Case Study: Saturn 3D Radial Probe Delineates Low-Mobility Oil Zone in Carbonates

Light oil with 0.04-mD/cP mobility identified by DFA where low-resistivity logs are inconclusive, the Middle East

Challenge: Sample multiple stations to delineate oil and water zones in a tight carbonate interval where low-resistivity logs are inconclusive.

Solution: Deploy the Saturn 3D radial probe with its large surface flow area of multiple elliptical ports and high differential pressure capability to establish circumferential flow and acquire representative fluid from low-mobility formations for downhole fluid analysis (DFA).

Result: Confidently established the thickness and contents of the oil zone after extensive pumping collected mobile light oil at a depth that had been considered water-wet because it has a low-resistivity response similar to that of the water zone.

Tight carbonate reservoir with ambiguous low-resistivity response

The extent of the oil zone in a tight carbonate reservoir in the Middle East was not clear. Openhole logs strongly indicated that the top of the formation was oil bearing and the bottom was water-wet,but the fluid contents of the middle zone were ambiguous. The middle zone had a lower resistivity response that was similar to that in the underlying water zone. The location of the oil/water contact could not be determined from the logs alone, and conventional formation tester probes would not be able to acquire fluid samples from the tight formation.

Circumferential fluid flow in very low permeability

The Saturn 3D radial probe creates true 3D circumferential flow around the borehole even in very low-permeability formations. The four self-sealing elliptical ports have the industry’s largest surface flow area, totaling more than 79 in2, to quickly establish and maintain flow from the entire circumference of the wellbore instead of funneling fluid from the reservoir to a single access point. The Saturn design also minimizes storage volume effects. The result is quicker cleanup times and the efficient performance of pressure measurements, especially in low-mobility formations where conventional probes cannot function.

Oil sampled at 0.04-mD/cP mobility

Samples were successfully collected in the top, middle, and bottom of the carbonate reservoir. Openhole logs indicated that the top of the formation is oil bearing, and extensive pumpout by the Saturn 3D radial probe confirmed light oil through DFA. A radial flow regime was established with an estimated horizontal permeability of approximately 1 mD. The station at the bottom of the reservoir yielded water and had a similar permeability. DFA then identified mobile light oil in the middle of the reservoir, and the operator was able to determine the thickness of the oil zone with confidence. Pumpout for the middle station was achieved with a 4,900-psi pressure differential for 15 h, resulting in a mobility determination of 0.04 mD/cP.

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Oil Flowed from 0.04-mD/cP Carbonate Reservoir

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Fluid Flow and Pressure Data Where Not Previously Possible

Saturn 3D Radial Probe
The self-sealing Saturn 3D radial probe flows fluid circumferentially from the reservoir to extend formation testing to low permeabilities, heavy oil, unconsolidated reservoirs, near-critical fluids, and rugose boreholes.
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