11a. A number such as 11, 555 or 8888: r?p?n?t
12a. A grass-green silicate mineral: o?s?a?i?e
27d. Pertaining to the very dep regions of an ocean: b?n?h?l
Thank you all. I think the setter has something wrong though; according to Google a repunit is a number consisting only of 1s, eg 11, 111 etc.
Also I think benthic is better than benthal, but the across clue is definitely right, (Beverley HiLls) so it must be benthal.