Uncertainty Analysis Turns Failed Infill Well into an Economic Success

Abstract The M oil field is located offshore within the Malacca Strait PSC, Indonesia. Reservoirs are sandstones in the Lower Sihapas (LS) Formation. They have strong water drive, are under-saturated, low viscosity/high API oil, low GOR and high dip angle. Oil production started in 1986. Current oil rates are 0.6 Mbopd from ten wells with commingled completions. The current recovery factor is over 50%. Major challenges to further develop this field are high water cuts, and old surface facilities. In December 2010, the M-10 well was drilled as an attic well. Unfortunately, the oil rate was far below than forecasted, as the six target sands were 42–53 ft deep to prognosis, and oil has already been swept to the offset wells. Only the A sand, and an untargeted Upper Sihapas Formation sand contained clear indications of oil. However, reservoir deliverability from the sands was low due to depleted reservoir pressure and low permeability. In 2012, reservoir modeling using a geostatistical approach created 21 realizations to cover uncertainty in facies distribution, porosity, permeability and oil-water contact. We adopted three models to represent the P10, P50 and P90 cases. The three models are history-matched based on analysis of probability of OOIP distribution. These models and C//O log as additional data consistently indicated that the B and E sands in M-10 should have good amount of remaining oil, despite the negative indications from gas shows and logs. Nodal analysis showed no cross flow would occur if we commingled these sands with the existing perforation. Based on these studies, we performed a simple workover operation. After perforation, the oil rate increased to 280 BOPD and settled down to 200 BOPD. A combination of reservoir simulation, uncertainty analysis, C/O log and nodal analysis turned the M-10 well from zero to hero. Introduction The M field was discovered in 1981 and first oil flowed in 1986 from the Sihapas Formation. The reservoirs produce 42° API oil with low GOR. All wells produce commingled from multiple sands with Electric Submersible Pumps (ESP). The reservoir has strong water drive mechanism combined with gravity drainage that make reservoir have high recovery. Currently, over 50% of oil in place has been produced.