was run during drilling of A-A(close to a major fault zone) to obtain Real-Time identification of open fractures & early Kick / Loss detection for safe drilling. This was the first time in West Kuwait Jurassic Team that accurate fracture & early Kick/Loss detection via advanced flowmeter was performed in oil base mud.

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