I have seen lot of links which say DD4T 1.31 supports SDL web 8 (Inprocess) but i am not able to figure out which provider to use as we don't have any SDL web 8 provider in DD4T 1.31.
Can i use same SDL tridion 2013 provider with SDL web 8?
SDL Web 8 in-process CD APIs are fully compatible with Tridion 2013 SP1.
So, you can just use the DD4T Provider for Tridion 2013 SP1. You only need some so-called assembly binding redirects because the assembly versions are different.
For an example of assembly binding redirects, see: https://github.com/sdl/dxa-web-application-dotnet/blob/master/Site/Web.config