Reservoir Pressure Prediction Using Time-Lapse Seismic Prestack Elastic Parameter Inversion Method
Authors: Zhao Wei , Zhu Zhenyu , Jiang Xiudi 
Published: May 2016

Abstract
In this article, the author introduces a time-lapse seismic inversion method based on the difference of seismic data at different times. Based on the synthetic model bSuilt from the real data, pore pressure change SSSSin a gas reservoir is computed. Also we predicted the reservoir pressure variation for a China offshore gas field as a real case study. Model experiment and real data application to describe the gas pressure variation show that this method is practical and efficient.
It is well known that time-lapse seismic has been taken as a powerful tool for reservoir surveillance. With the widespread application of 4D technology, many attentions have been paid on the quantitative prediction of reservoir variation via time-lapse seismic data. Through time-lapse seismic prestack elastic impedance inversion, many elastic parameters variation can be obtained. Hereafter we can setup the statistic relationship between reservoir parameters variation and elastic parameters variation. Thus reservoir parameters variation can be estimated.
There are two methods to achieve time-lapse seismic elastic impedance inversion process. One method is to invert each seismic data at different times separately, and then the impedance difference can be obtained from two inverted impedance results. This way is the general inversion scheme which is available in traditional commercial software. The other method is to firstly compute the difference of time-lapse seismic data at different times, on the base of which the impedance difference can be obtained by inversion directly. In this article, the author introduces the workflow and technology on how to conduct the inversion with the second method mentioned above.
Model experiment and real data application have been done with both methods to compare the results and the advantage of each method. The comparison between the computation results and reservoir numerical simulation data shows that the method of inverting the difference of time-lapse seismic data directly is practical and efficient. It can reduce the computation amount greatly; simplify the computation process and enhance the precision.

Introduction
As we all known, with the development of the oilfield, the low rate of recovery has been the key problem affecting the profit and decision making on further development. Residual oil has been taken as great resource in recent years, but the complex underground structure and complex reservoir condition cause the difficulties in development scheme. How can we know the distribution of the remaining oil and reservoir parameters such as reservoir pressure variatiozn at different times of development?
Time-lapse seismic is one of the technologies helping to understand reservoir. Based on the basic principle of the reservoir production, reservoir variation caused by the production can induce the change of seismic reflection characteristics around the pay zone. By comparing this difference, we can identify the change of the fluid, understand the distribution of the residual oil, therefore achieve the dynamic monitoring of residual oil and finally increase the recovery factor.