Increasing Production by Identification of Drilling-Mud-Influenced "Low Contrast" Pay at Sangatta Field, Kutei Basin, Indonesia

S. R. Agustinus, B. N. Susanto, Senodji, Ricky Adi Wibowo, and Parada D. Silitonga
PT Pertamina EP, Jakarta, Indonesia

Salted muds are commonly utilized during drilling operations for many reasons, primarily to maintain borehole stability while drilling as a clay expansion inhibitor. However, the impact of these salts effect on the log readings are rarely noted, particularly with regard to the past drilling operation. This practice had obviously diminished some potential pay zones leading to bypassed reserves.

The Sangatta field, which is a medium sized oil field located in the prolific Kutei Basin, onshore East Kalimantan. It was discovered in 1938 prior to the Second World War. During the field development period of 1980-1990, it was also subjected to the utilization the KCl polymer that initially intended as clay swelling retarder. Some of these wells drilled in this period after quick look formation evaluation were exhibited low contrast resistivity regardless their structural position and deemed as non prospective, then they were subsequently abandoned without testing.

Recently, some new though are introduced to counter inconsistencies between well appearance to the geological model as well as seismic attributes. It drives the ideas to re-complete and re-open the suspected anomalous zones and even to re-drill. One of the well that being re-evaluated was the ST-114 that is located on a structural high but was deemed wet. This well was subsequently being twinned as ST-144 that revealed the low contrast zone potential as exhibited by production test that successfully delivered almost 1,000 BOPD having only traces of water. Extending this success, several workover candidates were also exhibited consistent result, thus becoming focus area for further field development.