جداسازي نمونه هاي سنگ آهك و ماسه سنگي با استفاده از نتايج آزمايشگاهي ضرايب پواسون و لامه در شرايط مخزن براي يكي از ميدان هاي نفتي جنوب غرب ايران

Lithology discrimination using Poissonʹs and Lame coefficients under reservoir condition-a laboratory test-on samples from a field in the southwest of Iran

Introduction: In the rock physic evaluation, experimental results are interpreted by theory, therefore both experimental data and theory are necessary for rock physics study. The main research in theories has been done by Gassman (1951) and Biot (1956). Also laboratory tests have been performed by Han et al (1986), Eberhart-Philips et al (1989), Wang and Nor (1992) and Wang (2000). Poissonʹs ratio and Lame coefficients are the main data for discrimination of two kind of lithology, especially limestone and sandstone, in the reservoir. In this study, Poissonʹs ratio and Lame coefficients have been calculated by measuring Vp and Vs in saturated samples as a laboratory test. Also and (a.p have been calculated using porosity, density, compressional and shear waves velocities of plug samples. X is more sensitive to fluids within the pores whereas \i is affected by rigidity of rock samples. In this research, after sample preparations, density, porosity and permeability of the samples were measured. Then compressional and shear waveʹs velocities were measured in both dry and water saturated conditions at several pressures, especially reservoir pressure. Finally, limestone and sandstone samples were separated by expanding Poissonʹs ratio and Lame coefficients in various diagrams. Methodology: Core plugging was accomplished as vertical plugs with 3.81cm diameter and 6cm length. Porosity, permeability and density of samples were measured to calculate bulk and shear modules in the rock physic models. Corrected density was calculated from measured density in dry condition and compared with resistivity log density together. According to petrophysical parameters plug samples were classified into three classes, as sandstones with more than 18% porosity and limestones with more than 10% porosity and the last one limestone with less than 10% porosity. Acoustic wave velocities were measured in dry and water saturated conditions at several confining pressures, such as 30 Gpa for the Sarvak samples and 45Gpa for the Gadvan samples as their reservoir pressure. Density, compressional and shear wave velocities are the three main rock physics parameters for lithology prediction of reservoir rock. Two kinds of lithology (sandstone and limestone) with different Poissonʹs ratio are detached after calculation and plotting of Poissonʹs ratio in both dried and water saturated states. In fact the Poissonʹs ratio for dried and saturated conditions is more than 0.17 and 0.25 respectively for limestone samples and lower than 0.17 and 0.25 for the sandstone samples. Lame coefficient (X.p and jn.p) were calculated by using density, compressional and shear wave velocities in water saturated and reservoir conditions. By drawing ji.p versus A,.p as a cross plot, the samples are divided into three divisions as sandstone with more than 18% porosity and limestones with higher than 10% porosity and the last one limestone with lower than 10% porosity. Results: • Prediction of lithology (limestone and sandstone) using Poissonʹs ratio under reservoir condition by plotting various diagrams. • Discrimination of lithology at reservoir condition using Lame coefficients in plotted (j,.p versus ^.p. re Poissonʹs ratio and Lame coefficient which are used for lithology-a laboratory test- accompaniment reservoir characterizations software which interpret 2D or 3D seismic data could be extended for predicting the lithology of all the formations in a field