--> Improving Frame Flexibility Factor Extraction From Seismic Inversion Using Rock Physics Analysis to Characterize the Pore Type of Carbonate Reservoir Rocks of the Early Miocene Baturaja Formation, MLD Area, Northwest Java Basin

AAPG ACE 2018

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Improving Frame Flexibility Factor Extraction From Seismic Inversion Using Rock Physics Analysis to Characterize the Pore Type of Carbonate Reservoir Rocks of the Early Miocene Baturaja Formation, MLD Area, Northwest Java Basin

Abstract

The carbonate reservoir rock of the Baturaja Formation (BRF), has complex pore structure due to diagenetic alterations, which contributes to poor seismic-velocity-porosity relationship. The BRF can be divided into three members: (1)lower; (2)shale; and (3)upper unit. The shale unit is a mud-dominated interval with an intercalation of the thin bed of glauconitic sandstone. Such carbonate depositional environment mixed with a siliciclastic input presents a seemingly insurmountable challenge to seismic inversion. In this study, we introduce an integrated method of seismic inversion of clay volume and pore structure by using the frame flexibility factors (γ, γµ) in a rock physics model, called the Sun model, to distinguish the members and characterize the pore type of the BRF.

We, first, use the product of the shear frame flexibility factor with porosity (γµ*Φ) that has a good correlation with the shear velocity and impedance, to transform the seismic impedance into γµ*Φ. The proposed workflow is confirmed and constrained by the inverse relationship between γµ*Φ and shear modulus in the approximation form of the Sun model. The next step is to convert the density (ρ) and γµ*Φ volumes iteratively to obtain porosity (Φ), solid shear modulus (µs), and solid bulk modulus (Ks). These parameters are further used to extract bulk frame flexibility factor (γ) and gamma ratio (γµ/γ) through the model formulation.

The γµ and γ are used to describe the spatial distribution of the macroporosity (e.g. vuggy, inter- and intraparticle) and microporosity (e.g. intercrystalline)-dominated pore types. We observe that the low values of γ (<=~7) and γµ (<=~4) correlate with the macroporosity while the high values of γ (>~7) and γµ (>~4) correlate with the microporosity-dominated pore type. The γµ/γ proves to be a sensitive parameter to differentiate vuggy and interparticle pores. Additionally, we could distinguish the members of the BRF by utilizing the volume of clay derived from rock physic analysis and seismic inversion.

Using a quantitative thin-section image analysis, core measurement, and frame flexibility factors we could identify two pore-structure types (PST). PST-1 corresponds to the rocks that have high porosity and permeability values while PST-2 relates to the lower values. The ability to localize PST-1 from PST-2 in the inter-well region using seismic data could provide a better insight to recognize reservoir zone that has high storage capacity and production potential.