Process for isomerizing olefins

A process for producing a synthetic hydrocarbon drilling fluid product comprising contacting a linear alpha olefin feed, the olefins having at least 12 carbons and no more than 18 carbons, with a Group VIII metal-free, intermediate pore size molecular sieve catalyst under isomerization conditions including at a temperature between 100.degree. C. and 400.degree. C. such that the synthetic hydrocarbon product is unhydrogenated and is a mixture of branched and linear olefins with the mixture containing at least about 5 wt. % branched olefins and less than 20 wt. % alpha olefins.