Heatwave Inflow Performance Source Characterization (HIPsource)

In order to optimize production from oil wells, it is essential to know zonal production distribution along the wellbore, such as what flows where and how much? A possibility may then be to shut off zones that produce mainly water. There are a number of measurement technologies currently available ranging from the installation of chemical tracers in the well to real-time downhole production logging tools. They each have their own limitations regarding high interpretation uncertainty or high cost. HIPlog is a new measurement system under development that will address some of these limitations. The system utilizes heat pulses released into the well fluid at given times in order to achieve real-time downhole flow monitoring. The HIPlog system comprises autonomous heat sources pre-installed in the well, downhole temperature sensor(s) after the production zone (already present in many wells), and interpretation software for the estimation of zonal flow rates based on the measured heat pulses. This project has worked with developing improved models for the generated heat pulses as they appear inside the wellbore fluid. This is critical information to simulate downstream transport, all the way to temperature sensors (i.e. heat source characterization). A key objective was to improve the understanding of heat transfer from very hot surfaces to surrounding fluids under the high pressures and temperatures typically present in oil reservoirs. Tailored experiments were performed to support model development. The acquired knowledge has been included in numerical models that form the basis for the HIPlog interpretation software. A significant number of heating and cool-down experiments were performed in 2020. In these experiments the pressures ranged from 1 bar to 200 bar and the fluids were water, model oil and crude oil. The SINTEF wheel flow loop was filled half with gas (methane). Rotation of the wheel results in a flow of the liquid and a relative velocity between the heat source and the fluid. A large number of heat transfer situations (film boiling, natural convection with nucleate boiling, forced convection with nucleate boiling, mixed convection) were examined. The experiments covered situations where the heated rod was heated for given times, positioned in the gas or in the liquid, and where the rod was stationary or was moved into the liquid at a given convective velocity. During 2021 the data from the Tiller "Wheel-loop" tests were analyzed. It was clear that the data, transferring heat from an electric resistance heated 10 mm diameter Kanthal rod, to the fluid (single phase or two phase), was generally of good quality. However, issues related to the temperature measurements during the phase transition (generating vapor from the liquid) were analyzed in greater detail. In the experiments surface temperatures above 1000 °C was produced for shorter times. A mathematical model to predict the temperature evolution in the Kanthal rod was developed and used to interpret the heat transfer coefficient needed to reproduce the data. Based on these analyses, the complexity of transient surface temperature measurements inside boiling fluids became clear. These challenges have not been reported in the literature, indicating that there may be missing information in many experimental works. The solution to these challenges has been found and will be published. In a specially designed pressure cell (1-250 bar) it was found that at high pressures and surface temperatures around 950 °C carbon deposits may develop on the hot surface after repeated experiments. This was not seen in the Tiller "Wheel-loop" tests, where surface temperatures were lower. In both cases crude oils were explored. This knowledge is now explored to optimize the heat source. Earlier, we found that the cool-down is faster than expected as the film boiling regime is being killed by a nucleate boiling wave propagation mechanism. This "rewetting mechanism" contributs to fast delivery of thermal energy from the heat source to the liquids. The work with nucleate boiling in multi-component systems has led to challenges related to PVT that had to be clarified. Equivalent saturation temperature has been introduced as a concept for multi-component mixtures. Using this concept, one tries to simplify a multicomponent system to an equivalent single-component system. The needed data for equilibrium gas fraction and phase enthalpies are produced from PVT models. A model for heat transfer in multi-component boiling fluid has been developed. Included phenomena are thermal radiation, nucleate boiling and film boiling. This involves transport, creation and collapse of vapor bubbles together with heat and mass exchange with the continuous phase. The model predicts distribution of vapor bubbles through the boundary layer, and the effect of turbulence is included. The model can be applied directly in simplified models, or as sub-model ("wall function") in a CFD analysis.

For Wellstarter the main outcome of this project has been to improve the performance of the HIPlog system by improving the heat source models. The HIPlog system is developed to provide a cost-effective method to assess the inflow profile of a producing well at critical stages of a well's life (e.g. at start-up, during production, after water break-thru, prior to intervention/work-over). Main outcome for end users (oil producers): Better knowledge of inflow rate profiles ("what flows where and how much"). This may improve well productivity as well as increase reservoir recovery rates, i.e. improve resource utilization. As a result of HIPsource new knowledge about natural convection and forced convection heat transfer was acquired, using crude oil, model oils or water at well pressures and relevant surface temperatures. In addition, significant knowledge has been generated regarding how the heated fluids move and mix in the nearfield of the heat source. This information is critical for input to more simplified models that simulate the long-distance propagation of heat waves, and their interaction with well tubing and annular spacings. This enables improved predictions of measured temperature signals at downstream locations. This is the foundation of the inverse modeling strategy used by Wellstarter, and which allows accurate determination of the production flow for each case. Thanks to the improved understanding of the heat source performance, under operational conditions, better up-front assessments of the potential of the Wellstarter technology can now be performed, case by case. Main outcome for society: Improved resource utilization with less environmental impact. Impact for Wellstarter: Improved reliability of the flow interpretation tool will likely turn the business model more towards service-based and thereby more profitable revenue.

The HIPlog system uses heat pulses released into the well fluid for real-time downhole flow monitoring. The system comprises autonomous heat sources installed in the well and software for interpretation of measured heat pulses. This project seeks to create improved numerical models for the generated heat pulses. These models will be key part of HIPlog. The background for the HIPlog innovation is that traditional production monitoring techniques used for estimating downhole zonal production (permanent- or campaign-based) are limited in use due to high CAPEX and/or OPEX. The market therefore tends to use lower cost systems like permanent chemical tracers. These have valuable features such as locating first water breakthrough, but their reliability on rate monitoring are uncertain, especially with multiphase flow. They also feature offline and non-real time data, which is incompatible with modern digital fields. Environmental footprint of chemical tracer use may be minor, but still not negligible. The market value for production rate monitoring and associated services is huge and rising with today's reservoir complexity (> 1 Billion $). WellStarter aims at entering the national- and international markets with a new product line. The underlying idea is to trace fluids with non-material heat waves, operate at steady state and avoid many of the above-mentioned tracer problems. WellStarter aims at developing a robust product and the heat propagation research carried out under this project will be crucial. Improved heat source characteristics will improve the overall predictive power and will extend the applicability of the system towards more challenging wells. The models will be derived both from published literature, detailed 3D computational fluid dynamics simulations (CFD), and data from tailored lab-scale experiments. Different types of experiments will be performed at scales ranging from very small to more realistic dimensions.