here's a quote about oils from a medical article about IM anti-psych meds,

"A substance which acts as the vehicle for a medicine or another inert
substance necessarily incorporated into the formulation. Although
these are selected to be inactive, the patient could be allergic to them
or object to them on religious or cultural grounds (e.g. sesame oil, benzyl alcohol). Details of all excipients are available in the relevant SmPC"

http://www.cmhp.org.uk/pdfs/Injection_SOP_2011_3rd_Edition.pdf

that's the article if you wanna read about it, but it's kinda boring.

since the carrier oil is inactive in the body, it simply gets metabolized for its base components. these components are used by the body for whatever sustaining value they can find in them.

hope this helped

edit

some further info, say your carrier oil is grapeseed, this is the wikipedia link to info about grape seed oil (reliable source i know)

http://en.wikipedia.org/wiki/Grape_seed_oil

ok?
so grape seed oil is made up of these acids,

"
Acid Type Percentage
Linoleic acid ω−6 unsaturated 69.6%[10]
Oleic acid ω−9 unsaturated 15.8%
Palmitic acid
(Hexadecanoic acid) Saturated 7%
Stearic acid
(Octadecanoic acid) Saturated 4%
Alpha-linolenic acid ω−3 unsaturated 0.1%
Palmitoleic acid
(9-Hexadecenoic acid) ω−7 unsaturated less than 1"

that's what your body will break the oil down to eventually.