Sludge collected after de-mucking in cargo tank and disposed in sludge bags to Reception Facility. Is it entered in ORB or Garbage Record book ?

The first point that we need to clarify is "if this disposal would come under annex V or Annex I?

If it had to come under Annex V, there is only one category that the cargo sludge can fall into. That category is "Cargo Residues".

Let us see how Annex V defines cargo residues?

Cargo residues means the remnants of any cargo which are not covered by other Annexes to the present Convention and which remain on the deck or in holds following loading or unloading, including loading and unloading excess or spillage, whether in wet or dry condition or entrained in wash water but does not include cargo dust remaining on the deck after sweeping or dust on the external surfaces of the ship

So, the definition of cargo residues as per Annex V clearly says that only remains of cargo that does not fall under any other annex of Marpol would be covered under Annex V.

As the oil Sludge from the cargo tanks of an oil tanker falls under Annex I of the Marpol, this would definitely not fall under the definition of cargo residues as per Annex V.

So oil cargo sludge disposal needs to be entered in Oil record book and not garbage record book.

Cargo residues as per Annex V is considered to be generated on dry bulk carriers and occasionally on general cargo carriers when they transport dry cargoes in bulk. 

Now that we know that this cargo sludge disposal entry needs to be in cargo record book, it is important that the entry itself is made correctly

The entry needs to be made under heading J of the cargo record book. The entry could look something like this.