I often say a word that sounds like "mares-well", as a contraction of "might as well". E.g. if someone said "shall I throw away this bread" I might say "you might as well, it's totally mouldy", except I'd pronounce "might as well" as something like "mares-well" (where 'mare' is pronounced like the 'mare' in 'nightmare').
Is there a written form of this sound? If so, how do I spell it?