Schlumberger

Case Study: Efficient Saturn 3D Radial Probe Fluid Acquisition in Low-Permeability Dolomite

Increased flow rate by 650% for faster cleanup with less drawdown than extralarge-diameter probe, the Middle East

Challenge: Acquire fluid samples within 4-h time limit from multiple stations in a tight dolomitic limestone where no hydrocarbon is evident on openhole logs.

Solution: Determine fluid content using 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 for downhole fluid analysis (DFA) and sample collection.

Result: Accurately placed the oil/water contact by switching flow in the formation tester toolstring from a conventional single probe to the Saturn 3D radial probe, which increased the flow rate by 650% to obtain a representative sample within the station time limit.

Limited sample time in a dolomitic limestone

An operator in the Middle East had drilled across a carbonate formations using 76-lbm/ft3 KCl polymer and 75,000-ppm Cl water-base mud. The openhole logs did not indicate the presence of hydrocarbon, but the analysis was ambiguous because zones in a dolomitic limestone interval had resistivity values as low as 0.7 ohm.m. The operator wanted to conduct DFA and collect samples to resolve the identity of the reservoir fluids, but the time allowed at each sampling station was limited to 4 h in consideration of mud losses during the job.

Circumferential fluid flow improvement over single probes

The Saturn 3D radial probe acquires formation fluid by deploying four self-sealing elliptical ports that have the industry’s largest surface flow area, totaling more than 79 in2. Flow is quickly established and maintained 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 measurement, especially in low-mobility formations where conventional probes cannot function.

Reservoir fluid extraction at 650% higher rate than conventional probe

Schlumberger deployed an advanced wireline formation tester toolstring that included both the Saturn 3D radial probe and an extralarge-diameter conventional probe to acquire fluid at multiple stations in a single trip. A CFA composition fluid analyzer was positioned below the pumpout and the InSitu Fluid Analyzer DFA system was above the pumpout. At the top of the tool were multiple sample bottles.

After DFA at Station I clearly identified 60%–70% oil, which was supported by mud logging indications of higher methane readings at that depth, Station II was selected for determining the lowest mobile oil. The initial sampling attempt with the extralarge-diameter probe experienced a significant pressure drop, with 2,000-psi drawdown and a low flow rate of 5.2 L/h. The resulting pretest mobility was 1.5 mD/cP. After 1.5 h of pumping out, flow was switched to the Saturn 3D radial probe, and the rate increased 650% with only 680-psi drawdown. The performance of the Saturn 3D radial probe for the ratio of rate to pressure drop was a 19-times improvement over that of the extralarge-diameter probe for the 1.5-mD/cP mobility. Flowline resistivity stabilization was achieved with water identification at Station II within the 4-h limit for the well, and the water collected in the sample bottle confirmed the DFA results.


Download: Efficient Saturn 3D Radial Probe Fluid Acquisition in Low-Permeability Dolomite (0.92 MB PDF)

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Flow Rate Increased 650% from Tight Dolomite

Saturn 3D Radial Probe
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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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