Temperature Logging Guidelines and Factors that Affect Measurement Accuracy

Abstract

Abstract A robust reservoir surveillance program is the key to successfully managing a steamflood operation. Observation wells allow us to directly monitor changing reservoir conditions throughout the life of the steamflood using time lapse surveys. Temperature surveys are a primary data type collected from the observation wells to evaluate the reservoir heating, and to monitor the steamchest. Thus, accurate measurement and proper interpretation of temperature surveys is essential for steamflood management. The objective of this study was to look at factors that can impact a temperature log and steps that can be taken to improve temperature measurement accuracy. Several field examples are presented to illustrate the effects of logging speed, steamchest temperature, sensor type and wellbore fluid on recorded temperature data. Guidance on evaluating and interpreting different temperature signatures such as, interpretation of liquid level in an observation well, understanding temperature signatures in air, wellbore reflux phenomenon, and examples of logs from malfunctioning logging tools, are also provided. The main purpose of this work is to aid both the operators and the service companies to gather accurate temperature data for improved steamflood management. This study is based on an extensive study of field data, primarily gathered from a single company's steamflood operations in California (using over 1000 temperature observation wells). Additionally, an analytical model was developed based on reservoir heat transfer and the sensor response mechanism to understand the impact of steam chest temperature, logging speed and sensor response time on the accuracy of the temperature log data. Results from the analytical model support the field observations. Field data and analytical assessment show that several factors can impact the accuracy of a temperature log, which can subsequently affect our interpretation and operational decisions. Data suggests that higher logging speeds introduce greater error in measured temperature data and these errors are greater at elevated steamchest temperatures. Temperature tools with longer sensor response times need to be run at slower logging speed to get accurate measurements. Ensuring adequate level of thermally equilibrated liquid (typically water) in the observation well is essential both, for gathering accurate data and to mitigate possible safety concerns for the logging operator. The examples and guidelines provided in this study will aid the practitioners to improve the gathering and interpretation of temperature log data.