reservoirs to eliminate the clogging problem and because the operator can control the drawdown pressure during testing to prevent formation collapse. Moreover, the larger volume of investigation between the two packers yields more representative test results. In the deepwater Trident Gulf of Mexico
prospect, water depths reach 9,800 ft [2,990 m] and operating conditions are harsh. Unocal Corporation used the MDT probe to measure
reservoir pressure and to take fl uid samples on two wells, Trident Well 1 and Trident Well 2. How- ever, because many of the Wilcox zones are laminated and have low permeability, it was diffi - cult to acquire representative test data and fl uid samples using the MDT probe. Unocal investi- gated the dual-packer assembly for use on the next well, Trident Well 3. To fully exploit the dual-packer capability and reduce risk of forma- tion collapse, Unocal asked Schlumberger experts
Resistivity 60-in. Resistivity 30-in. Resistivity 20-in. Resistivity 10-in.
0
Gamma Ray API
Permeability 150 0.1 mD 100 0.2
ohm-m 200 Resistivity 90-in.
Neutron Porosity
0.6 vol/vol 0
Bulk Density 1.65 g/cm3
2.65 9,500
Packer pretest drawdown
8,500 X,510 7,500
interference test
drawdown X,520 6,500 Cleaning up Sampling Vertical
Packer pretest buildup
interference test
buildup Vertical
Resistive Conductive 0
OBMI Static Image
120 240 360 Orientation North
to perform sand-failure analyses on the fi rst two wells to determine the critical drawdown pres- sures in the reservoir section prior to running the MDT dual packers in Well 3. The Wilcox G zone in Trident Well 1 was identifi ed as potentially weak, and could fail under too much drawdown during MDT testing (previous page, bottom). Sand-prediction modeling was not possible on the third well because DSI data were not acquired. Because the Unocal asset team was confi dent in the correlation between wells, the critical drawdown pressures from the first two wells were used to design MDT tests in Well 3. With the drawdown limits defined for each Wilcox zone, the MDT dual packer was posi- tioned and the pressure tests and sampling were conducted accordingly (left). During the testing,
12.5 6.25
X,530
0123456 Time, hr
X,540
X,550
X,560
< MDT testing in the Wilcox G zone. Well-log data, including borehole image data, are displayed with the MDT test and sampling con guration (left). The pressure at the dual- packer module was recorded during the MDT tool testing and sampling sequence, and shows that the total drawdown was kept below the limits that were established by sand-prediction modeling (abov e). The testing and sampling operations were successful and provided Unocal with important data to help characterize the Wilcox reservoirs for future development.
X,570
X,580
33. Betancourt S, Fujisawa G, Mullins OC, Carnegie A, Dong C, Kurkjian A, Eriksen KO, Haggag M, Jaramillo AR and Terabayashi H: “ Analyzing Hydrocarbons in the Borehole,” Oil eld Rev iew 15, no. 3 (Autumn 2003): 54– 61.
Ayan C, Hafez H, Hurst S, Kuchuk F, O’ Callaghan A, Peffer J, Pop J and Zeybek M: “ Characterizing Permeability with Formation Testers,” Oil eld Rev iew 13, no. 3 (Autumn 2001): 2– 23.
Badry R, Fincher D, Mullins O, Schroeder B and Smits T:
“ Downhole Optical Analysis of Formation Fluids,” Oil eld Rev iew 6, no. 1 (January 1994): 21– 28.
Spring 2004
25
True vertical depth, ft
Pressure at packer, psia
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