The Application Of Poisson Impedance Inversion For Sandstone Reservoir Characterization In The Lower Talang Akar Formation, Case Study Melandong-West Java

Direzza, Angga; Andika, Komang
PERTAMINA EP, Jakarta, Indonesia.

Melandong area is located in the Tertiary North West Java Basin and has proven to be an excellent hydrocarbon field in Java. The Talang Akar Formation (TAF) is characterized as synrift to late rift continental style deposition. The lower part of the formation consist of lenticular, bar and channel-type sand bodies; they are medium grained and poorly sorted, with porosities ranging from 10 to 20 %.The sand layer has proven to be new deep gas and condensates reservoir in Melandong area due to the success hydrocarbon (HC) discovered at well JK-1 and KL-1.  

In the Lower TAF, the sandstone reservoirs cannot be clearly separated form shale by using Acoustic Impedance (AI) and Lambda-Mu-Rho (LMR) so that Poisson Impedance (PI) is applied as an alternative solution for reservoir characterization. Quakenbush, et.al (2006) proposed an idea to “extract” the PI value by performing the rotation to the crossplot of Acoustic Impedance (AI) vs. Shear Impedance (SI). Mathematically, this relation is called Poisson impedance and can be shown as PI =AI – cSI, where “c” is rotation parameter of impedances data or inverse of crossplot trending lithology and fluid (Humpson Russell). PI has a very close relationship with the “Fluid Factor” attribute where the simple idea of it is that points that lie further away from the brine wet trend are more likely to have hydrocarbons.  

The PI gives a better result of the sandstone reservoir from the non-reservoirs separation. The lower poisson impedance is in line with the presence of sandstone reservoir and HC bearing in the well, the sweet spot. In addition, the change of PI with saturation is estimated from Fluid Replacement Modeling (FRM). Combining with the petrophysical data and well test result, the FRM draw the line of optimum value of separation.  

3D seismic inversion and visualization provides good distribution and interpretation for the sweet spot. In another hand, tectonic setting and biostratigraphy data confirms the depositional environment of sandstone reservoirs. Several new prospects can be identified and convinced by deriving of its geological model.  

In conclusion, PI is very favorable tools for sweet spot identification in Melandong Area and with integrating geological, petrophysical, and well test data, the sandstone reservoir in the Lower TAF can be characterized properly.

AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012