Extended reach wells are drilled to access large areas of reservoir from a relatively small surface footprint. As a secondary zone becomes a target, other zones in the openhole drilled section may have already been subject to pressure depletion. These two challenges significantly increase the risk of conducting comprehensive formation evaluation.

Logging-While-Drilling (LWD) technologies have evolved over the last 25 years to provide much of the required formation evaluation data. In situations where conveying wireline tools would be difficult, LWD tools are incorporated into the drillstring and provide formation evaluation data. They also have much higher ratings for tension and compression and, coupled with the ability to rotate, reduce the risk of differential sticking. A key LWD technology developed recently is formation sampling while drilling (FSWD). FSWD is an evolution of formation-pressure-while-drilling (FPWD) tools that, in addition to making formation pressure measurements, can also capture and analyze samples of downhole fluid in the same manner as current wireline formation testers.

This paper recounts an FSWD operation conducted offshore Malaysia. The primary sampling objective was to collect representative in-situ samples of gas and water, which were not previously captured in this reservoir. Of key importance was the quality of the water samples in order to accurately measure salinity, refine water saturation calculations, and provide assays for corrosion considerations related to completion design and production planning.

Previously, a time-consuming operation—using a wireline formation tester conveyed on drillpipe—would have been the only way to capture quality downhole samples, but a major concern was differential sticking, caused by a highly deviated wellbore, that would potentially intersect depleted zones. As an alternative, the FSWD tool was deployed to measure formation pressures (used to infer large-scale reservoir connectivity) and to collect gas and water samples, all in a single drilling run.

Results demonstrated that in high-risk wellbores, FSWD tools could capture high-quality downhole fluid samples. Also, the real-time data transmitted using mud pulse telemetry was sufficient to identify fluid type during the pumpout, and tool controllability enabled fluid sampling in single-phase condition. Using FWSD tools eliminated unproductive time associated with a dedicated drillpipe conveyed wireline run, along with the associated additional openhole exposure time that could have jeopardized the success of the completion. The samples acquired with the FSWD tool were of a quality high enough that the operator was able to cancel wireline sampling operations planned for two additional wells, further saving time and reducing risk.