Crack-water Gas Reservoir Water Influx Dynamic Early Prediction Methods

Fractured and water-carrying gas reservoir as a typical macro heterogeneous gas reservoir exists in our country widely especially in Sichuan Basin. As is known to all, the water invasion in reservoir caused by fracture water-breakthrough will seriously influence gas production, making the gas reservoir recovery be reduced. Therefore, water invasion performance prediction becomes a very important work in the early stage of gas reservoir development.On the base of the studies and analyses on a great number of related references, this paper starts with the basic characteristics of gas reservoir, analyzes the characteristics of fractured and water-carrying gas reservoirs, the percolation of characteristics, and the water invasion damage by the numbers. And it thoroughly makes a study of the mode and mechanism of water invasion of fractured and water-carrying gas reservoirs.How to calculate the water invasion rate correctly while we study the performance and calculate the dynamic reserves of the gas reservoir with material balance equation is still a difficulty for long. The traditional method to calculate the water invasion rate is not very accurate, and it can make a large calculation error especially in fractured and water-carrying heterogeneous gas reservoir. In this paper, we proposed a novel method to predict the water invasion performance, the advantage of this method is that we can calculate the water invasion index instead of the water invasion rate directly. According to the theory of material balance, the mathematical model of the water invasion performance prediction of water-carrying gas reservoir has been established. The mathematical model is nonlinear equations. After studying the nonlinear optimization method thoroughly, we find a way to solve the mathematical model by automatic matching several time points with formation pressure and production data. And then, the water invasion performance prediction program of water-carrying gas reservoir has been developed with Visual Basic IDE, with this program and actual pressure data, the detailed water invasion performance prediction has been conducted on the actual well of water-carrying gas reservoir. With the results we can predict the target aim of water invasion performance such as the elastic energy of aquifer, intensity of water invasion, cumulative water invasion rate, velocity of water invasion and so on. The calculation results show that the methods presented in this paper are correct and reliable.