Dual Flow Regimes Research Articles

Data-driven EUR modeling and optimization in the liquid-rich Duvernay Formation, western Canada sedimentary basin, Canada

Estimated Ultimate Recovery (EUR) is one of the focuses of the feasibility assessment for oil and gas development projects. EUR is the utmost recoverable oil and gas volume under the current assumption of technology and economics. Many factors including geology, drilling, completion, operation, and commodity prices influence EUR, which makes the prediction a difficult task. Reservoir numerical simulation and production decline curve analysis (DCA) are two broadly accepted method to calculate EUR. However, the former requires substantial data and resources, while the latter is lack of causative mechanism to associate the fundamentals to productivity. This study proposes a machine learning (ML) procedure in EUR modeling, by which EUR is linked to fundamental variables from available data and the variation in EUR can be explained by various factors so that the results can be applied to optimize future projects. In the proposed procedure, the EUR was estimated using a probabilistic dual flow regime model and Markov Chain Monte Carlo (MCMC) simulation. The resulting EUR in each well was then modeled using a two-level stacked ensemble ML approach, while Shapley value was used to explain feature sensitivity in the trained model. In the last, the EUR is optimized by adjusting the most sensitive factors in the trained model. The trained ML model achieved high accuracy on EUR prediction, and the Shapley value analysis showed that completion length, condensate gas ratio and fracturing fluid volume are among the most important features to EUR. The EUR optimization result showed that there is large room for improvement by adjusting the key features. This proposed approach provides a new perspective to find associations between the fundamental factors and the well EUR which improves the understanding of oil and gas production in unconventional reservoirs.

Bayesian probabilistic dual-flow-regime decline curve analysis for complex production profile evaluation

Decline curve analysis (DCA) has been broadly applied in the oil and gas industry to predict future production and estimate reserves. The Arps decline model is one of the most popular DCA models used by the oil and gas industry. This model was designed for boundary dominated flow in conventional reservoirs. In practice, it has also been widely applied to both transient flow and boundary dominated flow in conventional reservoirs. Applied to a complex production profile involving dual flow regime from artificially enhanced tight/shale reservoir, each production segment needs to be analyzed separately. Although several analytical decline curve models have been developed in recent years to address the problem, none of them is flexible enough to model both production profiles from a single flow regime and a dual flow regime.In this study, we introduce a new production decline analysis model that can fit both production profiles from single flow regime and dual flow regime without the need to separate the production segments. We also introduce a probabilistic measure using Bayesian Markov Chain Monte Carlo simulation to determine the existence of dual flow regimes, the location of the regime switch, and uncertainties in parameter estimations with the new model. The proposed Probabilistic Dual Regime Decline Curve Analysis (PDR-DCA) method is tested on 344 horizontal Northern Montney gas wells.This proposed Bayesian approach provides a workflow to generate probabilistic decline curve for both single and dual segment production profile, probabilistic type well curve for a well group, and production prediction for well with very short production history.

Oil-water flow regimes in 4-mm borosilicate glass and fluorinated ethylene propylene channels: Effects of wall wettability

Formation water, found in oil deposits, is highly corrosive. By utilizing flow phenomena and surface tension forces in smaller channels (e.g., Eötvös number less than one), these fluids can be separated, thus altering corrosion and the pressure required for transport. This research investigates the effects of wall wettability on oil-water flow regimes and pressure drops. Oil-water flows were studied in 3.5-mm hydrophilic borosilicate glass and 4.0-mm hydrophobic fluorinated ethylene propylene (FEP) channels using Parol 100 mineral oil (i.e., density of 840 kg/m3 and viscosity of 0.0208 Pa s) and tap water (i.e., 997 kg/m3 and a viscosity of 0.001 Pa s). For these oil-water combinations, glass was water wetting (i.e., contact angle of 67° for a water droplet submerged in oil on glass) and FEP was water repelling (i.e., contact angle of 93° for a water droplet submerged in oil on FEP) under static conditions. Flow regimes and pressure drops were recorded for a range of oil superficial velocities [i.e., 0.31–3.7 m/s (glass) and 0.23–2.7 m/s (FEP)] and water superficial velocities [i.e., 0.080m/s–5.5 m/s (glass) and 0.060–5.5 m/s (FEP)]. Stratified, intermittent, annular, and dispersed flow regimes were observed in both tubes. Additional inverted and dual flow regimes were observed in the hydrophobic FEP; oil wetted the wall in inverted flows, and flow regimes occurred inside of another flow regime in dual flows (e.g., inverted-annular intermittent). The modified Weber number indicated whether the walls were wetted by oil, mixed oil and water, or water. Pressure drops were found to be correlated to the flow regime with increased pressure drops observed when oil fully or partially wetted the wall.

Linking principles of soil formation and flow regimes

Summary Preferential flow (PF) is a fundamentally important soil hydrologic process that controls a variety of soil physical, chemical, and biological functions. However, the lack of theory in this field and the existence of conceptual and technological bottlenecks continue to hinder the advancement of PF modeling and prediction. This paper explores three theoretical perspectives on the relationships between pedogenesis and flow regimes in field soils. First, we examine non-equilibrium thermodynamics as applied to open dissipative field soils with continuous energy inputs and mass exchanges with the surrounding environment. The dual-partitioning of pedogenesis (dissipating and organizing processes) is consistent with the theory of dissipative structure, which explains the genesis and evolution of soil architecture (structure + matrix) and organized heterogeneity found in various soils. Such organized heterogeneity leads to widespread potential for PF occurrence. Second, we investigate constructal theory to explain the tendency for dual-flow regimes in soils – one with high resistivity (Darcy flow) and the other with low resistivity (PF) – together, they form PF configuration that provides the least global flow resistance. This theory is applied to explain some general characteristics of weathering processes and related flow regime changes, which are supported by limited chronologic data from the literature on subsoil’s saturated hydraulic conductivity decrease after a soil reaches a certain age. Third, the theory of evolving networks sheds light on a variety of PF networks observed in field soils, which increase the effectiveness of energy and mass transfer in the subsurface. This is because networks are a part of the organization resulting from the minimum energy dissipation principle and far-from-equilibrium thermodynamics. All the three theories discussed support the notion that the potential for PF occurrence in field soils is likely universal. However, controversies and challenges associated with these theories require further efforts to rigorously test their applicability in natural soils and to formulate explicit quantitative relationships between PF occurrence and its controls. The principle of soil formation and evolution provides a useful guide to this endeavor.

The importance of observations on fluxes to constrain ground water model calibration

The aquifer system in the alluvial basin bordered by Adda, Po and Oglio rivers (Northern Italy) is characterised by a dual flow regime. In shallow sediments, which constitute a phreatic aquifer with high conductivity, great fluxes are driven by the interaction between ground water and the network of surface water, by the infiltration of rain and irrigation water, and by the fluxes drained from depression springs and river valley terraces. The underlying semiconfined aquifers are characterised by minor fluxes driven by water abstraction from wells of the public Water Works. Since most of the ground water flow occurs in the phreatic aquifer, an equivalent single layer 2D steady state flow model has been calibrated. The identification of the transmissivity field at the scale of the model has been obtained by solving an inverse problem with the comparison model method which requires an initial configuration, i.e., reference head, initial transmissivity field, source terms. Most of the head and source data are related to the phreatic aquifer, but most of the estimates of transmissivity are obtained with field tests conducted in deep wells pumping from the semiconfined aquifers, so that this kind of prior information cannot be used directly for model calibration. The inverse problem is underdetermined and a unique solution is not available. Furthermore information on surface hydrology is poor. Therefore many tests with different hypotheses about the initial configuration have been performed and some of them have been selected and used to initialise the automatic inversion procedure.

Open access to novel dual flow chamber technology for in vitro cell mechanotransduction, toxicity and pharamacokinetic studies

BackgroundA major stumbling block for researchers developing experimental models of mechanotransduction is the control of experimental variables, in particular the transmission of the mechanical forces at the cellular level. A previous evaluation of state of the art commercial perfusion chambers showed that flow regimes, applied to impart a defined mechanical stimulus to cells, are poorly controlled and that data from studies in which different chambers are utilized can not be compared, even if the target stress regimes are comparable.MethodsThis study provides a novel chamber design to provide both physiologically-based flow regimes, improvements in control of experimental variables, as well as ease of use compared to commercial chambers. This novel design achieves controlled stresses through five gasket designs and both single- and dual-flow regimes.ResultsThe imparted shear stress within the gasket geometry is well controlled. Fifty percent of the entire area of the 10 × 21 mm universal gasket (Gasket I, designed to impart constant magnitude shear stresses in the center of the chamber where outcome measures are taken), is exposed to target stresses. In the 8 mm diameter circular area at the center of the chamber (where outcome measures are made), over 92% of the area is exposed to the target stress (± 2.5%). In addition, other gasket geometries provide specific gradients of stress that vary with distance from the chamber inlet. Bench-top testing of the novel chamber prototype shows improvements, in the ease of use as well as in performance, compared to the other commercial chambers. The design of the chamber eliminates flow deviations due to leakage and bubbles and allows actual flow profiles to better conform with those predicted in computational models.ConclusionThe novel flow chamber design provides predictable and well defined mechanical forces at the surface of a cell monolayer, showing improvement over previously tested commercial chambers. The predictability of the imparted stress improves both experiment repeatability as well as the accuracy of inter-study comparisons. Carefully controlling the stresses on cells is critical in effectively mimicking in vivo situations. Overall, the improved perfusion flow chamber provides the needed resolution, standardization and in vitro model analogous to in vivo conditions to make the step towards greater use in research and the opportunity to enter the diagnostic and therapeutic market.

Holocene sea-level oscillations and environmental changes on the Eastern Black Sea shelf

A multi-proxy study of four sediment cores from the Eastern (Caucasian) Black Sea shelf revealed five transgressive–regressive cycles overprinted on the general trend of glacioeustatic sea-level rise during the last 11,000 14C yr. These cycles are well represented in micro-and macrofossil assemblages, sedimentation rates, and grain size variations. The oldest recovered sediments were deposited in the Neoeuxinian semi-freshwater basin (∼ 10,500–9000 14C yr BP) and contain a Caspian-type mollusk fauna dominated by Dreissena rostriformis. Low δ 18O and δ 13C values are measured on this species. The first appearance of marine mollusks and ostracodes from the Mediterranean is established in this part of the Black Sea at ∼ 8200 14C yr BP, i.e., about 1000–2000 yr later than the appearance of marine microfossils in the deeper part of the sea. The Early Holocene (Bugazian to Vityazevian) condensed section of shell and shelly mud sediments with at least two hiatuses represent a high-energy shelf-edge facies. It contains a transitional assemblage representing a mixture of Caspian and Mediterranean fauna. This pattern suggests a dual-flow regime via the Bosphorus after 8200 14C yr BP. Caspian species disappear and oligohaline species decrease in abundance during the Vityazevian–Prekalamitian cycle. Later, during the Middle to Late Holocene, low sea-level stands are characterized by shell layers, whereas silty mud with various mollusk and ostracode assemblages rapidly accumulated during transgressions. Restricted mud accumulation, as well as benthic faunal composition and abundance, suggest high-energy and well-ventilated bottom water during low sea-level stands. A trend of 18O enrichment in mollusk shells points to an increase in bottom-water salinity during the Vityazevian to Kalamitian transgressions (∼ 7000 to 5700 14C yr BP) due to a more open connection with the Mediterranean, while a pronounced increase in polyhaline species abundance is established during the Kalamitian to Djemetean transgressions (∼ 6400 to 2700 14C yr BP). However, the composition of the faunal assemblage indicates that bottom-water salinity never exceeded modern values of 18–20 psu.

Dual mixed convection flows in a vertical channel

The classical problem of the fully developed mixed convection flow with frictional heat generation in a vertical channel bounded by isothermal plane walls having the same temperature is revisited in this paper. The existence of dual solutions of the local balance equations is pointed out. They are either columnar upflows or cellular down–up–down flows. Below a maximum value Ξ max of the governing parameter Ξ = Ge Pr Re (the product of the Gebhart, Prandtl and Reynolds numbers), for any given Ξ a pair of different solutions occurs. The value Ξ max corresponds to a maximum value of the Reynolds number above which no laminar solution can be found. At this maximum value, the two solution branches bifurcate from each other. In the neighborhood of the bifurcation point Ξ max even small perturbations can cause transitions from one flow regime to the other. In the paper, the mechanical and thermal characteristics of the dual flow regimes are discussed in detail both analytically and numerically.

Experimental determination of sorption in fractured flow systems

Fracture “skins” are alteration zones on fracture surfaces created by a variety of biological, chemical, and physical processes. Skins increase surface area, where sorption occurs, compared to the unaltered rock matrix. This study examines the sorption of organic solutes on altered fracture surfaces in an experimental fracture-flow apparatus. Fracture skins containing abundant metal oxides, clays, and organic material from the Breathitt Formation (Kentucky, USA) were collected in a manner such that skin surface integrity was maintained. The samples were reassembled in the lab in a flow-through apparatus that simulated ∼2.7 m of a linear fracture “conduit.” A dual-tracer injection scheme was utilized with the sorbing or reactive tracer compared to a non-reactive tracer (chloride) injected simultaneously. Sorption was assessed from the ratio of the first temporal moments of the breakthrough curves and from the loss of reactive tracer mass and evaluated as a function of flow velocity and solute type. The breakthrough curves suggest dual-flow regimes in the fracture with both sorbing and non-sorbing flow fields. Significant sorption occurs for the reactive components, and sorption increased with decreasing flow rate and decreasing compound solubility. Based on moment analysis, however, there was little retardation of the center of solute mass. These data suggest that non-equilibrium sorption processes dominate and that slow desorption and boundary layer diffusion cause extensive tailing in the breakthrough curves.

Stratigraphy of the sediment infill in Bosphorus Strait: water exchange between the Black and Mediterranean Seas during the last glacial Holocene

The sediment infill over the Paleozoic bedrock in the Bosphorus Strait consists of four sedimentary units which were deposited in the last 26,000 14C years B.P. The stratigraphy of these units suggests that this part of the Bosphorus was a freshwater lake between 26,000 and 5,300 14C years B.P., depositing sands with a freshwater mollusc fauna of Black Sea neo-euxinian affinity (Dreissena rostriformis, Dreissena polymorpha, and Monodacna pontica). The first appearance of euryhaline Mediterranean molluscs (e.g., Ostrea edulis, Mytilus edulis) was observed at 5,300 14C years B.P. in this part of the Bosphorus. Deposition of coarse Mytilus-bank and Ostrea-bank units suggests that the establishment of the present dual-flow regime in the Bosphorus took place at about 4,400 14C years B.P.

Observations on Preferential Flow and Horizontal Transport of Nitrogen Fertilizer in the Unsaturated Zone

AbstractA study site underlain by a claypan soil was instrumented to examine the transport of fertilizer nitrogen (N) under corn (Zea mays L.) cultivation. The study was designed to examine N transport within the unsaturated zone and in intedlow (the saturated flow of water on top of the claypan). A 15N‐labeled fertilizer (labeled N), bromide (Br), and chloride (Cl) were used as field tracers. Rapid or prolonged infiltration events allowed water and dissolved solutes to perch on the claypan for brief periods. However, a well‐developed network of preferential flow paths quickly diverted water and solutes through the claypan and into the underlying glacial till aquifer. Excess fertilizer N in the unsaturated zone supplied a continuous, but declining input of N to ground water for a period of 15 mo after a single fertilizer application. Calculated solute velocities through the claypan matrix (6.4 × 10−6 cm s−1) were similar to horizontal transport rates along the claypan (3.5 to 7.3 × 10−6 cm s−1) but much slower than infiltration rates determined for preferential flow paths (1.67 × 10−3 cm s−1). These flow paths accounted for 35% of the transport. A seasonally variable, dual mode of transport (matrix and preferential flow) prevented the daypan from being an effective barrier to vertical transport. Simulations of selected field observations, conducted using the variably saturated two‐dimensional flow and transport model, VS2DT, confirmed the presence of a dual flow regime in the claypan.

Origin of the Sea of Marmara as Deduced from Neogene to Quaternary Paleogeographic Evolution of its Frame

The Sea of Marmara Basin (SMB) is connected to the fully marine Mediterranean by the Dardanelles strait and to the brackish Black Sea by the Thracian Bosporus. This linkage to two different marine realms with contrasting water chemistry has been a prime control on the sedimentary history of the SMB, which in turn was controlled by its tectonics. Isolation from any of these realms resulted in drastic changes in its paleoceanographic conditions and made it a part either of the global ocean system or of a brackish-marine environment, depending on the realm from which the connection was severed. The SMB represents the inundated part of the northwestern Anatolian graben system that resulted from the interaction between the North Anatolian fault (NAF) zone and the present N-S extensional tectonic regime of the Aegean. The geologic history of this basin began during the late Serravallian when the NAF was initiated. The first inundation of the basin coincided in both time and space with this initiation. The invading sea was the Mediterranean, which stayed there for a short period and subsequently was replaced by the Paratethys during the late Miocene. Paratethyan conditions prevailed in the basin until the latest Pliocene, when the second flooding from the Mediterranean occurred through the Dardanelles. Owing to glacio-eustatic sea-level changes during the Pleistocene, Paratethyan/Black Sea and Mediterranean conditions alternated. In the last (Würm) glaciation, the SMB was completely isolated and turned into a euxinic lacustrine environment, similar to the Black Sea at that time. Following the Würm glaciation, the Mediterranean Sea broke its way once more into the SMB and filled it with salt water. When sea level in the basin rose above the Bosporous sill at 7.5 Ka B.P., the present dual flow regime was established.

Velocity Profiles near a Vertical Ice Surface Melting into Fresh Water

An experimental determination is made of the velocity profiles which result from the free convective melting of a vertical ice sheet into fresh water at temperatures in the range from 2.0°C to 7.0°C. The results suggest that upward flows exist for water temperatures below 4.7°C. Entirely downward flowing boundary layers are suggested for temperatures above 7.0°C. For intermediate temperatures, an oscillatory dual flow regime is indicated.