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How to Calculate Vcarb and Vdol from well logs
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Author:  nsaeed [ Fri Nov 28, 2014 6:33 pm ]
Post subject:  How to Calculate Vcarb and Vdol from well logs
Hello All,
I am looking for method / formula to calculate volumes of Carbonate / dolomite from wireline logs. The estimated Vcarb or Vdol would be logs like Vshale log.

I know M-N crossplot would help in identifiying matrix minrals /lithology, but I need away to calculate Vcarb or Vdol.

Can any one advise on
1- how to calculate Vcarb or Vdol logs?
2- what type of logs to be used in estimating Varb or Vdol logs.

Thanks,
Nsaeed
Author:  kokokyi [ Mon Dec 01, 2014 1:25 am ]
Post subject:  Re: How to Calculate Vcarb and Vdol from well logs
You can estimate Vcalc (volume of calcite) and Vdol (volume of dolomite) using the PEF log. You need to assume that the carbonate interval does not contain any clays, other minerals, the hole is in gauge and the barite content of the mud is relatively low. The PEF for calcite is 5 around and the PEF for dolomite is around 3. In this case, following equation can be used to estimate Vcalc and Vdol.

PEF(from log) = 5*Vcalc + 3*(1-Vcalc)
Where, Vdol = 1 - Vcalc

Another way to estiamte Vcalc and Vdol is to use the Neutron/Density Crossplot and graphically solve for mineral volumes.
Author:  nsaeed [ Mon Dec 01, 2014 4:26 pm ]
Post subject:  Re: How to Calculate Vcarb and Vdol from well logs
Thank you for the info.
Cheers
Nsaeed
Author:  listmember [ Wed May 25, 2016 7:55 am ]
Post subject:  Re: How to Calculate Vcarb and Vdol from well logs
I dont want to start a new topic, question is somehow related with the subject of this one, so can limestone/dolomite volumes be calculated just with GR, RT and Sonic? Any idea how to do that? Thanks.
Author:  kokokyi [ Mon Jun 13, 2016 2:25 pm ]
Post subject:  Re: How to Calculate Vcarb and Vdol from well logs
The GR log responds to radioactivity in the formation, mainly clay minerals. Both calcite and dolomite, if they are clean and does not contain any radioactive minerals, you will have low GR readings. Therefore GR log cannot differentiate between calcite and dolomite.
The formation resistivity RT responds to formation water resistivity (or salinity), porosity and water saturation.
It does not respond to lithology. Therefore RT cannot be used to differentiate between calcite and dolomite.

The sonic log does respond to lithology, as well as formation porosity and the fluid inside the pore spaces.
If your carbonate formation does not have any porosity, in other words 100% tight carbonate, the sonic log may be used to compute the percentage composition of calcite and dolomite. The sonic log will be a proportional sum of the matrix transit times for calcite and dolomite. Even then, it is not going to be very accurate as the matrix transit times for calcite and dolomite are quite to close to each other.

Alternatively, if you know the formation porosity and transit time of the pore fluid, you can back calculate the matrix transit time using the sonic log and then derive the calcite and dolomite volumes from the formation matrix time.

Also, if your carbonate formation is 100% water bearing, you can back calculate the formation porosity from RT using an appropriate formation water resistivity. Once you get the formation porosity, you can compute the matrix transit time from the sonic log and then derive the volumes of calcite and dolomite from that.
Author:  listmember [ Sat Aug 13, 2016 2:06 pm ]
Post subject:  Re: How to Calculate Vcarb and Vdol from well logs
Very late thanks for the above answer.
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