Saturation Log Evaluation Contribution For Workover Success Ratio In Bunyu Field

Abstract

Bunyu Field is one of the mature fields that contribute most of the production in PT. Pertamina EP has a deltaic characteristic with bounded geometry distribution and high lateral heterogeneity reservoir quality. This condition gives the challenge for this field to maintain and increase the oil production because of the very high production decline rate that reaches out 70%
One of the strategies that used is to use saturation log for additional tool and method to evaluate formation, especially in a depleted reservoir. However, in a deltaic depositional environment, there is another challenge to the using saturation log in for improving workover success ratios, such as minimum applicable net sand and porosity. Furthermore, carbon content in the shale formation, good bonding cement, and open hole condition can affect the saturation log reading.
In January to May 2018, the workover result give unexpected result. The success ratio between initial target oil production to actual workover result using saturation log is 58% and without using it is 78%. After further discussion and analysis, there is some cause that gives this low result. The main cause that affects the saturation log readings is the quality of the formation such as porosity that below 15% and net sand with the carbon content in shale formation will give higher oil saturation than it should be. The other cause that effect of failed workover and misreading on the saturation log are the poor quality bonding cement, poor open hole condition, highly viscous fluid properties and unconsolidated sand formation. At the conclusion, the saturation log contribution in Bunyu Field workover success ratio is applicable with error 23 % for a formation that has net porous sand above 2.65 m, porosity above 19%, low viscosity fluid properties and consolidated sand formation also with good cement bonding and good open hole log condition