新疆天山地区地下流体地震前兆研究的现状与发展前景

系统地介绍了新疆天山重点震监视区下流体观测网，及其地质构造环境和地下水的成因类型，总结了２０年来地下流体地震前兆探索与地震前兆探索与地震预报研究的基本经验和成果。     

Conventional Oil—The Forgotten Part of the Water-Energy Nexus

The impacts of unconventional oil and gas production via high-volume hydraulic fracturing (HVHF) on water resources, such as water use, groundwater and surface water contamination, and disposal of produced waters, have received a great deal of attention over the past decade. Conventional oil and gas production (e.g., enhanced oil recovery [EOR]), which has been occurring for more than a century in some areas of North America, shares the same environmental concerns, but has received comparatively little attention. Here, we compare the amount of produced water versus saltwater disposal (SWD) and injection for EOR in several prolific hydrocarbon producing regions in the United States and Canada. The total volume of saline and fresh to brackish water injected into depleted oil fields and nonproductive formations is greater than the total volume of produced waters in most regions. The addition of fresh to brackish “makeup” water for EOR may account for the net gain of subsurface water. The total amount of water injected and produced for conventional oil and gas production is greater than that associated with HVHF and unconventional oil and gas production by well over a factor of 10. Reservoir pressure increases from EOR and SWD wells are low compared to injection of fluids for HVHF, however, the longer duration of injections could allow for greater solute transport distances and potential for contamination. Attention should be refocused from the subsurface environmental impacts of HVHF to the oil and gas industry as a whole.     

Deep Injection of Waste Water in the Western Canada Sedimentary Basin

Injection of wastes into the deep subsurface has become a contentious issue, particularly in emerging regions of oil and gas production. Experience in other regions suggests that injection is an effective waste management practice and that widespread environmental damage is unlikely. Over the past several decades, 23 km³ of water has been injected into the Western Canada Sedimentary Basin (WCSB). The oil and gas industry has injected most of this water but large amounts of injection are associated with mining activities. The amount of water injected into this basin during the past century is 2 to 3 orders magnitude greater than natural recharge to deep formations in the WCSB. Despite this large‐scale disturbance to the hydrogeological system, there have been few documented cases of environmental problems related to injection wells. Deep injection of waste appears to be a low risk activity based on this experience but monitoring efforts are insufficient to make definitive statements. Serious uncharacterized legacy issues could be present. Initiating more comprehensive monitoring and research programs on the effects of injection in the WCSB could provide insight into the risks associated with injection in less developed sedimentary basins.     

利用InSAR短基线技术估计洛杉矶地区的地表时序形变和含水层参数

美国南加州洛杉矶地区是自然和人为活动引起的地质构造活跃、石油及地下水抽取和回灌频繁的区域.本文利用19景ENVISAT ASAR降轨影像生成了71幅垂直基线小于300 m、时间间隔小于3年的解缠差分干涉图,并基于短基线集技术(SBAS),GPS和地下水水位数据估计了该区域2003年9月~2009年8月的地表时序形变及含水层贮水系数等物理参数.研究结果表明:(1)在InSAR干涉图中可以清楚的识别多处沉降明显的区域.例如,主要由于含水层地下水的抽取与回灌引起地表沉降的Pasadena盆地(~-2.5 cm/a)、San Gabriel流域(~-2 cm/a)、San Bernardino盆地(~-2.5 cm/a)、Pomona-Ontario盆地(~-4 cm/a)和Santa Ana盆地(~-2.5 cm/a),以及由石油抽取引起地面形变的Santa Fe Springs区域(~-1 cm/a)和Wilmington区域(~-1 cm/a)等;(2)InSAR时间序列形变与GPS投影在雷达视线方向上的形变结果具有较高的一致性,平均形变速率差异的均方差为0.39 cm/a;(3)InSAR时间序列形变与含水层地下水位的变化基本一致,并基于相关理论计算出了含水层的弹性贮水系数和非弹性贮水系数,分析了含水层的形变机理.     

Droplet breakup in subsurface oil releases – Part 1: Experimental study of droplet breakup and effectiveness of dispersant injection

Size distribution of oil droplets formed in deep water oil and gas blowouts have strong impact on the fate of the oil in the environment. However, very limited data on droplet distributions from subsurface releases exist. The objective of this study has been to establish a laboratory facility to study droplet size versus release conditions (rates and nozzle diameters), oil properties and injection of dispersants (injection techniques and dispersant types). This paper presents this facility (6 m high, 3 m wide, containing 40 m³ of sea water) and introductory data. Injection of dispersant lowers the interfacial tension between oil and water and cause a significant reduction in droplet size. Most of this data show a good fit to existing Weber scaling equations. Some interesting deviations due to dispersant treatment are further analyzed and used to develop modified algorithms for predicting droplet sizes in a second paper (Johansen et al., 2013).     

Towards quantitative evaluation of gas injection using time‐lapse seismic data

Of particular concern in the monitoring of gas injection for the purposes of storage, disposal or improved oil recovery is the exact spatial distribution of the gas volumes in the subsurface. In principle this requirement is addressed by the use of 4D seismic data, although it is recognized that the seismic response still largely provides a qualitative estimate of moved subsurface fluids. Exact quantitative evaluation of fluid distributions and associated saturations remains a challenge to be solved. Here, an attempt has been made to produce mapped quantitative estimates of the gas volume injected into a clastic reservoir. Despite good results using three accurately repeated seismic surveys, time‐delay and amplitude attributes reveal fine‐scale differences though large‐scale agreement in the estimated fluid movement. These differences indicate disparities in the nature of the two attributes themselves, which can be explained by several possible causes. Of most impact are the effects of processing and migration, wave interference effects and noise from non‐repeatability of the seismic surveys. This subject highlights the need for a more careful consideration in 4D acquisition, amplitude processing and use of true amplitude preserving attributes in quantitative interpretation.     

新疆天山地震带地下流体地震前兆和预报探索

概述了新疆天山地震带地下流体地震预报研究的主要进展。指出天山地区地下流体分布与地震活动间有成生联系。在中强地震震例分析基础上,进一步系统总结了地下流体地震前兆的综合异常特征,并对预报判据、指标和综合预报方法进行了初步探索。     

Foldback reflectors near methane hydrate bottom‐simulating reflectors: Indicators of gas distribution from 3D seismic images in the eastern Nankai Trough

Understanding of fluid behavior and gas distribution in the shallow subsurface are important considerations in gas hydrate formation and the global carbon cycle. Estimation of gas distribution based on reflection seismic surveys, however, is difficult because the boundary of a gas‐bearing zone is indistinct and not systematically defined. This study reports distinctive features related to gas‐hydrate distribution and possible fluid migration in high‐resolution 3D seismic‐reflection data from sediments of the eastern Nankai Trough. These features, here termed foldback reflectors (FBRs), descend in accordion shaped reflectors near the edges of bottom‐simulating reflectors (BSRs). FBRs generally correspond to lateral boundaries between two seismic facies, a ‘dimmed’ facies with relatively low amplitude and subdued high‐frequency components beneath the BSR and the contrasting facies around the BSR. The dimmed facies corresponds to areas of anomalously low velocity consistent with a small amount of free gas. FBR is mostly developed in well‐stratified formations in uplifted regions. Dip directions of the FBR appear to be restricted by orientation of the host formations. Edges of the FBR often correspond to high‐amplitude layers. Such occurrences of FBR suggest that regional uplift and layer‐parallel fluid migration are related to the formation of FBR as well as BSR.     

上地幔高导层与内生金属矿产及油气藏的关系

依据大地电磁测深所发现的上地幔高导层顶面深度可以给出大陆岩石圈-软流圈界面(LAB)的空间发育特征,为认识岩石圈结构及壳幔相互作用等提供重要信息.本文在1996年编制的中国大陆上地幔高导层顶面深度图的基础上,补充了1995—2010年大地电磁测深结果和大地热流数据,以1°×1°网度编制了新的中国大陆上地幔高导层顶面深度图.我国上地幔高导层顶面深度变化很大,具有南北分带,东西分块的特征,呈东浅、西深、北浅、南深的格局,从最浅的50~60km到最深的230km,平均深度为100~120km.据上地幔高导层顶面分布形态,全国共可划分出27个隆起区.通过与中国已知内生金属矿产和油气田的分布对比,发现我国大陆80%以上中生代内生金属矿床分布在上地幔高导层隆起带或其梯度带上方.中国大陆东部含油气盆地主体对应上地幔隆起区,油气田多位于隆起区上方或其边部的过渡带上;西部主体位于幔坳区,主要油气田对应盆地中心的幔坳向周边幔隆过渡的梯度带上;中部表现为仅盆地腹地对应幔坳,盆地周边对应规模较大的上地幔隆起带,主要油气田位于隆起带.总的来看内生金属矿床一般分布在上地幔隆起区靠近造山带一侧,而油气田一般分布在上地幔隆起区靠近盆地一侧.软流圈的不断上隆,造成岩石圈减薄、拉张,张性断裂的出现成为地球深部物质和热量向地壳上部运移的有利通道,为内生金属矿产的形成提供了成矿物质和能量保障,也为含油气盆地带来了生烃催化剂、热能和无机成因的石油与天然气.地球深部超临界流体的存在对上地幔高导层的形成、成矿物质运移可能发挥了重要作用.     

Sub‐sample time shift and horizontal displacement measurements using phase‐correlation method in time‐lapse seismic

Hydrocarbon production and fluid injection affect the level of subsurface stress and physical properties of the subsurface, and can cause reservoir‐related issues, such as compaction and subsidence. Monitoring of oil and gas reservoirs is therefore crucial. Time‐lapse seismic is used to monitor reservoirs and provide evidence of saturation and pressure changes within the reservoir. However, relative to background velocities and reflector depths, the time‐lapse changes in velocity and geomechanical properties are typically small between consecutive surveys. These changes can be measured by using apparent displacement between migrated images obtained from recorded data of multiple time‐lapse surveys. Apparent displacement measurements by using the classical cross‐correlation method are poorly resolved. Here, we propose the use of a phase‐correlation method, which has been developed in satellite imaging for sub‐pixel registration of the images, to overcome the limitations of cross‐correlation. Phase correlation provides both vertical and horizontal displacements with a much better resolution. After testing the method on synthetic data, we apply it to a real dataset from the Norne oil field and show that the phase‐correlation method can indeed provide better resolution.     

Effects of wettability and pore-level displacement on hydrocarbon trapping

We use a three-dimensional mixed-wet random network model representing Berea sandstone to extend our previous work on relative permeability hysteresis during water-alternating-gas (WAG) injection cycles [Suicmez, VS, Piri, M, Blunt, MJ, 2007, Pore-scale simulation of water alternate gas injection, Transport Porous Med 66(3), 259–86]. We compute the trapped hydrocarbon saturation for tertiary water-flooding, which is water injection into different initial gas saturations, S_gi, established by secondary gas injection after primary drainage. Tertiary water-flooding is continued until all the gas and oil is trapped. We study four different wettability conditions: water-wet, weakly water-wet, weakly oil-wet and oil-wet. We demonstrate that the amounts of oil and gas that are trapped show surprising trends with wettability that cannot be captured using previously developed empirical trapping models. We show that the amount of oil that is trapped by water in the presence of gas increases as the medium becomes more oil-wet, which is opposite from that seen for two-phase flow. It is only through a careful analysis of displacement statistics and fluid configurations that these results can be explained. This illustrates the need to have detailed models of the displacement processes that represent the three-phase displacement physics as carefully as possible. Further work is needed to explore the full range of behavior as a function of wettability and displacement path.     

Determination of predevelopment denudation rates of an agricultural watershed (Cayaguás River, Puerto Rico) using in-situ-produced Be in river-borne quartz

Accurate estimates of watershed denudation absent anthropogenic effects are required to develop strategies for mitigating accelerated physical erosion resulting from human activities, to model global geochemical cycles, and to examine interactions among climate, weathering, and uplift. We present a simple approach to estimate predevelopment denudation rates using in-situ-produced cosmogenic ¹⁰Be in fluvial sediments. Denudation processes in an agricultural watershed (Cayaguás River Basin, Puerto Rico) and a matched undisturbed watershed (Icacos River Basin) were compared using ¹⁰Be concentrations in quartz for various size fractions of bed material. The coarse fractions in both watersheds bear the imprint of long subsurface residence times. Fine material from old shallow soils contributes little, however, to the present-day sediment output of the Cayaguás. This confirms the recent and presumably anthropogenic origin of the modern high denudation rate in the Cayaguás Basin and suggests that pre-agricultural erosional conditions were comparable to those of the present-day Icacos.     

Surface flow boundary conditions in modeling land subsidence due to fluid withdrawal

Land subsidence due to subsurface fluid (water, gas, oil) withdrawal is often predicted by either finite element or finite difference numerical models based on coupled poroelastic theory, where the soil is represented as a semi-infinite medium bounded by the traction-free (ground) surface. One of the variables playing a most important role on the final outcome is the flow condition used on the traction-free boundary, which may be assumed as either permeable or impermeable. Although occasionally justified, the assumption of no-flow surface seems to be in general rather unrealistic. A permeable boundary where the fluid pressure is fixed to the external atmospheric pressure appears to be more appropriate. This paper addresses the response, in terms of land subsidence, obtained with a coupled poroelastic finite element model that simulates a distributed pumping from a horizontal aquifer confined between two relatively impervious layers, and takes either a permeable boundary surface, i.e., constant hydraulic potential, or an impermeable boundary, i.e., a zero Neumann flow condition. The analysis reveals that land subsidence is rather sensitive to the flow condition implemented on the traction-free boundary. In general, the no-flow condition leads to an overestimate of the predicted ground surface settlement, which could even be 1 order of magnitude larger than that obtained with the permeable boundary.     

Is anthropogenic land subsidence a possible driver of riverine flood-hazard dynamics? A case study in Ravenna,Italy

We investigate possible changes in flood hazard over a 77-km² area around the city of Ravenna. The subsidence rate in the area, naturally a few mm year^?1, increased dramatically after World War II because of groundwater and natural gas extraction, exceeding 110?mm year^?1 and resulting in cumulative drops larger than 1.5?m. The Montone–Ronco river system flows in the southern portion of the area, which is protected against frequent flooding by levees. We performed two-dimensional simulations of inundation events associated with levee breaching by considering four different terrain configurations: current topography and a reconstruction of ground elevations before anthropogenic land subsidence, both neglecting and representing the main linear infrastructures (e.g. roads, artificial channels). Results show that flood-hazard changes due to anthropogenic land subsidence (e.g. significant changes in computed water depth and velocity) are observed over less than 10% of the study area and are definitely less important than those resulting from construction of the linear infrastructures.     

Numerical Investigation of a Methane Leakage from a Geothermal Well into a Shallow Aquifer

The potential environmental impacts on subsurface water resources induced by unconventional gas production are still under debate. Solving the controversy regarding the potential adverse effects of gas leakages on groundwater resources is therefore crucial. In this work, an interesting real-world case is presented in order to give further insight into methane multiphase and transport behavior in the shallow subsurface, often disregarded compared to the behavior in the deep subsurface. Multiphase flow and solute transport simulations were performed to assess the vulnerability of an existing shallow unconfined aquifer with respect to a hypothetical methane leakage resulting from a well integrity failure of a former deep geothermal well. The analysis showed that migration of gaseous methane through the aquifer under examination can be extremely fast (of the order of a few minutes), occurring predominantly vertically upwards, close to the well. By contrast, dissolved methane migration is largely affected by the groundwater flow field and occurs over larger time scales (of the order of months/years), covering a greater distance from the well. Overall, the real concern for this site in case of gas leakages is the risk of explosion in the close vicinity of the well. Predicted maximum gaseous fluxes (0.89 to 22.60 m³/d) are comparable to those reported for leaking wells, and maximum dissolved methane concentrations may overcome risk mitigation thresholds (7 to 10 mg/L) in a few years. Therefore, surface and subsurface monitoring before decommissioning is strongly advised to ensure the safety of the site.     

京北地热田开发对地下流体动态的影响

在地震地下流体动态研究中发现有多种干扰,特别是地下水资源开发的干扰较为普遍,地下热水开发的干扰较为严重,影响地下流体动态监测的效果,因此需要关注、调查与研究地下水开采对地下流体动态的影响问题。作者在研究京北地热田区水文地质条件及热水开采的历史与现状的基础上,重点分析了热水开采对不同水文地质条件与离开采井距离不等的观测井地下流体动态的影响及这种影响在不同测项上表现的差异。研究结果表明,在京北地热田区热水开采对地下流体动态的影响距离为5km,对位于导水断裂带附近的观测井动态影响最为明显;就测项而言,对水位与水温动态的影响最为明显,其次是逸出气(Rn,Hg)动态的影响,对土壤气(CO2)动态的影响不明显     

Is anthropogenic land subsidence a possible driver of riverine flood-hazard dynamics? A case study in Ravenna,Italy

ABSTRACT

We investigate possible changes in flood hazard over a 77-km² area around the city of Ravenna. The subsidence rate in the area, naturally a few mm year^?1, increased dramatically after World War II because of groundwater and natural gas extraction, exceeding 110?mm year^?1 and resulting in cumulative drops larger than 1.5?m. The Montone–Ronco river system flows in the southern portion of the area, which is protected against frequent flooding by levees. We performed two-dimensional simulations of inundation events associated with levee breaching by considering four different terrain configurations: current topography and a reconstruction of ground elevations before anthropogenic land subsidence, both neglecting and representing the main linear infrastructures (e.g. roads, artificial channels). Results show that flood-hazard changes due to anthropogenic land subsidence (e.g. significant changes in computed water depth and velocity) are observed over less than 10% of the study area and are definitely less important than those resulting from construction of the linear infrastructures.     

Constraints on Upward Migration of Hydraulic Fracturing Fluid and Brine

Recent increases in the use of hydraulic fracturing (HF) to aid extraction of oil and gas from black shales have raised concerns regarding potential environmental effects associated with predictions of upward migration of HF fluid and brine. Some recent studies have suggested that such upward migration can be large and that timescales for migration can be as short as a few years. In this article, we discuss the physical constraints on upward fluid migration from black shales (e.g., the Marcellus, Bakken, and Eagle Ford) to shallow aquifers, taking into account the potential changes to the subsurface brought about by HF. Our review of the literature indicates that HF affects a very limited portion of the entire thickness of the overlying bedrock and therefore, is unable to create direct hydraulic communication between black shales and shallow aquifers via induced fractures. As a result, upward migration of HF fluid and brine is controlled by preexisting hydraulic gradients and bedrock permeability. We show that in cases where there is an upward gradient, permeability is low, upward flow rates are low, and mean travel times are long (often >10⁶ years). Consequently, the recently proposed rapid upward migration of brine and HF fluid, predicted to occur as a result of increased HF activity, does not appear to be physically plausible. Unrealistically high estimates of upward flow are the result of invalid assumptions about HF and the hydrogeology of sedimentary basins.     

南海前新生代残留盆地分布综合地球物理研究

为了对南海海域的前新生代残留盆地分布有个整体而全面的认识,本文开展了南海残留盆地宏观分布的综合地球物理研究.通过岩石物性分析,综合重、磁、震等地球物理方法,利用正演与反演方法,分区计算并求取了南海的重力基底和磁性基底埋深,得到了中生界及前中生界残余厚度,给出了整个南海前新生代残留盆地的宏观格架与残余厚度分布特征并讨论了...     

Simulated impacts of climate change and land‐clearing on runoff from a small Sahelian catchment

In the Sahel, there are few long‐term data series available to estimate the climatic and anthropogenic impacts on runoff in small catchments. Since 1950, land clearing has enhanced runoff. The question is whether and by how much this anthropogenic effect offsets the current drought. To answer this question, a physically based distributed hydrological model was used to simulate runoff in a small Sahelian catchment in Niger, from the 1950–1998 rain‐series. The simulation was carried out for three soil surface states of the catchment (1950, 1975 and 1992). The catchment is characterized by an increase in cultivated land, with associated fallow, from 6% in 1950 to 56% in 1992, together with an increase in the extent of eroded land (from 7 to 16%), at the expense of the savanna. Effects of climate and land use are first analysed separately: irrespective of the land cover state, the simulated mean annual runoff decreases by about 40% from the wet period (1950–1969) to the dry period (1970–1998); calculated on the 1950–1998 rainfall‐series, the changes that occurred in land cover between 1950 and 1992 multiplies the mean annual runoff by a factor close to three. The analysis of a joint climatic and anthropogenic change shows that the transition from a wet period under a ‘natural’ land cover (1950) to a dry period under a cultivated land cover (1992) results in an increase in runoff of the order of 30 to 70%. At the scale of a small Sahelian catchment, the anthropogenic impact on runoff is probably more important than that of drought. This figure for relative increase in runoff contributions to ponds, preferential sites of seepage to groundwater, is less than that currently estimated for aquifer recharge, which has been causing a significant continuous water table rise over the same period. Copyright © 2004 John Wiley & Sons, Ltd.