Seismic Reservoir Characterization Across Off-Structure Deep Jurassic Carbonate Reservoir in Kra Al Maru Field, Kuwait

Seismic reservoir characterization for carbonates is a significant challenging task due to its complexity in internal pore st ructure and depositional environment. The present case study involves seismic reservoir characterization of a carbonate reservoir in the West Kuwait area using P-impedance, Vp/Vs and other properties estimated from pre-stack simultaneous inversion. The goal of pre-stack simultaneous inversion is to determine P-wave velocity, S-wave velocity, and density to forecast the lithology and type of fluid present within the rocks. The Zoepritz’s equation provides an intuitive perspective on the amplitude of reflected and transmitted waves as a function of incident angles. Accordingly, seismic reflection amplitudes can be interpreted as a correlation between P-wave and S-wave velocities, density, and incident angles. To examine amplitude variations of seismic reflections from various bed boundaries, converted angle stacks were utilized instead of gathers. Pre-stack simultaneous inversion requires amplitude-preserved full stack quality data and a collection of near, mid, and far angle limited stacks as input. A reasonable near-mid-far stacking scheme is selected based on well log data and the effectiveness of the seismic data. In recent decades, the oil industry has concentrated on improving methods to address existing characterization challenges, such as modeling carbonate reservoirs in the Marrat formation of Kuwait. Techniques like post-stack, pre-stack, and elastic seismic inversions are among those that assist in characterizing hydrocarbon reservoirs. Latimer et al. (2000) note that it is common to observe empirical correlations between P-impedance and rock characteristics, including lithology and porosity. Although the P-impedance model can provide such insights, it fails to differentiate porosities between carbonates and shales (Li et al., 2003). Nevertheless, by examining P- impedance, S-impedance, and density models collectively, we can strengthen this assertion, as the various elastic properties derived from seismic data improve the classification of different rock types (Jarvis et al., 2007). The emergence of pre-stack inversion is driven by the necessity to extract additional information from seismic results to address geological issues that post-stack inversion cannot resolve. The Vp/Vs ratio and density data obtained from pre-stack seismic inversion can clarify, for instance, the duality of porosity in carbonates versus shales, a challenge that P-impedance alone cannot address. Consequently, S-impedance and density are vital for distinguishing between reservoir and non-reservoir rocks. In this regard, density serves as a key element that integrates petrophysical data with seismic inversion methodologies. One of the challenges associated with carbonate rocks is that, unlike sandstones, these lithotypes exhibit vertical and lateral heterogeneity, presenting a complex challenge for reservoir cha racterization. Primarily of biological origin, carbonates possess intricate textures and are prone to diagenetic alterations, resulting in changes to mineralogy and pore structure that complicate the modeling of these rocks (Eberli et al., 2003).