Porosity In Sandstones Research Articles

Reservoir Description, Diagenesis and Reservoir Quality of the Deep Marine Sediments in the Propagation Stage of Rift Basin

The exploration and exploitation of the downthrown side of the productive upthrown Pre-rifting reservoirs at the Gulf of Suez marked bring a renaissance to the rift basin Exploration. This work documents the reservoir performance, trap geometry, and structural style of the downthrown deep marine stratigraphic entrapment. In addition, it outlines the requirements necessary beyond the production mitigations and limits. To gain better understanding of Asl Formation (deep marine) reservoir characteristics early in the exploration program, Asl Formation was cored in the north October J-5 well. A continuous 366- foot (112m) core was recovered including the main reservoir interval, which is producing over 12,000 barrel of oil per day. The J-5 Asl Formation has been interpreted as a synthetic, mixed clastic-carbonate turbidity deposit. Three major lithofacies described are recognizable on electric log. These are sandstone, shale and carbonates. The sandstones dominate the lower portion of the core and are the main oil producing section. Sandstone porosity and permeability range from 17 to 27% and 30 millidarcies to 3 darcies, respectively. Compared to the sandstone, the carbonate turbidites have poorer reservoir quality. They dominate the upper portion of the core and are composed of coarse fossil debris, silica framework grains and rock fragments. Horizontal and vertical permeabilities with rock types. Both the sandstone and carbonate sections of the J-5 core have experienced a complex diagenetic history. Deposition of the cored interval was initiated by a convulsive geological event such as flashflood or earthquake. These events would likely generate sufficient energy for mobilization of onshore and/or near shore sediments into multiple gravity flows having regional extent. The reservoir quality is controlled by a combination of primary depositional fabric and subsequent diagenetic modification. This research work can guide future exploration of reservoir-prone deep marine deposits in the Red Sea Rift and provide a reference for the subsurface deep-water reservoir quality analysis in the propagation stage in the Rift Basins.

Evolution and controls of high reservoir quality in Oligocene sandstones from moderate to deep burial, Nanpu Sag, Bohai Bay Basin, China

The Oligocene sandstones characterized by highly variable reservoir quality are the main hydrocarbon exploration and development targets in the Nanpu Sag, Bohai Bay Basin, China. In this study, the evolution and controls of reservoir quality in Oligocene sandstones from moderate to deep burial were investigated using petrographic and petrological data. The results show that the Oligocene sandstones are mostly fine-to coarse-grained, subangular to subrounded roundness, moderately sorted feldspathic litharenites and lithic arkoses with an average Q/F/R distribution of 48.4: 29.1: 22.5. Three anomalously high porosity/permeability zones (AHPZs, hereinafter named AHPZ-I, AHPZ-II, and AHPZ-III, respectively) are developed at depth ranges of 2300–3100 m, 3200–3550 m, and 3700–4200 m, respectively. Notably, the three zones are featured by distinctly different pore types: mainly primary pores in AHPZ-I; pore combination (average primary pore volume > average secondary pore volume) in AHPZ-II; primary pores with a few microfractures in AHPZ-III. The pore-throat sizes controlling permeability in anomalously high porosity sandstones (AHPS) decrease steadily from AHPZ-I to AHPZ-III-1 and then increase significantly at AHPZ-III-2. The AHPS reservoirs are characterized by low displacement pressure, large pore throat and mercury intrusion saturation, and high free fluid index (FFI) and reservoir quality index (RQI).Compaction greatly degraded the reservoir quality of Oligocene sandstones; carbonate cementation further restricts the formation of high-quality reservoirs. The sandstones with low content (<10 %) of carbonate cements tend to have larger primary porosity and secondary porosity, hence a larger RQI. The formation of AHPZ-I and AHPZ-II is attributed to higher content of rigid particle components, lower carbonate cements, and strong dissolution. Moreover, good sorting, responsible for a higher original porosity, also plays a positive role in the cause of AHPZ-I. The coarse-grained particles and early petroleum emplacement are the keys to the preservation of primary porosity in AHPZ-III. The petroleum emplacement effectively inhibits the feldspar dissolution and kaolinite precipitation in the deeply buried sandstones with depths larger than 4000 m. In addition, the generation of crushed microfractures in coarse grains leads to relatively low porosity and high permeability.

Depositional controls on diagenetic evolution of the Lower Cretaceous Wealden Sandstones (Wessex Basin, southeast England)

Depositional processes hold crucial controls on the diagenetic processes, events and evolution in sedimentary basins. Using the example of non-marine, Lower Cretaceous Wealden Sandstones from Wessex Basin in southeast England, this study reveals the depositional controls on diagenetic evolution in a sedimentary basin. Seventy-four surface samples, from 6 field locations across the Wessex Basin in Dorset and Isle of Wight were subjected to laboratory analyses such as optical petrography, scanning electron microscopy and Quantitative Evaluation of Minerals by Scanning Electron Microscopy analysis. The degree of compaction in the Wessex Basin sandstones includes moderate packing with most grains in a mix of point and long contact, with rare grains displaying concave-convex or non-grain contact and a loose packing dominated by non-grain contacts, with minor point and long contacts. The authigenic mineral phases identified in the sandstones are quartz, kaolinite, calcite and halite in decreasing abundance. The dissolution of felspars observed in the Wessex Basin sandstones possibly provided the main source of silica for the quartz overgrowths, with silica sources adjacent to the site of cementation. The small amount of quartz overgrowths may have formed during shallow burial. The partial dissolution of quartz observed in the Wessex Basin sandstones is considered likely to be the result of flushing of organic-compound rich waters derived from shale interbeds, under low temperature conditions (c. 25–50 °C). The precipitation of authigenic minerals within the Wessex Basin had a limited impact on the porosity and permeability of sandstones. Detrital mineralogy appears to be the main depositional control on diagenesis and may also explain the low abundance of authigenic kaolinite in the Wessex Basin. Similarly, the shallow burial depth of the sandstones is considered to be the main factor inhibiting more pervasive quartz cementation within the basin.

Porosity prediction using semi-supervised learning with biased well log data for improving estimation accuracy and reducing prediction uncertainty

SUMMARY Porosity characterization is of profound significance for seismic inversion and hydrocarbon prediction. Although semi-supervised learning (SSL) based methods have been used to boost prediction accuracy and lateral continuity of supervised learning (SL) inverted subsurface properties, their variations are relatively limited since the relationships between the data and the parameter model are straightforward in most reported cases. To further figure out their essential differences, we proposed the SSL-based network (SSLBN) for reservoir porosity prediction using seismic and well log data with disparate complexity and quality, and compared it with the SL-based network (SLBN). The SSLBN comprises a data-driven inverse model named decoder and a data-driven forward model named encoder based on the bidirectional-gated recurrent units. The architecture of the SLBN is the same as the encoder. Trained by several seismic-to-well pairs and numerous unlabelled seismic logs, the SSLBN learns the physical process from input single-trace observed seismic log to the intermediate porosity log, and the inverted porosity to the output generated seismic log. We first prepare the porosity model with biased or unbiased labels, the convolution model (CM) and reverse time migration (RTM) based synthetic seismic data, and then implement SL- and SSL-based statistical tests. The synthetic data examples demonstrate that the SSLBN has significant preponderance over the SLBN in the scenes of the RTM imaged seismic data and biased porosity labels. Compared with the SLBN, the physical regularization of the data misfit in the SSLBN improves estimation accuracy and reduces prediction uncertainty of porosity. Finally, statistical tests on a braided river deposited field data example illustrate that the SSLBN can generate more geologically trustworthy porosity models and indicate the oil layers of high porosity sandstone reservoirs.

Experimental evaluation of microscopic pore structure and fluid migration characteristics of coal-measure sandstone reservoirs

Research on the microscopic migration characteristics of fluids in coal measure sandstone has always been a hot spot in the evaluation of reservoir properties. In this study, taking the Yan’an Formation sandstone reservoirs in the Block A of the Ordos Basin as an example, the pore structures and fluid migration characteristics of coal-measure sandstones are systematically studied using a large number of thin sections, SEM (Scanning Electron Microscope), NMR (Nuclear Magnetic Resonance), relative permeability and water-flooding test results. The results show that the Jurassic sandstones in the target layer mainly develop lithic quartz sandstone, and the main pore types are intergranular and dissolution pores, followed by a small amount of intercrystalline pores. The surface porosity of the target sandstones mainly ranges from 7.90 to 10.79%, with an average value of 8.78%. The good correlation between porosity and permeability indicates that the target layer is a pore-type reservoir. The T2 relaxation time of the target layer is mainly distributed within 100 ms. Moreover, the reservoir of the Yan’an Formation has a high saturation of movable fluids, which is mainly distributed in 43.17–71.24%, with an average value of 56.90%. Meanwhile, samples with fractures have higher movable fluid saturations. In addition, the average irreducible water saturation of the Yan’an Formation sandstone reservoir is 35.14%, and the final oil displacement efficiency is 51.14% on average. There is a good positive correlation between the oil displacement efficiency and the co-permeability zone. As the co-permeability zone range increased from 15 to 55%, the oil displacement efficiency increased from 30 to 65%. When the cores develop fractures, they have characteristics of high permeability, high oil recovery rate, high oil displacement efficiency in the anhydrous period, low irreducible water saturation and low residual oil saturation.

Permeability in the thin section

We compute the porosity and specific surface area of a two-dimensional (2D) pore-scale segmented image of a natural rock sample, add existing relations linking tortuosity to porosity, and then use the Kozeny-Carman equation to obtain estimates of the absolute permeability of the three-dimensional (3D) host sample. These estimates are very close to the true permeability, measured or computed, of the host sample in rocks with well-connected pore space, including high-porosity sand, glass bead packs, low-to-medium porosity sandstones, and some carbonates. They are higher than the true permeability in carbonates with relatively large pores connected by constricted conduits. They fail in impermeable synthetically constructed samples with disconnected pores. Still, this extremely simple method proves to be viable for a large class of natural rocks. Moreover, it can be used to construct a permeability-porosity trend from a microscopic 2D image by selecting subsections of this image and computing their permeability-porosity pairs. Because the measured or computed permeability-porosity pair of the host 3D sample falls upon such a trend, we argue that this trend may be applicable at a spatial scale much coarser that of the pore-scale image.

Experimental Investigation of Pore Characteristics and Permeability in Coal-Measure Sandstones in Jixi Basin, China

The research of pore and permeability characteristics of tight sandstone reservoirs in coal-measure is critical for coal-measure gas development. In this study, the pore systems of tight sandstones were studied based on low-field nuclear magnetic resonance (LF-NMR) data. The permeability of tight sandstones was obtained by the tester based on the pulse transient method. The permeability variation with the effective stress, grains, and pore characteristics was analyzed. The results show that the tight sandstone reservoirs in the coal-measure have low total porosity (2.80–4.14%), low effective porosity (0.51–1.56%), and low permeability (0.351 × 10−6–13.910 × 10−6 um2). LF-NMR T2 spectra of the testing sandstones show that the micropores are the most developed, but most of the micropores are immovable pores. The pore characteristics are significantly affected by the grain size of sandstones. The pore connectivity ranks from good to poor with decreasing sandstone particle size. The total porosity and effective porosity increase with the grain size. There is a near-linear negative relationship between permeability and effective stress when the effective stress is between 405 psi and 808 psi. The greater the number of movable pores and the larger the effective porosity, the bigger the permeability of the sandstone. The effective porosity of sandstones is a sensitive indicator for evaluating the permeability of tight sandstone reservoirs. The stress sensitivity coefficient of permeability (Ss) increases with the increase of the effective stress. The sandstone with lower permeability, smaller effective porosity, and finer grains has a higher Ss. The particle size of sandstone from coal-measure has a great influence on both permeability and Ss. The findings will provide a better understanding of the characterization of pore structure and permeability in the process the coal-measure gas extraction, which is useful for the efficient development of coal-measure gas.

Geochemical Characteristics and Gas Source Contributions of Noble Gases of the Sulige Large Tight Gas Field of Upper Paleozoic in Ordos Basin, China

Tight gas is the fastest developing unconventional natural gas resource, becoming the principal part for gas reserves and production growth in China. The Sulige gas field is the largest gas field and also the typical low porosity and low permeability tight sandstone gas field discovered in China, with an annual natural gas output exceeding 300 billion and cumulative output exceeding 290 billion, playing an important role in ensuring national energy provision, helping China’s energy transformation, and promoting green, low-carbon, environmental protection and high-quality development. Based on sample collection and laboratory analysis, natural gas compositions including hydrocarbons, non-hydrocarbons, light hydrocarbons, and noble gases of the Sulige gas field are systematically analyzed, their genetic identifications are identified, and finally gas source originations and contribution proportions are comprehensively discussed from the perspectives of noble gases and hydrocarbon gases. The main achievements are as follows: 1) natural gases in the Sulige gas field are mainly alkane gases, with high methane content, high drying coefficient, low heavy hydrocarbon contents, low non-hydrocarbon gas contents of CO2 and N2, and relatively low noble gas contents. The helium content is relative 2 order of magnitude higher than the atmospheric value, while neon, argon, krypton, and xenon are relatively about 1–2 orders of magnitudes lower than the atmospheric values. 2) The carbon and hydrogen isotopes of alkanes are generally positive sequence distributions with some part inversion. The 3He/4He values are mainly distributed in magnitude of 10−8, the 40Ar/36Ar is ranged from 506 to 1940, the 129Xe is relative loss, and the 132Xe is relative surplus. 3) Natural gases in the Sulige gas field are typical coal-formed gases generated from a humic organic mother material with maturity from high mature to over mature according to C7 and C8 light hydrocarbons and alkane carbon isotopes. Noble gases are typical crustal genesis, mainly originating from the radioactive decay of crustal source materials. 4) The gas source correlations of noble gases and alkane gases and their quantitative evaluations on source contributions show that natural gases in the Sulige gas field are originated from Carboniferous-Permian coal measure source rocks in Ordos Basin, mainly contributed by coals and supplemented by mudstones, accounting for 55–60% and 40–45%, respectively.

Analysing the Porosity Distribution in Stone Surfaces by Means of Unilateral NMR after Long-Term Outdoor Weathering

Porosity changes in the near-surface area of sandstones due to long-term weathering can produce deterioration. Therefore, porosity analyses on weathered sandstones are significant for detecting possible influences on the pore structure. Classical methods for determining the porosity and pore size distribution in sandstones can only investigate the entire sample volume. In contrast, in this publication, the porosity was analysed in 0.2 mm steps over a depth of 5 mm by means of single-sided NMR measurements on water-saturated sandstones under vacuum. Evaluations of Obernkirchener and Schleeriether Sandstones that were weathered outdoors in Germany for over 30 years are presented. The results showed that the water content in Vol.-% strongly correlated with the normalised NMR signal. The unweathered sandstones showed a uniform distribution of micro and capillary pores throughout the stone depth. As a result of 30 years of outdoor weathering, changes in the pore structure occurred at the sandstone surface due to weathering down to depths of about 0.6 mm. The porosity of the Schleeriether Sandstone samples, mainly the microporosity, clearly increased in this region. Due to the dominance of capillary pores in the Obernkirchener Sandstone, the changes were not as pronounced, but a shift towards smaller pores in the surface area was observable.

Pore and permeability properties of reservoir sandstone under a uniaxial compression CT test

For underground gas storage projects that use depleted gas reservoirs, cyclic gas injection will change the stress fields and cause rock deformation. In-depth knowledge of the stress-induced deformation of reservoir rocks is important for secure gas storage. In this study, we performed a uniaxial compression computed tomography (CT) test with a reservoir sandstone sample to investigate the influence of rock deformation on the pore and permeability properties. Based on scanned 3D images, we analyzed the axial strain evolution by using the digital volume correlation (DVC) technique and the variations in pore properties with the microstructures and permeability properties that were extracted by the pore network modeling method. The DVC analysis shows that strain localization develops gradually with increasing axial stress. The initial porosity distribution with sample height is inhomogeneous. The local porosity variations are not completely consistent with the global porosity variations under increasing axial stress. The level of inconsistency will decrease with increasing axial stress in both the volumetric compression and dilation stages. Increases in axial stress mainly induce the variations in pore numbers and pore volumes. The variations in pore connectivity are not significant. For the permeability evolution, X-ray CT scanning combined with pore network modeling can simulate the permeability decreases during volumetric compression. For high porosity sandstones (>15%), the permeability still decreases in the volumetric dilation stage due to grain size reductions and tortuosity increases. However, this technique has limitations in analyzing the permeability reductions in the volumetric dilation stage. The microcracks that are induced inside the grain particles are too small to be recognized. The variations in the relative gas and water permeabilities at different axial stresses are not significant.

Pore Structure Characteristics and Strength Variation of Red Sandstone under Freeze-Thaw Cycles.

To study pore structure characteristics and the strength of red sandstone under freeze–thaw cycles, the saturated red sandstone was studied by the combination of freeze–thaw cycle test, high-pressure mercury injection test, uniaxial compression test and theoretical analysis, and research shows that: with the increase of freeze–thaw cycles, the pores of red sandstone continue to expand and extend, macropore volume and the total pore volume increases gradually, and the pore size distribution curves become more continuous. Porosity of samples after 10, 30, 70 and 100 freeze–thaw cycles is 1.14 times, 1.17 times, 1.28 times and 1.44 times of that of 0 cycle, and the uniaxial compressive strength of samples is 0.68 times, 0.53 times, 0.26 times and 0.17 times of that of 0 cycle, respectively. With the increase of freeze–thaw cycles, freeze–thaw damage continues to accumulate, the crack propagation direction changes from axial through-through failure mode to transverse and axial simultaneous failure mode. Taken the change of porosity as a parameter, through the regression analysis of the test data, the functional relationship between uniaxial compressive strength and the change of porosity in red sandstone is established. The research results will provide a theoretical basis for stability research of slopes of railway subgrade in cold region.

Guaraní Aquifer System sedimentary petrography of outcropping formations and hydrogeologic implications

Petrographic analyses are presented for the Rivera, Tacuarembó and Cuchilla Ombú formations, which constitute the outcropping Guaraní Aquifer System in the Rivera and Tacuarembó departments, Uruguay. Sedimentary petrography studies were carried out with the objective of qualitatively and quantitatively evaluate the porosity of sedimentary rocks. To determine the porosity in sandstones, the method of impregnation of petrographic thin sections followed by point-counting of total pore area and interconnected pore area was used. Clast and matrix composition was determined using both optical microscope and scanning electron microscope (SEM), with an energy dispersive X-ray analyzer (EDS) The study shows average values of total porosity of 17% and effective porosity of 14% for the Rivera and Cuchilla Ombú aquifer units and average value of total porosity of 15% and effective porosity of 9% for the Tacuarembó unit. There are compositional differences between sandstones of the Rivera and Tacuarembó formations, the former being essentially quartz-arenites and the latter predominantly subarkoses and sublithic arenites.

The influence of grain shape and size on the relationship between porosity and permeability in sandstone: a digital approach

An accurate and reliable description of the porosity–permeability relationship in geological materials is valuable in understanding subsurface fluid movement. This is important for reservoir characterisation, energy exploitation, geological carbon storage (GCS) and groundwater contamination and remediation. Whilst the relationship between pore characteristics and porosity and permeability are well examined, further investigation into the influence of grain characteristics on porosity and permeability would be beneficial due to the inherent relationship between grains and pores. This work aims to determine whether incorporation of grain characteristics into a porosity–permeability model is effective in constraining this relationship. Two fully digital approaches to individual 3D grain analysis based upon watershed segmentation are compared to determine the most effective, yet simple, workflow applicable to core plugs of significantly compacted grains. The identification of an effective segmentation workflow will facilitate future work on similarly complex materials, removing the need for traditional time-consuming and manual techniques. We use the most effective approach of measuring grain shape (sphericity) and size (Feret diameter) alongside an established fully digital workflow to measure porosity and permeability to investigate the impact of grain characteristics on porosity and permeability. We show that grain sphericity and porosity exhibit a positive relationship whereas no such relationship exists with grain size. Measurements of grain sphericity are applied to calculate a Kozeny–Carman (K–C) type porosity–permeability fit which was found to be unsatisfactory, compared to a simpler fit excluding any grain parameters. This is possibly due to the lower sphericity of the studied grains, deviating significantly from the K–C assumption that grains are entirely spherical. The simpler fit is most suitable for the studied materials, showing that inclusion of grain characteristics is not effective for better defining the porosity–permeability relationship in a K–C paradigm for these samples. This highlights the need for a model capable of considering a range of grain sphericities to further constrain the porosity–permeability relationship.

Experimental study of the sequential porosity evolution of sandstone under acid erosion

To comprehensively understand the evolution of sandstone porosity during sandstone matrix acidizing is of significance to the petroleum exploration. In this study, a self-designed experimental apparatus was applied to simulate the sequential water-rock reactions of sandstone under acidic erosion. A combination of methods, including the ultrasonic velocity measurement, low-temperature nitrogen absorption tests and high pressure mercury injection (HPMI) measurements, scanning electron microscopy (SEM) imaging and computed tomography (CT) scanning were used to analyze the characteristics of porosity. The X-ray diffraction (XRD) and X-ray fluorescence (XRF) was applied to analyze the variations of minerals and elemental content in the sandstone specimens, an acidity meter and coupled plasma mass spectrometry (ICP-MS) was used to measure the chemical parameters change in the reacted solution. The results show that, the acidic erosion significantly increased the porosity abundance and decreased the minerals and elements content in the sandstone specimens, and improved the aqueous elemental Ca, Na, K and Mg concentrations in the reacted solution. These effects of acidic erosion decreased with increasing reacted distance. The porosity enhancement can be primarily attribute to the depletion of minerals in sandstone, and the reduction of acidic effect is not only due to the acid consuming, but also associated with the different sensitivity of minerals in response to H+. This study can provide some experimental references to sandstone matrix acidizing, and recommend a useful tool for further research works.

Effective reservoir development model of tight sandstone gas in Shanxi Formation of Yan'an Gas Field, Ordos Basin, China

Through a large number of rock thin section microscopic observations, scanning electron microscopy analysis, and fluid inclusion homogenization temperature measurement, the lithological composition of tight reservoirs in the Shanxi Formation of the Yan'an Gas Field in the southeast of the Ordos Basin was studied, lithofacies types were classified, and the diagenetic evolution of different types of rocks was combined with the burial history, thermal history, and hydrocarbon charging process to analyze the time matching relationship between the key oil and gas charging period and reservoir densification. Studies have shown that pure quartz sandstone and quartz-rich low-plasticity lithic sandstone mainly develop mechanical compaction, secondary dissolution, and kaolinite precipitation. Before the two essential hydrocarbons are charged, the porosity is 15.8%–31.5%, which is typical of medium and high permeability reservoir rocks. The porosity of the high tuffaceous heterogeneous quartz sandstone, plastic-rich granular lithic sandstone, and carbonate tight cemented sandstone ranges from 4.6% to 10.8%, indicating that the reservoir is ultra-low porosity-low porosity reservoirs before the first key hydrocarbon charge. It is difficult to charge the hydrocarbons in the later stage. Therefore, the diagenesis of pure quartz sandstone and quartz-rich low-plastic granular lithic sandstone that maintained high porosity and permeability during early oil and gas charging has been inhibited, and the physical properties of the reservoir are relatively good. They are the primary migration channels and accumulation spaces for late-natural gas. This constitutes a sweet spot in tight sandstone gas reservoirs. The research findings are critical for understanding the coupling relationship between reservoir densification and accumulation, clarifying the formation mechanism of effective reservoir rocks, and predicting the distribution of sweet spots.

THE IMPACT OF PLASTERING ON THE HYGROTHERMAL BEHAVIOUR OF HISTORICAL SANDSTONE LOCATED IN THE COASTAL REGION OF LEBANON

In an unusual trend in the conservation practice of built heritage in Lebanon, the external plaster layer, which protects the sandstone from weathering factors, is being removed for aesthetic reasons. These buildings are in a coastal region, hot humid climate in the summer and moderate cold weather in the winter. This paper discusses the importance of external and internal plastering of the historical sandstone bearing wall, by the mean of a computational tool that underlines the role of the plastering in the hygrothermal behaviour of the historical stone, in the aim to validate the practice of the ancestors in covering the envelope of their buildings to avoid the degradation of these natural stones. The methodology adopted in this paper is a comparative quantitative study, using a hygrothermal simulation modelling tool, named Wufi Pro, which is a standard program for evaluating moisture conditions in building envelopes developed by the Fraunhofer Institute for Building Physics (IBP) Stuttgart, Germany. The results are in the form of values for the heat and moisture fluxes through the high porosity sandstone assembly that composes the building envelope. These values represent the hygrothermal behaviour of the stone, and they are compared between two cases, one without plastering while the second has the inner and outer layers of traditional plaster. The analysis of the results is guiding to a conclusion that favours one of the two cases, taking into consideration the interstitial condensation threat avoided by the means of plastering.

Modeling hydrogen – rock – brine interactions for the Jurassic reservoir and cap rocks from Polish Lowlands

Hydrogen offers an opportunity to move away from fossil fuels, it may help to alleviate major drawbacks of intermittent renewable energy generation. The results of geochemical modeling of hydrogen-rock-brine interactions for sandstones, mudstones and claystones from the geological structures from Polish Lowland are presented. The pH of the pore water is a critical parameter that controls the extent of the reaction. Several dominant reaction schemes were distinguished, and goethite was indicated as responsible for the consumption of stored hydrogen. It was found that the changes in rock porosity in sandstones were much smaller than in mudstones and claystones. The Zaosie sandstones are more favorable for UHS than those from Chabowo. The degradation of cap rock integrity, requires each time further experimental research. The findings of this study can help for better understanding of the behavior of hydrogen, in terms of gas-rock-brine interactions, in conditions of its underground storage. • Iron compounds are crucial for hydrogen-rock-brine interaction reactions. • Pyrite destabilization and goethite decomposition effects should be included in UHS. • Significant changes in porosity result from hydrogen injection into clay rocks. • pH of the environment is critical parameter controlling the reactions taking place. • Degradation of cap rock integrity due to hydrogen injection requires tests each time.

Permian and Triassic hydrocarbon migration and accumulation in the Cainan area, Junggar Basin, China

Gas Chromatography-Mass Spectrometer (GC-MS), chloroform asphalt “A”, and carbon isotope measurements were used to determine hydrocarbon migration pathways. This study focused on hydrocarbon migration pathways and accumulation distribution in the Wucaiwan region, Junggar Basin, China. The biometric parameters were used to compare oil sources. Type and distribution characteristics of natural gas were determined in order to study the different strata. Quantitative grain fluorescence (QGF) and quantitative grain fluorescence on extract (QGF-E) were analyzed to determine the hydrocarbon migration and charging periods. Geochemical indexes, such as, n-alkane, triterpenoids, sterane, and hopane, were utilized to investigate the pathways of hydrocarbon migration. Recent studies on petroleum maturity have focused on comparison of source rocks and reported that the maturity effects of source rock and reservoir oil are weak, while those effects are high in the Liuchu area. Analysis of triterpenoid and steroid hydrocarbon biomarkers elucidate the underground petroleum migration pathways to the reservoirs. Geochemical analyses of hopane and cholestanes were used. The ααα C29 (20 S)/(20 S + 20 R), C29ββ/(αα + ββ), and C31 hopane 22R/C30 hoopane ratios, and C19/C21 tricyclic terpane ratio, C19/C21 tricyclic terpenes, C31 (22 S)/(22 S + 22 R), and C29 (20 S)/(20 S + 20 R) ratios were analyzed to determine the maturity of crude oil. Petroleum migrated along fault, sandbody, and unconformity, which suggest vertical and lateral migration occurred. Reservoir sandstone porosity and mudstone content of the thick caprock are likely to limit lateral hydrocarbon migration. Petroleum migration and accumulation primarily occurred by vertical migration and lateral migration was weak. The study offers an improved understanding of uncertain hydrocarbon migration pathways and further developed the hydrocarbon migration and accumulation models.

The genesis of authigenic minerals and the porosity evolution of various lithologies and their implications for identifying high-quality reservoirs in the fourth member of Xujiahe Formation (Northeast-Sichuan Basin, China)

With petroleum exploration extending to deeper reservoirs, it becomes more and more difficult to find relatively high-quality reservoirs in heterogeneous sandstones. This research integrates fluid inclusion analysis, petrographic, mineralogical, and geochemical data to determine the origin of authigenic minerals, establish the porosity evolution model and discuss diagenetic effects on reservoir quality of the fourth member of the Upper Triassic Xujiahe Formation. The main rock types of studied sandstones are identified by thin-section, SEM and XRD analysis-feldspathic litharenites, litharenites, calcareous sandstone and chlorite-rich sandstone. Of the four types of sandstone, reservoir porosity of the chlorite-rich sandstone is generally the highest. Target sandstones have experienced complicated diagenetic histories including mechanical compaction, three stages of carbonate cementation, the dissolution of K-feldspar or rock fragments, three kinds of authigenic chlorite precipitation, and two stages of quartz precipitation. Two reaction pathways between K-feldspar and kaolinite were determined and limited dissolution was generated in the closed diagenetic system. Diagenetic sequence and porosity evolution suggest that the critical factors in reducing reservoir quality can be attributed to early intense compaction and widespread calcite cementation. The genesis of high-quality reservoirs among the various lithologies is different. In feldspathic litharenites and litharenites, the key factors for the development of relatively high-quality reservoirs is the acidic dissolution of K-feldspar and less cement being present in the rock. Because chlorite helps retain primary pores by inhibiting quartz overgrowths, almost all chlorite-rich sandstone are relatively high-quality reservoirs. In general, the reservoir quality of calcareous sandstone is poor unless fractures exist that can improve permeability. Determining the porosity evolution of various lithologies is an effective method to predict relatively high-quality reservoirs, which can provide a useful reference for deep petroleum exploration in other areas.

Controls on composition and diagenesis of wave- and river-dominated deltas: impacts on reservoir properties. An example from the La Anita Formation (Argentina)

Wave-, tidal-, and fluvial-dominated deltas are important hydrocarbon reservoirs worldwide, and it is well known that depositional facies types, detrital composition and diagenetic products are key aspects when evaluating potential reservoir properties. Moreover, detrital composition and diagenetic products are controlled by external forces such as tectonism, climate, and depositional conditions.The Upper Cretaceous La Anita Formation (Austral-Magallanes Basin, Argentina) is a deltaic succession that shows a clear vertical variation in the relative role of wave, tidal and fluvial processes. The formation was accumulated during the foreland stage of the basin under relatively warm climate conditions. A detailed compositional and diagenetic analysis for these deposits is provided to evaluate the role of the controlling factors on the detrital and authigenic composition, and the impact on reservoir properties.Samples were analyzed by conventional petrography, X-ray diffraction and scanning electron microscopy to obtain a full spectrum of its detrital, authigenic and diagenetic composition. The analyzed sandstones were classified as lithic arenites which come from the fold-thrust belt region and from the magmatic arc located toward the westward. The clay mineral composition is characterized by variable proportions of illite, smectite, kaolinite and mixed-layer illite-smectite with the sporadic presence of chlorite. Stratigraphic variations in the abundance of authigenic kaolinite and smectite indicate a change in the climatic conditions during the depositions of the unit evolving from tropical to more temperate conditions. Diagenetic processes affecting the porosity are considered as controlled mainly by the lithological nature of the deposits and depositional facies type. Sandstone porosity is mainly primary in origin, moderate to good in abundance and show micropore to mesopore as the main pore-sizes.This work enhances that the diagenetic products are heavily controlled by the dominant depositional process. The presence of diagenetic products as quartz overgrowth and calcite and hematite cement reduces pore spaces and affects the reservoir properties. The development of these types of cement is conditioned by the relative dominance of wave and river processes. Under wave-dominated conditions, quartz tends to develop thick overgrowths. Conversely, under river-dominated conditions quartz overgrowths are thinner and calcite and hematite cementation patches are developed.