Temperature transient analysis models and workflows for vertical dry gas wells

Abstract

High resolution temperature sensors in downhole completions in the last decade has made high quality, transient temperature data available suitable for both qualitative and quantitative analysis. This data availability has stimulated the development of accurate models for the quantitative analysis of temperature transients. There are only a limited number of publications in the area of temperature transient analysis (TTA), the majority of which are limited to liquid production at the wellbore. One reason is that the compressible nature of gas results in a more complex mathematical problem when compared to that for incompressible liquids. The second reason is that more data is available from high precision, downhole temperature sensors installed in oil wells than from gas wells.This work is the sequel to previous work that derived an analytical solution for the transient sandface temperature of a vertical dry gas producing well (Dada et al. 2017). We discuss the derivation of interpretation models and workflow for estimating the flow characteristics of a dry, gas producing well from transient temperature data. The developed workflow linearizes the analytical equation describing flow into the well from a dry, gas reservoir. It has been successfully applied to both a synthetic and a real well production data set.The application area of the developed analytical solution is discussed. The two most important of the simplifying assumptions that affect the results concern (1) the impact of a gradual change in the flow rate and (2) non-Darcy inertial flow. Guidelines are developed to determine when the impact of a gradual flow rate change has died away. It was also concluded that the non-Darcy effect had little impact on the transient temperature log-time derivative, the key plot in TTA.The developed TTA workflow has therefore been validated for many practical TTA applications, as shown by its successful application and validation against conventional pressure transient analysis (PTA) for both synthetic and real-well data sets. TTA's unique ability to estimate the radius and permeability of a low permeability (formation damage) zone around the wellbore was also validated. This important parameter is not available from PTA. This work represents a further important step towards the development of a comprehensive PTA/TTA data analysis framework for multi-phase production wells.