Reservoir characterisation in laminated sand shale reservoir has always been a very challenging task. The presence of conductive shales between the resistive hydrocarbon bearing sand reduces its resistivity drastically. It happens as the current flows through them as resistors in parallel. Therefore, the classical shaly sand interpretation grossly underestimates the hydrocarbon potential of laminated reservoir.
Over the years many techniques have been developed to solve this problem. The development of latest resistivity tools like triaxial resistivity has also helped in addressing this problem. The introduction of these tools has helped upto a great extent to unlock the reservoir potential. However, the technology is very costly and sometimes may not be possible to run due the limited extent of the reservoirs. In those cases, it is important to find some alternate approach to addres the problem of low resistivity by using conventional logging tools.
The current study deals with the case history from the East coast deep water field in India. The field has many drilled wells where the latest resistivity tools have been run. Petrophysical interpretations are done using this resistivity anisotropy data and are available for validation with the new technique. The latest approach uses the conventional resistivity data. The critical part in the study is the type and distribution of the shale within the reservoir. If we can find out the same then using this information true resistivity can be inverted. The approach has been tried on several wells across the different fields and has given good results. The results from the resistivity anisotropy data and the new technique are comparable. Thus a very cost effective method of predicting true resistivity has been developed, which ultimately gives realistic hydrocarbon saturation in the laminated sand shale sequences.