1. In rest of the log, LLD and LLS values are nearly same.
2. Because of coal zone, the correlation coefficient between LLD and LLS is coming to 0.54.
3. Removing coal zone, the correlation between them is coming to 0.97.
Dear sde de,
The difference between LLD and LLS indicates the presence of oil and gas. In this case, MSFL log is better to use for detecting flushed zone. However, for more authentication, density and neutron log together are best to use.
Thank you.
You do not indicate what is the difference in reading between LLS and LLD. Could you please indicate it? Is LLD higher than LLS in coal? Is LLD lower than LLS in coal? In both cases there could be a "huge difference" in reading values.
Without this piece of information, it is only possible to guess that LLD reads higher than LLS against coal, and that the well is drilled with some type of conductive water-base mud. If this is true, high LLD may indicate gas saturation in the coal seam away from the borehole, and low (normal) LLS reading may indicate saline (conductive) water substituting gas in the coal cleats near the borehole.
@Roberto Benicni Than you for your response. In my case, LLD is reading high (around 13,000) in comparison to LLS (around 6000) at the same depth. In rest portion of the well log LLS value is almost similar to LLD. So, what do you think will be the cause of such difference? No, information about gas show is available to me from industry (data taken from).
LLD reading higher than LLS indicates that resistivity away from the borehole is higher than resistivity near the borehole. On second thought, if the borehole is drilled with conductive fluid (salt water), this could be due either to fresh water invasion of the coal cleats away from the borehole (fresh water is resistive), or, alternatively, to hydrocarbons (gas) being present in the cleats of the coal away from the borehole. If the coal is at shallow depth (a few hundred meter) and if the coal crops out not far from the well, it is likely that the resistive fluid in the coal cleats is fresh water (rain water), rather than gas.
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