10-in. Array Resistivity
0.2 0.2 0.2 0.2 Caliper 6 in. 16
Depth ft
X,000 0.2 0.2 ohm.m
20-in. Array ohm.m
30-in. Array ohm.m
60-in. Array ohm.m
90-in. Array ohm.m RXO
ohm.m 2,000 2,000 2,000 2,000 Shell No. 1 2,000 2,000 1
T1 Cutoff ms
9,000 1
T1 Cutoff ms
9,000 1
T1 Cutoff ms
9,000
T1 Distributions Shell No. 4
Shell No. 8
Porosity, Shell No. 1 Bound Water
40 % 0 Bound Water 40
Porosity, Shell No. 4 %
0 40 Bound Water
Porosity, Shell No. 8 %
0 700 Water
Pressure psig
900
Heavy Oil Oil
Free Water Magnetic Resonance 4D Fluid Analysis
Heavy Oil Oil
Free Water
Heavy Oil Oil
Free Water
Coal Clay
Clay Water Quartz
Moved Oil Oil
X,050
X,100
X,150
X,200
Shell No. 1
Shell No. 4 Depth X,040
Shell No. 8
Shell No. 1
Shell No. 4 Depth X,155
Shell No. 8
Oil Water
100 ms
Oil Water
100 ms
T1
, ms
T1
, ms
T1
, ms
T1
, ms
T1
, ms
T1
, ms
> The big picture in heavy oil. The D-T1 maps from X,155 ft show bound-fluid and heavy-oil signals in the Shell No. 1 plot (bottom right). The free-water signal above 100 ms decreases progressively from shallow to deeper DOIs. The fluid analysis (top, Tracks 5 through 7) shows a steady decrease in free water from Shell No. 1 to Shell No. 8. The interpretation is that the source of the water signal is the mud filtrate, which displaced heavy but movable oil in the reservoir; the water signal would remain constant if filtrate were displacing formation water. For the zone from X,020 to X,050 ft, the interpretation is more difficult. The resistivity is lower (Track 1), and there is a water signal at each DOI. D-T1 maps from X,040 ft (bottom left) provide fluid information. Because the water signal from filtrate invasion is present in Shells No. 1 and No. 4 but disappears in Shell No. 8, the interpretation is that filtrate displaced heavy oil that cannot be measured by the NMR tool. The strong water signal present in all three shells is from irreducible water, so the zone should produce water-free oil.
valid for borehole-rugosity and thick-mudcake effects, but heavy oil impacts the NMR measurements even when the borehole is in good condition.
Because heavy oils have short relaxation times and rapidly decaying signals, NMR tools invariably fail to measure all the heavy oil. This is true even with the shortest echo spacings currently available from downhole tools. Sequences with longer echo spacings miss even more of the heavy oil. The MR Scanner tool’s deeper shell measurements have longer echo spacings than those of the shallower shells. Consequently, the volume of heavy oil that is measured by the tool decreases with DOI. The oil volumes will always be underestimated in these heavy-oil environments.
Winter 2008/2009
Despite this shortcoming, the effects of heavy oil on the measurement can still be used to understand the formation fluids. The measured NMR porosity decreases with DOI as a result of the missing heavy-oil signal. The measured volume of immovable bound water will not change with DOI. Invading filtrate will displace only movable water or movable hydrocarbon. Thus, the 4D inversion can be used in a manner similar to that used with hole rugosity, but the interpretation focus will be on the changes in free fluid and total porosity rather than borehole effects.
The 4D processing provides a marked improvement over that of conventional 3D inversion. The first 30 ms of the inversion are
constrained to be common across all three shells because it is assumed that bound fluid and the heavy-oil signals are stable in this time range at each DOI. This is in contrast to the processing used when borehole rugosity or whole-mud invasion is a problem; here, only the first 10 ms are constrained. Well data show the free-water signal above 100 ms decreasing progressively from shallow to deeper shells (above). This leads to an interpretation that the source of the free-water
15. Heaton N, Bachman HN, Cao Minh C, Decoster E, LaVigne J, White J and Carmona R: “4D NMR— Applications of the Radial Dimension in Magnetic Resonance Logging,” Transactions of the SPWLA 48th Annual Logging Symposium, Austin, Texas, June 3–5, 2007, paper P.
17
Amplitude
Diffusion
Amplitude
Diffusion
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