Petrophysical Study on UAE Carbonates

More than sixty percent of world’s hydrocarbon reserves are found in carbonates; however, there have been few laboratory experiments to analyze and understand the complex pore system of carbonates and its effect on petrophysical properties. The understanding of complexity of pore system in carbonates can help in modeling the seismic response and in inferring petrophysical properties. We present a laboratory study of twenty five outcrop carbonates samples from UAE which include quantitative mineralogy, total and effective porosity, permeability and compressional and shear wave velocity as a function of effective pressure. The relationships between porosity and velocity with effective pressure as well as velocity with porosity agree with previous findings. The velocity of samples also showed a dependency on mineralogy. The presence of dolomite decreased the Vp/Vs ratio and increased the Vp and Vs in dry and in saturated (brine and dodecane) samples.

Biot-Gassmann equations are used to model saturated velocities from dry measurements. The model overestimates the Vp by as much as 11% in both brine and dodecane saturated cases. The magnitude is observed to be a function of porosity. The samples with higher porosity had the least differences in calculated and modeled responses. 80% of dodecane saturated samples and 65% of brine saturated samples showed increase in shear modulus thus agreeing with the Biot-Gassmann model.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California