Gas Water Distribution Research Articles

Comparative Study on the Reservoir Characteristics and Development Technologies of Two Typical Karst Weathering-Crust Carbonate Gas Reservoirs in China

Carbonate reservoirs are the main reservoir types in China, which occupy the large ratio of reserves and production at present. The high-efficiency development of carbonate reservoirs is of great significance to assure the stability of national energy supply. The Lower Paleozoic reservoir in Jingbian gas field and the Sinian reservoir in Anyue gas field are two typical carbonate gas reservoirs, and their successful development experiences can provide significant references for other similar carbonate gas reservoirs. For Jingbian gas field, it is a lithological-stratigraphic reservoir developed in a westward monocline and multiple rows of nose-fold structures, and is a stable craton basin with simple palaeognomy distribution and stable connectivity, which has complex gas-water distribution. However, for Anyue gas field, it is a lithological-structural reservoir with multiple tectonic high points and multiple fault systems, and is biological dune beach facies under extensional setting with highly differentiated inside of the block in palaeognomy characteristics, which has limited connectivity and tectonic side water is in a local area. The difference of gas reservoir characteristics leads to the diverse development strategies. For these two gas reservoirs, although there are some similar aspects, such as the screen of enrichment areas, the application of irregular well pattern and reservoir stimulation techniques, the criteria of enrichment areas, the well types, and the means of reservoir stimulation are absolutely different. In addition, due to the differences of control reserves and production capacity for these two kinds of reservoirs, the mode of stable production is also different. The effective development of Jingbian gas field can give some references to the future exploitation on the Sinian gas reservoir. Firstly, the sedimentary characteristics should be studied comprehensively. Secondly, the distribution pattern and distribution characteristics of the palaeognomy should be found and determined. Thirdly, the distribution of fracture system in the reservoir should be depicted finely. Finally, dynamic monitoring on the production performance should be strengthened, and the management for this gas field should be improved further. The findings of this study can help for better understanding of the Karst weathering-crust carbonate gas reservoir formation characteristics and the optimal development technologies that should be taken in practice.

Characteristics of coal-measure source rock and its controlling effect on gas-water distribution of tight sandstone of He8 Member in Sulige Gas Province, Ordos Basin

Characteristics of complex gas-water distribution affect the efficient exploration of tight gas. The paper aims at tight sandstone gas-water distribution characteristics of He8 Member in Sulige Gas Province (SGP), describes thickness and TOC of source rocks from Benxi Formation in Carboniferous to the Second Member of Shanxi Formation in Permain, evaluates its hydrocarbon generation potential, discusses its controlling effect on tight sandstone gas-water distribution, and determines the threshold values of Ro and HGI of commercial gas flow wells. Research shows that the coal-measure source rock has the characteristics of extensive and superimposition. The coal seam and dark mudstone is the lithology of source rock, and its Ro is chiefly distributed 1.2% ∼ 2.1% in the stage of high mature thermal evolution, which is mainly type III kerogen. Among them, the thickness of coal seam is mainly ranged from 5 ∼ 15 m with an average of 9.32 m, and its average TOC is 64.08% and the distribution of HGI is (1∼36) ×108 m3/km2. No.8 and No.5 coal seams are relatively stable. The extent of thickness of dark mudstone is mainly between 10m and 30m with an average of 21.2m, and its average TOC is 2.11%, HGI is between (0.2∼10)×108m3/km2. Gas reservoir of He8 Member is tight sandstone lenticular reservoirs with the large-area quasi-continuous distribution. When the gas testing production is less than 1 × 104m3/d, the controlling effect of Ro and HGI are relatively obvious, and its controlling effect is obviously weakened with the increase of gas production. When Ro is more than 1.6%-1.7%, or HGI is larger than 15 × 108m3/km2, the decreasing trend of water/gas ratio is evident, especially in commercial gas flow wells (including high producing gas flow wells). In comparison, the controlling effect of HGI is stronger than Ro. 1.33% and 8 × 108 m3/km2 are the threshold values of Ro and HGI for commercial gas flow wells, respectively.

Reconsideration of the Adsorption/Desorption Characteristics with the Influences of Water in Unconventional Gas Systems

The exploration and development of unconventional resources have been of growing interest in the industry in recent years. It is widely known that the adsorption and desorption mechanisms of unconventional gas have great significance for gas accumulation and exploration. However, major researches based on the mechanism of solid-gas interface have failed to reveal it completely, which introduce large discrepancies between actual and predicted production. In this paper, the mechanism of solid-liquid-gas adsorption and desorption interface is enlightened to describe the characteristics of unconventional gas. The validity of the proposal was verified preliminarily by building a conceptual model which redefines the gas-water distribution. Furthermore, the possibility of production of gas trapped in micropores was first investigated. The findings of this study can help for better understanding of the adsorption, desorption, and production mechanisms and in unconventional gas system. Accordingly, the explanation of variation between experiment result and actual production rate even with physical parameters was reasonable in theory. Therefore, this work should provide a basis for improving the accuracy of production predictions in actual reservoirs and should assist analysts in determining reasonable unconventional gas target.

Observing Oxygen Transport in Polymer Electrolyte Water Electrolysis Via Operando X-Ray Tomographic Microscopy

The power-to-gas process using polymer electrolyte water electrolysis (PEWE) to produce hydrogen, is increasingly attracting interest as a mean to store the surplus electricity generated from intermittent renewable sources. However, high capital and operational costs limit the widespread implementation of the PEWE technology in the current energy system. The operational costs are dominated by electricity prices and therefore improving PEWE efficiency is crucial. In PEWE cells, water is supplied at the anode side and it is distributed to the active electrode (catalyst layer, CL) through a porous transport layer (PTL). During operation, oxygen is produced at the anodic CL and it is discharged at the flow channel. However, the undesired accumulation of oxygen in the anodic porous transport layer (PTL) may interfere with the transport of water to the active sites, contributing to efficiency losses, especially for high current density operations.The evolution and transport of oxygen in PEWE leads to a complex two-phase flow regime that is governed by a complex interplay of viscous and capillary forces in the PTL microstructure. To date, the precise relationship between current density, PTL morphology (pore dimensions, shape) and oxygen pathways is largely unknown. Furthermore, the overall influence of the water/gas transport on the mass transport losses in PEWE is still largely debated.In the past decade, many studies have been conducted to directly observe the oxygen transport within operating PEWE cells. Neutron radiography has been employed to compute the average water-gas saturation in PTLs for different current densities, temperature, or operating pressures [1, 2]. Furthermore, X-ray radiography was used to examine bubble formation and growth in the flow channel [3]. However, radiographic studies can only provide average information on the gas-water distribution in PTLs and a spatially-resolved description of the oxygen pathways at the microscale is crucially needed.In this work, we present the first operando X-ray tomographic microscopy (XTM) experiment where oxygen pathways inside a representative PTL material are imaged in three dimensions. The shape, dimension, and connectivity of oxygen pathways in the PTL microstructure are described for current densities ranging from 0.1 to 2.5 Acm-2. Furthermore, a precise measure of oxygen saturation in the PTL porosity is discussed in terms of current density and distance from the catalyst layer. Finally, the differences in oxygen saturation between regions under the channel and rib are also presented. We believe that these results will represent a step forward in the understanding of two-phase flow in PEWE cells, paving the way for a more rational design of better performing PTL materials.[1] Zlobinski, M., et al., 2020. Transient and steady state two-phase flow in anodic porous transport layer of proton exchange membrane water electrolyzer. Journal of the Electrochemical Society[2] Selamet, O.F., et al., 2013. Two-phase flow in a proton exchange membrane electrolyzer visualized in situ by simultaneous neutron radiography and optical imaging. International Journal of Hydrogen Energy 38, 5823–5835.[3] Hoeh, M.A., et al., 2015. In operando synchrotron X-ray radiography studies of polymer electrolyte membrane water electrolyzers. Electrochemistry Communications 55, 55–59 Figure 1

A New Classification and Description of Shale Pore System: from the Burial History Perspective

Accurate micro-storage and mechanism of shale gas is important for defining and describing the adsorption characteristics, and for gas-in-place estimation. In this paper, reservoir forming process is divided into early stage and late stage, and the initial gas-water distribution in different stage is redefined. Different from the widely used solid-gas interface adsorption theory, the pore system in original shale reservoir is divided into solid-gas system and solid-liquid-gas system. Gas pores existing in organic matters belong to solid-gas system, and are classified into residual gas pores and metamorphic gas pores. Plant tissue pores in organic and mineral pores belong to solid-liquid-gas system. Their characteristics are described.

Development and Practice Development and Practice of Comprehensive Water Control Technology for Volcanic Bottom Water Gas Reservoir in Xushen Gas Field

Xushen gas field mainly exploits volcanic reservoirs of Yingcheng Formation. The gas reservoir type is mainly the bottom water gas reservoir. The number of water wells and water production are increasing year by year, which affects the development effect of the gas field. In view of the increasingly severe situation of water invasion and water production in gas fields, water invasion evaluation and comprehensive water control of gas reservoirs have been carried out, and a three-level evaluation process of water invasion qualitative identification, water invasion quantitative evaluation and water invasion impact quantitative evaluation has been formed. Based on the results of water invasion evaluation, combined with the characteristics of gas reservoir connectivity, structure, gas-water distribution, and water production, the three-level evaluation process has been formed. The integrated water control mode of the block (volcanic body) and single well water control mode by classification have been applied in each block, and good results have been achieved, which effectively supports the rational development and long-term stable production of bottom water gas reservoirs in Xushen gas field.

Seepage channel model and gas–water differentiation of near-vertical coal reservoirs in the Kuba coalfield, China: implication for coalbed methane development

The coal seams in Kuba coalfield are near-vertical distributed, and the composition of the seepage channel and gas–water differentiation is quite different from that of the horizontal coal seam. By using high-precision tectonic fracture mapping technique, fine observation and dissection technique of coal reservoirs in the underground, and microscopic observation, the seepage channel model of near-vertical coal reservoir is established, and the gas–water distribution is researched. The seepage channel is mainly composed of four fractures, that is, tectonic fractures, bedding fractures, cleats, and micro-fractures. Furthermore, the characteristics of the four fractures are studied in detail; the dominant direction of coal reservoir permeability is analyzed. Coal seam water and gas in near-vertical coal reservoir have serious gas–water differentiation. Coal seam water moves to the lower coal and gas to the upper coal due to the influence of gravity. The seepage channel model and gas–water differentiation of near-vertical coal reservoir research the high-permeability area of coalbed methane (CBM) development block from the vertical and horizontal directions, which is of great significance for CBM development.

Natural Gas Reservoir Characteristics and Non-Darcy Flow in Low-Permeability Sandstone Reservoir of Sulige Gas Field, Ordos Basin

In order to reveal the gas–water distribution and formation mechanism of the low-permeability sandstone gas reservoir, the gas reservoir distribution and the formation mechanism in a low-permeability sandstone gas reservoir are investigated using data obtained from a physical simulation experiment of gas percolation. The exploration and experimenting for petroleum in the upper Paleozoic gas pool of the Sulige gas field in the Ordos basin in this paper. Results showed that the gas reservoir is characterized by low gas saturation, a complex distribution relationship of gas–water, and weak gas–water gravity differentiation. The characteristics of gas distribution are closely related to permeability, gas flow, and migration force. The capillary pressure difference is the main driving force of gas accumulation. There exists a threshold pressure gradient as gas flows in low-permeability sandstone. The lower that permeability, the greater the threshold pressure gradient. When the driving force cannot overcome the threshold pressure (minimal resistance), the main means of gas migration is diffusion; when the driving force is between minimal and maximal resistance, gas migrates with non-Darcy flow; when the driving force is greater than maximal resistance, gas migrates with Darcy flow. The complex gas migration way leads to complicated gas- water distribution relationship. With the same driving force, gas saturation increases with the improvement of permeability, thus when permeability is greater than 0.15 × 10−3 µ m2, gas saturation could be greater than 50%.

Hydrocarbon accumulation processes and mechanisms in Lower Jurassic tight sandstone reservoirs in the Kuqa subbasin, Tarim Basin, northwest China: A case study of the Dibei tight gas field

The Dibei gas field is a large tight gas field located in the Kuqa subbasin, Tarim Basin, northwestern China. The reservoir is within the Lower Jurassic Ahe Formation (J1a) and has porosity and permeability ranges of 2%–8% and 0.01–1 md, respectively. Two episodes of hydrocarbon charge are identified based on a detailed study of fluid-inclusion petrography and microthermometry, fluorescence spectroscopy characteristics, and the thermal maturity of both gas and light oil. Low-maturity oil as represented by hydrocarbon inclusions with yellow-green fluorescence entered the reservoir circa 23–12 Ma, whereas high-maturity hydrocarbons, as indicated by hydrocarbon inclusions with blue-white fluorescence, have charged the reservoir since 5 Ma. The hydrocarbon charge process combined with porosity evolution determined the present gas–water distribution characteristics in the Dibei gas field. Porosity in the J1a sandstone reservoir was relatively high during the first episode of hydrocarbon charge, which allowed oil to migrate upward and accumulate in structural highs under buoyancy. From 5 Ma to the present, the Dibei gas field experienced strong tectonic compression associated with intense thrust-fault reactivation, causing deformation and oil leakage from the reservoir. Continuous tight sand deposits along the slope areas, located far away from the active faults, became favorable accumulation sites for gas derived from the underlying Triassic source rocks. Hydrocarbon accumulation along the slope area in the Ahe Formation is dominantly controlled by equilibrium between hydrocarbon-generation pressure and capillary pressure.

Controlling factors for the accumulation and enrichment of tight sandstone gas in the Xujiahe Formation, Guang’an Area, Sichuan Basin

Tight sandstone gas characterized by a wide distribution, local enrichment and a complex gas–water distribution has high exploration potential. This study, using the Xujiahe Formation in the Guang’an gas field as an example, aims to determine the main controlling factors of the enrichment of tight gas through comprehensive analyses of the source rock and reservoir characteristics, pressure evolution and structural effects by using various methods including well logging, geochemistry, mercury injection, reservoir physical properties and formation pressure. The results show that the proximal-source, interbedded hydrocarbon accumulation results from a dispersed hydrocarbon supply, which is the root cause of the widely distributed tight sandstone gas. The abnormally high reservoir pressure caused the enrichment of tight sandstone gas even under insufficient hydrocarbon generation dynamics; in addition, natural gas preferentially accumulated in the relatively high-quality reservoirs under the same hydrocarbon supply, which means that differences in the reservoir physical properties control gas charge in the reservoir. Structure controls the gas–water differentiation under the stable tectonic background, and the higher the structure is, the more abundant the gas–water differentiation is, and the easier pure gas reservoirs form. Therefore, the accumulation and enrichment of tight sandstone gas in the Xujiahe Formation is controlled by source rocks, abnormally high reservoir pressure and the physical properties and structure of the reservoir.

Visualized Experimental Investigation on the Gas-Water Distribution Characteristics in Intersecting Fractures

In coal-bed methane recovery, water is generally drained out along with gas. In order to address the influence of different gas-water ratios, fracture intersecting angles, and gas desorption positions on gas and water distributions along fractures and hence understand the two-phase flow behavior in fracture network, an experimental study was conducted on three artificial models with intersecting fractures. The results show that (1) with gas and water injected at different rates, the flow of water and gas is divided into three stages. In the first stage, gas flowed as small bubbles. The transport of gas was stable, which was similar to single-phase laminar flow. The difference in gas injection positions led to totally contrary flow results of water and gas. (2) In the second stage, larger gas bubbles were formed and the interactions between water and gas became serious. The gas-water distribution was dominated by different inertias between water and gas. The difference in gas injection positions did not take much effect on the gas-water distribution. (3) In the third stage, the influence of the inertia difference was still important, but some other factors also influenced the gas-water distribution. The difference in gas injection positions led to different distribution results. (4) The water injection rate has impact on the distribution of the water flow rate in each outlet. In the second stage, when water was injected at small rates, the difference between the cases in which gas was injected from different positions can be neglected. When water injection rates became larger, this difference became obvious. (5) The intersecting angle of the fractures influences the distribution of water and gas. The larger the intersecting angle is, the larger the inertial effect will be. Consequently, the intersecting angle influences the length of the second stage, which is dominated by the inertial effect.

Occurrence and distribution characteristics of fluids in tight sandstone reservoirs in the Shilijiahan zone, northern Ordos Basin

High-yield gas layers, low-yield gas layers and (gas bearing) water layers of Upper Paleozoic coexist in the Shilijiahan zone in the northern Ordos Basin, but gas–water distribution characteristics, laws and influence factors are not understood well, so the exploration and development of natural gas in this zone are restricted. In this paper, statistical analysis was carried out on the data of Upper Paleozoic formation water in this zone, e.g. salinity, pH value and ion concentration. It is shown that the formation water in this zone is of CaCl2 type. Then, the origin, types, controlling factors and spatial distribution characteristics of formation water were figured out by using core, mud logging, well logging and testing data, combined with the classification and evaluation results of geochemical characteristics of formation water. Besides, the logging identification chart of gas, water and dry layers in this zone was established. Finally, the occurrence and distribution laws of reservoir fluids were defined. The formation water of CaCl2 type indicates a good sealing capacity in this zone, which is favorable for natural gas accumulation. It is indicated that the reservoir fluids in this zone exist in the state of free water, capillary water and irreducible water. Free water is mainly distributed in the west of this zone, irreducible water in the east, and capillary water in the whole zone. The logging identification chart has been applied in many wells in this zone like Well Jin 86. The identification result is basically accordant with the gas testing result. It is verified that gas and water layers can be identified effectively based on this logging identification chart.

In-Operando Neutron Radiography Studies of Polymer Electrolyte Membrane Water Electrolyzers

Polymer electrolyte membrane water electrolysis cells were studied using in-operando neutron radiography, revealing insights into the gas-water distribution inside the cells. Cells were operated at current densities up to 2 A/cm² and for water flow rates ranging from 0.5 ml/(min cm²) up to 5 ml/(min cm²). The averaged gas amount in the flow channels was quantified, revealing that the ratio of gas to water inside the channels decreases for an increasing water flow rate on the anode side. This examination also demonstrates that neutron radiography is very suitable to study gas/water two-phase flow phenomena in running electrolysis cells.

In-Operando Neutron Radiography Studies of Polymer Electrolyte Membrane Water Electrolyzers

Polymer Electrolyte Membrane Water Electrolysis (PEMWE) is increasingly attracting interest from academia and industry as it offers an option for storing renewable energy from sources such as wind or solar [1]. Further, electrolysis is considered one of the few available pathways to achieve a 100% renewable electricity supply [2]. In PEMWE, water is typically supplied via flow channels and distributed across the catalyst layer through a porous transport layer (PTL). Gas evolution occurs at the catalyst layer, and the gas is transported back through the PTL and discharged into the flow channels where it is then transported out of the cell as a two-phase mixture with the feed water. This evolution of oxygen and hydrogen in the surrounding water leads to distinct two-phase flow phenomena, which are investigated in this study in-operando inside operating PEMWE cells using synchrotron X-ray radiography as well as neutron radiography. In the past, both methods have allowed to visualize processes inside operating fuel cells, elucidating water management issues [3], the formation of liquid water, its accumulation rate and transport in polymer electrolyte membrane fuel cells (PEFC) [4], as well as the carbon dioxide evolution in liquid fed direct methanol fuel cells (DMFC) [5]. PEM water electrolysis systems are currently scaled to the megawatt range, necessitating an increase of the active area of an individual cell. This scale-up goes along with challenges concerning media distribution on large cell areas. Information about the oxygen saturation and distribution inside the PTL at different points of operation but also at different locations a large area PTL is therefore of special interest. In this work, operating PEMWE cells are examined using synchrotron X-ray radiography at BESSY II and using neutron radiography at BER II (both Helmholtz-Zentrum Berlin). In both setups, a synchrotron X-ray beam or a neutron beam is directed at the running cell, and the attenuation dependence of the beam on the elements inside the cell allows visualizing the processes occurring inside the cells. Both methods are to a certain degree complimentary – the synchrotron radiography setup allows inspecting small areas of some mm² with a spatial resolution of a few µm, while the neutron radiography allows inspecting areas of several cm² with a spatial resolution of lower than 100µm. The especially strong neutron attenuation in hydrogen offers the possibility to visualize the gas/water distribution on large areas, while the comparably low neutron attenuation in metals allows using a typical cell setup with only minor adjustments. The PEMWE cells examined using neutron radiography contained different PTLs, which were compared in terms of the gas/water distribution under different operating conditions. On the anode side, an additional injection of oxygen from the bottom of the cell was used to simulate the effects occurring in a scaled cell exhibiting a larger area. This setup allowed examining the dynamics in the transport and quantifying the distribution along the cell area. In the PEMWE cells examined using synchrotron radiography, oscillations in the gas bubble discharge from the PTL into the flow channel were investigated in terms of their frequency and the gas discharge volumes. Furthermore, the implications of this on the gas transport within the PTL are discussed, and the number of gas bubble discharge sites is correlated with the current density. Thereby it is demonstrated that both synchrotron X-ray and neutron radiography represent valuable tools to study transport processes and to gain insights into the gas-water distribution inside running PEMWE cells. These results pose important implications for the design of cell components with facilitated gas removal, for the modeling of two-phase flow in PEMWE cells and for the modeling of mass transport losses in PEMWE.

Mechanism of gas-water flow at pore-level in aquifer gas storage

By means of the pore-level simulation, the characteristics of gas-water flow and gas-water distribution during the alternative displacement of gas and water were observed directly from etched-glass micromodel. The results show that gas-water distribution styles are divided into continuous phase type and separate phase type. The water lock exists in pore and throat during the process of gas-water displacement, and it reduces the gas flow-rate and has some effects on the recovery efficiency during the operation of gas storage. According to the experimental results of aquifer gas storage in X area, the differences in available extent among reservoirs are significant, and the availability of pore space is 33%–45%.

The Research of Gas-Water Relations in Low-Permeability Tight Sand Gas Reservoir - Taking Zizhou Gas Field for Example

The gas-water relations of low-permeability tight sand gas reservoir are complex and not necessarily linked to the structural relief, phenomenon that water is distributed in high structural position while gas in low structural position is common what makes it difficult to make a refined description of gas-water relations and distribution low. The article takes Zizhou gas field for example, establishes 4 gas-water relations modes of single well to analyze some profiles where there is abnormal phenomenon water up gas down, the fact is that water and gas are distributed in different sand bodies and Zizhou Gas Field is not a deep basin gas reservoir. The research shows the phenomenon that water up gas down does not exist, the gas-water relations are normal. The research results have certain significance for the determination of gas-water distribution law.

Distribution regularity and formation mechanism of gas and water in the western area of Sulige gas field, NW China

Abstract Serious water production and the confusion about the distribution regularity and formation mechanism of gas and water affect the progressive development in the western area of Sulige gas field. Making use of drilling, logging, and testing data, this comprehensive study determines the gas-water distribution regularity and formation mechanism, and establishes the evolution modes of gas-water distribution. The results show that, (1) the gas-water distribution appears complementarily, and relatively water-rich area is located in the northwest; (2) source rock, reservoir physical property and structure are the key controlling factors of gas-water distribution, and formation water is distributed in areas with less developed source rocks, areas of poor properties, and structural lows within connecting bodies; (3) source rocks play a key role in controlling the distribution of gas and water, source area of low maturity is rich in formation water, while source area of high maturity is rich in gas. This research gives direction for favorable areas and well site selection in the progressive development of the gas field.

A SUMMARIY OF THE DEVELOPMENT PRESENT SITUATION FOR THE VOLCANIC-ROCK GAS RESERVOIR

According to the successful example of the exploration and exploitation for the volcanic rocks gas reservoir of domestic and overseas. Geologic feature and development characteristic of general volcanic rocks gas reservoir was analyzed and summarized. That is to say, volcanic rocks gas reservoir has numerous rock type, complex rock formation nature, complicated pore structure, special and diversified reservoir space, small porosity and low permeability. The differential of porosity and permeability was big. The reservoir heterogeneity was serious. The containing gas area and effective thickness change a lot. The gas-water distribution is complex. The reservoir is moderate porosity and low permeability double porosity reservoir. It is key to analyze the geologic feature and development characteristic of volcanic rocks reservoir for Shengping Gas- field. The yield of Shengping Gas- field is steady. The reservoir pressure of Shengping Gas- field declined a little. The output of gas well is closely related with fracture. The fracture spacing has an important guide meaning for well position deployment. The incremental production measure and reservoir protective measure of volcanic rocks gas reservoir was presented.