Integrated Crosswell Seismic Application Across a Giant Carbonate Field for High Resolution Reservoir Properties Estimation
Authors: Miranda Francesco , Dagosto Claudio , Terzuoli Silvia , Grana Dario 
Published: May 2016

Abstract
This paper describes the application of Integrated Crosswell Seismic (ICS) in a carbonate reservoir at a giant carbonate field to estimate reservoir properties, petrophysics and facies, from seismic information. Besides high resolution seismic imaging for structural information, sections of porosity, gamma ray and volume of clay distribution were estimated to determine the vertical and lateral facies changes between the selected wells.
Two different approaches were used to estimate reservoir properties section from crosswell seismic results. The first consists of a linear regression between porosity and acoustic impedance in carbonates whereas the second is a two-step statistical approach based on crosswell seismic inversion (acoustic inversion) and probabilistic petrophysical properties estimation by means of statistical rock physics model. The estimated properties section are compared with log information from the wells and show a good match. The results showed that the statistical approach for reservoir properties estimation using crosswell seismic data provides a better fit with log data at the well locations, compared to the linear approach. Crosswell seismic data is able to show vertical and lateral facies changes with a resolution of approximately 5 m.

Introduction
Statistical rock physics models for reservoir properties estimation have been presented in several recent papers with different features and approaches (Avseth 2005, Doyen 2007, Bachrach 2006, and Buland 2008). Statistical workflows in rock physics are based on deterministic relations between elastic attributes and petrophysical properties which provide a training dataset to establish probabilistic rock physics transformations. The main goal of statistical approaches is to include the uncertainty due to natural variability, heterogeneity and data errors. In our methodology we introduce more sophisticated models overcoming the common assumption of gaussianity of petrophysical properties distribution to describe the non Gaussian behavior observable in real data measurements (Grana et al. 2009).
Integrated Crosswell Seismic (ICS) is a technique that can directly image detailed reservoir features and provide high resolution information in seismically difficult areas where surface seismic is poor quality. ICS has been widely used (Antonelli et al. 2004, D'Agosto et al. 2008 and Grana et al. 2009) improve reservoir characterization along profiles up to 1km long and in field operations use wireline deployed tools. The implementation of ICS methodology requires the use of two or more wells at the same time: a receiver string is deployed in one well while a source tool is deployed in another well. In this way it is possible to obtain a high resolution seismic section and velocity section, as first deliverables, between the source and receiver well. Among the advantages of the application of this technology are:-Extremely high resolution (as much as 1m vertically) for the geology and structural imaging (i.e. 10 to 100 times better than that obtainable by surface seismic);-Measurements are directly referenced in depth and colocated with log data;-bypassing of the near surface effects (e.g. topography, weathering, gas sands, etc.); and-integration with data acquired at different scales (eg wireline logs and cores).