Sandface Temperature Research Articles

Prediction of Production-Inflow Profile of a Well Producing Single-Phase Flow of Slightly Compressible Fluid from Multilayer Systems by Temperature and/or Pressure Transient Data

Summary This study focuses on the prediction of the production-inflow profile of a well producing a single-phase flow of slightly compressible fluid (water or oil flow) in a multilayered system using the layer permeability and skin values estimated by history matching spatial and temporal temperature and/or pressure data sets along the completion interval. Such data may be acquired by wireline formation testing, production-logging-tool (PLT), or distributed temperature sensing (DTS) fiber-optic cables. We use an in-house thermal, transient coupled reservoir/wellbore simulator developed during this study. It solves transient mass, momentum, and energy conservation equations simultaneously for both reservoir and wellbore. The effects of the Joule-Thomson (J-T), adiabatic expansion, conduction, and convection are all included for predicting the flow profiles across the wellbore. The results from our in-house simulator are verified with the results from a commercial simulator for the single-phase fluid flow of a vertical well producing geothermal brine and oil in a two-zone multilayer system. We also compare the results from our rigorous transient coupled wellbore/reservoir model with the results from a model assuming steady-state thermal wellbore model used in the previous studies. We find that the steady-state thermal wellbore model used in the previous studies that ignore accumulation terms in mass, momentum, and thermal energy balances is a reasonably accurate model for predicting wellbore pressures and temperatures when it is coupled with a nonisothermal reservoir model for slightly compressible fluid because the transient effect in the wellbore is less important with the slightly compressible fluid. We investigate the nonlinear parameter estimation problem based on the use of single or multiple observed temperature and/or pressure (if available) profiles recorded spatially inside the wellbore and at the sandface. The purpose is to identify if the wellbore or sandface data profiles are more useful to accurately estimate the permeability and skin information and predict a production-inflow profile of the well depending on the representation of an actual multilayer system by a reduced-layered or fine-layered model. We show that using an upscaled-layered model (e.g., representing each heterogeneous layer with a lumped single layer with uniform permeability and skin) provides estimates that are more toward the thickness-average permeability and skin factors of the layers and may not provide a good prediction of the well’s production-inflow profile. We show that including the sandface temperature data in regression worsens, while the use of wellbore temperature data sets improves the quality of parameter estimation if an upscaled multilayered model is used. We also show that regressing on multiple temperature profiles, preferably at the sandface, alone could be used to predict the production-inflow profile accurately if a “fine” multilayered heterogeneous model is used. We also investigate if including or excluding the temperature and/or pressure measurements at the nonperforated sections along the completion interval could help enhance the parameter estimation problem. The results show that when multiple profiles of temperatures including the data at nonperforated zones at different production rates are regressed, reliable estimates of the individual layer properties that predict the production-inflow profile accurately can be obtained, though layer permeability and skin factors may often exhibit wide 95% confidence intervals and high correlations among them. Adding sandface or wellbore pressure data, if available, into observed data sets in history matching always improves the quality of parameter estimation.

An Analytical Solution and Nonlinear Regression Analysis for Sandface Temperature Transient Data in the Presence of a Near-Wellbore Damaged Zone

This study presents an approximate analytical solution for predicting drawdown temperature transient behaviors of a fully penetrating vertical well in a two-zone radial composite reservoir system. The inner zone may represent a damaged (skin) zone, and the outer (non-skin) zone represents an infinitely extended reservoir. The analytical solution is obtained by solving the decoupled isothermal pressure diffusivity equation and temperature equation for the inner and outer zones with the Boltzmann transformation. The convection, transient adiabatic expansion and Joule–Thomson heating effects are all accounted for in the solution. The developed solution compares well with the results of a thermal numerical simulator. The analytical solution is used as a forward model for estimating the parameters of interest by nonlinear regression built on a gradient-based maximum likelihood estimation (MLE) method. A methodology, based on semilog analyses of pressure and temperature data as well as log–log diagnostic plots of pressure- and temperature-derivative data, is proposed to obtain good initial guesses of parameters, which derive the MLE objective function to have reliable optimized estimates. The statistical measures such as estimated standard deviation of noise in pressure and temperature data, confidence intervals for parameters and correlation coefficients between parameter pairs are used to evaluate the goodness of fit and reliability of the estimated parameters from history matching pressure and/or temperature data sets. The results show that the rock, fluid and thermal properties of the skin zone and non-skin zone can be reliably estimated by regressing on temperature transient data jointly with pressure transient data in the presence of noise.

Transient, sandface temperature solutions for horizontal wells and fractured wells producing dry gas

Measured, bottom-hole transient temperature has been proven to be a valuable source of information. Similar to transient pressure (i.e. well testing) the temperature can also be used to estimate formation properties like permeability-thickness or to be used for flow rate allocation. Moreover, transient temperature has the unique advantages being sufficiently sensitive to identify the properties of the near-wellbore zone properties and/or the flowing fluid composition.That is why in the past decade, following the introduction of the modern in-well temperature sensing technology, the value of Temperature Transient Analysis (TTA) has been widely recognised and a number of useful solutions and workflows developed and tested, mostly for the vertical wells due to the reduced complexity of their TTA mathematical problem in the radial flow conditions. TTA requires the installation of high--precision, real-time temperature gauges/sensors close to the sandface. They are most frequently found in intelligent wells, the majority of which are either horizontal or highly deviated. Such high deviation well designs introduces the additional complexity to the data analysis, such as a wider range of flow regimes observed or the magnified impact of formation anisotropy on the reservoir response.There are currently very few published TTA solutions for oil producing horizontal wells and none for the horizontal wells producing gas. This work aims to fill this gap by developing analytical and semi-analytical solutions for the transient, sandface temperature of a gas producing horizontal well.This work first develops transient sandface temperature solutions assuming linear flow into a planar sink as a representation of a horizontal well (or a fractured well). Simplified forms of these equations are developed, making the application of TTA easier. Finally, the effects of heat transfer between the formation and the surroundings, and the effects of flow convergence into horizontal wells are considered. The combination of these for TTA in a horizontal gas well when combined with the existing TTA solutions for a liquid producing horizontal well lays the basis for a comprehensive transient analysis framework for multi-phase production, horizontal wells.

Temperature transient analysis for bounded oil reservoir under depletion drive

The significant pressure and temperature signals at wellbores associated with hydrocarbon production can be very useful for reservoir characterization and production analysis purposes. Temperature transient analysis is emerging partly due to the advancement of the downhole temperature monitoring system. Among different flow regimes encountered during the production of a vertical well, the long-lasting boundary dominated flow is crucial since most oil in conventional reservoirs are recovered during this period. The production induced temperature response behaves transient for boundary dominated pressure response and can be analyzed for reservoir property estimation. In this work, we derive a novel temperature transient analytical solution to model sandface temperature signal under boundary dominated flow. Our approach to obtaining the analytical solution from the governing energy balance equation uses Laplace transform with the input of pseudo-steady state pressure equation. This solution can be integrated with previous temperature transient analytical solutions to model the temperature signal from a depletion drived production well. The temperature modeling results acquired from this analytical solution are validated against those from numerical simulation in multiple cases and present distinct behavior under boundary dominated flow. Compared to the heating Joule-Thomson effect in the transient period near the production well, a cooling effect is observed throughout the reservoir after pressure transient reaches the reservoir outer boundary. The magnitude of this cooling effect is proportional to production time. This finding shows the potential of using temperature data at observation wells away from the production well during boundary dominated flow. Further parametric analyses are conducted on eight reservoir, production, and fluid properties to investigate their impacts on the temperature modeling results. These parameters are categorized based on their sensitivities on periods of transient and boundary dominated flow, in which total compressibility and production drainage area are sensitive to the temperature signals under boundary dominated flow only. Unlike the drawdown test, we find that the buildup temperature behavior under boundary dominated flow is identical to that during the transient period. After presenting the forward temperature modeling results, we extend existing reservoir characterization procedures to incorporate the boundary dominated flow. Drainage area and the distance to the closest boundary from the production well can be estimated from the measured temperature data acquired at both production and observation wells. Decent accuracies of the estimations are achieved for the examples presented in this work. The effects of thermal conduction and heat loss may not introduce significant errors in both forward and inverse thermal modeling for the long-lasting boundary dominated flow period.The temperature transient analytical solution under radial boundary dominated flow introduced in this paper considerably extends the scope for temperature transient analysis. This solution enables observation well temperature transient analysis, which seems promising for field application during the boundary dominated flow period. The analytical solution presented herein helps to advance the temperature transient analysis over the whole well production period and forms a basis for future studies on variable rate temperature transient analysis (rate-temperature transient analysis).

Temperature transient analysis models and workflows for vertical dry gas wells

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.

Numerical and analytical modelling of sandface temperature in a dry gas producing well

The oil and gas reservoir pressure response to the changes in the fluid production rate has been traditionally used to estimate the reservoir properties. Numerous analytical and numerical models have been developed to describe the transient pressure in and around a production well so as to interpret the in-well pressure measurements. Pressure Transient Analysis (PTA) is routinely used by Production and Reservoir Engineers at various stages in a wells life; initially for reservoir characterisation and, later, for well performance monitoring and (wider) reservoir surveillance. The recent application of high precision, downhole, temperature sensors has resulted in PTA being complemented by Temperature Transient Analysis (TTA). Recent TTA research has shown that comprehensive information on the state of the near-wellbore zone and fluid flow rates and composition can potentially be derived from such measurements. However, the derivation of useable TTA solutions describing the mass and energy transfer in porous media is challenging since it is necessary to simultaneously account for both the thermodynamic and the transient transfer effects. This paper reports a step in the development of a novel Temperature Transient Analysis (TTA) workflow. This is the first publication, to our knowledge, where the gas production TTA solutions, properly accounting for the compressible gas nature, are presented and discussed. A numerical model for determining sandface transient temperature in a dry gas producing well is developed. Simulations studies are run to understand the physics of transient temperature change and to make realistic assumptions to simplify the analytical model so as to derive an early-time, analytical solution. Finally, the limitations of the developed analytical solution are presented. This work is an important step towards a comprehensive PTA/TTA data analysis framework for multi-phase production wells.

Novel Solutions for Transient Sandface Temperature in Dry-Gas-Producing Wells

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 181057, “Novel Solutions and Interpretation Methods for Transient Sandface Temperature in Vertical Dry-Gas-Producing Wells,” by Akindolu O. Dada, Khafiz M. Muradov, and David R. Davies, Heriot-Watt University, prepared for the 2016 SPE Intelligent Energy International Conference and Exhibition, Aberdeen, 6–8 September. The paper has not been peer reviewed. The application of high-precision downhole temperature sensors has resulted in pressure-transient analysis (PTA) being complemented or replaced by temperature-transient analysis (TTA). However, the derivation and use of TTA solutions is challenging because of the small value of the measured temperature change and the more-complex nature of the governing physics and equations. In particular, analysis work flows for wells producing gas or gas/liquid mixtures are still lacking because most published liquid TTA solutions cannot be applied in the presence of gas. The complete paper addresses a work flow for a dry-gas-producing well. Introduction Applications of downhole temperature measurements can be divided into two broad classes based on the type of temperature models used and the reservoir-flow regimes analyzed. The first class uses semisteady-state models, usually in conjunction with measurements made at a single point in time by distributed-temperature sensors (DTSs). The second class of models uses TTA with both point and distributed measurements made over a period of time. TTA is relatively tolerant to measurement accuracy. It essentially requires data on the rate of temperature change, which is normally measured one or two orders of magnitude better than the absolute values (i.e., the difference between the sensor’s resolution and the sensor accuracy). The combination of TTA and PTA potentially allows the comprehensive estimation of zonal reservoir properties and flow rates from a single transient event. However, this will be realized only when a comprehensive set of TTA solutions is available for the heat- and mass-transfer models in porous media required to cover all the downhole scenarios frequently encountered during well production. Most of the work performed in the area of transient-sandface-temperature modeling has been limited to slightly compressible fluids (liquids), a limitation that allowed the introduction of simplifying assumptions to the thermal models. In contrast, the essential step of extending TTA to compressible fluids (gases) results in a highly nonlinear mathematical problem that is more difficult to solve. The complete paper develops analytical models for predicting transient sand-face temperature in gas-producing wells and illustrates their use for reservoir monitoring and flow-rate allocation. As such, it represents a major contribution to the development of a comprehensive TTA work flow. Underlying Physical Processes Full details of all equations, assumptions, derivations, and work flows regarding related phenomena are provided in the complete paper.

Transient temperature behavior and analysis of single-phase liquid-water geothermal reservoirs during drawdown and buildup tests: Part I. Theory, new analytical and approximate solutions

This work focuses on transient temperature responses of single-phase liquid-water geothermal reservoirs to constant-rate drawdown and buildup tests. New analytical and approximate solutions are presented for predicting drawdown and buildup sand-face transient temperature behaviors of a fully penetrating vertical well in an infinite-acting homogeneous reservoirs. The solutions account for the effects of Joule-Thomson (J-T) heating/cooling, transient adiabatic fluid expansion/compression, convection, and conduction. The solutions are compared and verified with the solutions from three different non-isothermal simulators that solve the mass and thermal energy balance equations rigorously and simultaneously. The impacts of various parameters such as wellbore storage, skin zone near the wellbore, thermal conductivity, and outer reservoir boundary conditions on the sand-face temperature responses are also investigated and discussed. Drawdown and buildup sand-face temperature data are shown to exhibit three infinite-acting radial flow (IARF) periods (represented by semi-log straight-line equations); early-time IARF reflecting the adiabatic expansion/compression effects in the skin zone if it exists, intermediate-time IARF reflecting the J-T effect in the skin zone, and late-time IARF reflecting the J-T effect in the non-skin zone. In an accompanying paper (Part II), we present an interpretation and analysis methodology based on the analytical solutions derived here for parameter estimation from temperature transient data jointly with pressure transient data.

Transient temperature behavior and analysis of single-phase liquid-water geothermal reservoirs during drawdown and buildup tests: Part II. Interpretation and analysis methodology with applications

In this work, we present new semi-log straight line and temperature-derivative methods for interpreting and analyzing temperature transient data acquired during drawdown and buildup tests in an infinite acting homogeneous, single-phase liquid-water geothermal reservoirs. The methods are based on the analytical solutions derived in our accompanied paper (Part I) accounting for the effects of Joule-Thomson (J-T) heating/cooling, transient adiabatic fluid expansion/compression, convection, and conduction. Drawdown and buildup sand-face temperature data are shown to exhibit three infinite-acting radial flow (IARF) periods; early-time IARF reflecting the adiabatic expansion/compression effects in the skin zone if it exists, intermediate-time IARF reflecting the J-T effects in the skin zone, and late-time IARF reflecting the J-T effect in the non-skin zone. Semi-log straight-line analyses based on the identified proper IARF regimes and their time intervals on a log-log diagnostic plot of the absolute value of temperature-derivative vs. elapsed time, jointly with conventional pressure transient analysis (PTA), provide estimates of porosity, J-T coefficient of fluid, mobility of skin and non-skin zones as well as radius of the skin zone, which are not readily accessible from PTA alone. The applicability of the proposed analysis methods is demonstrated by considering two synthetic test examples and one field test data set.

Influence of Flow Geometry on Sandface Temperatures During Single-Phase Oil Production: Dimensionless Analysis

Summary This paper evaluates the impact of flow geometry on sandface temperature behavior under conditions of high drawdown in which Joule-Thomson thermal effects are significant. The temperature behavior of both radial- and linear-flow regimes is evaluated under steady-state and transient conditions. Through a dimensionless analysis of the thermal-energy equation, a systematic evaluation of the contributing terms is presented. The steady-state analysis is based on analytic solutions that demonstrate identical temperature behavior at asymptotic limits but are offset by a geometric factor at intermediary Péclet numbers. The transient analysis is based on a combination of analytical and numerical solutions. The transient analysis demonstrates that temperature changes occur earlier in time for the radial geometry compared with the linear geometry. The impetus behind this study is to address the impact of transient-temperature development in hydraulically fractured vs. nonhydraulically fractured vertical completions. The flow regime in nonhydraulically fractured vertical completions is radial whereas in hydraulically fractured vertical completions a linear-flow regime can dominate a significant portion of the flow history. All analyses assume that skin, wellbore-storage, and thermal-storage effects are negligible.

Temperature transient analysis in horizontal wells: Application workflow, problems and advantages

This article will present a set of analytical equations for the calculation of early-time, sandface temperature for the case of a slightly compressible fluid production. The equations provide the full, transient temperature solution for the flow of low compressible fluids (i.e. liquids and, sometimes, gases) into horizontal wells. The solution is essential for temperature transient analysis in smart wells—a monitoring approach of great potential, but in early development stage. A numerical simulation model will confirm the analytical equations as well as the multi-rate inflow test calculations.The methods proposed here can be applied to a wide variety of well completion types, flow conditions and system properties. They form the basis for the flow rate allocation in multi-zone wells smart wells. The TTA workflow description will be provided, complemented by the real, smart well data analysis. A discussion on the calculation model's robustness based on the claimed sensor resolution is also provided.The main value of the presented solution is that it is a valuable contribution towards a comprehensive temperature transient analysis methodology and the associated benefits which will be especially important for efficient, real-time, intelligent well monitoring.