Aug 13 (Reuters) - Santos Ltd STO.AX :
* ASX ALERT-SANTOS GROWS COOPER BASIN NATURAL GAS WITH FOURTH RIG-STO.AX
* ANNOUNCES A FOURTH RIG, ENSIGN 965, HAS STARTED OPERATIONS IN COOPER BASIN
* FOURTH RIG MEANS SANTOS WILL NOW BE ABLE TO DRILL ALMOST 90 WELLS IN COOPER BASIN THIS YEAR
* ON TRACK TO SUPPLY ABOUT 70 PJ OF GAS INTO EAST COAST DOMESTIC MARKET IN 2018