Tool For Petroleum Exploration Research Articles

Abnormality of geothermal gradients in Iraqi western desert inferred from borehole temperatures

Geothermal gradient is an important tool in petroleum exploration and critical to several reservoir evaluations. Borehole Temperature data from 14 wells are utilized to find the geothermal tendency of the Western Desert in Iraq. The discrepancies in geothermal gradients throughout the area are a consequence of variability of sediment’s thermal conductivity, direction of groundwater flow, fault pattern, and heat generation. High value converts liquid hydrocarbon to dry gas and low value will not help organic matter to reach maturity level. The lowest gradient within the units above Palaeozoic Era’s section is 12.2 °C/km for well KH-9/7 in the eastern part of the area and the highest is 31.3 °C/km for well KH-5/4 in the middle part of the region. Whereas, the highest geothermal gradient which is 61.0 °C/km within the Palaeozoic section is recorded within Akkas Formation in 2100-2350 m subsurface. The mean geothermal gradient in Western Desert is 26 °C/km within the units younger than the Palaeozoic, but this average rises up to 40 °C/km within Palaeozoic units due to existence of Silurian hot shales and heat flow from the Proterozoic section especially from Halaban Group andesites.

Characterization of heavy oils from the Campos Basin, Brazil: Free biomarkers in oils, adsorbed and occluded in asphaltene structures

The Campos Basin is considered an important Brazilian petroleum province, with the most of its oils consisting in a mixture of biodegraded and non-biodegraded oils, which is related to more than one generation and migration pulse coupled with biodegradation events during successive stages of reservoir filling. Its turbidites reservoirs are also structural controlled through faults generated by halokinesis comprising the main route of oil migration from underlying source rocks. Throughout the biomarkers analyses of free hydrocarbons in oil, adsorbed, and occluded in the asphaltene structures, samples from different oilfields, and distances from the main fault responsible for its reservoirs filling, were comprehensive studied. The gas chromatography coupled mass spectrometer (GC-MS) methodology was applied. The results of biodegradation, source, and thermal maturation parameters reveals that the free and adsorbed saturated hydrocarbons are similarly altered, but differ in biodegradation degrees and pathways between oils, while occluded hydrocarbons and all fractions of aromatic compounds are well preserved. The predominance of biodegradation process over the recharge is suggested for distant samples from the main fault in each area, contributing to the local models of oil migration. The occluded hydrocarbons showed source similarities regardless of oilfield. According to thermal maturity based on unaltered aromatics compounds, the occluded hydrocarbons showed lower mature ratios than those free. This study introduces the application and limitations concerning biodegradation, source, and thermal maturation inferences from occluded hydrocarbons in asphaltenes covering Brazilian oils, in view to improve a concise geochemical tool in petroleum exploration.

Geochemistry and provenance of Oligocene to middle Miocene sandstones in the Qiongdongnan Basin, northern South China Sea

The Qiongdongnan Basin (QDNB) is a petroleum-bearing basin in the northern margin of the South China Sea (SCS). Provenance analysis is an important tool in petroleum exploration and is helpful in predicting the distribution of good reservoirs in areas with less drilling. However, the provenance of the QDNB remains controversial, and further research is needed. Here, we apply whole-rock geochemistry, petrography, and heavy minerals combined with published detrital zircon U-Pb ages to constrain the provenance of Oligocene to middle Miocene sandstones in the QDNB and the tectonic environment of their deposition. The Oligocene to middle Miocene sandstones from the QDNB are geochemically immature. These sandstones were derived from a weakly weathered source area characterized by dominantly felsic igneous rocks, with a particular slight addition from recycled sedimentary sources. And the Lingshui Formation underwent less weathering than the upper and lower strata. The tectonic setting of the sandstones in the basin belongs to a continental island arc (CIA) or an active continental margin (ACM). Heavy mineral assemblages and detrital zircon U-Pb ages reveal sediment input from multiple sources. Hainan Island was a major and continuous source area contributing to the basin from the early Oligocene to the middle Miocene. In addition, intrabasinal uplift regions could have supplied material to local areas. While these sedimentary source patterns appear to have changed very little in the late Oligocene, a provenance from central Vietnam was explicitly discerned in the western QDNB in the late Oligocene. It is possible that the paleo-Pearl River supplied large volumes of sediment to the eastern QDNB from the late Oligocene to the early Miocene.

Seismic analysis of growth faults to predict sequence stratigraphic reservoir properties: A case study of the middle to late Miocene Coastal Swamp strata, Niger Delta Basin, Nigeria

This paper presents a graphic relationship between the throw of depositional units across a growth fault and their corresponding depth in the hanging wall on a 2-D seismic profile in predicting lithological variations. A mechanism that elucidates differential stress creating subsidence rate, on account of growth-faulting: topographic creation unthickened-shale and topographic filling thickened-sandstone sedimentation intervals in the hanging wall. The graphic relationship plot was used to analyze a seismic stratigraphic series between 1500 and 2800 ms two-way traveltime. The aim is to test the rare advantage of the method as a stratigraphic predicting tool. In addition, to use the approach to predict sequence stratigraphic reservoir properties of depositional cycles in the subsurface from a seismic profile. In particular, well data have been compared with a synthetically derived lithological column obtained with the plot. The result affirms that the technique is a satisfactory and reliable tool to predict stratigraphic surfaces, lithologies, and the net-to-gross ratio of alternating sand-shale facies sequences from 2-D seismic data. Furthermore, the study documented a relationship between lithologies and the throw-depth plot slope values in relation to sediments compaction to predict potential reservoirs and seals. The prediction technique may be employed to depict syndepositional fault-generated topographic information. Moreover, it can be a predrilled field interpretation tool for petroleum exploration in siliciclastic extensional settings.

Quick, Easy, and Economic Mineralogical Studies of Flooded Chalk for EOR Experiments Using Raman Spectroscopy

Understanding the chalk-fluid interactions and the associated mineralogical and mechanical alterations on a sub-micron scale are major goals in Enhanced Oil Recovery. Mechanical strength, porosity, and permeability of chalk are linked to mineral dissolution that occurs during brine injections, and affect the reservoir potential. This paper presents a novel “single grain” methodology to recognize the varieties of carbonates in rocks and loose sediments: Raman spectroscopy is a non-destructive, quick, and user-friendly technique representing a powerful tool to identify minerals down to 1 µm. An innovative working technique for oil exploration is proposed, as the mineralogy of micron-sized crystals grown in two flooded chalk samples (Liége, Belgium) was successfully investigated by Raman spectroscopy. The drilled chalk cores were flooded with MgCl2 for ca. 1.5 (Long Term Test) and 3 years (Ultra Long Term Test) under North Sea reservoir conditions (Long Term Test: 130 °C, 1 PV/day, 9.3 MPa effective stress; Ultra Long Term Test: 130 °C, varying between 1–3 PV/day, 10.4 MPa effective stress). Raman spectroscopy was able to identify the presence of recrystallized magnesite along the core of the Long Term Test up to 4 cm from the injection surface, down to the crystal size of 1–2 µm. In the Ultra Long Term Test core, the growth of MgCO3 affected nearly the entire core (7 cm). In both samples, no dolomite or high-magnesium calcite secondary growth could be detected when analysing 557 and 90 Raman spectra on the Long and Ultra Long Term Test, respectively. This study can offer Raman spectroscopy as a breakthrough tool in petroleum exploration of unconventional reservoirs, due to its quickness, spatial resolution, and non-destructive acquisition of data. These characteristics would encourage its use coupled with electron microscopes and energy dispersive systems or even electron microprobe studies.

Microseeps as pathfinder and regional filtering tool in petroleum exploration

Microseeps as pathfinder and regional filtering tool in petroleum exploration

Carbon and hydrogen isotopic compositions of n -alkanes as a tool in petroleum exploration

Abstract Compound-specific isotope analysis (CSIA) of individual organic compounds is a powerful but underutilized tool in petroleum exploration. When integrated with other organic geochemical methodologies it can provide evidence of fluid histories including source, maturity, charge history and reservoir processes that can support field development planning and exploration efforts. The purpose of this chapter is to provide a review of the methodologies used for generating carbon and hydrogen isotope data for mid- and high-molecular-weight n -alkanes. We discuss the factors that control stable carbon and hydrogen isotope compositions of n -alkanes and related compounds in sedimentary and petroleum systems and review current and future applications of this methodology for petroleum exploration. We discuss basin-specific case studies that demonstrate the usefulness of CSIA either when addressing particular aspects of petroleum exploration (e.g. charge evaluation, source rock–oil correlation, and investigation of maturity and in-reservoir processes) or when this technique is used to corroborate interpretations from integrated petroleum systems analysis, providing unique insights which may not be revealed when using other methods. CSIA of n -alkanes and related n -alkyl structures can provide independent data to strengthen petroleum systems concepts from generation and expulsion of fluids from source rock, to charge history, connectivity, and in-reservoir processes.

Hydrocarbon seeps in Romania: Gas origin and release to the atmosphere

Romania is one of the countries with the largest number of surface hydrocarbon seeps in the world. Seeps may be an important tool for petroleum exploration as they can provide useful information regarding source rock maturity, reservoir quality, and secondary gas alterations. Seeps also represent an important source of methane, ethane, and propane to the atmosphere. To date, the genetic characterization of natural gas in Romania has only been based on molecular composition, without isotopic information. Here, we present an overview of investigations performed over the past 15 years for the main Romanian hydrocarbon seeps, and report the molecular and isotopic compositions of gas, and the fluxes of methane, ethane and propane to the atmosphere. We assessed gas origin and secondary alterations in 17 seeps from several Romanian petroleum systems, and potential source rock types and maturity have been evaluated. As previously inferred, gas within the Transylvanian Basin is largely microbial, but also displays indications of a minor thermogenic component that is likely related to a deep petroleum system. Carpathian Flysch and Foredeep petroleum systems contain thermogenic gas, with clear evidence of biodegradation in some cases. Thermogenic gas generation modelling and maturity plots suggest that most Romanian gases originate from mature type II and III kerogen (%Ro: 2–3). For cases of high flux seeps, gas has the same hydrocarbon molecular composition as the reservoir, while in weaker seeps and some mud volcanoes gas is altered by molecular fractionation (a loss of C2 and C3 during gas migration). Gas seep geochemistry, in general, reflects the different geological and maturity conditions of basins where seeps are located. A vertical sequence of petroleum systems has been suggested in some basins by seeps displaying different maturity and secondary alterations. Measurements of methane flux to the atmosphere from 94 seeps display a wide range of emissions (kilograms to hundreds of tons per year), with a total, conservative estimated methane emission of approximately 3000 t y−1. Microseepage may also release a similar quantity of methane. Consequently, seepage is a substantial contributor to natural emissions of methane on a national level.

Exploration of intramolecular 13C isotope distribution in long chain n-alkanes (C11–C31) using isotopic 13C NMR

n-Alkanes are ubiquitous and useful biomarkers in the biogeochemistry field. Their carbon isotope composition in sedimentary organic matter is therefore of particular importance for inferring their origin. The commonly used technique for δ13C determination, isotope ratio mass spectrometry (IRMS), gives access to the isotope composition of n-alkanes at the molecular level, but does not provide information on their intramolecular isotope distribution. Here, we evaluate the potential of isotopic 13C nuclear magnetic resonance (NMR) spectrometry for the determination of the intramolecular isotope composition of long chain n-alkanes (C11–C31). The relative isotope composition of the three terminal carbon positions can be determined with a precision of 1.2‰ or better. The results from commercially available samples show that (i) the intramolecular 13C isotope distribution is opposite between odd and even numbered n-alkanes in the C16–C31 range and (ii) those in the C11–C15 range show a 13C depletion of ca. 12‰ in the methyl position and no difference between odd and even numbered compounds. The results are consistent with a biological origin of heavy n-alkanes whereas lighter ones are proposed to originate from abiogenic degradation such as thermal cracking. Overall, although only partial intramolecular 13C patterns are obtained, the approach appears as promising tool in petroleum exploration and in the biogeochemistry field.

MASS BALANCE CALCULATIONS FOR DIFFERENT MODELS OF HYDROCARBON MIGRATION IN THE JEANNE D'ARC BASIN, OFFSHORE NEWFOUNDLAND

Basin and petroleum systems modelling is a powerful tool in petroleum exploration, but uncertainties remain in terms of the evaluation of a petroleum accumulation's size and quality, even when the petroleum system is well known and the latest modelling technology is applied. In order to interpret the results of a modelling exercise, it is necessary to understand the advantages and disadvantages of the various possible approaches used to assess petroleum migration and accumulation. This paper attempts to compare the influence of different migration modelling techniques – the flowpath, Darcy “hybrid” and invasion percolation approaches – on basin‐wide mass balance calculations for a temperature‐ and pressure‐calibrated, numerical four‐dimensional basin model. The study was performed using PetroMod® software.The study area is the well‐known Jeanne d'Arc Basin located offshore Newfoundland, eastern Canada. Model predictions were verified against pre‐existing data including the quantity and quality of discovered hydrocarbons in the basin. Modelling results showed that the Darcy method produced substantially different results compared to the other migration techniques and this was due to the high accumulation efficiency. The flowpath method, and a combination of flowpath and Darcy methods (referred to as the “hybrid” method) yielded similar results; furthermore, the hybrid method predicted the petroleum composition quite accurately. The invasion percolation method gave similar results to the hybrid approach, but little or no variation in API and GOR across the basin was predicted.The adsorption model initially applied did not adequately reproduce the natural behaviour of source rocks with respect to petroleum expulsion efficiency. Therefore a revised model was implemented in which the adsorption capacity was reduced with increasing maturity. This revised adsorption model led to more realistic volumes of hydrocarbons being retained within the source rock. The application of this approach had only a minor impact on the volume and quality of the petroleum present in the reservoir units.

“Uniform geothermal gradient” and heat flow in the Qiongdongnan and Pearl River Mouth Basins of the South China Sea

The Pearl River Mouth Basin (PRMB) and Qiongdongnan Basin (QDNB) are oil and gas bearing basins in the northern margin of the South China Sea (SCS). Geothermal survey is an important tool in petroleum exploration. A large data set comprised of 199 thermal conductivities, 40 radioactive heat productions, 543 measured geothermal gradient values, and 224 heat flow values has been obtained from the two basins. However, the measured geothermal gradient data originated from diverse depth range make spatial comparison a challenging task. Taking into account the variation of conductivity and heat production of rocks, we use a “uniform geothermal gradient” to characterize the geothermal gradient distribution of the PRMB and QDNB. Results show that, in the depth interval of 0–5 km, the “uniform geothermal gradient” in the PRMB varies from 17.8 °C/km to 50.2 °C/km, with an average of 32.1 ± 6.0 °C/km. In comparison, the QDNB has an average “uniform geothermal gradient” of 31.9 ± 5.6 °C/km and a range between 19.7 °C/km and 39.5 °C/km. Heat flows in the PRMB and QDNB are 71.3 ± 13.5 mW/m 2 and 72.9 ± 14.2 mW/m 2, respectively. The heat flow and geothermal gradient of the PRMB and QDNB tend to increase from the continental shelf to continental slope owing to the lithosphereic/crustal thinning in the Cenozoic.

石油探鉱における石灰質ナンノ化石の役割 その生層序学，シーケンス層序学および古海洋学的有効性

Calcareous nannofossil as a powerful tool for petroleum exploration was discussed from the aspects of biostratigraphy, sequence stratigraphy and paleoceanography.This minute fossil is a biostratigraphically useful indicator, especially for the Plio-Pleistocene and the lower to middle Miocene marine sediments distributed along the coast of the Sea of Japan in the northeast of Japan. It is utilized for the recognition and distinction of the three foraminiferal markers, Globorotalia inflata beds, otherwise frequently confused each other.Calcareous nannofossil is used for sequence stratigraphic analysis as well, in petroleum exploration. The peaks of calcareous nannofossil abundance are assigned to the condensed sections in the Gulf of Mexico. They are widely traceable in the region, and they are also useful for the identification of sequences and systems tracts. The change of calcareous nannofossil assemblages caused by sea level changes was apparently recognized in the Quaternary section of boreholes drilled on the edge of the shelf.Finally, calcareous nannofossil is applied to the reconstruction of paleoceanographic changes in the pelagic environment. The TN value based on the composition of the Recent calcareous nannoplankton shows a good correspondence with the δ18O curve in three cores collected from the Tasman Sea. The TN curves are obviously related to glacial/interglacial cycles. Therefore, it indicates that the change of sea surface temperature was recorded as the change of nannofloral assemblage.

ＦＴ法の最近の成果と石油探鉱へのジルコンの応用

Zircon Fission-Track Analysis (ZFTA) as a geological clock is based on zeta age calibration and track length measurements. Fission-track dating samples are classified into four types according to combination of two factors of 1) homogeneity in fission track age and 2) heating effect to fission track age. The four types of samples are (a) homogeneous and unheated, (b) heterogeneous and unheated, (c) homogeneous and heated and (d) heterogeneous and heated. As an example of ZFTA applied to the four-type samples, the author reviewed recent fission track dating studies in Japan as follows: (a) volcanic ash layers of the Kazusa Group in the Boso Peninsula, (b) the Pliocene Hirosegawa Tuff Member of the Sendai Group in Northeast Honshu, (c) the MITI “Honjo-oki” well and (d) the MITI “Mishima” well, respectively. Studies on the two exploratory test wells show ZFTA is a useful tool for petroleum exploration in Japan.

Sequence Stratigraphy Enhancement of Biostratigraphic Correlation with Application to the Upper Cretaceous of Northern Siberia: A Potential Tool for Petroleum Exploration

Sequence stratigraphy can be used as a tool to bolster weak or low-resolution biostratigraphic correlation. On the basis of sequence stratigraphy, very high resolution correlations can be made if differences in local depositional and tectonic environments are taken into account. We have applied this tool to the Upper Cretaceous of northern Siberia, a frontier area with well-studied biostratigraphy, but with only feeble correlation with the Western world. The Upper Cretaceous biostratigraphy of northern Siberia can be defined on the basis of inoceramids, but this basis fails in detail both at the local level and for the purpose of interregional correlation. The situation can be remedied in part by the application of sequence stratigraphic concepts. These concepts have been developed primarily for passive margins and other rapidly subsiding basins, but with some modifications can be used to correlate depositional and eustatic events recorded in northern Siberian strata with those observed elsewhere througho...

The neodymium isotope system as a tool for petroleum exploration

Mineralogical, petrological, geochemical, and neodymium isotopic investigations strongly suggest isotopic and chemical exchange between authigenic silicate phases and petroleum. Alteration of organic matter, sulfur reduction, generation of aqueous-acidic solutions with the resultant dissolution of K-feldspar leads to in situ crystallization of illite and chlorite as well as neodymium isotopic equilibration between the silicate phases and petroleum. These findings are of significance not only to understand the mechanisms leading to neodymium isotopic equilibration between authigenic clay minerals in detrital sediments but also to source rock-petroleum (in reservoir) correlations, in particularly when biomarker molecules (i.e., isoprenoid hydrocarbons) have been obliterated by prolonged, severe diagenesis.

Field and Modeling Studies of Cyclic Carbonates: A Predictive Tool for Petroleum Exploration: ABSTRACT

In cyclic sequences containing large numbers of 1 to 10-m carbonate cycles, lack of well-defined markers generally prevents construction of detailed stratigraphic cross sections showing detailed facies changes. Fischer plots that graph cumulative cycle thickness corrected for linear subsidence using average cycle period can be used to correlate sections and show relation of individual cycle types to third-order sea level cycles. Interaction between simple or complex sea level curves defined by various frequencies and amplitudes; the sediment-surface, water-depth dependent sedimentation rate; lag time; and subsidence through time can be shown using one-dimensional models. Isostatically balanced two-dimensional models that incorporate the above variables, plus initial platform slope and thermotectonic subsidence (divided into rotational and regional components), can be used to construct detailed cyclic facies cross sections of carbonate platforms. These can be used to define regional relations between cycles; likely vertical and lateral facies changes; distribution of disconformities, conformities, and tidal-flat caps; relative water depths of facies likely to be developed on the platform; as well as likely location of early diagenesis. The integration of field and modeling studies provides a rigorous analysis of cycle deposition that could be of great predictive value in the exploration and development of petroleum reservoirs.

Surface organic geochemical prospecting for hydrocarbons: multivariate analysis

A database of analyses of C 1 and C 7 hydrocarbons from an oil and gas producing region in Mexico has been assembled from gas samples collected at depths of 3, 15 and 30 meters from surficial holes drilled in traverses over producing and barren structures. The surface consisted of subtropical swamps; depth to structure was 3500 to 5800 meters. Hydrocarbon analysis from six structures (three producing and three barren) selected from the database were subjected to multiple discriminant function analysis to produce a retrospective statistical test of the ability of geochemical prospecting to distinguish producing from non-producing structures. The hydrocarbon spectra from 3 meters depth yielded ambiguous results; those from 30 meters produced clear distinction between barren and producing structures. Further, the discriminant functions established a base of geochemical characteristics, founded on known areas (retrospective), to which additional unknown areas (prospective) may be compared for classification. This suggests a bootstrapping approach to exploration in which an increasing number of “known” results can be used to continually update and refine the predictive power of the discriminant function. This indicates the practical ability of a combined geochemical-multivariate statistical prospecting approach as an exploration tool, particularly within a single geochemical/geological province. Geochemical prospecting, perhaps with relatively deep (30 m) penetration, combined with multivariate data analysis is a rapid, potent and relatively inexpensive additional tool for petroleum exploration.

Field and Modeling Studies of Cyclic Carbonates: A Predictive Tool for Petroleum Exploration: ABSTRACT

Field and Modeling Studies of Cyclic Carbonates: A Predictive Tool for Petroleum Exploration: ABSTRACT

Gamma-Ray Spectrometry of Marine Shales in Outcrop--A Tool for Petroleum Exploration and Basin Analysis: ABSTRACT

Gamma-ray spectrometry was conducted on outcrops of marine shale and chalk deposited in the Cretaceous Western Interior seaway. Study of the Cenomanian-Turonian Greenhorn cyclothem of Colorado, New Mexico, and Utah showed that profiles of gamma-ray spectra are useful in evaluating organic carbon content, interpreting paleoenvironments, and correlating otherwise homogenous sequences of marine shale. Gamma-ray spectra provide estimates of total gamma radiation and K, U, and Th contents. Th/U and K/U ratios can be used to estimate relative abundances of detrital minerals and organic matter, whereas the Th/K ratio is an indicator of clay mineralogy. Variations in these ratios reflect both local depositional processes and widespread events that can be correlated for hundreds o kilometers across lithofacies boundaries. Profiles of total gamma radiation can be used to help map shale facies. Spectrometer surveys can be used to show directions of sediment transport, to indicate proximities of paleoshorelines, and to aid in estimation of lateral and temporal variations in paleosalinity. Outcrop profiles can be compared directly with well logs of gamma-ray spectra. Gamma-ray spectrometry of shale outcrops is a versatile technique. Results can be interpreted in the field, the sampling program can be modified as it progresses, and the effects of event deposits such as bentonites and bone beds can be characterized. If lead shielding is used to keep sample mass and geometry constant, reproducible results can be obtained even from shales that contain below-average concentrations of K (< 2%), U (< 2 ppm), and Th (< 10 ppm). End_of_Article - Last_Page 542------------

Three-Dimensional Simulation of Basin Evolution, Geothermal History, and Hydrocarbon Generation and Accumulation Potential--New Tool in Petroleum Exploration: ABSTRACT

End_Page 1006------------------------------Increasing demand and decreasing supply of hydrocarbon products require increased activities in petroleum exploration and production and especially improvement in exploration success. Improvement in exploration success both in previously explored and unexplored areas can only be possible with the integration of all the information and data obtained from geologic, geophysical, geochemical, hydrodynamic, and thermodynamic studies. A three-dimensional deterministic, dynamic model is constructed to calculate all the above measurable values with the help of mass and energy transport equations, and by equations describing the physical and/or physico-chemical changes in organic matter as a function of temperature in sedimentary sequences. Input data consist of heat flux, initial physical and thermal properties of sediments, paleobathymetric estimates, sedimentation rate and amount, and type of organic matter. Then, the model computes pressure, temperature, physical and thermal properties of sediments, maturity of organic matter, and generation and accumulation potential of hydrocarbons as a function of space and time. This model has been successfully applied to four basins with different lithologies (clastics, carbonates, and cyclic sediments) and various structural patterns (halokinesis, faulting, and folding). The allowable error limits are ±3°C for temperature, and ±10% for maturity of organic matter. End_of_Article - Last_Page 1007------------