The initial charge history due to two source rocks Makhul and Kazdumi caused a special distribution of heavy components in the Greater Burgan field. There is also strong evidence that water washing, supported by the strong edge water drive, can explain the occurrence of high viscosity oil in several wells that are positioned in areas of paleo oil-water contact. The challenge was to map high viscosity oil for Burgan reservoirs for further development and planning.
Greater Burgan field is producing mainly from Burgan reservoirs and remaining oil maps are updated yearly on the basis of highest known water (HKW) contact using PNC logs. To produce from bypassed oil (oil below HKW) is a challenge especially for Lower Burgan reservoir due to presence of highly viscous oil. A study was done to identify and map high viscosity oil. MDT data including mobility and gradient was used to validate heavy oil pay flags. The next challenge was to see any movement of heavy oil on the basis of shift in the latest PNC log.
Previous works on high viscosity oil focused mainly on its occurrence within one hundred feet of original oil water contact. This work mapped high viscosity oil for all the Burgan reservoirs, and then integrated with MDT data for validation. Another new aspect was the detection of movement of high viscosity oil due to production using Sigma logs and mapping them for each reservoir.
This work has helped identify high viscosity oil within the bypassed oil zone of Lower Burgan reservoir to help in development planning for high viscosity oil. Yearly tracking of high viscosity oil expected in upcoming wells has greatly helped in advanced planning for relevant data acquisition. A program including MDT and ultra-slow pump rate for fluid sampling is planned to improve the reliability of prediction.