1 河海大学地球科学与工程学院, 南京211100
2 东北石油大学三亚海洋油气研究院, 三亚572000
3 中石化石油物探技术研究院有限公司, 南京211100
4 National Institute of Oceanography and Applied Geophysics (OGS), Trieste, Italy
Effects of pressure and fl uid properties on S-wave attenuation of tight rocks based on ultrasonic experiments
Xuming Pan, Jing Ba*, Rupeng Ma, Weihua Liu, Wei Cheng, José M. Carcione
1.School of Earth Sciences and Engineering, Hohai University, Nanjing, 211100, China.
2.Sanya Off shore Oil and Gas Research Institute, Northeast Petroleum University, Sanya, 572000, China.
3.SINOPEC Geophysical Research Institute Co., Ltd., Nanjing, 211100, China.
4.National Institute of Oceanography and Applied Geophysics (OGS), Trieste, Italy.
Abstract：
The tight oil/gas reservoirs in China have the great exploration prospects and high production potential, with the characteristics of low porosity, low permeability and significant heterogeneity in reservoir rocks. It remains a challenge to sort out the relations between reservoir wave responses and rock physical properties, and the further studies on the wave response patterns of tight reservoirs are in demand. The shear modulus and S-wave attenuation of rocks is affected by the properties of pore fluid and confining pressure. The ultrasonic wave experiments are performed on the 8 partially-saturated tight sandstone samples at the different confining pressures, and we have estimated S-wave attenuation with the spectral-ratio method. Results show that S-wave attenuation decreases with increasing confining pressure, and the water saturation case causes more loss compared to the oil saturation case, while the gas saturation case has the lowest attenuation. We observe generally the S-wave relaxation peak at an intermediate water saturation for the gas-water partial-saturation case. S-wave attenuation increases with increasing porosity or permeability. Based on the measured rock physical properties, combined with the Voigt-Reuss-Hill (VRH) average, differential effective medium (DEM) model and squirt-flow model, a tight rock attenuation model is proposed for analyzing the attenuation characteristics of fluid-saturated rocks at the different confining pressures. The model reasonably describes the characteristics of S-wave attenuation. The model predictions of S-wave attenuation show apparent pressure- and fluid-sensitivity at the full saturation and partial saturation conditions. For sample TS1-19 at the condition of full saturation and varying confining pressure, the S-wave peak attenuation predicted by the model ranges from 11.6 to 69.5, and decreases with confining pressure, while the relaxation frequency shifts to high frequency end. For the partial saturation condition of the sample, the predicted S-wave peak attenuation ranges from 15.5 to 39.8 at 30MPa confining pressure, and increases with water saturation, while the relaxation frequency shifts to low frequency end. For all the samples at 30MPa confining pressure, the predicted S-wave attenuation ranges from 5.6 to 38.6. At the full-saturation case, the predicted S-wave attenuation increases with porosity and decreases with confining pressure. For the partial saturation case, the S-wave attenuation predicted with the model and the Voigt and Reuss bounds generally increases with water saturation, while the experimentally-measured attenuation exhibits the peak attenuation at an intermediate saturation.
. Effects of pressure and fl uid properties on S-wave attenuation of tight rocks based on ultrasonic experiments[J]. APPLIED GEOPHYSICS, 2024, 21(2): 246-264.
2024, Vol. 21 
