Sand Formation Research Articles

Integration of Well Logs and Seismic Attribute Analysis in Reservoir Identification on PGS Field Onshore Niger Delta, Nigeria

AbstractIntegrated well dataset and seismics delineated the PGS field onshore Niger Delta for reservoir identification. Gamma ray, resistivity, Neutron and density Logs identified four lithologies: sandstone, shaly sandstone, shaly sand and shale. They consist of sand-shale intercalation with the traces of shale sometimes found within the sand Formation. Petrophysical parameters of the reservoirs showed varying degree of lower density, low gamma ray, high porosity and resistivity response with prolific hydrocarbon reservoir G due to its shale volume and the clean sand mapped as a probable hydrocarbon reservoir. 3D seismic data located both seismic scale and sub-seismic scale structural and stratigraphic elements. Risk reduction in dry hole drilling due fault missing in conventional seismic attribute analysis and interpretation, have to be integrated into the Oil companies standard practice.

Coupled hydro-mechanical evolution of fracture permeability in sand injectite intrusions

Sandstone “injectite” intrusions are generally developed by the fluidization of weakly cemented sandstones and their subsequent injection into fractured reservoirs. In this work, a continuum coupled hydro-mechanical model TOUGH-FLAC3D is applied to simulate the discrete fracture network in large-scale sand injectite complexes. A sand production constitutive model is incorporated to consider the formation of sand through plastic deformation and its influence on evolution of fracture permeability. Overpressures in the fluidized sand slurry drives the injection with sand dikes intruded upwards, typically into previously low permeability “tight” mudstone formations. The contrast in poroelastic properties of the underlying weak sandstone and overlying injectite receptor directly affects the evolution of fracture aperture both during and after intrusion. Fluid drainage into the unconsolidated matrix may reduce the extent of fracture aperture growth, through the formation of shear bands. The results of this work have broad implications related to the emplacement of sandstone intrusions and subsequent hydrocarbon accumulation, maturation and then production.

Mechanisms of Rhenium on Wettability and Interactions Between Nickel-Base Superalloy Melt and Al2O3-Based Ceramic Material

A systematic study on the wettability and interactions between superalloy melts with various Re contents and Al2O3-based ceramic moulds was presented in this paper. It was found that the increase of Re content inhibited the interfacial reactions to some extent. With regard to the 0, 1.5 and 3Re alloys, a double reaction layer containing Al2O3 and HfO2 was formed at the interface, but the thickness of reaction layer decreased with the increase of Re content. However, only Al2O3 phase was detected at the interface when the content of Re was 6 wt%, and the interface reaction was the weakest and the thickness of reaction layer was the thinnest. The wetting angle of the alloy/ceramic system increased as the level of Re increased. Moreover, the formation of viscous sand at the interface mainly depended on the change of wetting angle of the system.

Laboratory modeling for contaminant migration monitoring using electrical resistivity method

The rate at which contaminants migrate in the soil, such as hydrocarbons and saltwater, has long been studied. The contaminants might be as a result of spilled oil from the failed pipeline, sabotaged pipeline in Niger Delta, and saltwater intrusion. A laboratory modeling 2D electrical resistivity experiment was carried out to model the migration pattern of soil contaminants in a sand formation. The electrical resistivity methods are often being used to detect the contaminants’ plume in the subsurface using mini electrodes electrical resistivity imaging. This geophysical method was adopted before (baseline) and after the injection of the contaminant. The model tank was filled with sand, and the contaminants [petroleum and sodium chloride (NaCl)] were injected in four points into the model tank to a depth of 5 cm. A total of three (3) traverses for each segment were established within the tank. The dipole–dipole array was used for the investigation with electrode spacing (a) of 5 cm (0.05 m) and expansion factor (n) varying from 1 to 5. The traverse interval was 11.1 cm apart. A constant station separation of 5 cm (0.05 m) was adopted. The injected contaminants are organic (hydrocarbon) and inorganic (saltwater intrusion), and they are injected at station 9 and station 30 in between traverse 1 and 2 and traverse 2 and 3. Subsequently, the injection of the contaminant into the model tank was undertaken at 24 h. Experimental results obtained from this study show that 24 h after the injection of the organic substance, high resistivity value ranging from 350 to 800 Ωm buildup in some stations, which is directly related to organic (hydrocarbon) accumulation and low resistivity value, is because the porosity in these regions has been affected. 24 h after the injection of the NaCl, the three (3) traverses depict very low resistivity value ranging from 1.2 to 45 Ωm which is related to the presence of saltwater but in traverse 3 station 23 to 25 and traverse 2 station 17 to 18 depict high resistivity value ranging between 105 and 215 Ωm which indicates that the porosity in this region has been affected by the injected fluid. In general, the injected contaminant affected the porosity of the host material, which leads to the high resistivity value in the saltwater zone and low resistivity in the hydrocarbon zone.

Experimental and theoretical quantification of the relationship between electrical resistivity and hydrate saturation in porous media

An equivalent resistivity model is proposed and validated to determine hydrate saturation based on the experimentally measured resistivity. Experimentally, hydrate with different saturations is formed in an artificial sandpack to measure pressure, temperature, and resistivity as a function of time. The resistivity evolution includes induction of nucleation, large-scale hydrate nucleation, and hydrate rearrangement. Theoretically, a mathematical model on the basis of the parallel circuit principle is developed to quantify the relationship between resistivity and hydrate saturation by taking sand skeleton, temperature, brine salinity, and formation tortuosity into account. The formation tortuosity is expressed as a function of water relative permeability which can be determined by incorporating the existing semi-empirical models. In addition, the cementation exponent and saturation index in the Archie formula are empirically obtained by nonlinearly regressing the experimental measurements, while the sand skeleton resistivity, the correlation coefficient of formation tortuosity, and hydrate saturation index are introduced and determined in the equivalent resistivity models. It is found that the equivalent resistivity models are in a better agreement with the experimental measurements, while the Archie formula introduces an obviously larger error at higher hydrate saturation. Furthermore, it is recommended to use the dynamic porosity expressed as a function of hydrate saturation when characterizing the electrical properties and three-phase flow in porous media. Also, the equivalent resistivity models are found to have a less dependence on the accuracy of porosity compared with the Archie’s formula.

EFFECT OF SODIUM CHLORIDE CONCENTRATION IN SAND BED AND WELL ON THE INDICATION OF NEUTRON LOGGING INSTRUMENTS

The requirements to the accuracy and reliability of the results of borehole geophysical measurements of the porosity coefficient in oil and gas fields are constantly increasing. Studies of the influence of chlorine on the readings of neutron logging equipment with different types of probes were carried out by mathematical modeling methods. Experimental evaluation of the simultaneous effect of sodium chloride concentration in the reservoir and in the well on the readings of neutron devices has not been carried out. A design description of the experimental bulk model of a porous watersaturated sand formation (a standard sample composition and properties of sand rock) crossed by a well created to study the effect of sodium chloride concentration in the formation and in the well on the readings of neutron logging equipment with various probes, as well as the results of metrological studies of the created model are given. A feature of the model design is the well simulator, made in the form of a cylindrical fiberglass cup and installed coaxially in a cylindrical stainless steel housing. The carriers of the model properties carriers are quartz gravel and an aqueous solution of sodium chloride (NaCl) in its pore space. Reproducible values of porosity model taking into account heterogeneity of crushed stone backfill (0.353 ± 0.002) with probability 1 defined by volumetric and gravimetric methods under normal conditions, the sandy layer, pore space which is filled with fresh drinking water. The results of experimental studies of the effect of aqueous NaCl solution in a sand formation and in a well with concentrations of 50, 100, 150 and 200 g/l on the indication of neutron logging equipment PRKL with probe NGK, RK5-76 with probe NNK-T and SRK-1 with probe NNKNT using individual calibration functions (CF). CF were built on the porosity standards of sandy water-saturated rocks with zero NaCl concentration in the Center of metrological research «Ural-Geo». Correction functions (CF) are given as a dependence of the correction to the readings of the equipment RK5-76 and PRKL on the concentration of NaCl in the formation at a fixed concentration in the well or on the concentration of NaCl in the well at a fixed concentration in the formation. The obtained results can be used in the development of techniques for performing downhole geophysical measurements of the porosity coefficient of rock formations in typical geological and technical conditions.

Detailed quantitative description of fluvial reservoirs: A case study of L6-3 Layer of Sandgroup 6 in the second member of Shahejie Formation, Shengtuo Oilfield, China

The steady development of the oil field is facing severe challenges due to the problems of small-layer division, unclear genesis period and unclear river channel distribution in the 4-6 sand formation in the second district of Shengtuo Oilfield. Based on the processing and optimization of logging data, this paper firstly divided the isochronous strata and established the high-resolution isochronous stratigraphic framework. Using the geo-statistics method in the stratigraphic framework, the sand bodies in each small layer were divided according to the principle of equal time of fluvial facies. On this basis, the distribution pattern of the sand bodies in each stage was simulated by the magnetic random walk model. The magnetic random walk model has obtained robust simulation results, which is consistent with the anatomy of reservoir architectures by experienced geologists. The results also show that the number of channels in each small-layer is different, while the overall distribution of NE direction is reflected. At present, the model can well simulate the position of the main channel line, but it cannot reflect the variation of the river width. The method of quantitative fine description based on logging data has great potential application in fluvial reservoir, especially the magnetic random walk model that can reveal the distribution of sand body in every stage. At the same time, the model can also reflect certain randomness and facilitate the uncertainty analysis of geological factors. Cited as : Li, J., Yan, K., Ren, H., Sun, Z. Detailed quantitative description of fluvial reservoirs: A case study of L6-3 Layer of Sandgroup 6 in the second member of Shahejie Formation, Shengtuo Oilfifield, China. Advances in Geo-Energy Research, 2020, 4(1): 43-53, doi: 10.26804/ager.2020.01.05

Radiocaesium sorption on natural glauconite sands is unexpectedly as strong as on Boom Clay

The Neogene-Paleogene glauconite sands of Belgium cover the Boom Clay deposits that are candidate host for radioactive waste disposal. It is unclear if the highly permeable sand formations may act as an additional barrier for radiocesium (137Cs) or could be added as a complementary sorption sink in a surface disposal concept. Glauconite is an Fe-rich phyllosilicate that is mainly present as 250–125 μm sized pellets in sand, it is unknown to what extent and how fast these pellets may bind 137Cs. Pelletized clays embedded in sand may have poorly accessible high affinity sites for 137Cs. The 137Cs sorption on 11 different glauconite sands was measured in batch in a background solution of 0.1 M CaCl2 and 0.5 mM KCl. The log transformed 137Cs distribution coefficient Kd (L kg−1) after 30 days reaction ranged 3.4–4.3, surprisingly close to the Kd of the Boom Clay (3.5). Isolated glauconite fractions exhibited similar 137Cs sorption potentials (log Kd 4.1–4.3) as the reference Illite du Puy (4.4). The small Kd variation among the Neogene-Paleogene sands was explained by its glauconite content (r = 0.82). The 137Cs sorption kinetics (1–57 days) of milled pellets (<2 μm) confirmed slower reaction with intact pellets than with milled samples. Additionally, the Kd values of milled samples (57 days) sorption are 1.1–1.5 fold larger than the corresponding intact pellets, suggesting that not all Cs binding sites are accessible in intact pellets. Strongly weathered pellets exhibited cracks (visible with SEM). In these pellets the Kd was similar for milled and intact pellets suggesting that cracks increase the accessibility of the inner sorption sites. After 8.5 months the Kd values were 1.6–1.8-fold above corresponding 1 month data and these long-term reactions were more pronounced as total sand K content was larger. An adsorption-desorption experiment illustrated that 137Cs sorption is not fully reversible.

Geochemical characteristics and the provenance of aeolian material in the Hexi Corridor Desert, China

The Hexi Corridor Desert is in Gansu Province, northwestern China. The material provenance of desert formation and development is the primary factor of aeolian geomorphology, and it is still not fully understood in the Hexi Corridor Desert. To identify sources of aeolian sand in the formation of dunes in the Hexi Corridor Desert, we investigated 12 sites and collected 70 samples from the dune surface. This study used ratios between Na2O/Al2O3 versus K2O/Al2O3 and SiO2/Al2O3, Ba/Sr versus Rb/Sr and Rb/Sr versus Ce/Sr as well as CaO and Cl composition to identify sediment provenance. CaO was enriched relative to the composition of the upper continental crust (UCC), consistent with a previous study conducted in the Taklamakan and Badain Jaran deserts on adjacent fluvial, lacustrine and gravel deserts, but it differed from one study conducted in the Kumtagh and Tengger deserts. Cl concentrations differed in lacustrine and sand sediments, being higher in lacustrine sediments, followed by sand sediment. Sand sample geochemistry was similar throughout, indicating that sources of sand formation were also similar, which was confirmed by the multidimensional scaling (MDS) and principal component analysis (PCA) methods. Additionally, based on regional topography, the Hexi Corridor acts as a sediment sink not only for sediment from the Qilian Mountains but also for sediment from the Beishan Mountains. The MDS and PCA approaches also indicated that sediment provenance was similar in the Hexi Corridor and the Tengger, Badain Jaran and Kumtagh deserts. Therefore, it can be concluded that dry fluvial deposits, alluvial deposits and lacustrine sediments that combined comprised sand dune provenance were the sources of sand in the Hexi Corridor Desert, and these deposits derived from the Qilian Mountains in the southwest and the Beishan Mountains in the north through alluvial processes.

Geophysical signature of the Tunnunik impact structure, Northwest Territories, Canada

AbstractIn 2011, the discovery of shatter cones confirmed the 28 km diameter Tunnunik complex impact structure, Northwest Territories, Canada. This study presents the first results of ground‐based electromagnetic, gravimetric, and magnetic surveys over this impact structure. Its central area is characterized by a ~10 km wide negative gravity anomaly of about 3 mGal amplitude, roughly corresponding to the area of shatter cones, and associated with a positive magnetic field anomaly of ~120 nT amplitude and 3 km wavelength. The latter correlates well with the location of the deepest uplifted strata, an impact‐tilted Proterozoic dolomite layer of the Shaler Supergroup exposed near the center of the structure and intruded by dolerite dykes. Locally, electromagnetic field data unveil a conductive superficial formation which corresponds to an 80–100 m thick sand layer covering the impact structure. Based on the measurements of magnetic properties of rock samples, we model the source of the magnetic anomaly as the magnetic sediments of the Shaler Supergroup combined with a core of uplifted crystalline basement with enhanced magnetization. More classically, the low gravity signature is attributed to a reduction in density measured on the brecciated target rocks and to the isolated sand formations. However, the present‐day fractured zone does not extend deeper than ~1 km in our model, indicating a possible 1.5 km of erosion since the time of impact, about 430 Ma ago.

Comparison of Rock Type Determination Based on Permeability Estimation and FZI Value in Upper Cibulakan Shaly Sand Formation, ASR Field

Rock permeability is an important rock characteristic because it can help determine the rate of fluid production. Permeability can only be determined by direct measurement of core samples in the laboratory. Even though coring gives good results, the disadvantage is that it takes a lot of time and costs so it is not possible to do coring at all intervals. So that the well log is required to predict the level of permeability indirectly. However, the calculation of permeability prediction using well log data has a high uncertainty value, so rock typing is required so that the calculation of permeability prediction becomes more detailed. This research was conducted in an effort to determine the Hydraulic Flow Unit (HFU) of the reservoir in the well that has core data using the Flow Zone Indicator (FZI) parameter and FZI value propagation on wells that do not have core data so that the type of rock and permeability value are obtained from every well interval. From the results of the study, the reservoirs on the ASR field can be grouped into six rock types. The six rock types each have permeability as a function of validated porosity by applying it at all intervals. After FZI is calculated from log data and validated with core data, it can be seen that the results of the method produce a fairly good correlation (R2 = 0.92). Furthermore, from the permeability equation values for each different rock type, the predicted permeability results are also quite good (R2 = 0.81).

Seismic Property and Its Effect on Abrasion in the West Leihitu Coastal region, Ambon Island

This research was carried out in the West Leihitu coastal region, Ambon Island. The purpose of this study is to study seismic properties and their effects on coastal abrasion based on seismic geological conditions as an indicator of abrasion rate. Peak Ground Acceleration (PGA) values of each coastal area have a range (19,722-41,130) gal, with the highest value in the Negeri Liliboi at 41,130 gal. PGA values do not represent Ground Shear Strain (GGS) levels or have an impact on rock deformation in coastal areas. This can be seen from the GGS of the Negeri Liliboi coastal area which is higher (γ = 1.459 × 10-5) when compared to Negeri Alang coastal area (γ = 2,561 × 10-5) although the Peak Land Acceleration (PGA) value is large. Based on these results, Negeri Alang and Negeri Liliboy have high soil susceptibility resulting in soil structure cracking and soil degradation. This is the potential for abrasion in coastal areas. Geological conditions on the West Leihitu coastal region consist of land classification types II, III and IV namely gravel sand, alluvial rocks, and buff formations and alluvial rocks formed from sedimentation with a very thick layer thickness in general.

Assessing Aquifer Water Level and Salinity for a Managed Artificial Recharge Site Using Reclaimed Water

This study was carried out to examine the impact of an artificial recharge site on groundwater level and salinity using treated domestic wastewater for the Korba aquifer (north eastern Tunisia). The site is located in a semi-arid region affected by seawater intrusion, inducing an increase in groundwater salinity. Investigation of the subsurface enabled the identification of suitable areas for aquifer recharge mainly composed of sand formations. Groundwater flow and solute transport models (MODFLOW and MT3DMS) were then setup and calibrated for steady and transient states from 1971 to 2005 and used to assess the impact of the artificial recharge site. Results showed that artificial recharge, with a rate of 1500 m3/day and a salinity of 3.3 g/L, could produce a recovery in groundwater level by up to 2.7 m and a reduction in groundwater salinity by as much as 5.7 g/L over an extended simulation period. Groundwater monitoring for 2007–2014, used for model validation, allowed one to confirm that the effective recharge, reaching the water table, is less than the planned values.

Porothermoelastic response of an oil sand formation subjected to injection and micro-fracturing in horizontal wells

Stimulation of unconsolidated formations via horizontal wells has seen its vast implementation in the recent development of heavy oil reservoir to save the time and cost of preheating the reservoir before the steam-assisted gravity drainage (SAGD) process. A mathematical approach was proposed in this research that fully couples the hydraulic, mechanical and thermal responses of unconsolidated sandstone formations and also applies failure criteria for describing either shear dilation or tensile parting mechanism that generates microcracks. The approach was implemented to predict the porothermoelastic response of a pair of SAGD wells subject to injection and subsequent micro-fracturing using hot water. It was found that the predicted bottom hole pressures (BHPs) match closely with the field observed data. An elliptical dilation zone developed around the dual wells with relatively high pore pressure, porosity, permeability and temperature, implying good interwell hydraulic communication between both wells. The activation of microcracks dramatically accelerated the dissipation of pore pressure across the entire formation depth and also facilitated heat convection in between the dual wells, though to a lesser extent. In summary, the approach provides a convenient means to assist field engineers in the optimization of injection efficiency and evaluation of interference among multiple horizontal wells.

CFD STUDY OF SAND EROSION IN PIPELINE USING DIFFERENT PERCENTAGE OF ETHYLENE GLYCOL AND DEIONIZED WATER

Sand productions are inclusive of various types of major key challenges for gas and oil productions as the sand managements are rapidly growing in becoming significant to manage wells of high rates. Since approximately 70% of gas as well oil reserves around the globe are sand formations Sand production is an unavoidable by-product in oil and gas industry as 70% gas and oil reserves of the world oil are sand formation. Transportation of the particles from the wellbore to the surface will cause the damage to the amenities and tools. Wells producing gas and oils can potentially fail because of the erosion of the major solid particles. It can be illustrated through an example like producing wells having considerable amount of production of sand might affect negatively over the fitting and components of the pipeline, well tubing as well as the equipment used for the production. Thus can cause highly priced potential ecofriendly damages, equipment loss and downtime production. The current study provides outcomes gathered through examining and analyzing various factors for determining the severities and amount of the erosion of sand over the pipe bend. To solve the phenomena of the flow of the fluid, this study has used CFD. To design the pipe’s elbow, CATIA-V5 is brought in use and meshing is done with the help of the ANSYS. Different cases will be studied here by varying the percentage of water and EG with respect to sand particle size 160m and 370m. Erosion rate, Skin friction Coefficient and Swirl velocity are the three major effects which will be studied further. Through the observation of the study, it can be said that material’s character and flow velocity are the predominant factors which might affect the rate of sand erosion within the pipelines. The observation is made over every factor and is also analyzed.

An experimental investigation on strength characteristics by partial replacement of rice husk ash and Robo sand in concrete

The concrete is widely used in the construction industry. River sand is commonly used construction material. Natural weathering of rocks results in the formation of river sand, over millions of years. Robo Sand (R.S) which is eco-pleasant serves as a partially substitute material for the depleting river sand. The addition of Robo sand can reduce construction cost and also increase the strength of the concrete. Rice husk is by-product from crop growing waste and it is burnt to form Rice Husk Ash (R.H.A) which is used as partially substitute material for cement in concrete. In this study the concrete is prepared with RS as partially substitute material of fine aggregate in different proportions like 0%, 10%, 25%, 50%, 75%, and 100% and R.H.A as partially substitute material for cement in different proportions like 0%, 5%, 10%, 15%, and 20%. For normal and replaced concrete compression strength & split tensile strength is determined.

Overview of potential geothermal reservoirs in Denmark

AbstractThe Danish onshore subsurface contains very large geothermal resources that have the potential to make a significant contribution to transforming Danish energy consumption toward a more sustainable energy mix. Presently, only a minor fraction of this green energy is exploited in three small plants. The main factors that have hampered and delayed larger-scale deployment are related to uncertainties in the geological models, which inevitably lead to high economic risks that are difficult for smaller district heating companies to mitigate without support from a compensation scheme. To facilitate and stimulate much wider use of the Danish geothermal resources, the Geological Survey of Denmark and Greenland (GEUS) and other research institutes have conducted several regional research projects focusing on the geological and geochemical obstacles with the principal objective of reducing the exploration risks by selecting the best geological reservoirs.One of the most important geological factors causing uncertainty is the quality of the reservoirs and their ability to produce the expected volume of warm geothermal brine. Thus, great emphasis has been placed on investigating and understanding the relationships between reservoir sandstone, porosity, permeability, petrography, diagenetic processes and alterations related to variable sediment sources, basin entry points, depositional systems and climate, burial and thermal history. Mesozoic sandstones comprise the most important geothermal reservoirs in Denmark. Details concerning the reservoir quality are compiled and compared for the Lower Triassic Bunter Sandstone, Triassic Skagerrak, Upper Triassic – Lower Jurassic Gassum and Middle Jurassic Haldager Sand formations. The Bunter Sandstone Formation contains extensive aeolian and more confined fluvial sandstones with high porosity and permeability. However, highly saline formation water could be unfavourable. The Skagerrak Formation comprises well-sorted braided stream sandstones in the centre of the basin, and is otherwise characterised by muddy sandstones and alluvial fan conglomerates. An immature mineralogical composition has caused intensive diagenetic changes in the deepest buried parts of the basin. The Gassum Formation consists of shoreface, fluvial and estuarine sandstones interbedded with marine and lacustrine mudstones. In the upper part of the formation, the sandstone beds pinch out into mudstones towards the basin centre. Pervasive siderite- and calcite cement occurs locally in shallowly buried sandstones, and with burial depth the maximum abundances of quartz and ankerite cement increase. Sandstones of shallow burial represent excellent reservoirs. The relatively coarse grain size of the Haldager Sand Formation results in high porosity and permeability even at deep burial, so the formation comprises a high-quality geothermal reservoir.Substantial progress has been made, and a well-established regional geological model combined with reservoir quality is now available for areas with cored wells. This has enabled an improved estimation of reservoir quality between wells for exploration of geothermal reservoirs.

Pollen-spore assemblages of the Navarro Group (Maastrichtian) of Texas, USA: biostratigraphical and palaeoecological significance

Diverse assemblages of spore–pollen floras are present in all formations in the Navarro Group (Maastrichtian) in outcrops of the Austin Section and the subsurface Frio Section. The stratigraphic ranges and relative abundance of spore, pollen, dinoflagellate cysts and acritarchs were used to establish four biozones (A, B, C and D). Biozone A corresponds to the undifferentiated Neylandville Marl–Nacatoch Sand Formation; Biozone B corresponds to the Corsicana Marl Formation; Biozone C corresponds to the lower half of the Kemp Clay Formation; and Biozone D corresponds to the upper half of the Kemp Clay Formation. Biozonal boundaries do not always correspond to formation boundaries. Biozones A, B, C and D of the Austin section are correlated with the subsurface Frio section. The zonal boundaries based on spore–pollen distribution in the Austin and the Frio sections correlate well with the timelines established in these two sections based on dinoflagellate cysts and acritarchs. All Navarro Group formations except the Olmos were deposited in marine environments ranging from intertidal to outer shelf. Olmos Formation sediments were deposited in a range of coastal terrestrial environments with occasional minor influences of the sea. Three transgressive phases (T1, T2 and T3) separated by four regressive phases (R1, R2, R3 and R4) are recognized. During the Maastrichtian the floral composition in Texas changed from predominantly pteridophytic and bryophytic in the early Maastrichtian to predominantly angiospermous flora in the middle and late Maastrichtian. Tropical to subtropical climates prevailed in Texas throughout the Maastrichtian but highland regions such as Llano Uplift and nearby Marathon and Arbuckle Mountains were cooler regions with a temperate to sub–temperate climate. The upper part of the Navarro Group records a gradual cooling trend suggested by the dominance of temperate angiosperm pollen taxa.

Total organic carbon and pyrolysis analysis of the Lower Cretaceous in Compton Bay and Atherfield, Isle of Wight (England)

The Wessex Basin (United Kingdom) includes hundreds of meters of Lower Cretaceous clays, silts, and sands deposited in a wide range of depositional environments. Studies have investigated these depositional systems from the organic matter (OM) perspective. However, questions remain concerning the composition, source, and the overall depositional constraints on the distribution of sedimentary OM in this area. Elemental (carbonate % and total organic carbon - TOC) and pyrolysis analyses were conducted on representative lithofacies of the Lower Cretaceous from the Wessex Basin at the Compton Bay and Atherfield sections, Isle of Wight. The highest TOC contents were determined in the upper part of the Ferruginous Sands and Sandrock formations. These elevated TOC intervals are associated with predominantly estuarine deposition. Except for one sample from the Vectis Formation, Hydrogen Index (HI) in all studied units is low and indicates Type IV kerogen assemblages, interpreted to be linked with strongly variable climates (with pronounced dry periods) and significant water table fluctuations in the source area and during transport. The one sample with a Type II-III kerogen assemblage from the lagoonal Vectis Formation supports previous studies which suggested that OM in the Vectis Formation varied vertically as a function of fluvial sediment and terrestrial organic matter input to the lagoonal environment with changes in salinity, sediment resuspension, and turbulence as a result controlling the abundance of dinoflagellate cysts.

Petrophysical interpretation in shaly sand formation of a gas field in Tanzania

An onshore gas field (hereafter called the R field—real name not revealed) is in the southeast coast of Tanzania which includes a Tertiary aged shaly sand formation (sand–shale sequences). The formation was penetrated by an exploration well R–X wherein no core was acquired, and there is no layer-wise published data of the petrophysical properties of the R field in the existing literature, which are essential to reserves estimation and production forecast. In this paper, the layer-wise interpretation of petrophysical properties was undertaken by using wireline logs to obtain parameters to build a reservoir simulation model. The properties extracted include shale volume, total and effective porosities, sand fractions and sand porosity, and water saturation. Shale volume was computed using Clavier equation from gamma ray. Density method was used to calculate total and effective porosities. Thomas–Stieber method was used to determine sand porosity and sand fraction, and water saturation was computed using Poupon–Leveaux model. The statistics of the parameters extracted are presented, where shale volume obtained that varies with zones is between 6 and 54% volume fraction, with both shale laminations and dispersed shale were identified. Total porosity obtained is in a range from 12 to 22%. Sand porosity varies between 15 and 25%, and sand fraction varies between 33 and 93% height fraction. Average water saturation obtained is between 32 and 49% volume fraction.