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Application of the Russell fluid factor in tight sandstone gas detection

??The porosity of tight sandstone gas reservoirs is generally less than 12%, so the elastic parameter difference in pores caused by fluid difference is tiny. As a result, it is difficult to predict gas and water in tight sandstones by using the conventional AVO methods when the reservoirs are thin. In this paper, the existing fluid detection techniques were compared and the Russell fluid factor was selected as the effective parameter for fluid detection in tight sandstones. Then, single-boundary forward modeling was carried out. It is indicated that when the incident angle is less than 30°, the Russell fluid factor detection method is better fitted with Zoeppritz equation and its calculation results are of higher accuracy. By virtue of this method, fluid factor attributes can be fitted accurately from prestack gathers in the range of small incident angels. Feasibility study was carried out on this method based on the gas detection in He 8 Member tight sandstones of Lower Shihezi Fm, Lower Permian, Upper Paleozoic in the Sulige Gas Field, Ordos Basin. It is indicated that in the porosity range of effective reservoirs, the more obvious the negative anomaly of the Russell fluid factor is, the higher the gas saturation of reservoir is. To sum up, it is feasible and reliable to characterize the relative magnitude of gas saturation, perform gas detection in tight sandstones and indicate the lateral and vertical distribution of gas-bearing reservoirs by using the Russell fluid factor.