All fields in the Central Sumatra Basin have produced 10.65 BBO since its discovery. Most of that oil has come from high-quality Lower Miocene sands of the Sihapas Group. However, significant bypassed oil remains in lower-quality reservoirs whose recovery is typically in the range of 14%. These low quality reservoirs are estuarine shaly sands with net-to-gross of 65-75%, porosities of 18-24%, and permeabilities of 50-150 md. Completions in these sands in vertical wells yield very low fluid rates and are generally uneconomic. To facilitate the generation of strategies to economically exploit the reserves in the low permeability reservoir, a 3D geocelluar model of reservoir architecture and properties distribution was made. This model delineates distinct trends of estuarine, sand ridge, and margin facies throughout the field that reflect paleogeography. Additionally, reservoir properties and saturations were geostatistically populated within the model. The primary objective was to delineate the areas and volumes of remaining oil as guidance for developing recovery strategies. Horizontal wells were chosen as the preferred alternative to provide maximum exposure of reservoir layers and improve production and ultimate recovery compared to conventional vertical wells or fracturing jobs. Production from the horizontal well is approximately 3 times higher than vertical wells could achieve and predicted ultimate recovery has improved 15%. Worked with appropriate technology these sands provide an excellent opportunity to construct further field development strategies, monetize bypassed oil, and move reserves forward.
Author : Hendar S. M, Yuni B. Pramudyo, Komar E. Purwanto