Crosswell Seismic Amplitude-Versus-Offset for Detailed Imaging of Facies and Fluid Distribution Within Carbonate Oil Reservoirs

Authors: Sean P. Trisch, Wayne D. Pennington, and Roger Turpening, Michigan Technological University, Houghton, MI.

Venue: Seismological Society of America’s annual meeting in Waikaloa, Kona, HI., April 11–13, 2007

Abstract: Imaging of the Earth’s crust is increasingly being accomplished through the use of borehole-based sensors. Experience gained in recent crosswell seismic surveys may assist endeavors to image the near-borehole environment near plate boundaries or other places of scientific interest. A high-resolution crosswell seismic data set was collected over a Silurian (Niagaran) reef in Michigan’s Lower Peninsula. The survey was optimized for both reflection imaging purposes and the gathering of a wide range of incidence angles. The reflection image was intended to aid in interpretation of the reef structure at a level of detail never before possible with seismic methods. The survey was also conducted to maximize data available for study of the dependence of amplitudes with angle-of-incidence. Prestack angle data were processed to half-degree intervals and utilized for enhanced interpretation of the seismic image through partial stacks and through amplitude variation with angle (AVA) analyses. Frequencies as high as 3,000 Hz (the limit of the source sweep) were recorded, with a predominant signal at about 2,000 Hz; the well separation was 600 m, and the target reef is at 1,400–1,525 m depth. Many of the interfaces present within the area have small reflection amplitudes at narrow angles that increase substantially near the critical angle. Analyses were performed on various interfaces in the seismic section to compare with Zoeppritz-equation solutions, using rock data acquired through an extensive library of seismic and well logging data available for the area. These models were then compared with the actual AVA character acquired at the interface and matched as closely as possible. Through this analysis and match process, various rock property estimates were inferred or refined.

Related NETL Project: The goal of the related NETL project entitled “Crosswell Seismic Amplitude-Versus-Offset for Detailed Imaging of Facies and Fluid Distribution Within Carbonate Oil Reservoirs" (DE-FC26-04NT15508) is to provide a methodology that will allow operators of oil reservoirs in carbonate reefs to better image the interior structure of those reservoirs and to identify those areas that contain the most oil remaining after initial production.

NETL Project Contacts
NETL - Purna Halder (purna.halder@netl.doe.gov or 918-699-2083)
Michigan Tech - Wayne Pennington (Wayne@mtu.edu or 906-487-2531)