--> ABSTRACT: Porosity and Heterogeneity Effect on Vp/Vs Ratio in Carbonate Rocks from a Reservoir in the Middle East

Datapages, Inc.Print this page

Porosity and Heterogeneity Effect on Vp/Vs Ratio in Carbonate Rocks from a Reservoir in the Middle East

Mokhtar, El Amin 1; Vega, Sandra 1; Abed hassan, Ahmed 1; Mohamed Al Baloushi, Mariam 2
(1) Petroleum Geosciences, Petroleum Institute, Abu Dhabi, United Arab Emirates. (2) Sahil, ADCO, Abu Dhabi, United Arab Emirates.

Acoustic velocity measurements on carbonate rocks are often influenced by the level of heterogeneity particularly in texture and pore type. This phenomenon in return, affects the relationship between P and S wave velocity ratio (Vp/Vs) and porosity. Our objective in this study is to improve our understanding of how heterogeneity affects these relations. For this purpose, we analyzed 78 core plug samples at dry and ambient conditions. These samples were taken from a producing reservoir in the Middle East. We conducted the measurements of porosity and acoustic velocities (Vp and Vs). In addition, we used Dunham’s carbonate rock classification to sort the core samples into smaller groups that are less heterogeneous and have distinguishable rock types. Vp and Vs cross plots were generated to investigate the acoustic velocities ratio general trends to porosity and rock class.

Our preliminary results confirmed that the Vp and Vs relation is generally linear, with an average Vp/Vs ratio of 1.74. Our findings also showed that dense limestones with relatively low porosities tend to have the highest average Vp/Vs ratio (1.89) while skeletal peloidal packstones and wackstones tend to have the lowest average Vp/Vs ratio (1.68 and 1.70 respectively). In addition, the cross plot between Vp/Vs ratio and porosity, suggested that the Vp/Vs ratio decreases as porosity increases. Moreover, when taking into consideration the rock classification, we found that dense limestones and grainstones showed the sharpest decline in Vp/Vs value as porosity increased. On the other hand, wackstones Vp/Vs values proved to be the least affected by the increase in porosity. In conclusion, the Vp/Vs ratio correlation with porosity confirms an inversely proportional relation that slightly varies between the different carbonate rock classes, which is probably caused by their level of heterogeneity. These correlations have the potential of identifying different carbonate rock types from Vp/Vs ratio and porosity cross plots.

 

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.