Reservoir Characterization of Mid Main Carbonate (MMC)interval in Cipadati Field (North West Java Basin, Indonesia) to Support Detailed Reservoir Zonation

• Main Authors: Winardi, Sarju, Toha, Budianto, Surjono, Sugeng Sapto
• Format: Conference or Workshop Item PeerReviewed
• Language: English
• Published: 2013
• Subjects: Petroleum and Coal Geology; Sedimentology
• Online Access: https://repository.ugm.ac.id/274972/1/25-2013-Winardi-Toha-Surjono.pdf; https://repository.ugm.ac.id/274972/
• Institution: Universitas Gadjah Mada

Generally the MMC is known as a carbonate build up interval in the North West Java Basin, Indonesia, which contains hydrocarbons in some fields such as Rengasdengklok and North Cilamaya. In the Cipadati Field the MMC was drilled by the Explo#1 well and had a thickness of 79 meters. Previously the MMC was assumed to be a homogeneous carbonate reservoir, so petrophysical values gained from the Explo#1 well were used as default values along the entire interval. Further characterization of the MMC is needed to gain a deeper understanding of the heterogeneity of the reservoir including depositional stages, geometry, vertical facies changes, secondary pore types and porosity value. These parameters provided petrophysicists with the information necessary to divide the MMC reservoir into more detailed reservoir zones. The most reliable data to characterize the reservoir is core data, however core is non-continuous through the interval so image logs were used as support data in the non-cored intervals. Well calibration was done using image logs, especially in combination with core, thin sections, cuttings and other log data. Lithological texture could be observed within the image logs, so, based on Dunham limestone classification the lithofacies was identified. Seismic facies analysis, supported by well data, was also conducted to reveal the development of carbonate stages and their geometry during the formation of the MMC. The high resolution of the image log tool provided detailed observation of porosity types greater than 2.5 mm. The reservoir zonation was done based on lithofacies, pore types and porosity value. The result of characterization shows that MMC is not a continuous single homogeneous carbonate but formed in 12 depositional stages. Externally the geometry of the MMC is of a carbonate buildup (classified as a skeletal mound carbonate), but internally the geometry of each stage varies from mound to sheet drape. Overall the MMC was deposited onto the shelf platform. The MMC in this area does not represent a reef build up. Various lithofacies are found ie alternation between wackstone and packstone in lower part and some shale interruption near the top of the interval. Secondary pore types which are observed along interval are vugular (isolated vugs, interconnected vugs, channeling vugs) and fracture porosity (open fracture and partially mineral filled fracture). The result of porosity calculation shows a variation between 5 and 19 percent. Based on its characteristic the reservoir can be divided into 19 zones (11 reservoir zones and 8 nonreservoir zones). Acknowledgements The authors thank to SKK Migas and PT. Pertamina EP for their data support.