Abstract
An attribute analysis was conducted in an attempt to reduce the risks involved in developing the Austin Chalk. The objective is to identify a set of attributes that directly indicate regions of intense fracturing using short offset 3-D seismic data. After studying various attributes, it was determined that there is no direct evidence of these fracture zones, but areas that are more prone to fracturing can be deduced from lithology. "Clean chalk, or areas that lack shale interbeds, is more brittle, and therefore more prone to fracturing than shaley chalk. Clean chalk is characterized by high magnitude anomalies of amplitude and covariance. The cause of the amplitude anomalies is the increase in velocity that results from the lack of shale and ash interbeds. This increase in velocity causes an increase in the impedance contrast between the Austin Chalk and the lower velocity Eagleford Shale below. High covariance results from the homogeneity of the medium. "Good" rock alone is not enough, however. A fracturing mechanism, in this case, faulting, is needed. Faults can be determined by using travel time gradient maps, where the amount of relative offset along the fault can be inferred from the magnitude of the anomaly, Amplitude, instantaneous reflection strength, RMS amplitude, and average reflection strength were compared. Values calculated over a time window had a better correlation than their "instantaneous" counterparts due to the improved signal to noise ratio. For RMS amplitude studies, a time window equal to the duration of the center lobe of the seismic wavelet proved to be most accurate, while a time window equal to the interval between maximum troughs resulted in the best correlation for avera e reflection 9 strength. It is the author's belief that by utilizing these attributes the petroleum industry can maximize production from the Austin Chalk while reducing their risk. Application of this method will enable operators to high-grade leasing and drilling opportunities, and ultimately improve their chance for success.
Bafia, Daniel Joseph (1998). Identifying fracture zones in the Austin Chalk using seismic attributes. Master's thesis, Texas A&M University. Available electronically from
https : / /hdl .handle .net /1969 .1 /ETD -TAMU -1998 -THESIS -B34.