Seismic estimation of fluid saturation based on rock physics: A case study of the tight-gas sandstone reservoirs in Ordos Basin

2021 ◽  
pp. 1-47
Author(s):  
Chao Li ◽  
Peng Hu ◽  
Jing Ba ◽  
José M. Carcione ◽  
Tianwen Hu ◽  
...  
Keyword(s):  
Ordos Basin ◽  
Rock Physics ◽  
Gas Production ◽  
P Wave ◽  
Quantitative Prediction ◽  
Rock Fragment ◽  
Tight Gas ◽  
Fluid Saturation ◽  
Sandstone Reservoirs ◽  
Tight Gas Sandstone

Tight-gas sandstone reservoirs of the Ordos Basin of China are characterized by high rock-fragment content, dissimilar pore types and a random distribution of fluids, leading to strong local heterogeneity. We model the seismic properties of these sandstones with the double-double porosity (DDP) theory, which considers water saturation, porosity and the frame characteristics. A generalized seismic wavelet is used to fit the real wavelet and the peak frequency-shift method is combined with the generalized S-transform to estimate attenuation. Then, we establish rock-physics templates (RPTs) based on P-wave attenuation and impedance. We use the log data and related seismic traces to calibrate the RPTs and generate a 3D volume of rock-physics attributes for the quantitative prediction of saturation and porosity. The predicted values are in good agreement with the actual gas production reports, indicating that the method can be effectively applied to heterogeneous tight-gas sandstone reservoirs.

scholarly journals Estimation of the Pore Microstructure of Tight-Gas Sandstone Reservoirs with Seismic Data

2021 ◽  
Vol 9 ◽  
Author(s):  
Wei Cheng ◽  
Jing Ba ◽  
José M. Carcione ◽  
Mengqiang Pang ◽  
Chunfang Wu
Keyword(s):  
Seismic Data ◽  
Velocity Ratio ◽  
P Wave ◽  
Seismic Exploration ◽  
Variable Pressure ◽  
Well Log ◽  
Tight Gas ◽  
Tight Sandstone ◽  
Sandstone Reservoirs ◽  
Tight Gas Sandstone

Tight-sandstone reservoirs have a complex pore structure with microcracks and intergranular pores, which have a significant impact on the seismic properties. We have performed ultrasonic measurements at different confining pressures for 15 tight-gas sandstone samples of the Xujiahe formation in Western Sichuan Basin, and have available well-log and seismic data of this area. The aim of this work is to estimate the porosity and crack properties for variable pressure conditions. The EIAS (equivalent inclusion-average stress) model is adopted to compute the high- and low-frequency bulk and shear moduli as a function of crack aspect ratio and (soft) and (stiff) porosities. Then, we use the EIAS-Zener anelastic model to obtain the wave properties as a function of frequency, and compare results with those of the constant Q (Kjartansson) one for verification of the robustness of the approach. The corresponding P-wave impedance, density and phase velocity ratio (VP/VS) are computed in order to built 3D rock‐physics templates (RPTs) at the ultrasonic, well-log and seismic frequency bands. The methodology is applied to a survey line crossing two wells, which together with the laboratory experiments, provide calibration suitable data. The estimated stiff porosity and crack porosity and density are consistent with the available data and actual production records, indicating that 3D RPTs provide a useful interpretation tool in seismic exploration and prospect evaluation.

Effect of CO2 Content on the Natural Gas Production from Tight Gas Sandstone Reservoirs

2017 ◽  
Author(s):  
Mohammed Eliebid ◽  
Mohamed Mahmoud ◽  
Reyad Shawabkeh ◽  
Salaheldin Elkatatny ◽  
Ibnelwaleed Hussein
Keyword(s):  
Natural Gas ◽  
Gas Production ◽  
Tight Gas ◽  
Natural Gas Production ◽  
Sandstone Reservoirs ◽  
Tight Gas Sandstone

scholarly journals Rock Physical Modeling and Seismic Dispersion Attribute Inversion for the Characterization of a Tight Gas Sandstone Reservoir

2021 ◽  
Vol 9 ◽  
Author(s):  
Han Jin ◽  
Cai Liu ◽  
Zhiqi Guo ◽  
Yiming Zhang ◽  
Cong Niu ◽  
...  
Keyword(s):  
Rock Physics ◽  
Wave Dispersion ◽  
P Wave ◽  
Tight Gas ◽  
Tight Sandstone ◽  
P Wave Dispersion ◽  
Frequency Dependent ◽  
Gas Saturation ◽  
Avo Inversion ◽  
Tight Gas Sandstone

Gas identification using seismic data is challenging for tight gas reservoirs with low porosity and permeability due to the complicated poroelastic behaviors of tight sandstone. In this study, the Chapman theory was used to simulate the dispersion and attenuation caused by the squirt flow of fluids in the complex pore spaces, which are assumed to consist of high aspect-ratio pores (stiff pores) and low aspect-ratio microcracks (soft pores). The rock physics modeling revealed that as the gas saturation varies, P-wave velocity dispersion and attenuation occurs at seismic frequencies, and it tends to move to high frequencies as the gas saturation increases. The velocity dispersion of the tight gas sandstone causes a frequency-dependent contrast in the P-wave impedance between the tight sandstone and the overlying mudstone, which consequently leads to frequency-dependent incidence reflection coefficients across the interface. In the synthetic seismic AVO modeling conducted by integrating the rock physics model and the propagator matrix method, the variations in the amplitudes and phases of the PP reflections can be observed for various gas saturations. The tests of the frequency-dependent AVO inversion of these synthetic data revealed that the magnitude of the inverted P-wave dispersion attribute can be used to indicate gas saturation in tight sandstone reservoirs. The applications of the frequency-dependent AVO inversion to the field pre-stacked seismic data revealed that the obtained P-wave dispersion attribute is positively correlated with the gas production from the pay zone at the well locations. Thus, the methods of the rock physics modeling and the frequency-dependent AVO inversion conducted in this study have good potential for the evaluation of the gas saturation in tight gas sandstone reservoirs.

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