Borehole Temperature Data Research Articles

97/01739 Recovery of highly viscous products from open or closed storage areas such as tanks and sumps

The mudstones in the third member of the Shahejie Formation (Es3) are the primary source rocks in the Banqiao Depression of Bohai Bay Basin. They are rich in organic matter with Total Organic Carbon (TOC) content up to 3.5%. The sandstones in the Es3 member are the deepest proven hydrocarbon reservoir rocks with measured porosity and permeability values ranging from 3.6% to 32.4% and from 0.01 md to 3283.7 md, respectively. One, two and three-dimensional basin modelling studies were performed to analyse the petroleum generation and migration history of the Es3 member in the Banqiao Depression based on the reconstruction of the burial, thermal and maturity history in order to evaluate the remaining potential of this petroleum province. The modelling results are calibrated with measured vitrinite reflectance (Ro), borehole temperatures and some drilling results of 63 wells in the study area. Calibration of the model with thermal maturity and borehole temperature data indicates that the present-day heat flow in the Banqiao Depression varies from 59.8 mW/m2 to 61.7 mW/m2 and the paleo-heat flow increased from 65 Ma to 50.4 Ma, reached a peak heat-flow values of approximately 75 mW/m2 at 50.4 Ma and then decreased exponentially from 50.4 Ma to present-day. The source rocks of the Es3 member are presently in a stage of oil and condensate generation with maturity from 0.5% to 1.8% Ro and had maturity from 0.5% to 1.25% Ro at the end of the Dongying Formation (Ed) deposition (26 Ma). Oil generation (0.5% Ro) in the Es3 member began from about 37 Ma to 34 Ma and the peak hydrocarbon generation (1.0% Ro) occurred approximately from 30 Ma to 15 Ma. The modelled hydrocarbon expulsion evolution suggested that the timing of hydrocarbon expulsion from the Es3 member source rocks began from 31 Ma to 10 Ma with the peak hydrocarbon expulsion shortly after 26 Ma. Secondary petroleum migration pathways in the Es3 member of the Banqiao Depression are modelled based on the structure surfaces at 26 Ma and present-day, respectively. The migration history modelling results have accurately predicted the petroleum occurrences within the Es3 member of the Banqiao Depression based on the calibration with drilling results of 10 oil-producing wells, one well with oil shows and 52 dry holes. Six favorable zones of oil accumulations in the Es3 member of the Banqiao Depression are identified especially oil accumulation zones I and II due to their proximity to the generative kitchens, short oil migration distances and the presence of a powerful drive force.

Climate Change in the Urals, Russia, Inferred from Borehole Temperature Data

Borehole temperatures in the central and south Urals were analysed for the past ground surface temperature (GST) signal. 31 highquality temperature logs were selected for this purpose and inverted with algorithms based on the generalised least squares theory. The signal to noise ratio was improved by averaging the results of individual borehole inversions. No distinct regional trends were found in the studied region except for some indications of more pronounced warming in the south. The mean GST history (GSTH) was characterised by cooling down to −0.6 °C in the 18th century and subsequent warming to 0.5 °C above the longterm mean at the beginning of this century, and to 1 – 1.5 °C by 1980. The stability of the mean GSTH was tested in dependence on the number of holes used for the averaging. It showed that any subset of 15 holes yielded a GSTH similar to that obtained from the whole set. A surface air temperature (SAT) time series comprising the period 1832 – 1989 was combined from 17 meteorological records. Its least squares warming rate of 1.1 °C per 100 years is somewhat higher than that of the GST (0.7 – 0.8°C/100 years) in the same period.

Thermal history of the eastern margin of the Gulf of Suez, I. reconstruction from borehole temperature and organic maturity measurements

The Gulf of Suez is a Tertiary continental rift associated with prominent flank uplift. Despite numerous studies which focused mainly on the western and central parts of the graben, the thermo-mechanics controlling the tectonic evolution of the Gulf of Suez is still enigmatic. We have integrated borehole temperatures and organic maturity measurements in the eastern margin of the Gulf of Suez, in order to study rift-related paleothermometry and the present-day thermal regime. The data obtained suggest that the present thermal regime represents the maximum heat flow and temperatures for the sedimentary section in the basin. Furthermore, lateral distributions of geothermal gradient and heat flow in the Gulf of Suez do not correlate, mainly because of extensive variability in lithology and thermal conductivity. Rift-related heat flow increases systematically and subparallel to the rift axis, from about 60 mW/m 2 in the Darag subbasin in the north to about 80 mW/m 2 in the Ras Garra area in the south. Both values are higher than 45 mW/m 2, the average heat flow assumed for the pre-rift stage and the characteristic level for the present-day heat flow away from the rift. The north to south increase in heat flow probably reflects the southward increase of extension as well as lateral transfer of heat flow from the Red Sea. This latter conclusion is supported by the fact that heat flow in the southern Gulf of Suez recorded by the paleothermometric reconstructions and borehole temperature data is somewhat higher than that estimated by model calculations for the extension derived from structural and subsidence reconstruction.

Inference of ground surface temperature history from borehole temperature data: a comparison of two inverse methods

The problem of inferring ground surface temperature history (GSTH) from borehole temperature-depth data, like virtually every other geophysical inverse problem, is characterized by nonuniqueness because of an inadequate amount of data, and instability due to presence of noise. As such, the inverse solution for a given data set depends on model representation (parameterization), optimization method, and the subjective view of the researcher. In this work we attempt to identify the cause of differences that arise from the application of two inverse methods that are currently widely used in inferring a GSTH: a generalized non-linear Bayesian formulation based on the method of least squares called Functional Space Inversion (FSI), and a linear formulation solved by the method of singular value decomposition (SVD). We use the same forward solver and spatial and temporal discretizations in the two methods in order to eliminate possible differences arising from these sources. Experiments with synthetic noise-free data show that when noise is not a factor both methods are essentially equal in their ability to identify and represent both the pre-existing reference state and the transient excursion therefrom. However, in the presence of noise, differences arise between the different model representations, particularly when the borehole site has experienced a net warming or cooling in the recent millennium. For such a site, the two methods can give significantly different estimates for the prior baseline or reference surface temperature, and for the subsequent changes in surface temperature. SVD is less effective at recovering the steady-state reference temperature when the mean of the transient deviates significantly from the prior steady-state temperature. In FSI, the use of an a priori null hypothesis for the deviation from the steady-state, along with the imposition of smoothing constraints, yields a robust estimate of the prior steady-state, but a conservative estimate of the transient.

Resolution of ground temperature histories inverted from borehole temperature data

Inversion methods have been used to determine ground temperature history from borehole temperature data. This paper examines the resolution of an inversion method based on singular value decomposition. The method includes in the constraints the rate of change of subsurface if available. The response of the Earth to a unit pulselike change in surface temperature and the model resolution were calculated to determine the details of ground temperature variations obtainable from geothermal data. The model parameters estimated by the inversion correspond to averages over time intervals of increasing length with time. For a unit impulse temperature change occurring at time t before present, the estimated ground temperature history shows the event “spread” over at least 60% the time of occurrence. In practice, the resolution is not improved by increasing the sampling frequency of the data. Likewise, the simultaneous inversion of the temperature profile and of its time derivative does not significantly improve the resolution. Selection of a particular parametrization may improve resolution of the chosen parameters, but not the actual resolution since the parameters represent longer time averages. Temperature data from the Minchin Lake borehole in western Ontario, which was logged twice over 15 years, have been inverted to illustrate these conclusions.

Ground temperature history in central Europe from borehole temperature data

SUMMARY Ground temperature histories (GTH) are inferred from temperature measurements in several boreholes of south-eastern Germany and western Bohemia (Czech Republic). The GTHs that can be extracted from these boreholes, ranging in depth between 150 and 700m, cover the past 250yr. Both data sets were inverted separately and yield consistent GTHs. They were also inverted jointly to yield a regional GTH of the past 250yr for this part of Europe. The results indicate two main episodes in the mean ground temperature with (1) a cooling period from 1750-1800 to 1930-1950, followed by (2) short colder and warmer periods until now. The same trends are found in the meteorological records at four nearby weather stations (Bayreuth, Jena, Munchen and Praha), but the meteorological record in Berlin is clearly distinct. The GTH for this part of Europe is also markedly different from one obtained in central France. These differences are consistent with the spatial variability of climatic trends.

Effects of subsurface heterogeneity on the inference of climate change from borehole temperature data: Model studies and field examples from Canada

All existing approaches to the analysis and interpretation of borehole temperatures in terms of a ground surface temperature history are based on the one‐dimensional theory of heat conduction. Deviations from this idealization are manifest as noise in the interpretation. We present numerical experiments that explore the effects of three‐dimensional subsurface heterogeneity on ground surface temperature histories inferred from borehole temperature profiles. Inversions of steady state temperature profiles containing such three‐dimensional “noise” reveal that in an inversion formulation incorporating a priori information, spurious temperature histories can emerge when the a priori constraints on subsurface temperatures and thermophysical properties are too tight, i.e., when arbitrarily small variations in subsurface temperatures and thermophysical properties are interpreted to have significance for the derived climate history. Relaxation of the a priori constraints enables an effective muting of the spurious histories. Similar experiments conducted on synthetic transient signals confirm the steady state results but also reveal that relaxation of the a priori constraints will also lead to a loss of signal if the level of relaxation is excessive. Our experiments suggest that relaxation of constraints on thermal conductivity is more efficient than relaxation of borehole temperatures in suppressing artifacts arising from the three‐dimensional effects. We identify a range of constraints in which reasonable noise suppression and signal recovery are both achieved and then reprocess data from 22 Canadian boreholes for which surface temperature histories had earlier been derived by ourselves and others. Our reprocessed results reveal a remarkably simple surface temperature history common to much of eastern Canada. This history comprises a recent warming interval commencing in the nineteenth century, in which the surface temperature increased by some 1–4°C. Approximately 0.5–1.0°C of this increase was a recovery from a preceding cooler interval in which the temperature was below the long‐term mean. The remainder of the increase represents warming that exceeds the long‐term mean.

Subsurface temperature—depth profiles, anomalies due to climatic ground surface temperature changes or groundwater flow effects

Climatic temperature changes at the ground surface propagate downward to the subsurface creating transient disturbances to the temperature—depth ( T( z)) profile. Due to the poor thermal diffusivity of rocks the disturbances are preserved long times in the bedrock, and in a conductive regime it is possible to reveal the ground surface temperature (GST) history from borehole temperature data with inversion techniques. Geothermal temperature measurements thus provide a source of palaeoclimatic information which so far has not been utilized extensively. Inversion of GST history is, however, not straightforward and any disturbing effects should be excluded before the data can be utilized in inversion. Groundwater flow is of special importance in this respect because it is a common phenomenon in bedrock and convection often produces temperature—depth profiles resembling those affected by palaeoclimatic GST changes. In interpreting temperature—depth ( T( z)) logs it is therefore not always clear whether the recorded vertical gradient variations should be attributed to the effects of palaeoclimatic ground surface temperature (GST) changes or to groundwater circulation. Using several synthetic T( z) profiles and applying general least squares inversion techniques we simulate a situation of “misinterpreting” the curvature of the T( z) profile in terms of palaeoclimatic GST changes, although it is actually produced by convective heat transfer due to groundwater flow. For comparison the opposite case is also studied, namely, genuine palaeoclimatic effects are misinterpreted as being due to disturbances caused by groundwater flow. A homogeneous half-space model is used to model T( z) profiles disturbed conductively by GST changes during the time interval 10–10000 yr B.P. and a one-dimensional porous layer model is applied for convective heat transfer calculations. The results indicate that a given T( z) profile can be attributed to either of these effects with reasonable parameter values. In addition to the synthetic T( z) profiles, a case history from a 958 m deep drill hole at Lavia, southwestern Finland, is presented. Special care is needed in analyzing T( z) data. A knowledge of geothermal data, such as temperature, thermal conductivity and diffusivity is not necessarily adequate for determining which of the phenomena (or whether a combination of them) provides the most probable interpretation of a T( z) profile. Additional information on the hydrogeological properties of the drilled strata is essential.

Least-squares optimum-order regional geothermal gradient determination from deep borehole temperature data with application to the Western Desert of Egypt

This paper discusses an approach to determining the least-squares optimum order of a polynomial fit to temperature-gradient data. The optimum is reached when two successive least-squares regional maps are sufficiently similar. This similarity is measured by the correlation factor between the polynomials.

A comparison of five different analyses in the interpretation of five borehole temperature data sets

To assess the effectiveness of various methods in inferring ground surface temperature history (GSTH) from perturbed borehole temperature data, five synthetic and real data sets were prepared and disseminated to interested groups for analysis. This report summarizes the results obtained by five different groups using different inverse methods. The five inverse methods yield similar results inasmuch as the salient features of the GSTH are concerned. However, the estimated GSTHs differ in details of the timing and the magnitude of changes. This is attributed to the differences in parameterization schemes and to the different a priori constraints imposed on the GSTH. Better agreement among the inverse methods may be obtainable when information other than that contained in the borehole data is incorporated.

A comparison of five different analyses in the interpretation of five borehole temperature data sets

To assess the effectiveness of various methods in inferring ground surface temperature history (GSTH) from perturbed borehole temperature data, five synthetic and real data sets were prepared and disseminated to interested groups for analysis. This report summarizes the results obtained by five different groups using different inverse methods. The five inverse methods yield similar results inasmuch as the salient features of the GSTH are concerned. However, the estimated GSTHs differ in details of the timing and the magnitude of changes. This is attributed to the differences in parameterization schemes and to the different a priori constraints imposed on the GSTH. Better agreement among the inverse methods may be obtainable when information other than that contained in the borehole data is incorporated.

A comparative study of inverse methods for estimating climatic history from borehole temperature data

The inference of ground surface temperature (GST) history from subsurface temperature-depth ( T- z) profiles is an ill-posed inverse problem; due to the different ways in which the problem may be parameterized and constraints imposed, the solution is method-dependent. As such, when attempting to reconstruct GST patterns by juxtaposing results obtained with different inverse methods, it is essential that a systematic evaluation and comparison of the methods be conducted. In this study, we consider three least squares methods: the functional space inversion (FSI), the spectrum inversion (SI), and the singular value decomposition (SVD), all of which are based on the theory of 1-D heat conduction in a layered medium. We describe briefly the three methods, with emphasis on their formulational differences and similarities, and then present both synthetic and real examples to illustrate their effects. It is shown that, despite the theoretical differences, the three methods have the potential of giving similar results, provided that the constraints, imposed to stabilize the solutions, are appropriately chosen. Since these constraints are to some extent specific to the actual GST history, it is desirable that some information, such as the amplitudes and time scales of GST variations, be incorporated in the inversion in order to achieve optimal results.

Combining borehole temperature and meteorologic data to constrain past climate change

Geothermal observations from a suite of boreholes in western Utah, USA, combined with meteorologic data at nearby weather stations are used to test the hypothesis that temperatures in the earths subsurface contain an accurate record of recent climate change. The change in air temperature over the last hundred years successfully predicts detailed subsurface temperature profiles to better than ±0.05°C, indicating that ground temperatures tract air temperatures over long periods and that climate change signals are conducted into, and recorded in, the solid earth by the process of heat conduction. We combine borehole temperature data with meteorologic data from the nearest weather station to determine the time averaged difference between surface ground temperature and surface air temperature for borehole-weather station pairs and to infer the long term mean air temperature prior to the observational record. For our western Utah sites the preobservational mean temperature is close to the average surface air temperature for this century suggesting that up to 0.5°C of warming deduced from the last 100 years of weather station data may be attributed to recovery from a cool period at the turn of the century.

The extent of temporal smearing in surface-temperature histories derived from borehole temperature measurements

The ability of borehole temperature data to resolve past climatic events is investigated using Backus-Gilbert inversion methods. Two experimental approaches are considered: (1) the data consist of a single borehole temperature profile, and (2) the data consist of climatically-induced temperature transients measured within a borehole during a monitoring experiment. The sensitivity of the data's resolving power to the vertical distribution of the measurements, temperature measurement errors, the inclusion of a local meteorological record, and the duration of a monitoring experiment, are investigated. The results can be used to help interpret existing surface temperature histories derived from borehole temperature data and to optimize future experiments for the detection of climatic signals.

A comparative study of inverse methods for estimating climatic history from borehole temperature data

The inference of ground surface temperature (GST) history from subsurface temperature-depth ( T- z) profiles is an ill-posed inverse problem; due to the different ways in which the problem may be parameterized and constraints imposed, the solution is method-dependent. As such, when attempting to reconstruct GST patterns by juxtaposing results obtained with different inverse methods, it is essential that a systematic evaluation and comparison of the methods be conducted. In this study, we consider three least squares methods: the functional space inversion (FSI), the spectrum inversion (SI), and the singular value decomposition (SVD), all of which are based on the theory of 1-D heat conduction in a layered medium. We describe briefly the three methods, with emphasis on their formulational differences and similarities, and then present both synthetic and real examples to illustrate their effects. It is shown that, despite the theoretical differences, the three methods have the potential of giving similar results, provided that the constraints, imposed to stabilize the solutions, are appropriately chosen. Since these constraints are to some extent specific to the actual GST history, it is desirable that some information, such as the amplitudes and time scales of GST variations, be incorporated in the inversion in order to achieve optimal results.

The extent of temporal smearing in surface-temperature histories derived from borehole temperature measurements

The ability of borehole temperature data to resolve past climatic events is investigated using Backus-Gilbert inversion methods. Two experimental approaches are considered: (1) the data consist of a single borehole temperature profile, and (2) the data consist of climatically-induced temperature transients measured within a borehole during a monitoring experiment. The sensitivity of the data's resolving power to the vertical distribution of the measurements, temperature measurement errors, the inclusion of a local meteorological record, and the duration of a monitoring experiment, are investigated. The results can be used to help interpret existing surface temperature histories derived from borehole temperature data and to optimize future experiments for the detection of climatic signals.

Combining borehole temperature and meteorologic data to constrain past climate change

Geothermal observations from a suite of boreholes in western Utah, USA, combined with meteorologic data at nearby weather stations are used to test the hypothesis that temperatures in the earths subsurface contain an accurate record of recent climate change. The change in air temperature over the last hundred years successfully predicts detailed subsurface temperature profiles to better than ±0.05°C, indicating that ground temperatures tract air temperatures over long periods and that climate change signals are conducted into, and recorded in, the solid earth by the process of heat conduction. We combine borehole temperature data with meteorologic data from the nearest weather station to determine the time averaged difference between surface ground temperature and surface air temperature for borehole-weather station pairs and to infer the long term mean air temperature prior to the observational record. For our western Utah sites the preobservational mean temperature is close to the average surface air temperature for this century suggesting that up to 0.5°C of warming deduced from the last 100 years of weather station data may be attributed to recovery from a cool period at the turn of the century.

Climatic changes in central and eastern Canada inferred from deep borehole temperature data

We analyzed data from 23 boreholes at 19 sites in central and eastern Canada, for the purpose of estimating ground surface temperature (GST) histories. These boreholes were logged down to at least 550 m depth with thermistor probes. Thermal conductivity measurements had been previously made at small depth intervals for the entire depth ranges of most of the boreholes. The temperature profiles of these boreholes do not indicate water disturbance. We estimated terrain effects for each borehole using a time dependent solid-angle method. The thermal perturbations caused by lakes or deforestation near the borehole sites are insignificant in most cases. However, four of the holes were found to be severely influenced by terrain effects. GSTs estimated from the borehole data less influenced by the terraineffects form two groups. The first group, which are generally from data of better quality, show a cold period near the end of the last century before the recent warming trend; the second show it 80–100 years earlier. We consider the former typical of the climate of the Boreal climatic region of Canada. The difference between the two groups may reflect the spacial variability of the climate. Four GST estimates do not belong to either type, and the reasons are discussed.

Climatic changes in central and eastern Canada inferred from deep borehole temperature data

We analyzed data from 23 boreholes at 19 sites in central and eastern Canada, for the purpose of estimating ground surface temperature (GST) histories. These boreholes were logged down to at least 550 m depth with thermistor probes. Thermal conductivity measurements had been previously made at small depth intervals for the entire depth ranges of most of the boreholes. The temperature profiles of these boreholes do not indicate water disturbance. We estimated terrain effects for each borehole using a time dependent solid-angle method. The thermal perturbations caused by lakes or deforestation near the borehole sites are insignificant in most cases. However, four of the holes were found to be severely influenced by terrain effects. GSTs estimated from the borehole data less influenced by the terraineffects form two groups. The first group, which are generally from data of better quality, show a cold period near the end of the last century before the recent warming trend; the second show it 80–100 years earlier. We consider the former typical of the climate of the Boreal climatic region of Canada. The difference between the two groups may reflect the spacial variability of the climate. Four GST estimates do not belong to either type, and the reasons are discussed.

Geothermal Evidence from Canada for a Cold Period Before Recent Climatic Warming

Three deep boreholes in a small area in Quebec, each having two high-accuracy temperature logs separated by 22 years, allow reliable determination of the ground surface temperature history during the past few centuries. The temperature logs show that the recent climatic warming was preceded by a cold period near the end of the 19th century in this area. The presence of such a cold period is also suggested by borehole temperature data from other areas in Canada.