Re: Splice the logs from different runs
Yes, Javacob is right. Before you splice your different runs of GR
logs, you should correct them for respective hole size (using a caliper log) and mud weight used for that hole section. This way all your GR logs will be normalized back to 8 inch hole filled with water. Most petrophysical software will have an environmental correction module for GR log to do that.
After making the environmental corrections, you can then splice you GR logs from different runs.
Even then, you may find that there are still some small shifts between the GR log from each successive run. In this case you can probably shift the GR as required and splice them together.
Watch out for the sections just below the casing shoe for each run. This is where the GR will be most affected by the washout section below the casing shoe. Usually this is also a shale section, as casing shoes are normally set in shale intervals.
Contrary to what you said, the first GR run in the hole will be most affected by the hole size and mud weight, as the top hole is always the biggest size and the formation also tends to washout more because it is usually unconsolidated.
You also need to watch out for the different types of GR tools, different contractors and different modes of recording the GR log, either on LWD or wireline. The LWD tools come in different sizes for different hole sizes, whereas wireline usually has only one size of GR tool (either 3 3/8" or 3 5/8").
Ko Ko Kyi