Solving the Inter-Well Problem: Pore Shape and Connectivity from Seismic Inversion in a Carbonate Reservoir

Guido Bracco Gartner¹, Ralf Weger², Jeremy Hendrson¹, Jarrod Dunne¹, and Wenche Asyee^1
1Shell International Exploration and Production B.V, Rijswijk, Netherlands
²University of Miami, Miami, FL

Porosity and permeability distribution in the inter-well space is always an enormous challenge in carbonate reservoirs. Pore type variation and sparse well data in particular make this task very complex. Seismic inversion provides a means to predict inter-well porosity by tracing differences in acoustic and elastic impedance, but generally scatter in porosity vs. impedance cross plots prevent an accurate prediction. In porous media, both sonic velocity and permeability are largely controlled by porosity and the pore structure within the rock. Previous studies have shown that a pore geometry factor, gk, derived from poroelasticity equations is a good quantitative indicator of pore types in carbonates. By separating porosity and pore structure contributions using a seismic inversion the link with permeability can be made.
Our case study was carried out on an isolated carbonate platform in the Luconia Basin. This Miocene platform has good quality seismic data and is penetrated by three vertical and four horizontal development wells. A probabilistic offset inversion for both porosity and gk was run on near and far seismic stacks simultaneously. The results show that it is now possible to extract the pore structure information from the impedance cube via a seismic inversion. As a quick look exercise the combination of porosity and gk can aid in finding ‘sweet spots'. Calibration with core and well test data leads to an estimate of permeability from seismic data by using an empirical relationship.

AAPG Search and Discovery Article #90072 © 2007 AAPG and AAPG European Region Conference, Athens, Greece