string s = "Min Pool Size=1;Max Pool Size=10;Provider=OraOLEDB.Oracle;Pooling=true;User ID=usr;Password=pwd"; Data Source=" + descriptor + ";";
Your string formation looks incorrect.
Try:
string s = "Min Pool Size=1;Max Pool Size=10;Provider=OraOLEDB.Oracle;Pooling=true;User ID=usr;Password=pwd;Data Source=" + descriptor + ";";
Make use of debugger and see your connection string is correctly formed (as anticipated).