Abstract Underwater gas and liquid escape from the seafloor has long been treated as a mere curiosity. It was only after the advent of the side‐scan sonar and the subsequent discovery of pockmarks that the scale of fluid escape and the moon‐like terrain on parts of the ocean floor became generally known. Today, pockmarks ranging in size from the ‘unit pockmark’ (1–10 m wide, &lt; 0.6 m deep) to the normal pockmark (10–700 m wide, up to 45 m deep) are known to occur in most seas, oceans, lakes and in many diverse geological settings. In addition to indicating areas of the seabed that are ‘hydraulically active’, pockmarks are known to occur on continental slopes with gas hydrates and in association with slides and slumps. However, possibly their potentially greatest significance is as an indicator of deep fluid pressure build‐up prior to earthquakes. Whereas only a few locations containing active (bubbling) pockmarks are known, those that become active a few days prior to major earthquakes may be important precursors that have been overlooked. Pockmark fields and individual pockmarks need to be instrumented with temperature and pressure sensors, and monitoring should continue over years. The scale of such research calls for a multinational project in several pockmark fields in various geological settings.

M. Hovland

J. V. Gardner

A. G. Judd

Geofluids

The significance of pockmarks to understanding fluid flow processes and geohazards

麻坑对理解流体流动过程及地质灾害的重要性

AVO inversion is a seismic exploration methodology used to predict the earth’s elastic parameters and thus rocks and fluid properties. It is built up on elastic theory and does not consider the seismic dispersion in real strata. Recent experiments and theory of rock physics have shown that in hydrocarbon-bearing rocks, especially in gas-bearing ones, the change of seismic velocity with frequency may be pretty remarkable for fluid flow in pore space. Some scholars proposed methods about seismic dispersion, such as frequency-dependent AVO inversion, to forecast oil and gas reservoirs underground. In this paper, we demonstrate an improved scheme of frequency-dependent AVO inversion, which is based on conventional Smith-Gidlow’s AVO equation, to extract seismic dispersion and predict the hydrocarbon underground. A simple model with gas-bearing reservoir is devised to validate the inversion scheme, and further analysis indicates that our scheme is more accurate and reasonable than the previous scheme. Our new scheme applied to the tight gas reservoirs in Fenggu area of western Sichuan depression of China finds that regions with high dispersion gradients correlate well with regions with prolific gas. Analysis and case studies show that our scheme of frequency-dependent AVO inversion is an efficient approach to predict gas reservoirs underground.

Jiong Liu

Jun-rui Ning

Xi-wu Liu

Chun-yuan Liu

Tian-sheng Chen

An Improved Scheme of Frequency-Dependent AVO Inversion Method and Its Application for Tight Gas Reservoirs

频率依赖AVO反演方法的改进方案及其在致密气藏中的应用

Pore pressure and fluid flow during the deformational history of geologic structures are directly influenced by tectonic deformation events. In this contribution, 2D plane strain finite element analysis is used to study the influence of different permeability distributions on the pore pressure field and associated flow regimes during the evolution of visco-elastic single-layer buckle folds. The buckling-induced fluid flow regimes indicate that flow directions and, to a lesser degree, their magnitudes vary significantly throughout the deformation and as a function of the stratigraphic permeability distribution. The modelling results suggest that the volumetric strain and the permeability distribution significantly affect the resulting flow regime at different stages of fold development. For homogeneous permeability models (k > 10 21 m), low strain results in a mostly pervasive fluid flow regime and is in agreement with previous studies. For larger strain conditions, fluid focusing occurs in the buckling layer towards the top of the fold hinge. For low permeabilities (<10 21 m), local focused flow regimes inside the buckling layer emerge throughout the deformation history. For models featuring a low-permeability layer embedded in a high-permeability matrix or sandwiched between high-permeability layers, focused flow regimes inside the folded layer result throughout the deformation history, but with significant differences in the flow vectors of the surrounding layers. Fluid flow vectors induced by the fold can result in different, even reversed, directions depending on the amount of strain. In summary, fluid flow regimes during single-layer buckling can change from pervasive to focused and fluid flow vectors can be opposite at different strain levels, that is the flow vectors change significantly through time. Thus, a complete understanding of fluid flow regimes associated with singlelayer buckle folds requires consideration of the complete deformation history of the fold.

A. Eckert

X. Liu

P. Connolly

Pore pressure evolution and fluid flow during visco-elastic single-layer buckle folding

粘弹性单层褶皱变形过程中的孔隙压力演变与流体流动

The hypothesis that basinal brines inherited their major ion chemistries and elevated salinities from evaporated paleoseawaters is tested by comparing the compositions of basinal brines in Silurian (Michigan basin, Illinois basin, Appalachian basin in eastern Ohio) and Jurassic/Cretaceous (Central Mississippi Salt Dome basin, Arkansas shelf, and south‐central Texas) host rocks, when the world oceans were ‘CaCl2seas’, with those from Permian and Pennsylvanian rocks (Palo Duro basin, Central Basin Platform, and Delaware basin, Texas and New Mexico) when the world oceans were ‘MgSO4seas’. Basinal brines examined are assumed to have originally formed from evaporation of the same seawaters that produced major evaporites. Sulfate, Mg and K levels in basinal brines are below the concentrations expected from evaporation of seawater of any type, which emphasizes the importance of diagenetic mineral–brine interactions in controlling basinal brine chemistry. There are no major differences in SO4, Mg and K concentrations between basinal brines hosted by rocks originally formed during ages when the world oceans were MgSO4seas versus CaCl2seas. Basinal brines in Pennsylvanian–Permian rocks are compositionally distinct (relatively high Na and low Ca) from basinal brines in Silurian, Jurassic and Cretaceous host rocks, which may reflect original differences in seawater chemistry. Basinal brines enriched in Ca and depleted in Na relative to evaporated seawater of any type have traditionally been interpreted to form by albitization of plagioclase feldspar. A new explanation for Ca enrichment and Na depletion of basinal brines is the mixing of evaporated CaCl2‐type seawater with more dilute water. Some basinal brines are similar in major ion composition to evaporated seawater of a particular age, for example basinal brines in the Cretaceous Edwards Group carbonates, Texas, where dolomitization is the only reaction required to convert evaporated Mesozoic CaCl2seawater into Edwards Group brine.

T. K. LOWENSTEIN

M. N. TIMOFEEFF

Secular variations in seawater chemistry as a control on the chemistry of basinal brines: test of the hypothesis

盆地卤水化学受海水化学长期变化的控制：假设检验

Formation water is produced during gas well production, which can seriously affect gas well productivity, especially in deep and ultradeep tight sandstone gas reservoirs. In this paper, we have studied the formation water production and geochemical properties of the ultradeep tight sandstone gas reservoir in the Cretaceous Bashijiqike Formation of the DK gas field in the Kuqa Depression. The results indicate that the formation water can be classified as condensate water, gas-water transition zone water, mixed water, and isolated formation water, all of which are acidic and of CaCl2 type, with increasing salinity or chloride ion content. Sodium/chloride ratio (ρNa+/ρCl-), metamorphic coefficient (ρ(Cl--Na+)/ρ(Mg2+)), desulfurization coefficient (100×ρSO42−/ρCl−), and trace elements concentration parameters show that the formation water was formed in a closed and reductive environment and experienced strong water-rock interaction. The formation water may have been influenced by early seawater, but it is not significant and is more likely to have been influenced by water seepage from the overlying gypsum strata. The Sr, H, and O isotopes reveal that the different types of formation water have good homology and are not affected by atmospheric precipitation, which is propitious to the preservation of natural gas.

Xiaobo Guo

Libin Zhao

Wei Han

Longfei Zhou

Zhilong Huang

Xiongwei Sun

Xuejun Yang

Tonghui Zhang

Chenglin Zhang

Geochemistry of Formation Water and Implications for Ultradeep Tight Sandstone of DK Gas Field in Kuqa Depression

库车坳陷DK气田超深层致密砂岩地层水地球化学特征及意义

Calcite veins in Paleoproterozoic granitoids on the Baltic Shield are the focus of this study. These veins are distinguished by their monomineralic character, unusual thickness and closeness to Neoproterozoic dolerite dykes and therefore have drawn attention. The aim of this study was to define the source of these veins and to unravel their isotopic and chemical nature by carrying out fine‐scale studies. Seven calcite veins covering a depth interval of 50–420 m below the ground surface and composed of breccias or crack‐sealed fillings typically expressing syntaxial growth were sampled and analysed for a variety of physicochemical variables: homogenization temperature (Th) and salinity of fluid inclusions, and stable isotopes (87Sr/86Sr,13C/12C,18O/16O), trace‐element concentrations (Fe, Mn, Mg, Sr, rare earth elements) and cathodoluminescence (CL) of the solid phase. The fluid‐inclusion data show that the calcites were precipitated mainly from relatively low‐temperature (Th= 73–106°C) brines (13.4–24.5 wt.% CaCl2), and the87Sr/86Sr is more radiogenic than expected for Rb‐poor minerals precipitated from Neoproterozoic fluids. These features, together with the distribution of δ13C and δ18O values, provide evidence that the calcite veins are not genetic with the nearby Neoproterozoic dolerite dykes, but are of Paleozoic age and were precipitated from warm brines expressing a rather large variability in salinity. Whereas the isotopic and chemical variables express rather constant average values among the individual veins, they vary considerably on fine‐scale across individual veins. This has implications for understanding processes causing calcite‐rich veins to form and capture trace metals in crystalline bedrock settings.

O. M. Maskenskaya

H. Drake

C. Broman

J. K. Hogmalm

G. Czuppon

M. E. Åström

Source and character of syntaxial hydrothermal calcite veins in Paleoproterozoic crystalline rocks revealed by fine‐scale investigations

通过精细尺度研究揭示的古元古代结晶岩中顺层热液方解石脉的来源与特征

Rainfall and reservoir level fluctuation are two of the main factors contributing to reservoir landslides. However, in China’s Three Gorges Reservoir Area, when the reservoir water level fluctuates significantly, it comes at a time of abundant rainfall, which makes it difficult to distinguish which factor dominates the deformation of the landslide. This study focuses on how rainfall and reservoir water level decline affect the seepage and displacement field of Baijiabao landslide spatially and temporally during drawdown of reservoir water level in the Three Gorges Reservoir Area, thus exploring its movement mechanism. The monitoring data of the landslide in the past 10 years were analyzed, and the correlation between rainfall, reservoir water level decline, and landslide displacement was clarified. By the numerical simulation method, the deformation evolution mechanism of this landslide during drawdown of reservoir water level was revealed, respectively, under three conditions, namely, rainfall, reservoir water level decline, and coupling of the above two conditions. The results showed that the deformation of the Baijiabao landslide was the coupling effect of rainfall and reservoir water level decline, while the latter effect is more pronounced.

Nenghao Zhao

Bin Hu

Qinglin Yi

Wenmin Yao

Chong Ma

The Coupling Effect of Rainfall and Reservoir Water Level Decline on the Baijiabao Landslide in the Three Gorges Reservoir Area, China

降雨与水库水位下降对三峡库区白家包滑坡的耦合效应

Abstract Salar Ignorado is a shallow acid saline lake hosted by a small intervolcanic basin high in the Andes Mountains of northern Chile. Modern surface waters have 3.3–4.1 pH , 0.5–3% total dissolved solids ( TDS ) and are actively precipitating gypsum crystals. The gypsum crystals trap the acid saline water as fluid inclusions, providing a record of recent surface water characteristics. Salar Ignorado gypsum contains three distinct types of primary fluid inclusions, which result from growth of the gypsum from surface waters. Petrography and microthermometry were performed on 27 gypsum crystals from Salar Ignorado to gain an understanding of recent water chemistry of the salar. One 18.3‐cm‐long gypsum crystal, hosting primary fluid inclusions along 28 successive growth bands, was the focus for fluid inclusion studies and allowed a record of high‐resolution chemical trends. This crystal showed a change in parent fluids during growth, from low salinity, to high salinity, back to low salinity. At the bottom of the crystal, the lowest six fluid inclusion assemblages have salinities of 1.7–5.1 eq. wt. % NaCl. The next nine fluid inclusion assemblages have significantly higher salinity (18.6–27.4 eq. wt. % NaCl) inclusions. The twelve fluid inclusion assemblages near the top of the crystal have low salinity (0.9–8.3 eq. wt. % NaCl) like those at the bottom of the crystal. The high‐salinity fluid inclusions in the middle of this gypsum crystal are interpreted to have formed during a pulse of magmatic/hydrothermal fluids to the surface, perhaps during local active volcanism. Secondary evidence of a magmatic influence on surface waters includes hydrogen sulfide and high molecular weight solid hydrocarbons within some fluid inclusions. This study is among the first detailed fluid inclusion studies of gypsum and suggests that fluid inclusions in gypsum can be paleo‐hydrogeologic proxies.

F. J. Karmanocky

K. C. Benison

A fluid inclusion record of magmatic/hydrothermal pulses in acid Salar Ignorado gypsum, northern Chile

智利北部酸性地热伊格诺拉多石膏中的流体包裹体记录的岩浆/热液脉冲

Water-based hydraulic fracturing for the exploitation of shale gas reservoirs may be limited by two main factors: (1) water pollution and chemical pollution after the injection process and (2) permeability decrease due to clay mineral swelling upon contact with the injection water. Besides, shale rock nearly always contains fractures and fissures due to geological processes such as deposition and folding. Based on the above, a damage-based coupled model of rock deformation and gas flow is used to simulate the fracturing process in jointed shale wells with CO 2 fracturing. We validate our model by comparing the simulation results with theoretical solutions. The research results show that the continuous main fractures are formed along the direction of the maximum principal stress, whilst hydraulic fractures tend to propagate along the preexisting joints due to the lower strength of the joints. The main failure type is tensile damage destruction among these specimens. The preexisting joints can aggravate the damage of the numerical specimens; the seepage areas of the layered jointed sample, vertical jointed sample, and orthogonal jointed sample are increased by 32.5%, 29.16%, and 35.05%, respectively, at time <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M1"><mml:mi>t</mml:mi><mml:mo>=</mml:mo><mml:mn>39</mml:mn></mml:math> s compared with the intact sample. The preexisting horizontal joints or vertical joints promote the propagation of hydraulic fractures in the horizontal direction or vertical direction but restrain the expansion of hydraulic fractures in the vertical or horizontal direction.

Qi Zhang

Dan Ma

Jiangfeng Liu

Jiehao Wang

Xibing Li

Zilong Zhou

Numerical Simulations of Fracture Propagation in Jointed Shale Reservoirs under CO<sub>2</sub> Fracturing

CO<sub>2</sub>压裂作用下节理页岩储层裂缝扩展的数值模拟

Using changes in ground temperature to reflect the flow status of groundwater is one of the methods for predicting mine water inrush. In this study, in order to make this method suitable for different geological conditions, an improved method for predicting mine water inrush is established based on the theories of heat transfer and nonlinear water flow in fractal porous media. A water inrush judging criterion based on the critical pressure gradient of nonlinear flow is first established. Then, an internal structural model of the crushed rocks and a mathematical model of nonlinear flow in crushed rocks are derived based on the fractal theory. Finally, a thermal, hydraulic, and mechanical (THM) coupling model is established to study the nonlinear water inrush process and temperature changes. The improved method is established based on the numerical simulation results of the THM coupling model. Results show that the water inrush judging criterion can simultaneously consider the water‐resisting capacity of intact and crushed rocks and quantitatively calculate the water‐resisting capacity of crushed rocks compared with the traditional method. The improved method is suitable for different cases with different water‐resisting capacities, ground temperature change ranges and gradients, and aquifer water pressures, which can improve the applicability of using ground temperature to predict mine water inrush.

Fuli Bo

Jiyuan Zhao

Weitao Liu

Hao Li

Mengke Han

An Improved Method for Predicting Mine Water Inrush Based on Temperature Changes With Nonlinear Flow in Fractal Porous Media

基于分形多孔介质中非线性流动的温度变化预测矿井突水的改进方法

GEOFLUIDS 是一份经过同行评审的开放获取期刊，为与流体在地壳的矿物学、化学和结构演化中的作用相关的原创研究和评论提供了一个论坛。其明确目标是在开展地流体研究的各个子学科范围内传播思想。为此，鼓励作者强调其研究的跨学科相关性和国际影响。还鼓励作者尽可能让其他子学科的读者能够访问他们的工作。GEOFLUIDS 强调整个地壳中地下流体的化学、微生物和物理方面。 GEOFLUIDS 涵盖地下水、陆地或海底地热流体、盆地盐水、石油、变质水或岩浆流体的研究。

GEOFLUIDS is a peer-reviewed open-access journal that provides a forum for original research and reviews related to the role of fluids in the mineralogy, chemistry, and structural evolution of the Earth's crust. Its explicit aim is to disseminate ideas across various sub-disciplines involved in geofluid research. Authors are encouraged to highlight the interdisciplinary relevance and international impact of their work, and to present their findings in a manner accessible to readers from other sub-disciplines. GEOFLUIDS emphasizes the chemical, microbial, and physical aspects of subsurface fluids throughout the crust, covering studies on groundwater, terrestrial or submarine geothermal fluids, basin brines, petroleum, metamorphic waters, and magmatic fluids.

GEOFLUIDS 是一本经过同行评审的开放获取期刊，专注于流体在地壳中的矿物学、化学和结构演化方面的原创研究和评论。期刊的目标是传播与地流体研究相关的各个子学科的思想，鼓励作者强调其研究的跨学科相关性和国际影响力。同时，作者也被鼓励以便于其他子学科的读者理解的方式呈现他们的工作。GEOFLUIDS 强调地下流体在整个地壳中的化学、微生物和物理特性，涵盖地下水、陆地或海底地热流体、盆地盐水、石油、变质水和岩浆流体等研究。

Journals	Geofluids
ISSN	1468-8115, 1468-8123
h-index	68
Journal Impact	1.08
Quartiles(Global)	GEOLOGY(Q2)
Quartiles(China)	地球科学(4区)地球科学地球化学与地球物理(4区)地球科学地质学(4区)