Reservoir Distribution Identification Using Integrated Acoustic Impedance Modeling and Seismic Facies Analyses

By

 Ngakan Alit Ascaria¹, Rusalida Raguwanti¹, Yosi Hirosiadi¹, Saptawati Iriani¹

(1) Pertamina Upstream, Jakarta, Indonesia

 Kamundan block is Pertamina own operation area located to the north of Wiriagar Deep and proved the presence of gas bearing in Paleocene turbidite sequence. Seismic acquisition and drilling have proved the economic significance of these discoveries containing about 9 TCF of dry gas. As a frontier area in which data is limited, an integrated modelling acoustic impedance and seismic facies are aplied to identify reservoir distribution in paleocene turbidite laterally.

Regionally the prospect located in low area whereas the two wells as references Tarof-2 and Ayot-2 lies in high domain. Data obtained from Well corellation only an age of the lithology without knowing their distribution in low area.

The method used to overcome this problem are modelling acoustic impedance and seismic facies analyses. Sparse spike inversion is done using 2D seismic data tie in with Wiriagar Deep-1 well. This well is chosen due to its position and has a complete sequence from Mezosoic through Cenozoic. Facies analyses is done by determining a sequence characteristic in which present from seismic section and used to control the interpretation of Acoustic Impedance data.

Seismic facies analyses carried out in this domain shows two type of sequence i.e. mounded interpreted as fan system and sigmoid in which indicate a channel fill. Acoustic impedance data shows a low impedance value, equivalent with high porosity, in mounded and sigmoid types in which represent a sandstone distribution in fan and channel systems. In Wiriagar deep this sequence is interpreted as basin floor fan from turbidite system and proven as a good reservoir for hydrocarbon. The same exploration play concept identified in Kamundan Block although the reservoir is not as thick as in Wiriagar area. Integrating this two method are found useful in terms of enhance the resolution and confident level to generate new prospect for exploration campaign.