True Formation Temperatures Research Articles

New insights on source rock maturation in the southern Gulf of Gabes (Tunisia) via 1-D modeling: effect of combined corrected borehole temperature and thermal conductivity on heat flow distribution

Effective quantitative modeling of petroleum generation processes requires a reasonable knowledge of various factors controlling the transformation of organic matter into oil or gas. Nevertheless, it is widely accepted that thermal conductivity and temperature have the dominant roles in controlling generation. In Tunisia, previous source rocks burial and maturity modeling were mostly carried out using corrected borehole temperature after applying formula which were set to fit domains other than Tunisian basins. The main purpose of this work is to propose a suitable method of temperature correction to fit the studied area but more importantly to emphasize the impact of thermal conductivity on heat flow distribution. For that, a total of 222 temperature values including 170 bottom hole temperatures (BHT) and 52 drill stem tests (DST) were collected from 30 onshore and offshore boreholes. The proposed equation generates corrected temperature close to true formation temperatures. As thermal conductivity depends on the relationships between a sedimentary interval component, two equations were used to determine the conductivity of each unit which are the harmonic and the geometric means. To assess the importance of applied corrections, three scenarios were tested for an Albian source rock using the 1-D Basin-Mod software. The combination of corrected BHTs and thermal conductivity provide higher source rock maturation than when uncorrected data are used. Amounts of generated hydrocarbons are estimated to become two times higher. This would guide for complementary reserves estimations to be applied in the region for better calculation accuracy.

海上钻井中运用泥浆温度测算地温梯度方法研究

海上钻井中运用泥浆温度测算地温梯度方法研究

The Geothermal Regime in Sirt Basin, Libya: The Geological Role and Heat Flow Studies

Bottom hole temperatures (BHTs) and static formation temperatures (DSTs) of 70 deep exploratory wells are used to evaluate the geothermal regime in the northeastern part of Sirt Basin. A linear regression was derived between the BHT’s and the DST’s, for correcting the bottom hole temperatures from the drilling factors that lower them from the true formation temperatures. The geothermal gradients were calculated using the corrected BHT’s and the heat flow has been estimated. Interpretation of the geothermal data, utilizing subsurface maps and isothermal geologic cross section, revealed a shallow, local semi-thermal reservoir of Oligo-Miocene age (at depths 1000 m). The geothermal gradients and heat flow values of this reservoir are ranging from 40 - >60°C/Km and from 80 up to >130 mW/m2, respectively. At deeper depths (>1000 m until the maximum depth of investigation), the area has more or less moderate to low geothermal gradients that range from 40 to 2. The study indicates that the vertical and the lateral variations of the formation temperatures, geothermal gradients and the heat flow values are controlled by the structural, groundwater movements as well as lithological and thermal characteristics of the subsurface sequence.

Estimation of true formation temperature from well logs for basin modeling in Persian Gulf

Abstract Static formation temperature should be determined as accurately as possible for a number of reasons; especially it is an essential parameter in petroleum system modeling. In this study, the commonly used empirical methods for log derived temperature correction are reviewed. After that, new correlation was developed by adapting previously presented methods to calibrate log recorded temperature by using true formation temperature from reservoir tests like DST and MDT in Persian Gulf basin. A correction factor formula was proposed by considering both depth and TSC directly. The adapted method provides an accurate calibration of log recorded temperature. In addition, a sensitivity analysis was carried out to reveal the effect of log recorded temperature calibration on 1D petroleum system modeling.

Heat flow in the rifted continental margin of the South China Sea near Taiwan and its tectonic implications

Temperature measurements carried out on 9 hydrocarbon exploration boreholes together with Bottom Simulating Reflectors (BSRs) from reflection seismic images are used in this study to derive geothermal gradients and heat flows in the northern margin of the South China Sea near Taiwan. The method of Horner plot is applied to obtain true formation temperatures from measured borehole temperatures, which are disturbed by drilling processes. Sub-seafloor depths of BSRs are used to calculate sub-bottom temperatures using theoretical pressure/temperature phase boundary that marks the base of gas hydrate stability zone. Our results show that the geothermal gradients and heat flows in the study area range from 28 to 128°C/km and 40 to 159mW/m2, respectively. There is a marked difference in geothermal gradients and heat flow beneath the shelf and slope regions. It is cooler beneath the shelf with an average geothermal gradient of 34.5°C/km, and 62.7mW/m2 heat flow. The continental slope shows a higher average geothermal gradient of 56.4°C/km, and 70.9mW/m2 heat flow. Lower heat flow on the shelf is most likely caused by thicker sediments that have accumulated there compared to the sediment thickness beneath the slope. In addition, the continental crust is highly extended beneath the continental slope, yielding higher heat flow in this region. A half graben exists beneath the continental slope with a north-dipping graben-bounding fault. A high heat-flow anomaly coincides at the location of this graben-bounding fault at the Jiulong Ridge, indicating vigorous vertical fluid convection which may take place along this fault.

Shallow geothermal regime in the Perth Metropolitan Area

Exploration of Perth's geothermal potential has been performed by the Western Australian Geothermal Centre of Excellence (WAGCoE). Detailed vertical temperature and gamma ray logging of 17 Western Australia Department of Water's (DoW) Artesian Monitoring (AM) wells was completed throughout the Perth Metropolitan Area (PMA). In addition, temperature logs from 53 DoW AM wells measured in the 1980s were digitised into LAS format. The logged data are available in the WAGCoE Data Catalogue. Analysis of the gamma ray logs yielded the first estimates of radiogenic heat production in Perth Basin formations. Values by formation ranged between 0.24 and 1.065 μW m−3. The temperature logs provide a picture of true formation temperatures within shallow sediments in the Perth Basin. A three-dimensional model of the temperature distribution was used to produce maps of temperature at depth and on the top of the Yarragadee aquifer. The temperature data were interpreted with a one-dimensional conductive heat model. Significant differences between the model and the observations was indicative of heat moving via non-conductive mechanisms, such as advection or convection. Evidence of non-conductive or advective heat flow is demonstrated in most formations in the region, with significant effects in the aquifers. Average conductive geothermal gradients range from 13°C km−1 to 39°C km−1, with sandstone formations exhibiting average gradients of approximately 25°C km−1, while insulating silt/shale formations show higher average gradients of over 30°C km−1. To produce preliminary heat flow estimates, temperature gradients were combined with thermal conductivities measured elsewhere. The geometric mean heat flow estimates range between 64 mW m−2 to 91 mW m−2, with the standard deviation of the arithmetic mean heat flow ranging between 15 and 23 mW m−2. The study characterises the shallow temperature regime in the Perth Metropolitan Area, which is of direct relevance towards developing commercial geothermal projects.

Deriving geothermal parameters from bottom-hole temperatures in Wyoming

This article describes a method to determine geothermal gradients and formation temperatures using bottom-hole temperatures (BHTs) from wireline-log headers and then tests the method by applying it to analyses from more traditional sources. Bottom-hole temperatures, depths, and times since circulation ended were collected from at least one well in every township that had been drilled for petroleum exploration in the state of Wyoming. Using approximately 3500 BHTs collected from almost 2000 wells, equations were developed for average formation temperatures and geothermal gradients across the state. A method of correcting the average data to true formation temperatures in each individual well was also developed. The geothermal temperatures so derived very closely match temperatures from production BHTs that are the normal industry standard for formation temperatures and suggest that BHT information is much more accurate than commonly thought. The use of BHT measurements to compute temperature gradients was also developed. The effects upon formation temperatures of common data recording errors; of vertical circulation of groundwater, especially above 1700-m (5577-ft) depth; and of lateral groundwater circulation through deep aquifers are documented. The methods developed offer promising avenues for research in the areas of hydrogeology, geothermal exploration, determining formation temperatures, and heat flow.

Bottom-hole temperature correction – the Chad Basin, N.E., Nigeria case study

Correction of the effects of drilling on bottom-hole temperatures, BHTs, measured in drilled wells require multiple measurements in the same well at the same depth but at different elapse times in order to predict true formation temperatures, TFTs. The relaxation of the same-depth requirement for depths differing by less than 100 m allowed the application of two such methods to a qualifying pair of single BHTs from where estimates of Horner plot slope and thermal diffusivity, κ were obtained. By assuming both the slope and к to be typical of the basin, several correction methods were employed to estimate TFTs from a dataset collected from the log-headers of wells drilled for oil and gas exploration in the Chad basin, N.E., Nigeria. Although the different TFT estimates did not agree, sensitivity of the methods to variations of either the slope or к enabled the results to be used to define the range within which the actual TFTs lie. TFT estimates obtained using empirical temperature correction methods were observed to fall within the defined range, and suggest that the data are amenable to empirical correction. Based on significant correlations, empirical equations relating correction and drilled well parameters were therefore derived. Keywords: bottom-hole temperature (BHT), true formation temperature (TFT), horner plot slope, thermal diffusivity, same-depth relaxationGlobal Journal of Geological Sciences Vol. 3(2) 2005: 133-142

Testing Models for Bottom-of-Hole Temperature Recovery, Cooper Basin, South Australia

A set of temperature data from 61 deep petroleum wells drilled in the Cooper Basin of South Australia has been used to test the accuracy of four commonly used models of borehole thermal reequilibration. Models tested include the Horner plot as derived from Bullard (1947), the theoretical dual-media zero circulation cylindrical model of Cooper and Jones (1959), the empirical semi-log plot of Pitt (1986) and the exponential model of Nakaya (1953).The selected models have been fitted to bottom-of-hole temperature data recorded during the recovery period of each well, and are used to predict a value for True Formation Temperature (TFT). These values are then compared with actual temperature measurements derived from Cement Bond Logs (CBL). Recorded on average 482 days after the end of drilling, these temperature measurements are likely to represent TFT.Analysis of the accuracy of model prediction relative to CBL temperature suggests that on average most models tend to underestimate TFT to some degree. The magnitude of this bias is found to be dependent upon assumptions implicit in each model. In most cases, model prediction is improved where at least one perturbed bottom hole temperature (BHT) has been recorded ≥ 20 hours after the end of drilling. To date the best results are derived from the semi-log plot extrapolated to 50 hours.

Correction of Single Log-Derived Temperatures in the Danish Central Graben, North Sea

An equation for correcting log-derived temperatures measured at well depths between 1200 and 5400 m has been derived by comparing log-derived temperatures from wells in the Danish Central Graben (North Sea) with DST temperatures, from the same wells, that are believed to represent true formation temperatures. Equations developed previously using data over different depth ranges from Malaysia and Mexico yield fair results when applied to the North Sea. However, a better fit to the Danish data was obtained using new equations that are similar to those published in the earlier studies. The correction method here is based principally on time since end of circulation (TSC), but it also includes a small dependence on depth. In this study the true subsurface temperature (Ttrue) (°C) is given by \(\hspace*{10pc}T_{\rm true} = T_{\rm surf}+f\cdot(T_{\rm meas} - T_{\rm surf})\) where the correction factor f = 3.07·TSC(−0.09)/(0.47·Z(0.175)), Tsurf is the seafloor temperature in °C, Tmeas is the measured log temperature in °C, TSC is in hours, and Z is the depth below seafloor in meters. When TSC is not known, maximum probable, minimum probable, and most likely values can be estimated from the observed trend of TSC with depth.

Estimation of static formation temperatures in geothermal wells

Stabilized formation temperatures were estimated at different depths in 40 wells from the Los Humeros geothermal field, Mexico, using the Horner and the spherical radial flow (SRF) methods. The results showed that the Horner method underestimates formation temperatures, while the SRF method gives temperatures that are closer to the true formation temperatures. This was supported by numerical simulation of a combined circulation and shut-in period in several wells, and results for well H-26 are presented. Numerical reproduction of logged temperature is more feasible if an initial temperature profile based on the SRF method is employed instead of using an initial temperature profile based on the Horner method.

A simple statistical method for correcting and standardizing heat flows and subsurface temperatures derived from log and test data

Data from subsurface temperature measurements provide widely used and vital input data for maturity modeling_ Because maturity calculations are very sensitive to thermal history, and because reconstruction of the thermal history begins with the modern temperature profile, accurate knowledge of true formation temperatures is vital. Temperature data used in maturity modeling come from a variety of sources, including BHTs derived from single logging runs, BHTs obtained from multiple logging runs at the same depth and corrected using the Horner plot method, RFTs, DSTs, and production tests (PTs)_ However, temperatures obtained using most of these techniques require some correction before they represent true formation temperatures. Unfortunately, the need for these corrections is not generally recognised, leading most modelers to consistently underestimate modern subsurface temperatures_ Such errors can lead to major errors in subsequent calculations of hydrocarbon generation and cracking, and can thus have profound effects on exploration decisions_ In an effort to evaluate the accuracy of data from single logging runs, Horner plots, RFTs, and DSTs or PTs, an extensive temperature data base was developed for the Malay Basin. Basal heat flows calculated for many wells using each type of temperature data were compared. It was found that all other temperature data considerably underestimated subsurface temperatures compared to DSTIPT data, which were assumed to represent true formation temperatures. Results were analyzed using two different statistical approaches, which gave quite consistent conclusions, and average correction factors for each type of temperature data were developed. To be equivalent to heat flows calculated from DSTI PT temperatures, heat flows calculated using single BHT data already subjected to a standard 10% correction had to be corrected upward by an additional 16%, those calculated from Horner plot extrapolations by an additional 14%, and those obtained from uncorrected RFT data by 9%. Measured subsurface temperatures were corrected using a more complex set of equations that take surface temperature (T.) into account. The corrected subsurface temperature To is given by one of the following formulas, where Tb is the uncorrected temperature from a single logging run, Th is the extrapolated temperature obtained from a Horner plot, and Tr is the uncorrected RFT temperature. To = (1.1 eTb - T.)e1.16 + T. To = (Th - T.)e1.14 + T. To = (Tr - T.)e1.09 + T. Although these correction factors were developed for the Malay Basin, evidence presented by other workers suggests that corrections are needed in other basins as well, and that the magnitude of the corrections suggested here is reasonable for other areas. Future work should test these hypotheses and extend this calibration to ·other types of basins in other parts of the world. The correction factors established in this study only represent statistical averages, and cannot be expected to work well in all cases. Whenever DST or PT data are available, they should be weighted considerably more heavily than any other type of data, even those corrected by the best methods available. In the absence ofDST or PT data, however, these correction methods will greatly increase our confidence in subsurface temperatures from RFTs or from wireline logs.

Temperature Corrections for Bore Hole Data as Part of Thermal State, Source and Maturation Investigations of Basins

Subsurface temperature data are vital for many aspects of petroleum exploration (and development), especially maturation and basin thermal history. However, much of the older temperature data that have been obtained in Australian petroleum exploration are of limited usefulness, mainly because of restricted information concerning circulation times and time(s) of logging. Only very occasionally during petroleum exploration are temperature data obtained after the perturbing (mainly cooling) effects of drilling have subsided. Hence corrections need to be applied by using circulation time and time since circulation for correcting the original temperature measurements for a logging suite. Provided several logging runs have been made, and the data obtained are reasonably accurate, then it is generally accepted that a good approximation to the true formation temperature can be obtained if "corrections" are applied. For older wells for which only limited temperature and time data are available a simple procedure has been established to correct temperature data — by adding 15% or 10% to measured temperatures (first to last in a logging suite). If that procedure is applied to fuller data sets, it is found that there is good agreement between the various correction techniques. Accurate temperature data can provide the basis for determining temperature gradients and heat flow and thence can be useful for correlation (between wells and with other data) and for maturation studies, including burial history. Useful temperature data — for analysis and for prediction — in petroleum exploration is necessary for a full understanding of the thermal setting of a sedimentary basin. Temperature studies can also be useful in exploration for and studies of groundwater, metallic mineral deposits and coal.

Formation temperatures determined from stochastic inversion of borehole observations

SUMMARY Hole Temperature (BHT) observations are generally influenced by drilling-induced thermal disturbances which must be corrected for. This paper presents a correction method based on a 1-D conductive finite element model and an inverse procedure for parameter estimation. While the technique may be applied to any section of the borehole this paper focuses on the correction of bottom hole temperatures. Model parameters are mud temperature during drilling and circulation at the depth of BHT observations, borehole radius, thermal parameters of mud and formation, and the equilibrium formation temperature. Data are one or more successive BHTs and their standard deviations. Prior to inversion the model parameters are assigned reasonable values and standard deviations that reflect the confidence in those values. A high level of confidence implies small standard deviations and vice versa. The process of inversion extracts the most likely values of all free parameters including the equilibrium formation temperature. Furthermore, the initial uncertainties in all parameters and data are propagated into uncertainties in the final parameter estimates. The formation temperature estimate is an unbiased estimate of the true formation temperature when the u priori parameter estimates and their standard deviations are consistent with the actual physical conditions in the borehole and the formation. The method on average yields 5-10 per cent higher equilibrium temperature estimates than does the Horner plot method and displays a strong consistency with temperature obtained during production tests. This is of importance to the understanding of terrestrial heat flow density patterns, and thermal structure of sedimentary basins, and to the modelling of hydrocarbon generation. The theory and results from the processing of 41 BHT series from 27 industrial wells in the North Sea Central Graben are presented.

Application of bottom-hole temperature corrections in geothermal studies

Bottom-hole temperature (BHT) data measured in oil and gas wells constitute a large, low quality set of temperature observations commonly used in geothermal studies. Raw BHT data are, on the average, cooler than true formation temperatures. To estimate true formation temperatures, corrections must be applied. Empirical BHT corrections may be applied to BHT data for which only depths of measurement are known, but may not be valid outside of the area for which they are calibrated. If multiple BHT measurements from successive logging runs are available, the Horner plot correction procedure can be used. The accuracy of the Horner plot is limited by simplifying assumptions made in its derivation, and by the common lack of information on parameters such as duration of mud circulation. More detailed and complete treatments provide insight into the borehole equilibration process, but their application is similarly limited by a common lack of data regarding borehole thermal properties. A new type of empirical correction procedure may be derived in some areas and allows a correction to be made for BHTs for which only a depth and time of measurement are known. Noise is invariably present in the BHT data found on well log headers from oil and gas wells, and the consequence of noise in these data should be considered when choosing and applying a correction. Although the average nature and magnitude of error in raw BHT data may be approximately known, application of all BHT correction procedures to the typical data available from oil and gas well log headers usually involves an unknown amount of error. Reliable estimates of average geothermal conditions can be made only from suites of BHT data, and are condemned to be imprecise at best.

Estimation of formation temperature from bottom‐hole temperature measurements: COST ♯1 well, Norton Sound, Alaska

We recently developed a numerical method, the Formation Temperature Estimation (FTE) model, to determine formation temperatures by inversion of borehole temperature (BHT) measurements (Cao et al., 1988a). For more than two BHT measurements, the FTE model can estimate (1) true formation temperature [Formula: see text], (2) mud temperature [Formula: see text] at the time the mud circulation stops, (3) thermal invasion distance R into the formation before the formation is at the true formation temperature, (4) formation thermal conductivity K perpendicular to the borehole, and (5) efficiency factor F for mud heating in the borehole after mud circulation has stopped. The method optimizes three free parameters: τ (diffusion time‐scale), ε (scaling parameter related to the thermal invasion distance R), and [Formula: see text] (normalized efficiency factor for mud heating.

Formation temperature estimation by inversion of borehole measurements, Part II: Effects of fluid penetration on bottom‐hole temperature recovery

Using nonlinear inverse techniques, we show that the change in borehole temperature with time, after mud circulation has stopped, can be used to provide very precise estimates of true formation temperatures and of mud temperature at the time circulation stopped. In addition, ruggedly stable estimates can also be made of the thermal invasion distance, the formation thermal conductivity, and the efficiency of heating the mud by the thermal recovery wave. It is well known that convective heat flow into (or out of) the formation influences the thermal recovery. We show that the flow rate at the borehole can also be obtained approximately from the borehole temperature measurements using the inverse method. Fidelity and reproducibility of the inverse procedure arc examined using synthetic data. Applications to field data from three wells in the Cooper basin of Australia and four wells in the North Sea confirm the accuracy of the method in satisfying the observed data, in determining true formation temperatures, and in assessing the magnitude of fluid penetration into the formation.

Formation temperature estimation by inversion of borehole measurements

We describe a new numerical method that uses inverse methods to model thermal stabilization of a borehole after drilling mud circulation has stopped. The following five geophysical parameters can be estimated from the method: (1) true formation temperature [Formula: see text] (2) mud temperature [Formula: see text] at the time the mud circulation stops; (3) thermal invasion distance (R) into the formation before the formation is at the true formation temperature[Formula: see text]; (4) formation thermal conductivity (K) perpendicular to the borehole; and (5) efficiency factor (F) for heating mud in the borehole after mud circulation has stopped. Crucial input data for the model are the temperature measurements with shut‐in time taken at a fixed depth, more than two measurements being required, and the mud temperature at the surface at the time circulation stops. Other input data include the radius of the borehole, and the densities and specific heats of the drilling mud and of the formation on which the temperature measurements are made. Applications of the new inverse procedure to both synthetic data and field data show that the true formation temperature in many cases can be estimated precisely (to within about 0.4 percent); that the mud temperature can be estimated with acceptable accuracy (5 percent or so); while the thermal conductivity (K), the thermal invasion distance (R), and the efficiency factor (F) can be roughly estimated, provided high‐quality data are available.

Stabilization of bottom‐hole temperature in the presence of formation fluid flows

Reliable estimates of bottom‐hole temperature (BHT) in oil wells are of considerable interest in reservoir engineering problems as well as in geothermal research. Because BHT measurements are usually made soon after drilling, true formation temperature can be obtained only by correcting for the effects of drilling disturbances. The magnitude of drilling disturbance depends upon duration of drilling, time elapsed after stoppage of drilling, well characteristics, thermal properties of drilling fluid, and the nature of heat exchange between the well and the formation.

Determination of True Static Formation Temperature from Well Logs

Abstract Several concepts that attempt to determine static (true) formation temperature from log-derived BHT measurements with and without knowledge of drilling fluid circulation time have been reviewed. Whereas several refined models are available, the simple Horner-type technique provides quick and reliable static (true) formation temperature estimates.