Publications

The Lower Sihapas Formation in the M-Field consists of sandstones with subordinate inter-beds of mudstones, shale and coals. The C sand within the Lower Sihapas Formation is Darcy-permeability blocky sand. In 1987, the top of the C sand was perforated in the M2-03 well to drain oil from the entire sand. After 24 years of production, when the oil rate was 16 BOPD and the water cut was 98%, we ran a through-tubing C/O log to look for bypassed oil. To our surprise, the C/O log suggested that the C sand had-passed oil below the perforations. Other sources of data supported this idea such as production log data that showed the perforated zone sand productivity was lower than expected, suggesting the perforations did not connect to the entire sand and image scanner logs from offset wells suggested that the C sand was laminated, not blocky as regular wireline logs suggested. Our confidence grew that the thin shale below the existing perforation was sealing, and that the attractive water saturation in the lower sand of 40% from the C/O log might be real. So, we perforated the lower C sand using a through-tubing gun. After perforation, the oil rate spiked at 2000 BOPD and then settled down to 100 BOPD within 12 weeks. The cost for the C/O log and perforation was recovered within days. The through-tubing perforation was $250,000 cheaper than a “stronger” casing gun perforation via a workover. Productions logs and C/O logs continue to add value in these mature high water-cut oil wells, by identifying which sands are watered out and which sands contain by-passed oil. They have enabled us to slow * EMP Malacca Strait production decline, avoid workovers and extend the economic life of our platforms. Keywords: mature oil field, C/O log, by-passed oil, production optimization