Fiber Optic Measurements as Real Time PLT with New Transient Interpretation
Authors: Kortukov Dmitry , Shako Valery , Pringuey Thibault , Savenko Alexander , Haus Jacques , Kotlyar Lev , Malaniya Georgy 
Published: October 2019

Fiber Optic provides massive amount of information from downhole of the well. But as it is seen in practice, taking this data and converting into something valuable to Operator’s reservoir and production engineers is not straight forward and easy to achieve process. One of the major reasons for this situation is that existing interpretation techniques are mainly based on steady state type of analysis, which provides too many degrees of freedom in interpretation workflow. Respectively, the interpretation outputs have very high level of uncertainty and tuning the results to something sensible requires highly expertized engineer to perform interpretation. This prevented Fiber Optic to become real time PLT tool last several decades since its introduction.

Realized this gap, Schlumberger invested heavily in new concept of interpretation of DTS in production wells, which is based on Pressure-Temperature-Rate Transient Analysis.

Pressure-Temperature-Rate Transient Analysis or PTRA, is a concept of joint quantitative interpretation of full data set of the downhole and surface pressure-temperature-rate data for reservoir characterization and flow profiling. This approach opens a great deal of opportunities for reliable quantitative interpretation of the distributed measurements via adding much higher volume of the data to the interpretation workflow that could not be utilized otherwise with traditional steady-state techniques. One of the benefits is that it enhances the value of Pressure Transient Analysis (an established, robust and reliable reservoir testing tool) by introducing transient local and distributed downhole temperature measurements in the interpretation workflow to reduce uncertainty in the interpretation results and significantly reduce impact of the well-known problem of the non-uniqueness of the inversion.

PTRA involves model-based matching of the field pressure, temperature and rate data (logs and transients) and enables multiphase zonal allocation in wells of all inclinations, quantification of water and gas breakthrough as well as degassing in reservoir. It also enables more accurate injectivity profiling using the model-based match of the continuous DTS data recording while re-injection (hot- or cold-slug), as compared to traditional techniques. PTRA allows to quantify the dynamics of the reservoir properties over the well lifetime and integrate well-centric zonal allocation into multi-well interpretation for large-scale reservoir characterization.

This paper takes us into example of a production well, where we use sensitivity analysis to show level of interpretation uncertainty with conventional Steady State analysis and resulted improvement in interpretation output via applying PTRA analysis for quantitative interpretation of the full wellbore and surface data set recorded over some period of well life.

This example demonstrates how fiber optic data can be finally utilized approaching it to a real-time PLT tool even in horizontal wells, which opens to Reservoir management team new capabilities in maximizing well productions and improving Recovery factors of their assets.