ABSTRACT

Initial exploration in this area was Rose Run sandstone targets identified by seismic amplitude anomalies. Exploration targets quickly changed to zones within the Beekmantown dolomite after initial drilling penetrated thick, sometimes productive, Beekmantown, and Rose Run intervals that were brine saturated. A cross section through the area shows Beekmantown and Rose Run remnants (outliers) near the Rose Run sandstone subcrop position.

Seismic reflection data are commonly used to find erosional Beekmantown and Rose Run outliers. To be commercial, however, target intervals within the outliers must have good porosity. Acquiring seismic data that can be used to predict the thickness and porosity development of the dolomites is difficult. Shallow, glacially-filled valleys overlying targets cause static problems that reduce the fre- quency content of seismic data and increase random noise.

A variety of shooting parameters and processing have been used to compensate for signal degradation each with differing results. Extensive seismic modelling also has been employed in an effort to identify criteria to better predict Beekmantown porosity. The modelling process begins with a detailed geologic cross section constructed from known and expected stratigraphy. The model has a range of Beekmantown thickness that is typical of the area. Two models were constructed, a tight Beekmantown model and a porous Beekmantown model. One porosity zone was specified in the Beekmantown.

The seismic models were generated with wavelets representing normal and enhanced processing sequences. It is apparent at normal frequencies that accurate Beekmantown thickness cannot be determined. With higher frequencies, that have been recovered by enhanced processing, it becomes possible to determine Beekmantown thickness. It is also at these frequencies that it might be possible to determine porosity.

Two seismic lines are shown with Beekmantown anomalies. These anomalies are compared to the models.

Recommendations for seismic parameters to acquire high enough frequencies for Beekmantown exploration include; current 24 bit systems, 20 to 30 foot holes with 2 to 3 lb., of dynamite, 1 msec sample rate, 30 fold recording and notch out.