Paleo-heat Flow Research Articles

Thermal regime and petroleum systems in Junggar basin, northwest China

The conversion of organic matter into oil and gas depends upon temperature and time, and the study of thermal maturation of oil-source rocks in a petroleum system is of importance for formation of a petroleum system. Based on the temperature data from 196 wells and thermal conductivity measurements of 90 core samples, altogether 35 heat flow data are obtained in the Junggar basin. The results show that the Junggar basin is a relatively “cold” basin at present, with a mean temperature gradient and heat flow of 21°C/km and 42 mW/m 2, respectively. Thermal history reconstructed from vitrinite reflectance data indicates that the Paleozoic formations experienced their maximum paleotemperature during the Permian and Triassic at higher paleoheat flow of about 85 mW/m 2 and that the basin then cooled down to the present low heat flow. The high paleoheat flow can be attributed to the Carboniferous to Permian rifting. The thermal evolution has a quite important effect on the formation and evolution of the petroleum systems in the Junggar basin, i.e. the Permian and the Jurassic systems. The Jurassic petroleum system is quite limited in space for the cooled thermal regime during the Meso-Cenozoic and the source rocks of the Middle–Lower Jurassic entered the oil window only along the North Tianshan foreland region, where the Jurassic is buried to the depth of 5–7 km at present. In contrast, the Middle–Lower Permian source rocks have experienced oil and gas generation in late Permian to Triassic, and the Permian petroleum system was formed prior to the Triassic when the upper Paleozoic formations reached their maximum paleotemperature due to higher paleoheat flow.

Thermal history and tectonic subsidence of the Bohai Basin, northern China: a Cenozoic rifted and local pull-apart basin

The Bohai Basin is a part of the larger Bohai Bay Basin, a Cenozoic rifted intraplate basin. Heat flow measurements show that the Bohai Basin is characterized by present-day heat flow varying between 53 and 74 mW/m 2 with a mean of 63 mW/m 2. However, thermal history analyses derived from vitrinite reflectance (VR) and apatite fission track (AFT) data, indicate that tertiary cooling took place following a period of much higher paleo-heat flow (70–90 mW/m 2) prior to ∼25 million years to the present. Furthermore, tectonic subsidence analysis reveals that the Bohai Basin experienced episodic sub-rifting processes from the Eocene to the end of the Oligocene. The post-rift thermal subsidence was superimposed by intensified subsidence from the late Miocene (12 million years) in the Bozhong Depression and from the early Quaternary (2.4 million years) in the East Liao Bay, indicating a rejuvenation of sedimentation related likely to transpressional structures developed locally on strike–slip faults. The present results indicate that there is good agreement between the reconstructed thermal history and the timing of the tectonic subsidence stages within the Bohai Basin. The Bohai Basin is an early Cenozoic rifted and local pull-apart sub-basin of the larger Bohai Bay Basin.

ABSTRACT: The utilization of paleo heatflow to define a source rock maturity: case study at Ngimbang-01, North East Java Basin, Indonesia

ABSTRACT: The utilization of paleo heatflow to define a source rock maturity: case study at Ngimbang-01, North East Java Basin, Indonesia

Thermal maturity in the Shimanto accretionary prism, southwest Japan, with the thermal change of the subducting slab: fluid inclusion and vitrinite reflectance study

The P– T path of the Cretaceous Shimanto accretionary complex, western Shikoku, southwest Japan, was determined by a combination of vitrinite reflectance data and homogenization temperatures of fluid inclusion analysis. Within the complex, the P– T paths of the Upper Cretaceous Yokonami Melange and surrounding coherent strata were compared. No P– T difference was found between the Yokonami Melange and surrounding strata. At least two types of fluids: methane-rich and water-rich fluids, migrated at different stages during metamorphism within the complex. The methane-rich fluid was initially trapped in vein quartz under pressures of ~260 MPa and a geothermal gradient of ~24°C/km. The water-rich fluid was included in calcite at 95–125 MPa and a geothermal gradient of 50°C/km. The complex sequence of occurrence of the vein minerals and radiometric age data suggest that the water-rich fluid was trapped during the Kula–Pacific ridge subduction into the Shimanto accretionary complex. The paleoheat flow values for the two stages of subduction are consistent with the changes in the inferred slab age. The metamorphism of the Shimanto accretionary complex was predominantly controlled by the thermal condition of the subducting plate.

Thermal structure and paleo‐heat flow in the Shimanto accretionary prism, Southwest Japan

Abstract Thermal structural analysis and paleo‐heat flow estimation provide clues to understanding the thermal evolution of the accretionary complex. The thermal structure and heat flow in the Jurassic Chichibu and Cretaceous to Tertiary Shimanto accretionary complex, Southwest Japan, have been investigated by vitrinite reflectance measurement and fluid inclusion analysis. As a result, the local and multistage metamorphisms were recognized as follows. First, the Tertiary complex around the Miocene Ashizuri granite underwent exposure to extra‐high temperatures. Second, the Okitsu Melange underwent exposure to higher temperatures than the surrounding strata and was formed concurrently with the Kula‐Pacific ridge subduction beneath the Japanese Islands in the Eocene. Finally, the thermal structure of most of the Cretaceous and southern Jurassic complexes is independent of the geologic structure, indicating that these areas suffered thermal overprint. Regional radiometric dating studies show that most of the Cretaceous Shimanto complex was heated in the Eocene; the thermal overprint might have occurred as a result of ridge subduction. The heat flow during peak heating was estimated to be 95–120 mW/m2 except for the Cretaceous Okitsu melange and the Cretaceous Nonokawa formation, north of the Okitsu Melange; a much higher value of heat flow of ~200 mW/m2 was estimated in the Okitsu Melange. An estimation of heat flow failed for the non‐okawa formation because thermal equilibrium between the fluid and rocks has not yet been reached. It is probable that the southern strata underwent a higher heat flow. Such a trenchward increase in heat flow resembles the present situation of the Nankai Trough, although the heat flow in the Eocene was much higher.

Tectonic controls on the hydrogeology of the Rio Grande Rift, New Mexico

Mathematical modeling is used in this study to assess how tectonic movement of fault blocks and fault permeability influence the present‐day and paleohydrogeology of the Rio Grande Rift near Socorro, New Mexico. Our analysis focuses on active and ancient groundwater flow patterns and hot spring development within the southern La Jencia and Socorro subbasins. The best agreement between model results and present‐day and paleoheat flow data was achieved by representing faults as passive surfaces and incorporating 2 km of moderately permeable (10−14.0 m2) fractured crystalline rocks into the hydrogeologic model. Quantitative results indicate that changes in groundwater flow patterns across the basin are primarily generated by the truncation/reconnection of aquifers and confining units. Calculated flow patterns help to explain the annealing of apatite fission tracks within Eocene Baca Formation clasts to the east of Socorro, potassium metasomatism mass balance constraints within Oligocene volcanics and overlying Santa Fe Group deposits, and the timing of barite/fluorite ore mineralization within the Gonzales prospect on the eastern edge of the Rio Grande Rift. We estimate that about 5% of mountain front recharge penetrates to a depth of 2.8 km below the sedimentary pile. This may have implications for water resource planners who have historically focused on groundwater resource development within the shallow alluvial deposits along the Rio Grande Rift valley.

Modeling Petroleum Generation in the Southern Muglad Rift Basin, Sudan1

Maturity and petroleum generation have been modeled in a 120-km-long northeast-southwest cross section of the Southern Muglad basin, Sudan. The section passes close to the Unity and Kaikang areas, which provide well control on the structure interpreted from gravity and seismic reflection profiles. Modeling of geotherms from corrected bottom-hole temperatures indicates present heat flows around 60 mW/m2 in the well control areas. Using measured vitrinite data as calibrant, maturity can be modeled equally well with a constant paleoheat flow similar to the present day or with a complex heat flow pattern related to rifting. A geologically realistic complex heat flow model was employed to calculate the timing of generation and expulsion from the Lower Cretaceous lacustrine source rocks of the Abu Gabra and Sharaf formations. Kinetic (Easy% Ro) calculation of vitrinite maturity indicates a projected oil preservation depth limit around 4000 m shallowing to around 3500 m northeast of Unity near the basin margin.

Present heat flow and paleo-geothermal regime in the Canadian Arctic margin: analysis of industrial thermal data and coalification gradients

Calculations of the present geothermal gradient and terrestrial heat flow were made on 156 deep wells of the Canadian Arctic Archipelago. Corrected bottom hole temperature (BHT) data and drill stem test (DST) temperatures were used to determine the thermal gradients for sites for which the quality of data was sufficient. Thermal gradients evaluated for depths below the base of permafrost for the onshore wells and below sea bottom for the offshore wells were combined with the estimates of effective thermal conductivity to approximate heat flow for these sites. The present geothermal gradient is in the 15–50 mK/m range (mean = 31 ± 7 mK/m). Present heat flow is mainly in the 35–90 mW/m 2 range (mean = 53 ± 12 mW/m 2). Maps of the present geothermal gradient and present heat flow have been constructed for the basin. The analysis of vitrinite reflectance profiles and the calculation of logarithmic coalification gradients for 101 boreholes in the Sverdrup Basin showed large variations related in many cases to regional variations of present terrestrial heat flow. Paleo-geothermal gradients estimated from these data are mostly in the range of 15–50 mK/m (mean = 28 ± 9 mK/m) and paleo-heat flow is in the 40–90 mW/m 2 range (mean = 57 ± 18 mW/m 2) related to the time of maximum burial in the Early Tertiary. Mean values of the present heat flow and paleo-heat flow for the Sverdrup Basin are almost identical considering the uncertainties of the methods used (53 ± 12 versus 57 ± 18 mW/m 2, respectively). Present geothermal gradients and paleo-geothermal gradients are also close when means are compared (31 ± 7 versus 28 ± 9 mK/m respectively). A zone of high present heat flow and a paleo-heat flow zone coincide in places with the northeastern-southwestern incipient rift landward of the Arctic margin first described by Balkwill and Fox (1982). Correlation between present heat flow and paleo-heat flow for the time of maximum burial in the earliest Tertiary suggests that the high heat flow zone has prevailed since that time.

Unconventional Gas Traps: Low Permeability Sands and Gas Accumulations

This paper documents the presence of commercial gas production from tight, unconventional, pervasive gas accumulations in North America. The work consisted of two main phases: (i) library research and data collection; and (ii) application of both a reservoir engineering model and a basin analysis model to determine the origins of tight gas sands. The Wattenburg Field in the syncline of the Denver Basin, the Almond Sand trend in the Eastern Green River Basin, and the Canyon Sands of the Ozona-Sonora trend of the Val Verde Basin, all represent recent development projects in the USA in tight gas sands, while the Deep Basin trend of the Western Alberta Basin, including the giant Elmworth Field which was discovered in 1976, yielded a rapid development of this trend in the early 1980's. The main products of the first phase of this work are the Field Summary Sheets of Appendix A, and the Spreadsheets of Appendix B, which collect and categorize the data about each of the fields and reservoirs. The Field Summary Sheets gather the data on fields and allow the comparison of their main characteristics, with concentration on the geological characteristics of the 40 typical reservoirs examined in the study. This database was used to try to make sense of the often conflicting values of the parameters that these fields have in common. The main text of the paper attempts to summarize and synthesize this database. In the application to the Elmworth Field, the largest gas field of the Western Canada sedimentary Deep Basin, gas found in stratigraphic traps lies downdip from water, with no known permeability barrier between. A two dimensional quantitative analysis of the basin was undertaken in order to simulate such unconventional entrapment. The modeling shows how it is possible to accumulate gas in the low permeability sand reservoirs of the Lower Cretaceous. It appears that the Elmworth basin is a system in dynamical evolution, where gas loss due to migration is partly compensated for by contemporary gas generation. While the on-going gas generation is highly influenced by the recent paleoheat flow, the early migration has been controlled by cementation which, by lowering the permeability, reduces the gas loss with time, so that significant gas trapping can be obtained today. Overall, the accumulations are described in terms of an impedance trap where the presence of gas is a transient phenomena in terms of geologic time. The free flow of gas from the source rock to surficial escape is impeded by the tight sands, to the point where a commercial volume of gas is trapped in the basinal syncline or on monoclinal dip on the basin flanks. This paper describes how and why this trapping mechanism works, and what the accumulations have in common. The work presents a set of conditions leading to such unconventional gas accumulations and discusses the parameters influencing the total amount of gas accumulated at present day; characteristics of the sediments, such as porosity and permeability behavior through time, cementation parameters, amount of sediments removed during erosion events, or heat flow variation with time, are also bracketed in order that gas accumulations predicted are in agreement with those observed today. The underpressure due to gas saturated formations is also considered.

Mineral inclusions in diamonds from the River Ranch kimberlite, Zimbabwe

More than 99% of mineral inclusions in diamonds from the River Ranch pipe in the Late Archean Limpopo Mobile Belt (Zimbabwe), are phases of harzburgitic paragenesis, namely olivine (Fo92–93), orthopyroxene (Mg# = 93), G10 garnets and chromites. The diamond inclusion (DI) chemistry demonstrates a limited overlap with River Ranch kimberlite macrocrysts: the DI garnets are more Ca-undersaturated, and DI spinel and garnet are more Mg-rich. Most River Ranch diamond inclusions were equilibrated at T = 1080–1320 °C, P = 47–61 kbar, and fO2 between IW and WM buffers. The P/T profile beneath the Limpopo Mobile Belt (LMB) is consistent with a paleo-heat flow of 41–42 mW/m2, similar to calculations for Roberts Victor, but hotter than for the Finsch, Kimberley, Koffiefontein and Premier Mines. This is ascribed to the younger tectonothermal age of the LMB and its proximity to Late Archean oceans. Like diamond inclusions from all other kimberlites studied, the River Ranch DI have a lithospheric affinity and therefore indicate that an ancient, chemically depleted, thick (at least 200 km) mantle root existed beneath the Limpopo Mobile Belt 530–540 Ma ago. The mantle root might have developed beneath the continental Central Zone of the LMB as early as the Archean, and could be alien to the overthrust allochthonous sheet of the Limpopo Belt. Oxygen fugacity estimates for diamond inclusions at River Ranch are similar to other diamondiferous harzburgites beneath the Kaapvaal craton, indicating that the Kaapvaal mantle as a whole was well buffered and homogeneous with respect to fO2 at the time of peridotitic diamond crystallization.

Geohistory, thermal history and hydrocarbon generation history of the north-west South Caspian basin

Both the hydrocarbon potential of, and excess fluid pressure build-up in, the thick (25–30 km) sedimentary pile of the northwestern part of the South Caspian Basin were evaluated using a one-dimensional fluid flow/compaction model. The model consists of three parts: a geohistory model; a thermal history model; and a hydrocarbon generation model. Input data for the model are commonly used depth values of geological parameters: lithofacies, formation thicknesses, stratal ages, porosity, permeability, pore pressure, temperature, total organic carbon content, type of organic matter, vitrinite reflectance and other maturity indicators. In order to bracket oil generation in terms of timing and depth location, two extreme thermal histories were modeled: paleoheat flow values at one half and twice the present-day values with a linear variation through time to present day measured values. The most intensive oil generation occurs during the last 5.2 My, when the ‘oil window’ is confined to depths between 5–7.5 km in the northwest, 7–10 km in the west (onshore part of the study area), and 8–11 km in the central and southwestern parts of the area. Below the ‘oil window’ cracking occurs of oil into gas. Rapid sedimentation, which took place in the middle Pliocene through Quaternary, results in overpressure build-up across all of the study area. Maximum values of excess fluid pressure of 300–400 atm at 6–10 km are reached in the central and southeastern parts of the area, where the sedimentation rate is the highest. Isobaric contours of excess pressure are then at shallow depths compared to the previous history of the area. Because there is a laterally decreasing trend of excess pressure, oriented from the central and western parts of the area to the northeast and, in addition, the sand/shale ratio is increasing in the same direction, inferences that can be drawn on the most probable hydrocarbon migration directions suggest recent flows towards the northeast with hydrocarbon accumulations of gas and light oil likely to be more prevalent in the northeastern sands.

A fault-related coalification anomaly in the Blanzy-Montceau Coal Basin (Massif Central, France)

The Stephanian intramontane Blanzy-Montceau Coal Basin is situated along a Variscan fault complex bordering the Upper Paleozoic Blanzy-Le Creusot-Bert graben. The deposition of coal-bearing strata was controlled by a complex of early faults known as the “Faille de Bordure” (FB, Border Fault). Another complex of Permian faults known as the “Faille de l'Est” (FE, Eastern Fault) is situated along the more central part of the coal basin. Coalification in the basin follows three main trends: (1) Increasing rank from upper to lower coal seams in accordance with a general vertical trend (Hilt, 1873). The gradient of volatile matter is higher than normal, ranging from 3% to I I% Vdaf per 100 m or from 0.09%/0.16% to 0.7% R per 100 m. (2) Increasing rank within each seam towards the FB fault, an anomaly which cannot be explained by differences in lithology, present-day seam geometry or paleocover thickness. The FB fault complex controlled the paleoheat flow. The anomaly can be explained by means of convective circulation. Descending and ascending waters were presumably the main agents (negative and positive respectively) of heat transfer. The FE fault complex was relatively cold because of rapid Permian sedimentation which may have acted as a cooling factor. (3) Increasing rank towards the extensionally up-lifted, crystalline basement blocks. Coalification in the Blanzy-Montceau Basin started during the Stephanian and was probably completed prior to the Stephanian fault tectonics. Convective and conductive heat flow transfer played an important role. During the Permian, convective circulation probably had a cooling effect.

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.

Evolution of the Thermal Maturity in the Thrace Basin: Revisited

It is known that thermal maturity (vitrinite reflectance versus depth) profiles display a jump at a depth of about 3000 m in most of the wells drilled in the Thrace Basin. This jump is observed either in the Upper Eocene Ceylan or the Upper-Eocene-Lower-Oligocene Mezardere formations. Previous researchers have attributed this discontinuity to the higher-than-normal temperature gradients brought about either by higher paleo-heat flow in the early stages of basin formation or by the additional heat source of circulating hot water during the recent past. In this study, we attempted to model the observed jump in vitrinite-reflectance profiles using one-dimensional basin-modeling software. The results suggest that, in order to model these discontinuities in measured vitrinite-reflectance profiles, both a relatively high paleo-heat flow during the early stages of basin development and an unconformity involving as much as 3000 m of erosional removal have to be assumed. Neither of these assumptions are based on geological evidence. For instance, an erosional unconformity between the mentioned units (except an angular unconformity between Middle-Upper Eocene and Lower Oligocene units mapped along the basin margins) was not recognized either in seismic sections or at borehole locations in the basin. Because model-prediction of measured maturities was not possible using geologically reasonable models for burial and thermal histories, it is concluded that the observed jump in thermal maturity profiles may be due to non-geological (e.g., borehole cave-ins) factors. Information gathered from several wells seems to support this conclusion. This re-evaluation of the evolution of thermal maturity has important implications for the timing and type of hydrocarbon generation from the organic-rich Mezardere formation. The hydrocarbon generation histories obtained from two geologic scenarios matching the maturity trends above and below the jump are quite different. This re-evaluation, made in the light of the modeling results and what is known about the geology in the region, suggests that the geological-evolution scenario that produces a match with the thermal-maturity trend below the jump is more realistic. Accordingly, the Mezardere formation, which is rich in oil-generating Type II kerogen, generated most of its oil in the center of the basin at 22 mybp, during the Early Miocene. This episode of peak oil generation took place prior to the formation of major structural traps due to Late Miocene wrench tectonism. Consequently, most of the oil generated from the Mezardere formation did not accumulate in structural traps. This must be one of the reasons for the low success ratio in the basin.

The Low Vitrinite Reflectance Observed in the Miocene Formations in S.E. Asia- Suppressed or Cooler Thermal History?-: ABSTRACT

The vitrinite reflectance data in the Miocene formations in S. E. Asia are found too low relative to the measured bottom hole temperatures and lower than the vitrinite reflectance values predicted by basin modeling. Such observation appears on the data from Khmer Trough, Vietnam offshore, South China Sea, and Japan Sea. Two possibilities are accounted for: (1) the vitrinite reflectance is suppressed under the certain conditions such as over pressure or the existence of generated oil, and (2) the paleo-heat flow in the area was significantly lower than we postulated as a rift basin. The latter possibility has been rarely considered, however, one of the sites indicates that only suppression cannot recover the differences, but also the effect of low paleo-heat flow is necessary. It is considered the heat flow was high at the initial stage of forming a rift and it exponentially decreased, then it increased recently to indicate a relatively high heat regime at present stage. Introducing such assumption could solve the observed low value of vitrinite reflectance. Although this conclusion must be verified by other inorganic source such as Apatite Fission Track Analysis or X-ray diffraction of clays (smectite/ illite transformation), the thermal history with low heatmore » flow would affect significantly the timing of oil/gas generation and expulsion. Thus the observation of less mature vitrinite lead us a new exploration strategy for the area.« less

Implications of vitrinite-reflectance suppression for the tectonic and thermal history of the Malay Basin

Vitrinite-reflectance profiles for wells in the Malay Basin are generally consistent, and appear at first glance to accurately represent present-day thermal maturities. However, these measured Ro values are much lower than one would expect for wells with such high present-day geothermal gradients. Consequently, calculated Ro values can only be fitted to the measured Ro data by proposing a strong and recent heat pulse. In this scenario, the paleoheat flow was much lower than the present heat flow, and rose to the present levels within the last few million years or less. A plausible tectonic history for the Malay Basin can be constructed that justifies this scenario, because Quaternary volcanics and hot springs are known, and because the last 10 million years has seen renewed subsidence after a period of uplift during the Middle Miocene. However, FAMM (Fluorescence Alteration of Multiple Macerals) data obtained from seven wells indicate that the measured Ro values are much too low in most of the Malay Basin. Ro values have been suppressed by the presence of abundant liptinite and perhydrous vitrinite, probably as a result of marine influence, except along the western margin of the basin and in the far northwestern end. Calibration of the paleoheat flow with F AMM data permits use of a much more constant thermal history at each location. In this model, the main heat flow increased during Oligocene rifting in proportion to the amount of crustal extension, and then has subsequently decayed exponentially to modern levels. Using this paleoheat flow model, hydrocarbons are generated much earlier and maturities in the basin are much higher than if the paleoheat flow model is. calibrated using the measured Ro data. These conclusions in turn indicate that the recent tectonic history of the Malay Basin has probably been rather gentle, in keeping with evidence from sedimentation rates. Although we are not yet certain how common vitrinite suppression is globally or in the Malay Basin, these results indicate that (1) all data sets should be routinely checked for vitrinite suppression, especially in areas where the phenomenon has been recognized; (2) any thermal model requiring a significant recent heat pulse to match measured and calculated Ro values should be viewed with suspicion until validated independently; and (3) errors in reconstruction of thermal and tectonic history can often lead to significant errors in exploration decisions.

Thermal history of the periphery of the Junggar Basin, Northwestern China

Geochemical analysis of rock core samples show that the basin periphery has experienced low thermal stress; present-day heat flows are in the range of 25–35 mW/m 2 and have not been significantly higher than the worldwide mean of approx. 63 mW/m 2 since the mid-Permian. Present day heat flows were determined from corrected borehole temperatures and rock thermal conductivities. Paleo-heat flows were determined by first-order reaction kinetic modeling of several geochemical paleothermometers (vitrinite reflectance, clay mineral diagenesis and relative proportions of sterane and hopane biological marker diastereomers).

Thermal history reconstruction by inversion of down-hole S2 pyrolysis data: synthetic studies and case histories

Thermal history reconstruction, as seen by buried kerogen samples, relies upon both a kinetic scheme for kerogen break down in the sub-surface as well as paleoheat flux information. A numerical model to invert S2 data from routine Rock-Eval pyrolysis was developed and tested against synthetic data sets and real data from two wells. The synthetic tests show that the S2 inverse model is sensitive to the present day heat flux ( Q 0 , to parameters describing paleoheat flow, to the number of probability channels for activation energy, and to the range of activation energy. The synthetic tests also show that for a given S2 data set, there can be different sets of kinetic parameters which give not only the same degree of fit between the calculated and measured S2 values, but also similar S2 evolution patterns with burial paths, i.e. there is no unique kinetic solution for a given set of data. The applications of the S2 inverse model to two real well data sets show that the S2 data can be used as a thermal indicator to determine the paleoheat flow and that the results are as useful as those from other thermal indicators, provided high quality S2 data are available. For an S2 data set with a mixture of kerogen types, it is first necessary to perform an un-mixing procedure prior to using the inverse model in order to obtain equivalent single type kerogen contributions, or else results obtained will not be trustworthy.

Paleo heat flow of eastern Canada's passive margins

Tectonic subsidence rates, derived from several wells in the Labrador Sea and offshore Nova Scotia and Newfoundland, were used to estimate the paleo heat flow along the margins of eastern Canada. If tectonic subsidence is caused by the cooling of the lithosphere only, the transient component of the heat flow (i.e., the heat flow in excess of background heat flow) can be estimated directly from subsidence data. For the Nova Scotia and the Labrador Sea margins, the analysis shows that the transient component of the heat flow decreased markedly from 28–56 mW · m −2, immediately after rifting, to a present value between 7 and 14 mW · m −2 depending on boundary conditions. The analysis shows a distinctive difference between the evolution of the Labrador Sea and that of the northeastern Newfoundland margin where it is estimated that the transient component of the heat flow exceeded 100 mW · m −2 after rifting and dropped rapidly to very low values. The study suggests that the subsidence of the Newfoundland margin was not caused by cooling only but required an additional mechanism such as lower-crustal phase transformations or continuing extension after continental breakup with ductile deformation in the lower crust and upper mantle. The estimated transient heat flow was used to calculate the average present surface heat flow in eastern Canada's margins, which is the sum of heat flow from the mantle, crustal heat production, and the transient cooling of the lithosphere. The calculated heat flow compares well with heat flow density data obtained from bottom hole temperature measurements.

Modelling of subsidence and thermal history of Paleogene sequence in Dolna Kamchija depression, Western Black Sea Basin

One-dimensional modelling of subsidence and thermal history, using modelling system MAT98, is performed for borehole R-64 Longoza to evaluate the maturation history of a Paleogene sequence. The calibration of modelling is based on measured data set of sterane epimerization and vitrinite reflectance. Subsidence history of the sequence is complicated by the presence of three erosional events during Paleogene and Neogene times. Based on the performed modelling, the erosional history from Late Oligocene to Early Miocene time is evaluated to be the most important event for the subsidence history and present maturity level of sediments. The modelling of thermal history is closely related to the modelling of paleoheat flow which is assumed to decrease lineary up to present. The modelled variables - erosional and heat flow histories - can compensate each other to some extent in order to achieve a satisfactory fit with the measured maturity parameters. Assuming minimum value for one of them (constant paleoheat flow equal to present day one or no erosion) we can obtain the maximum possible value for the another. The results of modelling show maximum paleotemperatures of the Paleogene - Late Cretaceous boundary in the range of 72°C to 79°C. An amount of eroded sediments during Oligocene-Miocene erosional event about 500 m is proposed to be geologically plausible. The maturity of Paleogene sequence, based of the parameters of vitrinite reflectance and sterane epimerization is confirmed to be relatively low (%Ro<0.47%, Epi<0.32).