Reservoir Analogue Research Articles

Multiscale Characterisation of Fracture Patterns of a Crystalline Reservoir Analogue

For an accurate multiscale property modelling of fractured crystalline geothermal reservoirs, an enhanced characterisation of the geometrical features and variability of the fracture network properties is an essential prerequisite. Combining regional digital elevation model analysis and local outcrop investigation, the study comprises the characterisation of the fracture pattern of a crystalline reservoir analogue in the Northern Odenwald, with LiDAR and GIS structural interpretation. This approach provides insights into the 3D architecture of the fault and fracture network, its clustering, and its connectivity. Mapped discontinuities show a homogeneous length distribution, which follows a power law with a −2.03 scaling factor. The connectivity of the fracture network is heterogenous, due to a fault control at the hectometric scale. Clustering is marked by long sub-vertical fractures at the outcrop scale, and strongly enhance heterogeneity around weathered fracture and fault corridors. The multi-variable dataset created within this study can be used as input data for accurate discrete fracture networks and fluid-flow modelling of reservoirs of similar type.

Red Sea Holocene carbonates: Windward platform margin and lagoon near Al-Wajh, northern Saudi Arabia

ABSTRACTAnalysis of Holocene sedimentary seascape is focused on the Red Sea windward Al-Wajh platform margin, its central lagoon, and nearby isolated platforms based on data that include mapped ecological facies (habitats), water depths, grain sizes, and allochem types and abundances determined from thin sections. On this basis, a depositional model applicable to Red Sea Plio-Pleistocene and other ancient icehouse carbonate platforms is presented. The model highlights favorable reservoirs in analogous ancient systems to include coral crests and columnar framework habitats with primary porosity developed in boundstone lithologies and windward platform margins to contain considerable open pore space, including cavernous openings, of which not all should be anticipated to be occluded with marine cements and sediments. Meteoric diagenesis is expected to be minor as limited freshwater is available due to extreme aridity, but may play a role during glaciation.Most habitats have potential for secondary (enhanced) porosity resulting from dissolution of aragonite skeletons, particularly mollusk shells and calcareous coral (Scleractinia) endoskeletons. Central-lagoon habitats are expected to have the least favorable reservoir potential of environments considered because they are dominated by peloids. Central-lagoon sediment differs from other published localities, having higher peloid abundances, greater peloid distribution, and little or no association with Halimeda and quartz grains. Under the likely scenario that platform-interior sediments are completely bioturbated and comprise peloid-rich, grain-dominated fabrics, with many smaller peloids (most of them likely fecal pellets) at or near 4 μm in size (i.e., mud fraction), it is possible that grain size will control pore size once the considered deposits are lithified. If so, platform-interior sediments will lithify as mudstones, wackestones, or very fine-grained grainstones, an outcome which might otherwise be unexpected given the abundance of coarse peloid grains.The Al-Wajh platform is compared with 15 Holocene analogs and found to be unique with respect to rift-margin type, restricted-marine circulation, in having a lagoon with high peloid content, and lack of karst. In further comparison with ancient reservoir analogs, two greenhouse and four icehouse, it compares favorably to icehouse platforms deposited in rift basins with respect to mineralogy of deposition, meter-scale cycle thicknesses, and general peloid content and distribution. It provides a snapshot as to how an icehouse platform might have nucleated and attached along an active rift margin; it is a broadly applicable carbonate analog for the Red Sea Plio-Pleistocene and similar icehouse, rift basins.

Implications of palaeosols in low net-to-gross fluvial architecture reconstruction: Reservoir analogues from Patagonia and Spain

The changes in the geometry, density and distribution of the fluvial reservoir sand-bodies have been modelled both in the laboratory and from outcrop analogues. On the other hand, fine-grained floodplain deposits, often called “background” sedimentation, have not been in the spotlight. However, they provide a very important database for fluvial architecture reconstruction and therefore constitute a key tool in characterizing, correlating and modelling heterogeneous fluvial reservoirs. The methodology used in this work combines classical sedimentological and palaeopedological data. Palaeosols were identified in outcrops of the Cretaceous of Patagonia and Triassic red beds of Spain based on the main pedofeatures such as colour, soil structures, mottles, nodules, clay illuviation cutans, slickensides and rhizoliths. Palaeosol horizons, thickness and types of contact were described. The palaeosols classification was made through the comparison with the Soil Taxonomy. For the characterization of lateral palaeosols variability, several palaeopedological logs were constructed following the same stratigraphic level at both margins of the main channels. Small-scale or high-frequency palaeosol variations, identified in both fluvial succession are represented by the lateral and vertical superimposition of Inceptisols/Entisols, Vertisols and hydromorphic Vertisols/swamp deposits. We recognized a decrease in the drainage conditions within the palaeosols catena moving away from the main channel bodies. The most waterlogged palaeosol is located at 200 to 300 m from the main channels. Lateral changes of palaeosols are interpreted as the result of intrinsic factors to the depositional systems, such as the relative position within the floodplain and the distance from the main channels, that condition the particle size of parent material, the sedimentation rate and the palaeotopographic position which state the drainage conditions of palaeosols. Vertical stacking of different palaeosols is linked to avulsion processes and the relatively abrupt change in the distance to main channels as the system aggraded. The study of these two environmentally similar examples (low-gradient meandering fluvial systems subjected to a high rate of aggradation), although located in different tectonic and chronostratigraphic contexts, shows that the type of fluvial system acted as the main control of sedimentary and pedogenic processes; as well as the scale at which they occur. Thus, when choosing an outcrop fluvial reservoir analogue, the type of fluvial system and climate should be more important than the age or the tectonic framework of the succession to be studied.

Gravity data as a faulting assessment tool for unconventional reservoirs regional exploration: The Sergipe–Alagoas Basin example

This paper introduces a gravity regional interpretation workflow for mapping the natural fracture system, a challenge in unconventional reservoir exploration. The workflow comprises coupling two gravity data attributes, the tilt angle and the multiscale edge detection (worming), to build a high-resolution image structural framework of a given basin’s basement. That includes a description of the fault directions and fault density, consolidated in a fault distribution map. The proposed workflow was applied to available gravity data of a representative passive-margin basin, the Sergipe-Alagoas Basin, Brazil. The source rocks of Sergipe-Alagoas are organic-rich shale deposited in the principal depocenters during the rift phase of the basin’s evolution. These shaly units are the unconventional reservoirs in the basin. These organic-rich shales are acknowledged as syn-rift unconventional reservoir analogs of all Brazilian continental margin basins and many other passive-margin basins worldwide. The workflow recognized two fault trends in the studied area. A principal NE–SW and a minor NW–SE. 3D seismic interpretation validated the proposed workflow by successfully associating the gravity faults with traditional fault attributes. One advantage of this workflow is that it can be implemented over broad regions at a minimum expense. The proposed method can be used to rank opportunities in unconventional exploration.

Practical data acquisition strategy for time-lapse experiments using crosshole GPR and full-waveform inversion

Crosshole ground penetrating radar (GPR) methods are increasingly used in time-lapse studies of flow in the uppermost near subsurface with important implications for our understanding of e.g., water infiltration in the unsaturated zone, and fluid flow in the saturated zone. A particular challenge in such time-lapse crosshole studies is the trade-off between collecting sufficient data to be able to resolve how a tracer moves, and, minimizing the data acquisition time such that the data approximates a static state. We test how dense recording geometries are needed for resolving a gas bubble injected in a highly heterogeneous chalk reservoir analogue using a full-waveform inversion (FWI) approach for modelling the crosshole GPR data. We show that even relatively sparse geometries provide sufficient resolution of the permittivity contrast caused by the gas bubble, provided that the detailed background permittivity structure is known from prior (before gas injection) FWI analysis of densely recorded high-resolution data. The conductivity contrast caused by the gas is more challenging to recover and the resolution suffers to a higher degree when reducing the survey geometry or at higher noise levels. As long as the permittivity change during the time-lapse experiment is the main target, a significant reduction in acquisition time is therefore possible as compared to the time needed to record the background permittivity structure. This reduced acquisition time has important practical implications for time-lapse experiments under realistic conditions. Our results are based on synthetic analysis based on a realistic subsurface scenario closely linked to characterization of heterogeneous chalk reservoirs. However, our findings also have important implications for planning of future time-lapse studies in other settings.

Mechanical Response of Castlegate Sandstone under Hydrostatic Cyclic Loading

The stress history of rocks in the subsurface affects their mechanical and petrophysical properties. Rocks can often experience repeated cycles of loading and unloading due to fluid pressure fluctuations, which will lead to different mechanical behavior from static conditions. This is of importance for several geophysical and industrial applications, for example, wastewater injection and reservoir storage wells, which generate repeated stress perturbations. Laboratory experiments were conducted with Castlegate sandstone to observe the effects of different cyclic pressure loading conditions on a common reservoir analogue. Each sample was hydrostatically loaded in a triaxial cell to a low effective confining pressure, and either pore pressure or confining pressure was cycled at different rates over the course of a few weeks. Fluid permeability was measured during initial loading and periodically between stress cycles. Samples that undergo cyclic loading experience significantly more inelastic (nonrecoverable) strain compared to samples tested without cyclic hydrostatic loading. Permeability decreases rapidly for all tests during the first few days of testing, but the decrease and variability of permeability after this depend upon the loading conditions of each test. Cycling conditions do affect the mechanical behavior; the elastic moduli decrease with the increasing loading rate and stress cycling. The degree of volumetric strain induced by stress cycles is the major control on permeability change in the sandstones, with less compaction leading to more variation from measurement to measurement. The data indicate that cyclic loading degrades permeability and porosity more than static conditions over a similar period, but the petrophysical properties are dictated more by the hydrostatic loading rate rather than the total length of time stress cycling is imposed.

Petrographical and mineralogical study of detrital strata near and within the Ballık travertine deposit (SW Turkey): architecture of a mixed clastic–carbonate succession

The Ballik area (SW Turkey) was studied as a mixed clastic–continental carbonate reservoir analogue, in which kilometre wide and up to 70-m-thick tufa and travertine lithologies are found in an envelope of detrital sediments, which locally strongly interfinger with these porous carbonates. Former studies focussed on the carbonate lithologies, since they are considered as pre-salt analogues. This study aims to describe the adjacent non-carbonate lithologies, unravel their depositional setting, and address their influence on the overall sedimentary architecture. This study relies on an extensive field campaign, during which 142 samples of all different detrital lithologies were collected. Optical, fluorescence, cathodoluminescence, and Scanning Electron Microscopy (SEM) yielded important insights in the petrography of these lithologies, based on which 5 main lithologies were differentiated: i.e., (1) laminated marls, (2) polygenetic conglomerates, (3) massive marls, (4) tabular sandstones, and (5) coquina accumulations. These were interpreted to represent three different sedimentary facies corresponding to lacustrine, fluvial, and shoreline facies. The (clay) mineralogy of lacustrine sediments was extensively studied by bulk and clay-specific XRD. In this respect, special emphasis was laid on the depositional setting of the lacustrine facies, in which both authigenic palygorskite and poorly ordered dolomite were identified. Petrophysical properties of 16 plugs were determined by He porosimetry and N2-permeability, indicating that the detrital sediments are characterised by poor reservoir properties. The latter causes them to act, after assumed burial compaction, as potential barriers within a continental carbonate reservoir system.

Pore-scale dual-porosity and dual-permeability modeling in an exposed multi-facies porous carbonate reservoir

Fracture networks in porous carbonates can control, assist, or even contribute negatively to reservoir quality. In scenarios where fractures and matrix pore systems are of similar importance, a dual-porosity/permeability (DP/P) modeling approach is necessary or at least recommendable for the reservoir characterization. These workflows are well established at the reservoir scale, however at the microscale, the interaction between fractures and porous matrix needs to be further investigated.The aim of this work is to assess the contribution of meter-scale fractures (macrofractures) to the porosity and permeability in a porous carbonate reservoir analogue at the microscale. To reach this objective, we created DP/P models at the microscale through the integration of two different methods of 3D imaging such as, high-resolution synchrotron X-ray microtomography (SR micro-CT) and Structure from Motion (SfM) photogrammetry. Quantitative analyses of pristine rock and DP/P models were performed to evaluate the contribution of macrofracture segments to the porosity and connectivity of the pore network. These results were integrated with single-phase flow simulations for calculating permeability values. Different scenarios were modeled in order to systematically evaluate the control exerted by fracture roughness parameters (i.e., asperity height distribution and fractal dimension) on porosity and permeability in various lithofacies.The key analyzed samples come from the Roman Valley quarry located at the Majella Mountain (central Italy), which has been widely investigated due to the presence of consistent bitumen impregnations distributed in pervious medium-to-coarse grainstones and along two main fault zones. The results of this study demonstrate the utility of obtaining DP/P microscale models as complementary approach to explain the hydrocarbon distribution in fractured multi-facies porous carbonates. We document the potential of macrofracture segments to provide neo-connected porosity by linking up adjacent isolated or partially isolated matrix pore networks in impervious carbonate rocks. In pervious carbonate lithofacies, fault-related macrofractures can enhance permeability and contribute to bitumen migration and distribution, whereas the increment of storage capacity is limited since these rocks are already fully connected. In the case of impervious carbonate lithofacies, results indicate that the actual contribution of neo-connected pores to fluid transport is limited, which agrees with outcrop observations.

High-temperature high-pressure microfluidic system for rapid screening of supercritical CO2 foaming agents

CO2 foam helps to increase the viscosity of CO2 flood fluid and thus improve the process efficiency of the anthropogenic greenhouse gas’s subsurface utilization and sequestration. Successful CO2 foam formation mandates the development of high-performance chemicals at close to reservoir conditions, which in turn requires extensive laboratory tests and evaluations. This work demonstrates the utilization of a microfluidic reservoir analogue for rapid evaluation and screening of commercial surfactants (i.e., Cocamidopropyl Hydroxysultaine, Lauramidopropyl Betaine, Tallow Amine Ethoxylate, N,N,N′ Trimethyl-N′-Tallow-1,3-diaminopropane, and Sodium Alpha Olefin Sulfonate) based on their performance to produce supercritical CO2 foam at high salinity, temperature, and pressure conditions. The microfluidic analogue was designed to represent the pore sizes of the geologic reservoir rock and to operate at 100 °C and 13.8 MPa. Values of the pressure drop across the microfluidic analogue during flow of the CO2 foam through its pore network was used to evaluate the strength of the generated foam and utilized only milliliters of liquid. The transparent microfluidic pore network allows in-situ quantitative visualization of CO2 foam to calculate its half-life under static conditions while observing if there is any damage to the pore network due to precipitation and blockage. The microfluidic mobility reduction results agree with those of foam loop rheometer measurements, however, the microfluidic approach provided more accurate foam stability data to differentiate the foaming agent as compared with conventional balk testing. The results obtained here supports the utility of microfluidic systems for rapid screening of chemicals for carbon sequestration or enhanced oil recovery operations.

Unravelling the pore network and its behaviour: An integrated NMR, MICP, XCT and petrographical study of continental spring carbonates from the Ballık area, SW Turkey

AbstractApplying an integrated methodology, including petrography, mercury injection capillary pressure, laboratory nuclear magnetic resonance and X‐ray computed tomography, on continental spring carbonate reservoir analogue samples is a prerequisite to understand plug scale porosity and permeability heterogeneities. Depending on the dominant pore type in a sample, the orientation and distribution of the pores, pore network connectivity varies from poor to excellent in these continental spring carbonates. The latter exhibit large‐scale ranges for both porosity (3%–25%) and permeability (0.004–3,675 mD). Facies classification alone proved insufficient to link porosity and permeability, due to intrafacies pore network variability. Better assessment of reservoir properties can be achieved by subdividing facies into lithotype and pore type classes. Obtained pore network data addresses the pore types, pore (throat) sizes, number of pore compartments, and allow a subdivision of the pore size distributions into unimodal, bimodal and atypical types. There is no micropore compartment present in samples with unimodal mercury injection capillary pressure and nuclear magnetic resonance distributions. Decoupled micropore compartments are observed in samples with bimodal mercury injection capillary pressure and nuclear magnetic resonance distributions, which show isolating calcite rims, and have limited permeabilities. The cement rims decrease the macropore connectivity and decouple the micropore compartments, which reside in micritic dendrites. The micropore compartment (r < 1 µm) is coupled with the mesopore (r = 1–15 µm) and macropore compartment (r > 15 µm) for atypical samples which lack pore‐lining calcite rims.

Micro-Slimtube Shrinks EOR Screening From Months to a Week

Oilfield testing firm Interface Fluidics says it is one step closer to reinventing the industry’s pressure-volume-temperature (PVT) testing portfolio after the development of a smaller, faster version of yet another laboratory stalwart. Representing the newest alternative to the slimtube test is the micro-slimtube test. A conventional slimtube test involves flowing gas through a sand- or glass-bead-packed metal coil that may be 1 to 4 mm wide and some 40 to 80 ft long to see how it mixes and mobilizes oil with samples also inside the tube. The test and subsequent analysis usually take a few months to complete. For a generation, this has been considered time well spent by anyone preparing to invest millions of dollars to prop up an aged asset through gas-injection-based enhanced oil recovery (EOR). But the times are changing. Interface Fluidics’ innovation, which it developed in close partnership with Equinor, measures only about 1.5 in long and generates results in about a week - about 95% sooner than the conventional bench method. The new test also reduces costs by around 75% while using a reservoir fluid sample that’s 99% smaller (10 ml vs. 1 liter). “It’s the same story over and over again - we’re miniaturizing the big stuff and putting it on a chip,” said Stuart Kinnear, CEO of Interface Fluidics. Founded in 2016, the Calgary-based firm helped introduce microfluidic technology to the oil industry with glass and silicon chips that it calls “reservoir analogues.” A well-established enabler in the healthcare industry, microfluidic devices of various stripes are routinely used to rapidly screen new drugs or to study how blood cells move through tiny veins and capillaries. In the upstream industry, Interface Fluidics is part of much smaller group of specialists proving that the devices are also ideal for screening production-enhancing chemicals and to study how oil moves about the tiny pathways of a reservoir rock (SPE 188895). The firm first showed how this works by replicating reservoir rock samples onto its chips as an alternative to core flood experiments. For oil and gas producers and their chemical providers alike (SPE 189780), the lower-cost devices made it affordable to run dozens of tests to determine how various chemistries affect flow behavior in specific geologies.

Downhole heating and hybrid cyclic steam methods: evaluating technologies from the laboratory to the field

The development of heavy oil reservoirs under steam injection methods is facing multiple challenges due to the volatility of oil markets, energy efficiency, and new and stricter environmental regulations. This study aims to summarize the advances of a Research and Development (R&D) program established by Ecopetrol in 2018 to identify potential opportunities to improve the recovery performance of steam injection projects in heavyoil reservoirs in the Middle Valley Magdalena Basin (VMM) of Colombia.This paper summarizes an approach used to evaluate downhole heating and hybrid steam injection technologies assisted by basic benefit-cost ratios and energy and environmental indexes.Specifically, the methodology is described for the identification of optimum development plan scenarios for heavy oil wells. This study also summarizes recent advances in laboratory studies for the evaluation of hybrid steam flooding technologies (steam plus flue gas and solvents) and provides updates on the hybrid cyclicsteam-foam pilot carried out in two VMM wells.The proposed approach represents a fast screening method that has proven to be valuable in supporting management decision-making to allocate resources for laboratory and engineering studies to evaluate thermal enhanced oil recovery (tEOR) technologies in Colombia. The proposed methodology has also contributed to reducing the implementation cycle of tEOR technologies following the reservoir analog description ofreserve analysis. The latter was validated with the successful pilot results of the hybrid steam injection with foams implemented in July 2019.

Integrated outcrop and subsurface geomodeling of the Turonian Wall Creek Member of the Frontier Formation, Powder River Basin, Wyoming, USA

Inter-well heterogeneities influencing fluid migration in deltaic reservoirs are controlled by lateral lithofacies changes and vertical complexities such as low permeability thin-beds (i.e. mudstones). Subsurface tools cannot adequately predict the spatial and stratigraphic organization of these architectural elements, nor their influence on effective reservoir properties and connectivity. Our outcrop-based geomodeling study of the Turonian Wall Creek Member of the Frontier Formation in the Powder River Basin, Wyoming, USA, integrates subsurface production and flow simulation data to quantify the impact of multi-scale stratigraphic heterogeneity on analogous reservoir behavior and horizontal well design. The upscaled representation of thin-bed complexity in our 500 m × 715 m x 15 m geomodel is derived through flow simulation of internally nested, facies specific, centimeter-scale models (basic depositional element models or BDEMs). These BDEMs are populated with quantitative data of mudstone thin-bed geometries directly derived from digital outcrop measurements and measurements in the field, and aided by subsurface (core) petrophysical properties. Reservoir simulations are performed using various landing zone and completion configurations, and under both single-phase and multi-phase flow conditions history matched to subsurface production data.Results from our workflow demonstrate that, in heterolithic settings, the permeability of mudstone thin-beds impart the most significant impacts toward upscaled reservoir behavior, and deliver unique Kv/Kh flow anisotropies dependent on the governing depositional environment. Thin, laterally continuous and planar mudstone beds in the wave-and river-dominated distal delta front setting have the greatest negative effect on Kv and a minimal impact on Kh, promoting laterally continuous and vertically baffled flow units. Conversely, the more curvilinear and intersecting architectures of mudstone beds in the tidal dune facies maintain better vertical connectivity but decreased Kh compared to the wave-influenced facies. Reservoir flow is only sensitive to changes in engineering design (landing zone, well orientation, completion size) where thin-beds act as complete barriers rather than baffles to flow. Layer cake subsurface models failing to account for high-resolution stratigraphic architectures are likely to overestimate reservoir production where thin-beds act as barriers capable of appreciable reservoir compartmentalization, which in our models is more characteristic of the distal delta front setting. Synthesized results of this study are immediately applicable toward development planning in similar tight sandstone reservoirs.

Research and Application of the Composite Reservoir Stimulation Technology for Ultra-High-Temperature Ultra-Deep Naturally-Fractured Carbonate Reservoirs

The Ordovician buried-hill carbonate reservoir in the northern Jizhong Sag of China is seen with abundance in hydrocarbon resources. Nonetheless, attempts of multiple reservoir stimulation technologies have all failed to make breakthrough, due to its lithological complexity (mixture of dolomite and limestone), ultra-high temperatures (180°C) and high in-situ stress gradients (0.023 MPa/m), Given the aforementioned reservoir geological challenges, reservoir evaluation, technology optimization and plan design starting from the reservoir geological characteristics have been carried out, and the “composite” reservoir stimulation technology for ultra-high-temperature ultra-deep naturally-fractured carbonate reservoirs has been proposed. In terms of the short effective affected distance of acid under high temperatures (180°C), low conductivity sustainability owing to high closure stresses (induced by the burial depth of 5,000 m), extreme difficulties in expanding stimulated reservoir volumes (large lateral in-situ stress differences and long vertical spans), the practice of “multi-stage injection, temporary plugging and diversion, and propped acid fracturing” highlighting high pump rates and combination of low- and high-viscosity fluids (acid and fracturing fluids) has been developed and evolves into the network fracturing technology capable of inter-layer temporary isolation and within-layer diversion. The above technology has been applied in Well AT1x, with high volumes of fluid consumption and the maximum pump rate of 11 m3/min. Safe and efficient operation over six hours featuring challenges such as 3,000 m3 of composite fluids, ultra-high temperatures and ultra-high pressures is achieved. On-site monitoring such as the micro-seismic monitoring and simulation results show that compared with the previous reservoir stimulation, the developed technology presents SRV 3.5 times larger, and results in three-dimensional reservoir reconstruction. The post-fracturing daily gas production amounts to 409,000 m3 and daily oil production, 71 m3. In production testing, the wellhead pressure maintained over 25 MPa, and the daily gas production exceeds 100,000 m3, which indicate stable pressures and production, and a safe wellbore. The application accomplishes the design goal of integrated exploration and exploitation, and geology and engineering, and provides references for reservoir simulation of analogous reservoirs.

Contribution of drone photogrammetry to 3D outcrop modeling of facies, porosity, and permeability heterogeneities in carbonate reservoirs (Paris Basin, Middle Jurassic)

This study showcases the value of drone photogrammetry in creating a meter-scale geological model of complex carbonate geobodies. Although drone photogrammetry is now commonly used for modeling the sedimentary facies and architecture of sandstone outcrops, its use is not widespread in creating geomodels of carbonate geobodies. Drone photogrammetry can generate accurate line-drawing correlation and detailed architecture analysis along inaccessible vertical faces of outcrops and permits observations of unreachable places. This work models the Bathonian limestones of Massangis quarry (Burgundy) as an example. The quarry covers an area of 0.4 km2 and is considered as an analogue for the Oolithe Blanche geothermal reservoir in the center of the Paris Basin. The Massangis quarry model represents a good analogue for reservoir microporosity and secondary porosity associated with dedolomitization. Ten facies are described and grouped into three facies associations (1) clinoforms, (2) tidal to subtidal facies, and (3) lagoonal facies. The clinoforms are sets of very large marine dunes 15–20 m high that prograded N70° across the platform as part of a regressive systems tract. Moldic rhombohedral pore spaces associated with dedolomitization are well-expressed within clinoforms and in the bioturbated levels of lagoonal facies. Drone photogrammetry combined with the “Truncated Gaussian with Trends” algorithm implemented in Petrel® software is used to create a geological model that faithfully reproduces the facies architecture observed in the quarry cliffs. Drone photogrammetry can be combined with field work to describe and locate facies and so constrain the spatial distribution of petrophysical properties. It also helps constraining the shapes of geobodies in the model grid for more realistic geological static models and helps providing 3D petrophysical models from an outcropping analogue for geothermal and petroleum reservoirs.

Small-scale diagenetic facies heterogeneity controls porosity and permeability pattern in reservoir sandstones

The fluvial-aeolian Upper Rotliegend sandstones from the Bebertal outcrop (Flechtingen High, Germany) are the famous reservoir analog for the deeply buried Upper Rotliegend gas reservoirs of the Southern Permian Basin. While most diagenetic and reservoir quality investigations are conducted on a meter scale, there is an emerging consensus that significant reservoir heterogeneity is inherited from diagenetic complexity at smaller scales. In this study, we utilize information about diagenetic products and processes at the pore- and plug-scale and analyze their impact on the heterogeneity of porosity, permeability, and cement patterns. Eodiagenetic poikilitic calcite cements, illite/iron oxide grain coatings, and the amount of infiltrated clay are responsible for mm- to cm-scale reservoir heterogeneities in the Parchim formation of the Upper Rotliegend sandstones. Using the Petrel E&P software platform, spatial fluctuations and spatial variations of permeability, porosity, and calcite cements are modeled and compared, offering opportunities for predicting small-scale reservoir rock properties based on diagenetic constraints.

The transition from meandering river delta to braided river delta: Depositional characteristics and controlling factors from the second member of Shanxi Formation to the eighth member of Lower Shihezi Formation in Southeastern Ordos Basin

The Ordos Basin, as one of the most petroliferous basins in China, hosts 12.9 billion tons of oil reserves and 15.2 trillion cubic meters of natural gas reserves. The extensive hydrocarbon exploration and production shows that the southeastern Ordos Basin contains considerable potential in the Shanxi Formation and Lower Shihezi Formation. In this study, cores, wireline logs, thin sections, and heavy minerals are employed to carry out research on classification of sequence stratigraphy, identification of sedimentary facies, reconstruction of palaeo‐geomorphology, analysis of sediment supply, palaeo‐climate, and accommodation space changes. The results indicate that palaeo‐geomorphology gradient tends to be steep, which results in increasing hydrodynamics and turns to be wide and flat which results in decreasing accommodation space. In addition, heavy mineral distribution reveals the direction of sediment supply which indicates provenance changes. The palaeo‐climate changes commonly cause differences in lithology associations, monsoon and vegetation properties. The differences in temperature and humidity result in different colours of lithology associations which indicate various sedimentary environments. The prevalence of monsoon assists in the preservation of fluvial delta by controlling lateral migration of rivers through affecting vegetation and lithology associations. The accommodation space variations control the development of fluvial delta and result in various depositional characteristics of fluvial delta. All these factors trigger the transition from meandering river delta to braided river delta. The reconstruction of the transition and analysis of controlling factors play an important role on understanding the sedimentary evolution of analogous reservoir successions.

Characterizing scales of sedimentary heterogeneity in a fluvial—estuarine reservoir analog: An example from the Mulichinco Formation, Neuquén Basin, Argentina

An integrated stratigraphic, sedimentological and petrophysical analysis is presented to document the variety of sedimentary heterogeneities scales that can occur in a fluvial–estuarine reservoir analog. In this context, outcrops of the Mulichinco Formation (Neuquén Basin, Argentina) were investigated combining architectural analysis, vertical and lateral facies organization, and reservoir properties distributions in different channel-body types. Six main facies associations have been defined: gravelly–sandy to sandy braided channels, meandering channels, floodplain deposits, tidally influenced terminal channels, and subtidal to intertidal plains deposits, which we interpret the deposition in a proximal to distal fluvial and inner estuarine systems. Sequence stratigraphic analysis suggest the fluvial–estuarine succession evolved from a lower to an upper interval representative of low to high accommodation versus sediment supply ratios, respectively. Variations in accommodation and spatial changes from on-to off-axis locations within the fluvial system might performed as large-scale controls in stratigraphic and spatial variations of channel-deposits proportions and connectedness, which decreases vertically and horizontally towards the N and SE. Moreover, these trends could be overprinted by the avulsion influence. Distribution and preservation-style of fines within the channels define different intra-channel-body compartments controlled by distinct allogenic and autogenic processes. Cross-bedded sandstones represent the facies with the greatest reservoir quality, but they record the widest range in petrophysical values and textural variations, which represent unfavourable potential facies-scale reservoir compartments and barriers. Finally, variations in cement mineralogy would be the first-order control for permeability distribution and reservoir quality separation throughout the different channel units, since clay-rich cements contain the highest values of microporosity and permeability. Therefore, primary depositional processes followed by diagenesis strongly controlled the sandstone properties as reservoir. This work provides a characterization for stratigraphic-to pore-scale sedimentary heterogeneities and may contribute to the improvement of predictive models for exploration and development strategy of fluvial–inner estuarine reservoirs.

Rock fabric controls on pore evolution and porosity–permeability trends in oolitic grainstone reservoirs and reservoir analogs

Although the general influence of rock fabric on porosity and permeability (Φ–k) within carbonates is well documented, if and how pore evolution and Φ–k scatter quantitatively relate to depositional fabric remains poorly constrained. This project empirically explores this uncertainty within oolitic grainstones from a range of geologic ages and diagenetic histories to understand depositional sediment–pore relationships and how they can evolve with lithification. Integrating data from point counting, digital image analysis, nuclear magnetic resonance, and core analysis of Holocene, Pleistocene, Pennsylvanian, and Mississippian oolitic grainstones reveals quantitative relations among rock fabric, pores, and petrophysical parameters. Oolitic grainstones of similar sedimentology taken from distinct diagenetic scenarios display a unique combination of pore size, shape, spatial distribution, and Φ–k character. Within each scenario, pore attributes and k are correlated more closely with grain size, sorting, and type than with cementation and compaction. Collectively, these results are interpreted to suggest that sedimentology controls the trends or variability within an oolitic succession but that diagenesis defines the absolute values of pore attributes and petrophysical parameters. These findings suggest that petrophysical variability within oolitic reservoirs may closely follow sedimentologic trends, which may be predictable within a stratigraphic framework.

Characterization of sub-seismic resolution structural diagenetic heterogeneities in porous sandstones: Combining ground-penetrating radar profiles with geomechanical and petrophysical in situ measurements (Northern Apennines, Italy)

Deformation bands and structurally-related diagenetic heterogeneities, here named Structural Diagenetic Heterogeneities (SDH), have been recognized to affect subsurface fluid flow on a range of scales and potentially promoting reservoir compartmentalization, influencing flow buffering, and sealing during production. Their impact on reservoir hydraulic properties depends on many factors, such as their permeability contrast with respect to the undeformed reservoir rock, their anisotropy, thickness, geometry as well as their physical connectivity and arrangement in the subsurface. We used the Ground Penetrating Radar (GPR) for detection and analysis of the assemblage of deformation bands – carbonate nodules, in high-porosity arkose sandstone in Northern Apennines of Italy. 2D GPR surveys allowed the description of the SDH spatial organization, their geometry, and their continuity in the subsurface. Petrophysical (air-permeability) and mechanical (uniaxial compressive strength) properties of host rock, deformation bands, and calcite-cement nodules were evaluated along a 30-m thick stratigraphic log to characterize the permeability and strength variations of those features. The assemblage “deformation bands – nodules” degrade porosity and permeability and produce a strengthening effect of the rock volume, imparting a strong mechanical and petrophysical heterogeneity to the pristine rock. Different textural, petrophysical, and geomechanical properties between deformation bands, nodules, and host rock result in different GPR response (permittivity). Thus, GPR response could be used to extend outcrop data (petrophysical and geomechanical) of SDH to 3D subsurface volumes in a way to reconstruct realistic and detailed outcrop analogs of faulted aquifers and reservoirs in porous sandstones. • GPR effectively detects deformation bands and diagenetic heterogeneities in sandstones. • Deformation bands and cement nodules show high compressive strength and low permeabilities. • GPR response correlates with petrophysical and geomechanical rock properties. • An improved reservoir analog is obtained from integrating outcrop-based and GPR data. • Deformation bands and nodules impart anisotropy to the host rock.