Water sampling fails when the formation plugs

In a two-well logging campaign, the Energy & Environmental Research Center (EERC) at the University of North Dakota required water samples from a relatively permeable zone in an unconsolidated reservoir. A formation tester equipped with a conventional single probe was used in the first well; however, formation plugging that occurred after pumping for about 30 min rendered sampling impossible at all nine stations. Thorough analysis of the flowing response from the well deduced that fine mud particles were mobilized by the pumping to invade the formation and eventually plug the pore throats. The resulting significant decrease in permeability dropped the flowing pressure and the conventional probe was unable to function.

Reservoir requires a fit-for-purpose radial probe

Although the Saturn 3D radial probe's nearly 80 in2 of surface flow area makes it ideally suited for the evaluation of tight, low-permeability reservoirs where conventional probes typically fail, this industry- leading feature also improves fluid extraction in unconsolidated reservoirs that are prone to sanding. The drain assembly circumferentially seals to the wellbore to ensure pressure isolation and reduce the likelihood of a lost seal. The combination of the reliable seal and large flow area would enable the Saturn probe to employ flow rates similar to those of the conventional probe but at a much reduced flow velocity in the formation pore space.

Saturn probe successfully samples low-contamination water without causing plugging

At each of the six sampling stations in the second well, the large flow area of the Saturn probe made it possible to generate flow from the formation to clean up the samples without mobilizing the fine particles that had previously invaded the reservoir. No plugging occurred, as shown by the uniform flowing pressure, and low-contamination water samples were collected.