Reservoir Characterization for Elephant Oil Field in Libya

Reservoir characterization technique for Elephant oil field in Libya was applied in this study using 3D seismic data volume, well log data and production data.

3D reservoir model based on input data was established in order to compare the previous reservoir model made in 2004. Reservoir simulation was conducted for the previous reservoir model. Using the simulation results, we analyzed aquifer effect to the reservoir, water injection well effects to the reservoir, sealing faults effect to predict reserves variation.

Conclusion we obtained from the study

1) There is 649MMbbl of STOIIP difference between reservoir model 2004(2,058MMbbl) and reservoir model 2005(1,409MMbbl), since the depth of the top reservoir and the GRV(gross rock volume) of the reservoir model 2005 became lower due to the results of production well and reinterpretation of CRS seismic volume.

ㅇ When additional developing wells in the northern part and southern part of the reservoir are developed, STOIIP of the reservoir may be variable. Especially, It was strongly analyzed that STOIIP of the southern part of the reservoir could be variable becaus of the bad quality of the seismic data, low quality ot the velocity model, hardness of the time to depth conversion and ambiguity of the interpretation.

2) According to the reservoir simulation, it was also concluded that sealing fault in the El Feel reservoir could affect to the recovery. Even though when the aquifer was developed, sealing fault made a decrease of 20% of the recoverable reserves of the El Feel reservoir.

ㅇ A drop of the recoverable reserves could be overcame by the well-timed injection well. but the delayed-time injection well could influence the negative affect to the recoverable reserves. It means that the decrease of 20% of the recoverable reserves cannot retrieved by the delayed-time injection well.

ㅇ It was tried to confirm the size of the aquifer using the History matching. However, when using the production data for 15 months, the results of History matching showed the similar value. So it was considered that the sufficient production data are needed to confirm the size of the aquifer using the History Matching.

3) In the sensitivity analysis for the reservoir model 2005 pursuant of the variogram and variation of the facies, Increasing ration of the STOIIP and variogram is 6.5% and 3.9% in compliance with increase of the sandstone.