A prediction method of suspended natural gas hydrate saturation in sea area based on P-wave impedance

Abstract

A large amount of suspended natural gas hydrate (NGH) has been found in Shenhu sea area of China. At present, Wood method is considered to be a suitable method for predicting the saturation of suspended NGH. However, there are two problems in the application of this method in Shenhu sea area of China. First, this method is difficult to directly predict NGH saturation based on post-stack seismic data inversion, since it does not clarify the relationship between NGH saturation and P-wave impedance. Second, the prediction results of this method are quite different from the actual values in Shenhu sea area of China, which makes it difficult to obtain reliable resource estimation in this sea area. To clarify the relationship between NGH saturation and P-wave impedance, this paper proposes an improved Wood equation called Wood-Imp equation, which lays a foundation for predicting NGH saturation by using post-stack wave impedance data. For the second problem, the main reason for the large prediction error of Wood method is that the existing measurement technology cannot avoid the measurement errors in sediment composition, pore sizes, etc. Thus, Wood-Imp method is proposed based on non-NGH layer to reduce the of NGH saturation prediction error. Three comparison experiments are used to demonstrate the effectiveness of our proposed Wood-Imp method, including simulation data, well S data in Shenhu sea area, two-dimensional forward modeling of Shenhu sea area data. (1) Wood-Imp method has much higher accuracy in predicting NGH saturation than Wood method; (2) The predicted NGH saturation in Shenhu well S by Wood-Imp method is closer to that calculated by chloride ion method than that of Wood method; (3) Wood-Imp method has obtained better NGH saturation prediction accuracy based on P-wave impedance data obtained by post-stack inversion in two-dimensional forward modeling. Therefore, the Wood-Imp method proposed in this paper is more suitable for predicting suspended NGH saturation than the existing Wood method in Shenhu sea area.