Online Journal for E&P Geoscientists

Alhammadi, Miaad K.^*1; Vega, Sandra ¹; Jouini, Mohamed S.¹; Mokhtar, El Amin ¹
(1) Petroleum Institute, Abu Dhabi, United Arab Emirates.

Although seismic frequency is used variously as an attribute for seismic interpretation, or as an indicator of attenuation, fractures and stratigraphy; its correlation with rock properties and rock types is still not clear. This paper presents a study of the correlation between frequency response, rock properties and rock types, in four wells from a carbonate oil reservoir in the Middle East. In order to accomplish this, we used a total of 96 core plug samples; 38 from well 1, 17 from well 2, 20 from well 3, and 21 from well 4. Dunham’s rock classification and petrophysical laboratory measurements of porosity, permeability, and acoustic velocity (P- and S-waves) were previously provided.

We did a comprehensive spectral analysis of acoustic measurements using in-house codes. First, the high resolved full P- and S-wave forms were chosen for each sample. Second, Fast Fourier transform was used to convert the waves from time domain to frequency domain. Third, quality control was applied to studied samples, where some samples were rejected due to their low signal to noise ratio. Fourth, the dominant frequency of each accepted sample was determined. Fifth, samples were grouped in 5 to 7 groups per well, accordingly to Dunham’s classification. Finally, the dominant frequency of samples in each group was plotted against the petrophysical measurements to find the major trends.

In general, we found that the S-acoustic frequency response of carbonate rocks demonstrates inverse relation with permeability especially in Packstone and Rudstone groups. This decrease of frequency while propagating through the porous media can indicate attenuation within these rocks. Therefore, it seems that the higher the permeability, the higher the attenuation.

This study has the potential to improve building models for reservoir properties and rock type distribution, based in their frequency response. The reservoir model enhancement according to our main findings could done for specific rock types like Packstone and Rudstone. Our future work will investigate further theses relations and applications.