用电缆地层测试器实时定量评价CO_2含量以优化完井和钻杆测试决策

Real Time Carbon Dioxide Quantification Using Wireline Formation Tester to Optimize Completion and Drill Stem Testing Decisions

油气藏中非烃气体(如CO2和N2)的探测对于油藏的评价和管理非常重要。当利用钻杆测试(DST)来证实油藏产能和进行油藏评价时,高含量非烃气体会妨碍气体充分燃烧,进而对钻杆测试产生消极的影响。弄清油藏流体中非烃组分的特性对优化钻杆测试非常必要。地层流体中CO2含量很高时就不必进行钻杆测试。如果一口井中的所有层位都含有大量CO2,那么这口井就可以直接封堵弃井。传统的CO2含量测试是将试井过程中取得的井下或地面流体样品送到实验室进行分析,流体样品中易反应气体(如CO2)浓度可能会发生很大变化,因为在分析之前,这种气体会与样品中混有的地层水、泥浆滤液或者取样室中其他组分反应。CO2和pH值较高的水(如水基泥浆滤液)很容易形成碳酸盐。井下近红外(NIR)光谱测量可以在取得流体样品之前对流体中的CO2组分在井下进行实时分析。介绍了利用地层测试器进行实时井下流体分析的原理和应用,通过井下流体分析可实时测定井下流体中的CO2和烃类含量。结合现场实例,介绍了如何用井下实时测量CO2含量来优化完井和钻杆测试决策,并且经实例证实,实时测量的CO2浓度与随后实验室测定结果一致。

Detection of non-hydrocarbon gases in oil and gas reserves, such as carbon dioxide （CO2） and nitrogen gas （N2）, is important for reservoir assessment and management. When drill stem testing （DST） is performed to demonstrate production of discovered reservoirs and to fulfill in part of the requirements for estimating reserves, high content of non-hydrocarbon gases can preclude an efficient burn negatively impacting drill stem testing. It is very desirable to characterize the non-hydrocarbon fraction of reservoir fluids to optimize DSTs. The need for DSTs is obviated if the formation fluid contains too much CO2. If all zones in a well are shown to be dominated by CO2, the well may have to be plugged and abandoned. CO2 content in a hydrocarbon bearing formation is conventionally evaluated by taking fluid samples downhole or on surface during a well testing and sending the fluids to the laboratory for analysis. Concentration of reactive gas like CO2 in fluid sample can change significantly from reaction with formation waters, mud filtrates, or other components in a sample chamber prior to reaching an analysis facility. Carbonate solids can readily form with CO2 and water of high pH （such as WBM filtrate） thereby eluding detection. Downhole measurement of NIR （near-infrared） spectroscopy enables real time analysis of CO2 content in formation fluid before fluid samples are acquired. This paper describes principle and application of Downhole Fluid Analysis （DFA） in real-time determination of the contents of CO2 and hydrocarbons with formation tester tool. Field examples are also presented demonstrating downhole CO2 measurement in real-time were employed to optimize completion and DST decisions, and the measured CO2 concentrations were later confirmed by laboratories.