Roger M. Turpening

Attenuation Coefficient Tomogram And Q Distribution Image From Crosswell Survey In the Northern Reef Trend of Michigan Basin.

Many studies concerning seismic attenuation and the resultant Quality Factor (Q), which may be calculated from it, reveal its value in reservoir descriptions. Attenuation is an important measurement for our understanding of rock properties and has been used to quantify such characteristics as: Porosity, permeability, viscosity, saturation and rock composition. Attenuation and the resulting Quality Factor have played a key role in assisting in the targeted drilling of high porosity and naturally fractured streaks within reservoirs, intelligent completions programs, reservoir optimization, and accurate calculations of reserves.

Crosswell seismic imaging of acoustic and shear impedance in a Michigan reef

Acoustic and shear impedance images, obtained from deterministic simultaneous inversion of a high-resolution crosswell seismic survey, were used to obtain the internal structure of Niagaran reef in Michigan. The crosswell seismic survey was conducted using two monitor wells external to the reef. These wells had depths that extended beyond the depth of the reef, and imaging used reflections from above and beneath the reef, resulting in the best seismic images of any Niagaran pinnacle reef obtained to date. The top of the reservoir can be clearly distinguished, as well as its lateral extent or dipping edges. Reflection events internal to the reef are evident; some are fairly continuous across the reef and others are discontinuous.

Crosswell Seismic Imaging And Inversion of a Michigan Reef From Above And From Beneath

A high-resolution crosswell seismic survey was conducted using two monitor wells located external to a Silurian (Niagaran) reef, at Springdale field in northern Michigan. These wells extended to much greater depths than the reef, and imaging was conducted both from above and from beneath the reef. The resulting seismic images provide the best views of any Niagaran pinnacle reef obtained to date. The tops of the reservoir can be clearly distinguished, and its lateral extent or dipping edges can be observed along the profile. Reflection events internal to the reef are evident; some of them are fairly continuous across the reef and others are discontinuous. Inversion of the seismic data indicates which events represent zones of higher porosity and which are lower porosity or anhydrite-plugged. The full stacked images include angles that are beyond critical for many of the interfaces, and some reflections are visible only for a small range of angles, presumably near their critical angle. Strong apparent attenuation of signals occurs when seismic ray paths pass through the upper part of the Springdale reservoir; this may be due to intrinsic attenuation and/or scattering of events due to the locally strongly varying gas saturation and extremely low fluid pressures. The seismic images obtained, and interpretations of them, as assisted by inversion, provide additional insight into the internal geometry of this reef and provide data that should be useful for reservoir management.

Crosswell Seismic Amplitude-Versus-Angle Studies At a Niagaran Reef

SUMMARY 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. With this we can do a highly detailed interpretation using the post stack migrated data, and utilizing the prestack data for AVA (amplitude variation with angle) analyses. With the wide range of incidence angles and by comparing AVA observations with model predictions we can better determine and map the various litho-facies and fluid distributions within a carbonate reef oil reservoir. In addition to the extremely high resolution of the crosswell images, reflections are obtained from boundaries that have near-zero reflectivity at small angles of incidence because of the large reflectivity that occurs near the critical angle. This has implications in allowing operators of carbonate reef oil reservoirs to better image the interior structure of the reservoirs and to identify those areas that may still contain amounts of oil after initial production.