Understanding of the detailed permeability structure and internal heterogeneity of the target layers of CO2injection is important for any successful injection project. Yet, determining this structure by traditional hydraulictesting may be prohibitively cumbersome and expensive, while information obtained from core logs may not givea full picture of the connected permeability.Flowing FEC (Fluid electric conductivity) method provides a quick way of determining the hydraulic conductivitystructure of a reservoir layer. In combination with traditional pumping tests that can provide overallinterval transmissivities, the method can be used for obtaining a more detailed picture of the distribution of thetransmissivities, information that is crucial for CO2 injection experiments where the internal heterogeneity of thetarget layer may greatly influence the distribution of CO2. The method has been previously been successfullyapplied to several applications, ranging from granitic rock to mudstone formations (Doughty et al., 2008; Tsangand Doughty, 2003) and is here being used for preliminary hydraulic characterization of the target CO2 injectionlayer of the Heletz, Israel, the main injection site of the MUSTANG project.In this approach the wellbore water is first replaced by water of a constant salinity distinctly different fromthat of formation water. Next, the well is shut in and an electric conductivity probe is used to scan the FEC ofborehole fluid as a function of depth. After this, the well is pumped at constant rate, during which a series FEClogs at successive times are obtained. At depth locations where water enters the borehole, the logs display peaks.Analysis of the time evolution and skewness of these peaks allows estimation of the flow rate qi and salinity C,and further, if two or more logs are taken at different well flow rates, the initial ambient pressure heads hi of eachindividual inflow/feed point I can also be estimated. The depth resolution of the inflow locations is typically 10cm.These data can used to define the detailed transmissivity/permeability structure of the reservoir layer.The present presentation discusses the application of the method for characterizing the target layer of the Heletzinjection experiment, in terms of the data, model analysis and comparison of the results to those from core samples.
Tsang, C. F. and C. Doughty, Multirate flowing fluid electric conductivity logging method, Water ResourcesResearch, 39, 12, 1354-1362 (10.1029/2003WR002308), 2003.
Doughty, C., C.-F. Tsang, K. Hatanaka, S. Yabuuchi, and H. Kurikami. Application of direct-fitting, massintegral, and multirate methods to analysis of flowing fluid electric conductivity logs from Horonobe, Japan,WaterResour. Res., Vol. 44, doi:10.1029/2007WR006441, 2008.