Gregg Hofland

Twin Morrow Field: A case study

Upper Morrow sandstones in the Texas panhandle are often laterally discontinuous and small. Exploration and development of these sandstones can be precarious due to the rapid change from reservoir quality sandstone to shale. Successful incorporation of seismic data into reservoir delineation and characterization of the Upper Morrow sandstones could increase the success ratio and thereby enhance the economic feasibility of this type of exploration and development venture. Therefore, in 1989, Unocal shot a high resolution vibroseis line across Twin Morrow Field to analyze the seismic response of the productive Upper Morrow Sandstone, locally known as the Buckhaults Sandstone. The producing reservoir is an interpreted point bar deposit, three miles long and one mile wide with a maximum thickness of 55 ft. A reflector which is correlatable to the Buckhaults is present on the high resolution seismic data, but this sandstone is too thin for thickness resolution with current seismic methods.

3D Forward Ray Trace Seismic Modeling of Strike Lines In Complex Geology

Seismic data quality is notoriously poor in the southern sub-Andean belt of Bolivia. Rarely, if ever, does a seismic line unequivocally demonstrate critical closure. We believe that the best way to make a valid interpretation in such complex areas is by creating a depth model based on all surface geologic data and the seismic interpretation. This model is then refined as forward ray tracing alters the seismic interpretation and/or velocity field.

Building 3D velocity models fast and efficiently using a phased approach

Building an accurate velocity model can be a very time consuming step in the quest for an optimum depth migrated image. Various constraints, such as time and expense, force compromises in the quality of the velocity model and the subsequent depth image. This paper suggests using a phased approach to velocity model building, which employs fast simple techniques in areas of relatively simple geology, and more robust modeling techniques where the geology is more complicated. The accuracy of the model is constantly validated to ensure that the current model building technique is not introducing an unacceptable amount of error.

Seismic interpretation of meander channel point-bar deposits using realistic seismic modeling techniques

The study presented here revolves around a 3-D seismic model constructed using a segment of the Laramie River (T17 & 18N, R74W, Wyoming) as our template. The primary purpose of the Laramie River model was to analyze the seismic response of high‐velocity sand point‐bar deposits encased in lower velocity shales, to uncover interpretation pitfalls in 2-D data, and to reveal any advantages of 3-D seismic data and offset VSPs. The model’s secondary purpose was to illustrate that, under certain circumstances, sandstone point‐bar deposits can be detected and exploited with a variety of seismic tools. Modeling was divided into three types: 2-D, 3-D, and offset VSP.

Seismic Cross-borehole Imaging of the Near Surface Using Tomography And Prestack Migration In Elastic Physical Models

The problem of using seismic cross-borehole measurements to image the subsurface is an important one. There are applications to the analysis of abandoned mine workings, mapping of petroleum reservoirs and other valuable mineral deposits, delineation of fracture zones relevant to hazardous waste disposal, and military applications related to the detection of hostile tunnels. Raw cross-borehole data are complex. Energy is reflected and scattered in all directions. All possible reflected modes are usually present. Scattered events reach the seismic detectors from all directions. For these and other reasons, original, or “raw”, cross-borehole data are difficult to interpret. By using prestack migration, and/or cross-medium tomography, these raw data can be converted into images of the subsurface that indicate the location, size, and approximate shape of seismic reflectors. These images can often be interpreted geologically, and these can lead to an accurate geologic cross-section of the earth near the boreholes. Physical elastic models are useful to study crossborehole imaging. They yield very realistic 2and 3component data containing all reflection modes, dispersion, amplitude loss due to spreading and attenuation, and both random and coherent noise. Arbitrary reflecting boundary shapes are easily accommodated. Our results suggest that good quality subsurface images can be obtained with cross-borehole data using both migration and/or cross-medium tomography.