基于快速傅里叶变换的海上油气井试井解释潮汐效应消除方法

Elimination of tidal effect in well test interpretation of offshore oil and gas wells based on fast Fourier transform

针对不稳定试井中压力数据存在潮汐影响,且干扰模型判断和储层物性参数解释的问题,利用快速傅里叶变换方法识别并去除潮汐效应。将含有潮汐影响的压力数据进行规整化处理和快速傅里叶变换,使信号由时间域变换到频率域,各个潮汐分量在频率域表现为固定值,判断并识别出其频率,将各分潮所对应频率的幅值进行插值降幅处理,再经过快速傅里叶反变换和逆规整转换,得到处理后的压力数据。结果表明,原始数据经过快速傅里叶变换,噪声等信号会出现在相对高频区域;储层压力响应信息出现在相对低频区域;各潮汐分潮在频率域中以固定频率形式出现而被准确识别,插值降幅处理后压力的周期性波动得到抑制,压力导数径向流段和后期特征能够准确判断。该方法在处理原始压力数据的过程中不需要最优化拟合,避免了结果的多解性和繁杂的计算量,为含有潮汐效应压力数据的矫正提供了一种有效手段。

Tidal influence of pressure data in unstable well testing influencing model judgment and reservoir physical parameter interpretation. The fast Fourier transform method is used to identify and remove the tidal effect. The pressure data with tidal influence is processed by regularization and fast Fourier transform, so that the signal is transformed from time domain to frequency domain. Each tidal component is represented as a fixed value in frequency domain. Its frequency can be determined and identified. The amplitude of frequency corresponding to each tidal component can be interpolated and reduced, and then the processed pressure can be obtained through inverse fast Fourier transform and inverse regularization transformation. The results show that after FFT, noise and other signals will appear in the relatively high frequency region;the reservoir pressure response information appears in the relatively low frequency region;each tidal component appears in the frequency domain in the form of fixed frequency and is accurately identified;after interpolation and amplitude reduction, the periodic pressure fluctuation is suppressed, and the radial flow section and later characteristics of pressure derivative can be accurately determined. During the processing the original pressure data, the method does not need to optimize the fitting, which avoids the multi solution and complex calculation of the results and provides an effective means for the correction of pressure data with tidal effect.