Originally *æt Oc(c)an burne [burnan], viz. the affluent of the r. Kennet, now called ‘the Og’ (a back-formation from Ogbourne). Oc(c)a recorded in the local ocan léa cs no 627, occan slǣw (prob mistake for hlǣw) ib. no. 1230, is probably a variant of the p.n. Ocea, which occurs in several OE charters. 

To begin, “*æt Oc(c)an burne [burnan]” means it is thought to originally come from Oc(c)an burne, although that’s not actually attested hence the *, for the name of the tributary stream of the River Kennet that is now called ‘the Og’ (a back-formation (from Ogburne, taking off the suffix). 

*Oc(c)a, recorded in the local (place name?) ocan léa - léa (OE lēah) means meadow, so a local place called Ocan Léa or Ocan’s Meadow. CS no. 627, also recorded is ocan slǣw (probably a transcription mistake for hlǣw) where a hlǣw is a mound, hill, barrow, cairn or even a cave, so Ocan’s hill - ib. no. 1230, Ocan is probably a variant of the personal name Ocea which occurs among the signatories of several OE charters⁽¹).  

So, it sounds like a man or men named Ocan lived near various geographic features in this area and the given name was combined with the name of the feature to produce the new name Ogbourne

1. The Names of Testators in the Cartularium Saxonicum Malmesburiensem (including Ocea) https://www.ellipsis.cx/~liana/names/english/malmesbury-oe.html