电缆地层测试最小测试时间的确定

电缆地层测试器是重要的地层评价仪器，可以测量地层压力和渗透率、识别流体类型、确定油水界面.然而在低孔低渗地层中，由于泥饼的封闭性差而造成的地层增压现象，致使无法测量到地层真实压力.同时由于长时间的测试，容易将仪器卡在地层中而造成事故.本文提出一种确定电缆地层测试最小测试时间的方法.利用有限元方法计算泥饼和原状地层中的压力分布情况，求取泥浆柱静压力的影响半径，继而确定储层的最小测试时间，并且针对渗透性不同的储层给出了最小测试时间的范围.电缆地层测试最小测试时间的确定，可以确保电缆地层测试器在低孔低渗储层中测量到地层的真实信息，减小由于测量时间过长而引起工程事故发生率.

The minimum testing time determination for wireline formation tester

The wireline formation tester(WFT) is an important tool for formation evaluation,such as calculating formation pressure and permeability,identifying fluid type,and determining the interface between oil and water.However,in a low porosity and low permeability formation,the supercharge pressure effect exists,since the mudcake has a poor sealing ability.The mudcake cannot isolate the hydrostatic pressure of the formation around the borehole and the mud seeps into the formation,leading to inaccurate formation pressure measurement.This paper presents a method for determining the minimum testing time for the wireline formation tester.The pressure distribution of the mudcake and the formation were respectively calculated with the finite-element method.The radius of influence of the mud pressure was also computed,and the minimum testing time in low porosity and low permeability formation was determined within a range of different formation permeabilities.The determination of minimum testing time ensures an accurate formation data in low porosity /low permeability formation and minimizes possible accident due to long waiting and testing time.