(6)--6-Gas Flow Tests with Discrete R气藏工程气藏工程.ppt

5.6 Analysis of Gas well Flow Tests-15.6 Analysis of Gas well Flow Tests-1Gas Flow Tests with Discrete Rate Gas Flow Tests with Discrete Rate ChangesChangesGas wells are produced at conditions approximating constant well-head pressure or variable bottom hole rates,rather than at constant bottom-hole rates,in most gas field operations.In addition,many gas-well tests,especially deliverability tests,are conducted under variable-rate conditions.deliverability testBack pressure testInflow performance Relationship curve(IPR)We concentrate on analysis techniques for variable gas rates,including gas-well tests with discrete changes and tests in which the rates are smoothly changing.1 Constant-Rate Gas Flow Tests With constant rate,similar to the analysis of slightly compressible liquids,using adjusted variablesy=mx+b2 Gas Flow Tests with Discrete Rate Changesusing superposition in timeFirst,we consider the pressure drawdown in terms of adjusted pressures in an infinite-acting gas reservoir resulting from a single production rate.Second,we use superposition in time,assuming n wells located in the same location with different flow rate,so each well pressure drop can be expressed:Therefore,the total pressure drawdown resulting from n discrete rate changes can be obtained.Non-Darcy flow effects in a gas-well can be included by plottingD=（141.2 is a constant,and D is the non-Darcy flow coefficient.With the non-Darcy flow term,Example 5.1-Determining Permeability and Skin Factor From a Multi-rate TestTABLE 5.2-FLOW-AFTER-FLOW TEST DATA,Solution:1.Our objective is to prepare a plot ofuthe first step is to calculate the pressure/rate and time/rate plotting functions for each of the four flow periods.For example,at t=6 hours,n=1，t1=6 hours,and q1=2,711 Mscf/D,At t=9.5 hours,n=3,t3=9.5 hours,and q3=2504Mscf/D,At t=9.5 hours,n=3,t3=9.5 hours,and q3=2504Mscf/D,2.The effective gas permeability is calculated withmd3.Next,calculate the skin factor using5.6 Gas Flow Tests with Discrete Rate Changes（End)