Petrophysical Base of Reservoir Saturation Type Prediction in Interwell Space

Abstract

The integration of petrophysical and seismic data is a key technology for reservoir characterization and subsurface fluids monitoring. Rock physics as a link between seismic and logging data, it’s applied to predict reservoir parameters, such as lithologies and pore fluids, from seismically derived attributes. Fluid substitution procedure is the rock physics technique for understanding how seismic velocity and impedance depend on pore fluids. The conventional fluid substitution model (Gassmann’s model, 1951) assumes homogeneous water saturation without dividing on free and residual water shares.

On the base of petrophysical model of effective porosity we establish a new way of Gassmann’s relation application for fluid effect on elastic properties simulation. This fluid substitution model takes into account free and residual water volumes and properties separately and cement swelling as well. Developed model was applied for Western Siberia sandstones and Eastern Siberia carbonates investigations. Seismic responses on oil and gas reservoirs characteristics were modeled with presented approach. Reservoir parameters such as saturation type, residual water features, reservoir properties were studied in seismic field with AVO modeling and simultaneous inversion of synthetic seismograms. The determination of conventional and developed model accuracy characteristics is carried out with Monte-Carlo technique. The outcomes indicate that the estimated error of proposed model is in 1.3-1.5 times less than conventional one.

The results of stated work could be the petrophysical base of the technique for reservoir saturation type prediction from seismic data, which provides identification of pay-zones, reservoir saturation mapping and three-dimensional modeling in order to drill for oil and gas.

Introduction

The account of reservoir properties and saturation variation in the geological modeling is important in exploration and development of oil and gas fields. Seismic data are applied to solve this problem. Petrophysical modeling with well logging data plays an important role in assessing of the seismic inversion results informativity: the prediction of reservoirs productivity is based on the study of the saturation type influence on the elastic properties (the ability to predict the saturation from seismic data).

Simulation of the fluid substitution is the basis of the seismic data interpretation that are used to assess the reservoir saturation type: the investigation results of the relation between seismic wave velocities and type of pore fluid are used in the evaluation of saturation lateral variations on seismic velocities, acoustic impedance and other parameters. These studies are carried out in all areas, where seismic data are used while exploration, usually separately for the basic structures: the lithological complexes, and sometimes individual formations. For this reason, detailed investigations of the studied geological sections describe the main types of rocks; form the basis of modeling, which results could be applied as a reference for similar reservoir in other regions.