Case Study: Saturn Probe Delineates Contact in 12 1/4-in Wellbore in Low-Permeability Presalt Carbonate

Real-time identification of oil/water contact by obtaining low-contamination samples from 0.03- and 0.06-mD/cP mobilities, deepwater Brazil

Challenge: Accurately define the oil/water contact in a low-permeability zone of a 12 1/4-in deepwater well where conventional probe types returned only tight tests and the expected longer station times would increase operational risk.

Solution: Deploy the 9-in version of the Saturn 3D radial probe with the industry’s largest flow area of its circumferential drain assembly for readily inducing and sustaining flow in large-diameter wells to measure pressure and sample fluid.

Result: Efficiently established the contact with real-time downhole fluid analysis (DFA) of low-contamination water samples acquired at stations with estimated mobilities of 0.03 and 0.06 mD/cP in only 3.5 and 6.5 h, respectively, to save rig time and reduce risk.

Testing a low-permeability carbonate reservoir in a large-diameter well

An operator needed to accurately define the oil/water contact in a low-permeability zone of a presalt carbonate reservoir offshore Brazil. There were already concerns because of the expected low mobility that conventional probe types would not be able to make pressure measurements and obtain fluid samples in the water zone. Low mobility also implied that excessively long pumping times—with higher attendant operational risk—would be required to obtain representative pressure measurements and extract fluid with sufficiently low contamination in the 12 1/4-in-diameter deepwater well. The operator needed a more efficient approach that would reduce both operational risk and rig time for measuring pressure and acquiring representative fluid samples.

Flowing fluid circumferentially with the 9-in radial probe

The new 9-in version of the Saturn 3D radial probe can effectively extract fluid even in large-diameter wellbores and from low-permeability, low-mobility formations. The four self-sealing elliptical ports of the Saturn probe have the industry’s largest surface flow area of 79.44 in2 to quickly establish and maintain 3D flow. Flowing fluid circumferentially instead funneling it to the single point of a conventional probe greatly reduces the time necessary for cleaning up fluid samples and performing pressure measurements. The design of the Saturn probe also minimizes the effects of storage volume on testing.

Efficiently sampling low-contamination fluid

The 9-in Saturn probe was deployed with the MDT modular formation dynamics tester for conducting DFA on the extracted reservoir fluid from the water zone. Although a conventional probe had previously failed to define the pressure gradient in the transition and water zones, conducting only tight tests, the 9-in Saturn probe reliably sealed in the 12¼-in borehole to make multiple valid pressure measurements in the low-permeability carbonate reservoir.

Low-contamination water samples were acquired by the 9-in Saturn probe at two stations with estimated mobilities of 0.03 mD/cP and 0.06 mD/cP in only 3.5 and 6.5 h, respectively. DFA confirmed the purity of the flowed fluid. The real-time pressure and fluid data acquired with the 9-in Saturn probe efficiently achieved the test objectives while reducing operational time and the attendant risk.

Download: Saturn Probe Delineates Contact in 12 1/4-in Wellbore in Low-Permeability Presalt Carbonate (0.87 MB PDF)

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Real-Time Downhole Fluid Analysis of Low-Contamination Water Samples

Log shows the Saturn probe obtained low-contamination samples to confirm presence of water. Log confirms clean up of fluid samples.Borehole image log shows the Saturn's probe coverage.
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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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