Clastic Reservoirs Research Articles

Status and prospects of deep oil and gas resources exploration and development onshore China

Many significant breakthroughs have been made in regards to deep oil and gas exploration and development in recent years. However, a systematic analysis has not been carried out on the progress, challenges, and development trend of exploration and development of onshore deep oil and gas resources in China. This paper summarizes five main points of deep oil and gas resources: (1) more gas, less oil, and complicated phases; (2) high temperature and pressure, as well as profoundly different basins or formations; (3) multiple hydrocarbon sources and accumulations; (4) relatively tight but effective large-scale reservoirs; and (5) complicated accumulation process and multi-stage reconstructions. Based on the exploration and development history of deep oil and gas, this paper points out China's take on it is at the “large-scale discovery stage during which significant achievements have been obtained in carbonate, clastic, and volcanic reservoirs. Nonetheless, there are still four challenges, namely: (1) complex hydrocarbon generation, reservoir evolution, and accumulation restriction on how to determine exploration orientation and targets; (2) long well drilling and completion period, as well as high well construction cost delay petroleum discovery and efficient development; (3) undeveloped logging technology for HPHT slim holes that cannot ensure accurate identification of hydrocarbon reservoir; and (4) effective development and large-scale utilization of unspecific recovery technique and equipment limit. Finally, by the comprehensive analysis, it is concluded that onshore deep oil and gas resources are mainly distributed in three areas of six basins in China. The areas have a vast exploration potential and have strategically successive resources. It is suggested that petroleum companies and universities, as well as research institutes, should work together to overcome difficulties in theory and practical technology for deep oil and gas exploration and development. Such partnership could develop fit-for-purpose theories and technical systems to support deep oil and gas development.

Provenance of Permian Delaware Mountain Group, central and southern Delaware Basin, and implications of sediment dispersal pathway near the southwestern terminus of Pangea

ABSTRACTThe Delaware Basin is located near the southwestern end of the Alleghanian–Ouachita–Marathon orogenic belt. The basin is mostly filled by Permian clastic rocks of the Delaware Mountain Group with ramp- to shelf-carbonate rimming basin edges. The Delaware Mountain Group has been well-documented as a deep-water clastic reservoir unit in the prolific Permian Basin, but its sources and related sediment dispersal pathways remain inconclusive. In this study, a total of 55 samples of the Delaware Mountain Group were collected from whole core and sidewall core from the central and southern Delaware Basin, and sandstone modal analyses and U-Pb detrital zircon geochronology were applied to constrain their potential sources. Sandstone modal analyses show that the majority of samples fall within the transitional continental source field. Age spectra of detrital zircon from five selected samples include a prominent middle Palaeozoic age cluster (~490–275 Ma), a major Neoproterozoic to early Palaeozoic age cluster (~790–510 Ma), and a series of minor age clusters of the middle to late Mesoproterozoic (~1300–920 Ma), early Mesoproterozoic (~1600–1300 Ma), late Palaeoproterozoic (~1825–1600 Ma), and Archaean and Palaeoproterozoic (> ~1825 Ma). Integrating detrital zircon data from all potential sources and coeval sandstones from the northern Delaware Basin suggests that the majority of sediment was derived from the Appalachian foreland, the Ouachita orogenic system, and the peri-Gondwanan terranes. Variation in the abundance of the different age groups reveals a provenance shift between deposition of the Brushy Canyon Formation and the Cherry and Bell Canyon Formations. To accommodate the composition, and the stratigraphic and spatial age spectral variations, we proposed that the sediment dispersal pathway includes a transcontinental fluvial system from the Appalachian orogenic belt to the east, a regional scale fluvial system from the Ouachita orogenic belt to the north and northeast, and a local, proximal fluvial system from the peri-Gondwanan terranes to the south and southeast.

A study on the variation of zeta potential with mineral composition of rocks and types of electrolyte

Streaming potential in rocks is the electrical potential developing when an ionic fluid flows through the pores of rocks. The zeta potential is a key parameter of streaming potential and it depends on many parameters such as the mineral composition of rocks, fluid properties, temperature etc. Therefore, the zeta potential is different for various rocks and liquids. In this work, streaming potential measurements are performed for five rock samples saturated with six different monovalent electrolytes. From streaming potential coefficients, the zeta potential is deduced. The experimental results are then explained by a theoretical model. From the model, the surface site density for different rocks and the binding constant for different cations are found and they are in good agreement with those reported in literature. The result also shows that (1) the surface site density of Bentheim sandstone mostly composed of silica is the largest of five rock samples; (2) the binding constant is almost the same for a given cation but it increases in the order KMe(Na+) < KMe(K+) < KMe(Cs+) for a given rock.References Corwin R. F., Hoovert D.B., 1979. The self-potential method in geothermal exploration. Geophysics 44, 226-245. Dove P.M., Rimstidt J.D., 1994. Silica-Water Interactions. Reviews in Mineralogy and Geochemistry 29, 259-308. Glover P.W.J., Walker E., Jackson M., 2012. Streaming-potential coefficient of reservoir rock: A theoretical model. Geophysics, 77, D17-D43. Ishido T. and Mizutani H., 1981. Experimental and theoretical basis of electrokinetic phenomena in rock-water systems and its applications to geophysics. Journal of Geophysical Research, 86, 1763-1775. Jackson M., Butler A., Vinogradov J., 2012. Measurements of spontaneous potential in chalk with application to aquifer characterization in the southern UK: Quarterly Journal of Engineering Geology & Hydrogeology, 45, 457-471. Jouniaux L. and T. Ishido, 2012. International Journal of Geophysics. Article ID 286107, 16p. Doi:10.1155/2012/286107. Kim S.S., Kim H.S., Kim S.G., Kim W.S., 2004. Effect of electrolyte additives on sol-precipitated nano silica particles. Ceramics International 30, 171-175. Kirby B.J. and Hasselbrink E.F., 2004. Zeta potential of microfluidic substrates: 1. Theory, experimental techniques, and effects on separations. Electrophoresis, 25, 187-202. Kosmulski M., and Dahlsten D., 2006. High ionic strength electrokinetics of clay minerals. Colloids and Surfaces, A: Physicocemical and Engineering Aspects, 291, 212-218. Lide D.R., 2009, Handbook of chemistry and physics, 90th edition: CRC Press. Luong Duy Thanh, 2014. Electrokinetics in porous media, Ph.D. Thesis, University of Amsterdam, the Netherlands. Luong Duy Thanh and Sprik R., 2016a. Zeta potential in porous rocks in contact with monovalent and divalent electrolyte aqueous solutions, Geophysics, 81, D303-D314. Luong Duy Thanh and Sprik R., 2016b. Permeability dependence of streaming potential coefficient in porous media. Geophysical Prospecting, 64, 714-725. Luong Duy Thanh and Sprik R., 2016c. Laboratory Measurement of Microstructure Parameters of Porous Rocks. VNU Journal of Science: Mathematics-Physics 32, 22-33. Mizutani H., Ishido T., Yokokura T., Ohnishi S., 1976. Electrokinetic phenomena associated with earthquakes. Geophysical Research Letters, 3, 365-368. Ogilvy A.A., Ayed M.A., Bogoslovsky V.A., 1969. Geophysical studies of water leakage from reservoirs. Geophysical Prospecting, 17, 36-62. Onsager L., 1931. Reciprocal relations in irreversible processes. I. Physical Review, 37, 405-426. Revil A. and Glover P.W.J., 1997. Theory of ionic-surface electrical conduction in porous media. Physical Review B, 55, 1757-1773. Scales P.J., 1990. Electrokinetics of the muscovite mica-aqueous solution interface. Langmuir, 6, 582-589. Behrens S.H. and Grier D.G., 2001. The charge of glass and silica surfaces. The Journal of Chemical Physics, 115, 6716-6721. Stern O., 1924. Zurtheorieder electrolytischendoppelschist. Z. Elektrochem, 30, 508-516. Tchistiakov A.A., 2000. Physico-chemical aspects of clay migration and injectivity decrease of geothermal clastic reservoirs: Proceedings World Geothermal Congress, 3087-3095. Wurmstich B., Morgan F.D., 1994. Modeling of streaming potential responses caused by oil well pumping. Geophysics, 59, 46-56.

The Controls of Pore-Throat Structure on Fluid Performance in Tight Clastic Rock Reservoir: A Case from the Upper Triassic of Chang 7 Member, Ordos Basin, China

The characteristics of porosity and permeability in tight clastic rock reservoir have significant difference from those in conventional reservoir. The increased exploitation of tight gas and oil requests further understanding of fluid performance in the nanoscale pore-throat network of the tight reservoir. Typical tight sandstone and siltstone samples from Ordos Basin were investigated, and rate-controlled mercury injection capillary pressure (RMICP) and nuclear magnetic resonance (NMR) were employed in this paper, combined with helium porosity and air permeability data, to analyze the impact of pore-throat structure on the storage and seepage capacity of these tight oil reservoirs, revealing the control factors of economic petroleum production. The researches indicate that, in the tight clastic rock reservoir, largest throat is the key control on the permeability and potentially dominates the movable water saturation in the reservoir. The storage capacity of the reservoir consists of effective throat and pore space. Although it has a relatively steady and significant proportion that resulted from the throats, its variation is still dominated by the effective pores. A combination parameter (ε) that was established to be as an integrated characteristic of pore-throat structure shows effectively prediction of physical capability for hydrocarbon resource of the tight clastic rock reservoir.

The impact of heterogeneity on waterflood developments in clastic inner shelf reservoirs: an example from the Holland Greensand Member, Rotterdam Field, The Netherlands

Abstract A geological understanding of the way fluids flow through a reservoir is crucial when considering waterflood developments in heterogeneous reservoirs. Recent integrated production geoscience and reservoir engineering studies on the Holland Greensand oil reservoir (Aptian) of the Rotterdam Field in the West Netherlands Basin, are used to illustrate the geological controls on fluid flow through rocks deposited in a clastic inner shelf depositional setting. An integrated understanding of the subsurface has been gained through core, log and production data analysis. Analogous Early Cretaceous Upper Greensand Formation coastal exposures in SW England have been used to gauge the scale of lateral and vertical heterogeneity, and its impact on hydrocarbon and water flow paths. Argillaceous sandstones deposited at the distal margins of a subtidal sand-sheet provide internal reservoir baffles, while fluids are believed to preferentially follow flow paths through associated laterally extensive tempestites. Cemented layers observable in wells are interpreted to be laterally restricted and are not considered as major baffles. These observations have been used to steer static reservoir model construction and subsequent simulation. Results from field testing by production logging tool analysis support the geological concepts developed and the modelling approach used. This work has important implications for defining the approach for future reservoir management and redevelopment in the Rotterdam Field, in particular the well type and configuration and completion strategies post-reservoir flooding. The application of methodologies employed in this study is recommended for similar waterflood developments.

ПРАКТИЧЕСКИЕ АСПЕКТЫ МОДЕЛИРОВАНИЯ ПЕРЕХОДНЫХ НЕФТЕВОДОНАСЫЩЕННЫХ ЗОН В ТЕРРИГЕННЫХ КОЛЛЕКТОРАХ ЗАПАДНОЙ СИБИРИ ПО ДАННЫМ АНАЛИЗА КЕРНА И ГЕОФИЗИЧЕСКИХ ИССЛЕДОВАНИЙ СКВАЖИН

ПРАКТИЧЕСКИЕ АСПЕКТЫ МОДЕЛИРОВАНИЯ ПЕРЕХОДНЫХ НЕФТЕВОДОНАСЫЩЕННЫХ ЗОН В ТЕРРИГЕННЫХ КОЛЛЕКТОРАХ ЗАПАДНОЙ СИБИРИ ПО ДАННЫМ АНАЛИЗА КЕРНА И ГЕОФИЗИЧЕСКИХ ИССЛЕДОВАНИЙ СКВАЖИН

Reservoir description of Upper Cretaceous concretion-rich sandstone, Mississippi, USA: Example from Tinsley Field

Abstract The Upper Cretaceous Woodruff sand in Tinsley Field provides a good case study of addressing the challenges influencing the flooding process of a complex reservoir. It primarily consists of sandstone intervals that were deposited in a shallow marine, wave-dominated shoal environment and appears deceivingly simple on wireline logs. Deeper investigation finds that the clastic reservoir is actually rich in carbonate concretions with varying geometries and percentages. These carbonate concretions change from scattered ovoid to discontinuous thin beds alternating with bioturbated intervals throughout the structurally-separated fault blocks of the field. Evidence supports the concretions acting as baffles rather than barriers to flow within the reservoir. The main Woodruff rock types were categorized based on petrographic description of cores taken from different locations and fault blocks within Tinsley Field, and this approach helped to highlight the impact of diagenesis on the reservoir quality throughout the field. The probe permeameter data of the cored wells provided a discrete, high-resolution method to determine net reservoir sand. Calibration of probe permeability measurements from the cores with wireline log-based permeability provided a good control on the petrophysical properties throughout the field. The uncertainty related to distribution of reservoir properties was addressed by building a sector model representing one of the Tinsley fault blocks. Population of the properties was controlled by semi-variogram ranges. Although thickness and percentage of pay versus non-pay remained uncertain, validation of the sector model was achieved by matching the static properties and calculated pore volumes to the production history. The results of the flow simulation model demonstrated that the geological model had a reasonable distribution of properties to reflect actual reservoir behavior. The Woodruff geological model provides the foundation for detailed reservoir simulation study that can enhance the understanding of fluid flow within the reservoir intervals. This knowledge will greatly assist in deriving the optimum flooding strategy to maximize oil production, and ultimately, the oil recovery factor.

3D seismic and formation micro-imager (FMI) integrated study to delineate depositional pattern of Abu Madi (Upper Miocene) clastic reservoir rocks in El-Wastani gas field, onshore Nile Delta, Egypt

Ten wells (EW-4, EW-5, EW-6, EW-7, EW-8, EW-9, EW-10, EW-12, EW-13 and EW-15) were interpreted using the composite well logs, data of core analysis, gamma-ray logs, formation micro-imager logs (FMI), and 3D seismic data in SEGY format to understand the stratigraphy of the onshore, Nile Delta, Egypt.The amplitude analysis of 3-D seismic horizon slice of Lower Abu Madi rock unit together with the lithostratigraphic correlation through the study area depending on the gamma-ray log “HSGR” (left to right increasing), and the identification of type of bed geometry, nature of bed contacts, type of the sedimentary structures and the dominant formative paleocurrents by using some available borehole micro-resistivity images (FMI) and core photos. All of these techniques are used together to define the different depositional facies and depositional environment of the Messinian clastics (Lower Abu Madi rock unit), which is considered to be the main reservoir in the El-Wastani gas field, onshore Nile Delta, Egypt.The present study of depositional pattern of the Upper Miocene clastics reservoir (Lower Abu Madi rock unit) revealed that it is represented by high sinuous meandering channels or paleo-valley and three types of fluvial facies were defined; channel fill, channel margin, and floodplain basin.

Petroleum systems in Southeast Asian Tertiary basins

Productive Tertiary basins in Southeast Asia have essentially similar geodynamic developments, and share many hydrocarbon habitats and active petroleum systems. In order to facilitate understanding of the essential elements that contribute to the success of petroleum systems I have classified them into a number of groups or ‘associations’ according to their sedimentary facies. This facilitates use of them as valuable analogues. Five such facies associations, containing characteristic and distinct petroleum parameters have been recognised: (i) lacustrine (ii) paralic (iii) open marine shelf (iv) deeper marine and (v) pre-Tertiary. They belong to particular cycles or stages in basin development that provide the context within which the depositional environments and palaeogeography evolve. Lacustrine facies typify the early stages of synrift development in basins closer or more proximal to the Sundaland province in northern and western SE Asia. Open marine facies, on the other hand, typify the early postrift period and basins in palaeogeographically more distal areas, such as eastern Indonesia and The Philippines. Paralic and bathyal facies characterise the later stages of the synrift and postrift cycles and are widespread throughout the proximal and intermediate parts of the area. Pre-Tertiary source facies, which provide charge in parts of eastern Indonesia and Thailand, are mainly terrestrial in nature. These differences have important implications for petroleum occurrence, which can be summarised accordingly: • More proximal basins are dominated by lacustrine to paralic facies in the synrift cycle and have a mainly non-marine sedimentary fill. Petroleum systems with oil charge are dominant. • More distal basins are dominated by rapid postrift subsidence. In the open marine facies carbonate reservoirs are well-developed, while petroleum systems are mainly gas-prone. • Around Borneo thick late postrift passive margin delta sequences with oil- and gas-prone coaly source rocks and clastic reservoirs are developed in delta-top environments. Transported terrigenous organic material is commonly found in related deep marine environments and contributes to a marine source facies. Both give rise to prolific petroleum systems. • Many basins in the Sunda Shelf area lie in an intermediate situation, where a non-marine synrift is followed by a marine postrift cycle. Such basins benefit from lacustrine and paralic source rock and reservoir sequences in both the syn- and the postrift, and are often characterised by multiple petroleum systems. Evaluation of petroleum potential in Southeast Asian Tertiary basins requires a special approach: in most parts of the World, such as the Middle East and Northwest Europe, source rocks are of marine origin, are relatively consistent in type and quality and are located in well-defined formations of regional extent. In SE Asia the terrestrial and lacustrine source rocks are more difficult to locate, are variable in quality and are often distributed in thin beds throughout thick sequences. These differences mean that predictive extrapolations of charge quality and maturity, and therefore of basin prospectivity, are much more difficult in Southeast Asia: This probably explains why discoveries continue to be made after almost 130 years of exploration!

Petrophysical Study of Szolnok Formation, Endrod Gas Field, Hungary

Investigation of rock porosity and permeability is highly beneficial for geologists, petro-physicist and petroleum engineers in order to evaluate reservoir pore space geometry through the time and space. Clastic reservoir quality and classification could perform based on the petrophysical data correlations. Study of the Szolnok formation was our target. It is composed mainly of sandstones with clay-marlstone and siltstones. Two hundred thirteen-core samples of Upper and Lower Pliocene and Miocene age were subjected for petrophysical investigations. Pore size distribution using MICP, Mercury and Helium porosity, horizontal and vertical permeability were measured for studied core samples. The Szolnok Formation has two main lithologic facies: a. 141 clean sandstone samples and b. 72 siltstone and clay-marlstone samples. Ultrasonic laboratory measurements were carried out for only 30 selected sandstone core samples. Sonic viewer-120 is used to measure sonic velocities and other mechanical properties such as rigidity, bulk modulus and Young’s modulus. Gas permeability and Helium porosity were plotted versus sonic wave velocity indicates that both permeability and porosity could be outlined from either compressional or shear wave velocity. Effective pore radius is outlined from both of them. The highest sample porosity was recorded for the Miocene in age followed by the Lower Pliocene and then for the Upper Pliocene samples respectively. Miocene samples are relatively clayey free followed by Lower Pliocene samples because they have higher sonic velocity (Vp and Vs) than the Upper Pliocene samples. The Miocene and Lower Pliocene samples have relatively lower dynamic mechanical parameters than Upper Pliocene samples which represent good gas reservoirs in the Endrod field. Several regression line equations with high coefficient of correlation have been calculated to predict Szolnok reservoir parameters.

Reservoir characteristics and controlling factors of Silurian Lower Kepingtage Formation in Tahe area, Tarim Basin, NW China

With the breakthrough of exploration in Well TP16-1, the lower Kepingtage Formation becomes a key target for petroleum exploration of deep clastic reservoir in Tahe area. In this paper we focused on the research of the reservoir characteristics and its controlling factors in two sub-member formations (S1k 1 1 and S1k 1 3 ). Based on X-ray diffraction, conventional physical properties data (porosity and permeability) and reservoir storage space data (casting thin section and scanning electron microscope), we determined that the S1k1 Formation belongs to extra-low porosity and permeability reservoir, although the upper S1k 1 3 Formation shows relative better physical characteristic than the lower S1k 1 1 Formation. The development of storage space in the study area is controlled by sedimentary microfacies, diagenesis process. Reservoirs in S1k1 Formation are mainly located in channel (S1k 1 1 sandstones) and sand flat (S1k 1 3 sandstones). The sand flat sediments with a more coarse grain size compared with the channel. In diagenesis, compaction is the major controlling factor for reducing the porosity, followed by cementation. Dissolution of diagenesis is the major controlling factor in enhancing the reservoir porosities. Compared with channel (S1k 1 1 ) sandstones, sand flat sandstones (S1k 1 3 ) have better reservoir quality for its weaker compaction, cementation and stronger dissolution. On the basis of sedimentary characteristics (grain size and subfacies), physical property (porosity and permeability) and reservoir storage space, we divide the S1k1 reservoir into three categories (I, II and III). Type I reservoir is high quality reservoir. It is mainly distributed in the south area of S1k 1 1 and S1k 1 3 reservoir. Type II is moderate reservoir. It is located in the middle of S1k 1 1 reservoir and in the north of S1k 1 3 reservoir. Type III is the poor reservoir. It is only located in the north of S1k 1 1 reservoir.

Geochemical composition of oils in the Dunga Field, western Kazakhstan: Evidence for a lacustrine source and a complex filling history

The onshore Mangyshlak Basin, located in western Kazakhstan along the eastern coastline of the Caspian Sea, is a prolific hydrocarbon province and home to numerous oil and gas fields. The primary reservoirs are Jurassic clastic sandstones, but the Dunga Field contains hydrocarbons in Lower Cretaceous (Valanginian, Barremian, Aptian, Albian) clastic and carbonate reservoirs. The general perception is that these petroleum accumulations were charged from marine source rocks of likely Middle Triassic age. A detailed organic geochemical investigation of oils from the Cretaceous reservoirs of Dunga Field suggests that all were generated from the same lacustrine source rock facies (organofacies C) in mature kitchens in the offshore Mangyshlak Basin, followed by a complex filling history. The oils are characterised by relatively high wax content, low sulfur content (mainly < 0.2 wt%), typical lacustrine tricyclic terpane ratios (high T26/T25, high T24/T23, low T22/T21) and low H31R/H30 hopane ratios. Maturity of the source rock that generated the oils would tentatively correspond to a VR of ∼0.9–1.1 %Ro. The oils are non-biodegraded, but some minor water washing might have occurred. Diamondoid data suggest that the Barremian reservoir contains a mixed oil pool composed of the non-cracked lacustrine oil and another charge of oil that is cracked from 79% to 83% and likely also to be slightly fractionated. This requires a complex filling history of the Dunga Field involving two hydrocarbon charges, likely from two different fetch areas. One charge of non-cracked oil migrated into all four reservoirs whereas another charge was ‘hoteled’ and cracked before remigration to the Barremian reservoir only and mixed with the non-cracked oil.

On the development of a non-linear calibration relationship for the purpose of clay content estimation from the natural gamma ray log

The Shurijeh Formation of Early Cretaceous age is an important clastic sandstone reservoir rock in the Gonbadli field, NE Iran. The quantitative determination of Shurijeh clay minerals has been considered to be a very important and challenging task due to the heterogeneity of formation. The calibrated gamma ray log has been traditionally used as the primary estimator of volume of clay in the subsurface formations. The comparison between the core-measured values and the resulting estimates from the old calibration methods in Shurijeh Formation revealed that despite of applying old calibrations, the Shurijeh clay contents suffers from overestimations. Thus, the most accurate calibration for natural gamma ray log was developed, using the integration of quantitative mineralogical analyses from 76 core samples to estimate the volume of clay in Shurijeh Formation. The least percent relative error, i.e., 11.4%, was achieved in developing a new regression relationship in the form of a rational function acting as the most accurate non-linear clay indicator. The reliability of it was verified by the excellent correlation between the laboratory-measured clay contents in the core samples from another wells drilled in the mentioned Formation and the estimated values. The spectral log ratios have also been used to estimate the Formation depositional environment and different clay minerals types in it. It could truly be inferred that the Shurijeh was deposited in a marine environment with most of data having a thorium to uranium (Th/U) ratio in the range of 1–10. However, the indirect clay typing accomplished by several cross-plots, did not provide consistent results with the laboratory-determined types from the XRD test.

Origin of different chlorite occurrences and their effects on tight clastic reservoir porosity

The effects of chlorite on tight sandstone reservoirs have not been fully understood yet. In this paper, two different chlorite occurrences are observed in the Upper Triassic Xujiahe tight sandstones of Guang'an Area, Sichuan Basin (grain coating) and in the Permian Lucaogou tight sandstones of Jimusar Sag, Junggar Basin (pore filling), respectively. The effects these two chlorite occurrences having on reservoir quality are evaluated. Results show the influence of chlorite on porosity of tight clastic reservoir depends on its occurrences. Grain-coating chlorite has positive effect on porosity preservation, while pore-filling chlorite plays a negative role.Analysis of grain size indicates that grain-coating and pore-filling chlorites always occur in high-energy and low-energy environments, respectively. The water current carries an abundance of medium-grained saltating contents in strong hydrodynamic tractive current environment that leads to a relative motion between the saltating population and suspended clay in water. As indicated by Bernoulli's theory, the saltating grains are coated by clay on the surface because of the local flow pressure resulting from relative velocity. However, in the case of a weak hydrodynamic tractive current depositional environment, sand is entrained with clay, i.e., both sand grains and clays are in suspension and they have no relative velocity; thus, the clay cannot completely coat the grain surface. As the precursor of chlorite, occurrence of smectite-dominant clays determines the occurrence of chlorite during diagenesis, and therefore, determines whether the chlorite has a positive effect on porosity of tight clastic reservoirs.

An-integrated seismic approach to de-risk hydrocarbon accumulation for Pliocene deep marine slope channels, offshore West Nile Delta, Egypt

The Nile Delta basin is a hydrocarbon rich province that has hydrocarbon accumulations generated from biogenic and thermogenic source rocks and trapped in a clastic channel reservoirs ranging in age from Pliocene to Early Cretaceous. Currently, the offshore Nile Delta is the most active exploration and development province in Egypt.The main challenge of the studied area is that we have only one well in a channel system exceeds fifteen km length, where seismic reservoir characterization is used to de-risk development scenarios for the field by discriminating between gas sand, water sand and shale. Extracting the gas-charged geobody from the seismic data is magnificent input for 3D reservoir static modelling.Seismic data, being non-stationary in nature, have varying frequency content in time. Spectral decomposition analysis unravels the seismic signal into its initial constituent frequencies. Frequency decomposition of a seismic signal aims to characterize the time-dependent frequency response of subsurface rocks and reservoirs for imaging and mapping of bed thickness, geologic discontinuities and channel connectivity.Inversion feasibility study using crossplot between P-wave impedance (Ip) and S-wave impedance (Is) which derived from well logs (P-wave velocity, S-wave velocity and density) is applied to investigate which inversion type would be sufficient enough to discriminate between gas sand, water sand and shale.Integration between spectral analysis, inversion results and Ip vs. Is crossplot cutoffs help to generate 3D lithofacies cubes, which used to extract gas sand and water sand geobodies, which is extremely wonderful for constructing facies depositional static model in area with unknown facies distribution and sand connectivity. Therefore de-risking hydrocarbon accumulation and GIIP estimation for the field became more confident for drilling new development wells.

Uncertainty Analysis of Smart Waterflood Recovery Performance in Clastic Reservoirs

In recent years, numerous laboratory studies have documented the benefits of smart waterflooding as an emerging enhanced oil recovery (EOR) process, along with a few successful field applications, notably clastic reservoirs. In most cases, there are undeniable inconsistencies between lab and field results. This process has led to unpredictable outcomes and misleading prediction of smart waterflooding projects. Hence, this work is conducted to evaluate uncertainties in smart waterflooding from laboratory to field-scale. An one-dimensional (1-D) reactive transport model was developed and validated with flooding experiments. Validation shows that combinations of various matching parameters can be used to interpret the experiment. Different realizations lead to different results when extended to 3-D heterogeneous model. The sensitivity of parameters like grid size and heterogeneity in full-field model majorly influences smart waterflooding performance, which is responsible for the inconsistencies. Therefore, these parameters should be considered in field-scale simulation to fully demonstrate the potential of smart waterflooding.

Trimethyldibenzothiophenes: Molecular tracers for filling pathways in oil reservoir

Based on the thermodynamic stabilities and molecular simulation, two trimethyldibenzothiophene molecular indicators, that is, 2,4,6-/(1,4,6 + 1,4,8 + 3,4,6)-trimethyldibenzothiophene (TMDBT) and (2,4,7 + 2,4,8)-/(1,4,6 + 1,4,8 + 3,4,6)-TMDBT (the numbers indicate the position of methyl-substitute), were proposed to trace subsurface oil migration orientations and reservoir filling pathways. In this paper, we successfully applied the aforesaid parameters both in an Ordovician carbonate reservoir of the Tuoputai region of the Tarim Basin (NW China), and in an Eocene clastic lacustrine reservoir of the Fushan Depression in the Beibuwan Basin, South China Sea. Besides the migration fractionation is proven the main control factor for the relative contents of TMDBT isomers in corresponding oils, which indicates that the trimethyldibenzothiophene molecular parameters can serve as the effective oil migration tracer in an oil reservoir, especially in high to over mature and severely biodegraded oils.

Palynological, palaeoenvironmental and sequence stratigraphical analyses of a Turonian-Coniacian sequence, Beni Suef Basin, Eastern Desert, Egypt: Implication of Pediastrum rhythmic signature

Sixteen samples from the “E” to “B” members of the Abu Roash Formation encountered in the Beni Suef Basin, Eastern Desert of Egypt were palynologically analyzed for palaeoenvironmental and sequence stratigraphic investigations. The integrated palynofacies and lithofacies analysis of the studied section indicates deposition of five alternating regressive and transgressive sequences in well-oxygenated, proximal shelf settings. The Abu Roash “E” and the upper “D” to the lower “C” members were deposited during pronounced regressive phases in oxic, shallow marginal marine settings. The upper “B” Member was deposited during a recurring regressive phase but of a lower magnitude in oxic, shallow inner neritic conditions. The lower “D” Member was deposited during a minor transgression phase in dysoxic, shallow inner neritic settings. While the upper “C” to the lower “B” section was deposited during a stronger transgressive episode in a relatively deep, inner neritic environment of prominent dysoxic conditions. This interchange in the depositional setting was documented by the pronounced and concurrent, cyclic nature of the freshwater algae, peridinioid dinoflagellate cysts, pteridophyte spores, and reworked sporomorphs with variable intensities. Their increasing and conversely their diminishing trends clearly reflect alternating regressive-transgressive periods of reduced and relatively normal salinity conditions, respectively. Overall, sedimentation of the studied Abu Roash section indicates a recurring rise in sea level, which accentuated during the earliest Santonian time.The analogous peaking in the Pediastrum signals with those of the pteridophyte spores and reworked taxa indicate a good connection between these Pediastrum signals and the pronounced fluviatile influxes of terrigenous sediments during regressive phases. Accordingly, this can be used to identify regressive sequence boundaries and hence the clastic reservoirs. Even with the small counts recorded herein, we believe high ratios of peridinioid/gonyalulacoid dinocysts are significantly paralleled by peaking signals of freshwater algae and regressive sedimentation phases. This must be preliminary documented here. Probably future palynological studies will be able to fully interpret and address this important Pediastrum rhythmic event in different sequence stratigraphic settings.The palynological parameters, age controlled sporomorph marker taxa, lithology, and gamma ray data were used to differentiate the Abu Roash members into three distinctive 3rd order depositional sequences (AR SQ1, AR SQ2, and AR SQ3). These sequences match well with the global stratigraphic sequences Tu 3, Tu 4, and Co 1 and connect the local rise in sea level to the global eustatic sea level rise.

Fracture detection via correlating P-wave amplitude variation with offset and azimuth analysis and well data in eastern central Saudi Arabia

The late Carboniferous clastic Unayzah-C in eastern central Saudi Arabia is a low-porosity, possibly fractured reservoir. Mapping the Unayzah-C is a challenge due to the low signal-to-noise ratio (S/N) and limited bandwidth in the conventional 3D seismic data. A related challenge is delineating and characterizing fracture zones within the Unayzah-C. Full-azimuth 3D broadband seismic data were acquired using point receivers, low-frequency sweeps down to 2 Hz, and 6 km patch geometry. The data indicate significant enhancement in continuity and resolution of the reflection data, leading to improved mapping of the Unayzah-C. Because the data set has a rectangular patch geometry with full inline offsets to 6000 m, using amplitude variation with offset and azimuth (AVOA) may be effective to delineate and characterize fracture zones within Unayzah-A and Unayzah-C. The study was undertaken to determine the improvement of wide-azimuth seismic data in fracture detection in clastic reservoirs. The results were validated with available well data including borehole images, well tests, and production data in the Unayzah-A. There are no production data or borehole images within the Unayzah-C. For validation, we had to refer to a comparison of alternative seismic fracture detection methods, mainly curvature and coherence. Anisotropy was found to be weak, which may be due to noise, clastic lithology, and heterogeneity of the reservoirs, in both reservoirs except for along the western steep flank of the study area. These may correspond to some north–south-trending faults suggested by circulation loss and borehole image data in a few wells. The orientation of the long axis of the anisotropy ellipses is northwest–southeast, and it is not in agreement with the north–south structural trend. No correlation was found among the curvature, coherence, and AVOA in Unayzah-A or Unayzah-C. Some possible explanations for the low correlation between the AVOA ellipticity and the natural fractures are a noisy data set, overburden anisotropy, heterogeneity, granulation seams, and deformation.

Petrophysics and hydrocarbon potential of Paleozoic rocks in Kuwait

Well logs from nine deep exploratory and development wells in Kuwaiti oil fields have been used to study petrophysical characteristics and their effect on the reservoir quality of the subsurface Paleozoic Khuff and Unayzah formations. Petrophysical log data have been calibrated with core analysis available at some intervals. The study indicates a complex lithological facies of the Khuff Formation that is composed mainly of dolomite and anhydrite interbeds with dispersed argillaceous materials and few limestone intercalations. This facies greatly lowered the formation matrix porosity and permeability index. The porosity is fully saturated with water, which is reflected by the low resistivity logs responses, except at some intervals where few hydrocarbon shows are recorded. The impermeable anhydrites, massive (low-permeability) carbonate rock and shale at the lower part of the formation combine to form intraformational seals for the clastic reservoirs of the underlying Unayzah Formation. By contrast, the log interpretation revealed clastic lithological nature of the Unayzah Formation with cycles of conglomerate, sandstone, siltstone, mudstone and shales. The recorded argillaceous materials are mainly of disseminated habit, which control, for some extent, the matrix porosity, that ranges from 2% to 15% with water saturation ranges from 65% to 100%. Cementation, dissolution, compaction and clay mineral authigenesis are the most significant diagenetic processes affecting the reservoir quality. Calibration with the available core analysis at some intervals of the formation indicates that the siliciclastic sequence is a fluvial with more than one climatic cycle changes from humid, semi-arid to arid condition and displays the impact of both physical and chemical diagenesis. In general, the study revealed that the Unyazah Formation has a better reservoir quality than the Khuff Formation and possible gas bearing zones.