Environmental hazards posed by the Los Angeles Basin urban oilfields: an historical perspective of lessons learned

Urban encroachment into areas historically reserved for oil and gas field operations is an ever-present problem within the Los Angeles Basin. The recent frenzy in real estate development has only intensified what can be characterized as a conflict in land usage. Subsurface mineral rights are severed from surface ownership, often resulting in developments being approved without adequate consideration of the underlying oil and gas field consequences. Also, surface operations are frequently co-located within residential areas without consideration of the health and safety consequences of emissions of toxics to air. This paper presents a review of the environmental, health and safety hazards posed by urban oilfield operations, with an emphasis upon the lessons learned from the L.A. Basin: Original Urban Oilfield Legend (see Castle and Yerkes 1976; Denton and others 2001; Endres and others 2002; Kouznetsov and others 1994; Katz and others 1994; Schumacher and Abrams 1994; and Schoell 1983). The Los Angeles Basin has provided the authors with one of the largest natural laboratories in the world for studying the consequences of these issues. The results presented are part of a long-term research program based upon the application of geoscience and petroleum engineering principles in obtaining a fundamental understanding of the root causes of the environmental hazards posed. Topics addressed include: (1) vertical migration of gas to the surface along faults and improperly completed or abandoned wellbores (e.g., due to poor cementing practices), (2) subsidence caused by the fluid production and declining reservoir pressures, (3) soil and groundwater contamination resulting from historic oil and gas field operations, and (4) air toxics resulting from surface operations. A number of case histories are discussed that illustrate the seriousness of the problem. A clear case is made for the urgent need for closer coordination and education by the petroleum industry of the local government planning departments. These departments have the principal role in determining land use policies, acting as the lead agency in performing environmental site assessments (e.g., under the California Environmental Quality Act), and in establishing mitigation measures for dealing with the long-term environmental hazards. This paper establishes prudent practices on the part of oilfield operators for the monitoring and mitigation of these hazards.     

Considerations on a suction drill for lunar surface drilling and sampling: I. Feasibility study

In this paper, we consider a drilling method, which might prove useful both for applications on the Moon and for drilling on Mars, Venus, or other planetary surfaces. It is based on the use of a cold gas flow for pumping fine-grained debris particles out of the borehole, after they have been pulverized by the bore crown. We present a basic design and demonstrate by a hydrodynamic calculation that such a system should work effectively even on an airless body like the Moon, where the driver gas has to be provided from the associated lander or rover, which acts as the bore platform.     

Discrete-Element Computation of Averaged Tensorial Fields in Sand Piles Consisting of Polygonal Particles

This work is a contribution to the understanding of the mechanical properties of non-cohesive granular materials in the presence of friction and a continuation of our previous work (Roul et al. 2010) on numerical investigation of the macroscopic mechanical properties of sand piles. Besides previous numerical results obtained for sand piles that were poured from a localized source (“point source”), we here consider sand piles that were built by adopting a “line source” or “raining procedure”. Simulations were carried out in two-dimensional systems with soft convex polygonal particles, using the discrete element method (DEM). First, we focus on computing the macroscopic continuum quantities of the resulting symmetric sand piles. We then show how the construction history of the sand piles affects their mechanical properties including strain, fabric, volume fraction, and stress distributions; we also show how the latter are affected by the shape of the particles. Finally, stress tensors are studied for asymmetric sand piles, where the particles are dropped from either a point source or a line source. We find that the behaviour of stress distribution at the bottom of an asymmetric sand pile is qualitatively the same as that obtained from an analytical solution by Didwania and co-workers (Proc R Soc Lond A 456:2569–2588, 2000).     

Planet formation processes revealed by meteorites

The history of the solar system is locked within the planets, asteroids and other objects that orbit the Sun. While remote observations of these celestial bodies are essential for understanding planetary processes, much of the geological and geochemical information regarding solar system heritage comes directly from the study of rocks and other materials originating from them. The diversity of materials available for study from planetary bodies largely comes from meteorites; fragments of rock that fall through Earth's atmosphere after impact‐extraction from their parent planet or asteroid. These extra‐terrestrial objects are fundamental scientific materials, providing information on past conditions within planets, and on their surfaces, and revealing the timing of key events that affected a planet's evolution. Meteorites can be sub‐divided into four main groups: (1) chondrites, which are unmelted and variably metamorphosed ‘cosmic sediments’ composed of particles that made up the early solar nebula; (2) achondrites, which represent predominantly silicate materials from asteroids and planets that have partially to fully melted, from a broadly chondritic initial composition; (3) iron meteorites, which represent Fe‐Ni samples from the cores of asteroids and planetesimals; and (4) stony‐iron meteorites such as pallasites and mesosiderites, which are mixtures of metal and dominantly basaltic materials. Meteorite studies are rapidly expanding our understanding of how the solar system formed and when and how key events such as planetary accretion and differentiation occurred. Together with a burgeoning collection of classified meteorites, these scientific advances herald an unprecedented period of further scientific challenges and discoveries, an exciting prospect for understanding our origins.     

Using global node-based velocity in random walk particle tracking in variably saturated porous media: application to contaminant leaching from road constructions

Precise and efficient numerical simulation of transport processes in subsurface systems is a prerequisite for many site investigation or remediation studies. Random walk particle tracking (RWPT) methods have been introduced in the past to overcome numerical difficulties when simulating propagation processes in porous media such as advection-dominated mass transport. Crucial for the precision of RWPT methods is the accuracy of the numerically calculated ground water velocity field. In this paper, a global node-based method for velocity calculation is used, which was originally proposed by Yeh (Water Resour Res 7:1216–1225, 1981). This method is improved in three ways: (1) extension to unstructured grids, (2) significant enhancement of computational efficiency, and (3) extension to saturated (groundwater) as well as unsaturated systems (soil water). The novel RWPT method is tested with numerical benchmark examples from the literature and used in two field scale applications of contaminant transport in saturated and unsaturated ground water. To evaluate advective transport of the model, the accuracy of the velocity field is demonstrated by comparing several published results of particle pathlines or streamlines. Given the chosen test problem, the global node-based velocity estimation is found to be as accurate as the CK method (Cordes and Kinzelbach in Water Resour Res 28(11):2903–2911, 1992) but less accurate than the mixed or mixed-hybrid finite element methods for flow in highly heterogeneous media. To evaluate advective–diffusive transport, a transport problem studied by Hassan and Mohamed (J Hydrol 275(3–4):242–260, 2003) is investigated here and evaluated using different numbers of particles. The results indicate that the number of particles required for the given problem is decreased using the proposed method by about two orders of magnitude without losing accuracy of the concentration contours as compared to the published numbers.     

瓦斯抽采钻孔间距优化三维数值模拟量化研究

为了识别钻孔间距对煤层瓦斯抽采的影响及如何实现高效抽采,基于流固耦合模型,建立三维几何模型,使其更接近现场实际,借助COMSOL软件模拟某煤矿钻孔不同间距的瓦斯抽采过程,利用瓦斯压力为0.74 MPa等压面三维立体图使有效抽采区域可视化,通过计算有效抽采区域体积大小,量化分析钻孔间距对抽采效果的影响。结果表明:单一钻孔抽采120 d时,有效抽采半径约为1.5 m;当布置多个钻孔且钻孔间距d为5 m,抽采120 d时,瓦斯压力为0.74 MPa的等压面围绕所有钻孔近似呈圆柱状但向内部凹陷（即出现空白带）;钻孔间距d为2.1、3、4、5、6 m时,有效抽采区域体积V的大小顺序随着时间的增长而改变,抽采120 d时,V_{d=5 m}>V_{d=4 m}>V_{d=3 m}>V_{d=2.1 m}>V_{d=6 m}。综合分析瓦斯压力等压面三维立体图和有效抽采区域体积的大小顺序,确定该矿钻孔的较优间距为4 m。研究提出的以有效抽采半径、叠加效应、三维瓦斯压力等压面的形状及有效抽采区域体积大小为指标的钻孔间距数值计算考察方法,可为煤矿井下钻孔间距优化布置提供参考。      

废弃井“一井多用”瓦斯抽采关键技术及应用

煤矿区地面瓦斯废弃井改造再利用,可进行采动区瓦斯抽采,具有保障回采工作安全生产,瓦斯资源有效利用,减少瓦斯逸散对环境压力等经济环保多重效益。针对这一目的,结合采动区地面井和废弃井的特点,提出废弃井“一井多用”瓦斯抽采技术思路。通过分析试验工作面开采工艺、覆岩结构及废弃井的基本情况等条件,研究并提出了废弃井优选及判识、地面井改造工艺、防护装置安设、抽采系统布置及抽采控制技术等,改进了废弃井改造射孔造缝段长度确定方法。研发了基于油套环空动态调节、组合套管双重防护及筛管分级优化的安全防护方法,形成了废弃井“一井多用”地面井瓦斯抽采技术。选取晋城矿区岳城煤矿作为试验对象,完成了3口废弃井(井号为YC-50、YC-52、YC-54)再利用改造试验,其地面井瓦斯抽采量累计分别为257.88万、172.50万、129.60万m3。YC-50井改造运行后,地面井抽采范围内工作面上隅角瓦斯体积分数最大值从0.77%降至0.40%,降幅48.05%;YC-52井改造运行后,采煤工作面上隅角瓦斯体积分数降幅为52.38%,有效保障了回采工作面安全生产,实现了废弃井“一井多用”目标,取得了良好的经济与社会效益...     

DEM–SPH simulation of rock blasting

A numerical model is proposed for the simulation of rock blasting. A bonded particle system is utilized to mimic the behavior of rock. The particles interact at the contact points through normal and shear springs to simulate rock elasticity. To withstand the deviatoric stresses, the particles are glued to each other. If the applied force exceeds the contact strength, local failure occurs and microcracks are developed in the synthetic rock. For simulation of gas flow, the smooth particle hydrodynamic method is implemented. The interaction of gas particles with the rock grains is assumed to follow a perfect plastic collision model in which the initial momentum of the colliding particles is preserved. A detailed examination of the interaction of gas with blast hole is investigated. It is shown that the proposed hybrid model is capable of simulating the induced shock waves in the gas together with wave propagation in the rock material. The model successfully mimics crack propagation in rock. In particular, the crushed zone around the borehole, radial cracks, and surface spalling are all captured successfully. The results of numerical analysis suggest that gas–rock interaction can, in fact, generate a few successive compressive waves in the rock specimen, causing further extension of radial cracks with time as the weaker secondary and tertiary waves interact with the crack tips.     

Surface waves in a cylindrical borehole through partially-saturated porous solid

Propagation of surface waves is discussed in a cylindrical borehole through a liquid-saturated porous solid of infinite extent. The porous medium is assumed to be a continuum consisting of a solid skeletal with connected void space occupied by a mixture of two immiscible inviscid fluids. This model also represents the partial saturation when liquid fills only a part of the pore space and gas bubbles span the remaining void space. In this isotropic medium, potential functions identify the existence of three dilatational waves coupled with a shear wave. For propagation of plane harmonic waves along the axially-symmetric borehole, these potentials decay into the porous medium. Boundary conditions are chosen to disallow the discharge of liquid into the borehole through its impervious porous walls. A dispersion equation is derived for the propagation of surface waves along the curved walls of no-liquid (all gas) borehole. A numerical example is studied to explore the existence of cylindrical waves in a particular model of the porous sandstone. True surface waves do not propagate along the walls of borehole when the supporting medium is partially saturated. Such waves propagate only beyond a certain frequency when the medium is fully-saturated porous or an elastic one. Dispersion in the velocity of pseudo surface waves is analysed through the changes in consolidation, saturation degree, capillary pressure or porosity.     

Mineral ballast and particle settling rates in the coastal upwelling system off NW Africa and the South Atlantic

The ocean off NW Africa is the second most important coastal upwelling system with a total annual primary production of 0.33 Gt of carbon per year (Carr in Deep Sea Res II 49:59–80, 2002). Deep ocean organic carbon fluxes measured by sediment traps are also fairly high despite low biogenic opal fluxes. Due to a low supply of dissolved silicate from subsurface waters, the ocean off NW Africa is characterized by predominantly carbonate-secreting primary producers, i.e. coccolithophorids. These algae which are key primary producers since millions of years are found in organic- and chlorophyll-rich zooplankton fecal pellets, which sink rapidly through the water column within a few days. Particle flux studies in the Mauretanian upwelling area (Cape Blanc) confirm the hypothesis of Armstrong et al. (Deep Sea Res II 49:219–236, 2002) who proposed that ballast availability, e.g. of carbonate particles, is essential to predict deep ocean organic carbon fluxes. The role of dust as ballast mineral for organic carbon, however, must be also taken into consideration in the coastal settings off NW Africa. There, high settling rates of larger particles approach 400 m day⁻¹, which may be due to a particular composition of mineral ballast. An assessment of particle settling rates from opal-production systems in the Southern Ocean of the Atlantic Sector, in contrast, provides lower values, consistent with the assumptions of Francois et al. (Global Biogeochem Cycles 16(4):1087, 2002). Satellite chlorophyll distributions, particle distributions and fluxes in the water column off NW Africa as well as modelling studies suggest a significant lateral flux component and export of particles from coastal shelf waters into the open ocean. These transport processes have implications for paleo-reconstructions from sediment cores retrieved at continental margin settings.     

Thermal conductivity measurements of coarse-grained gravel materials using a hollow cylindrical sensor

We report on new results for the thermal conductivity of granular materials, in particular large-grained gravels. For these measurements, a cylindrical-shaped heated sensor was developed and used, which allows to include gravels with grain sizes in the several centimeter size range into the investigation. Such materials are, among else, important as construction materials for road and railway embankments. Measurements were done at different gas pressure levels (from normal atmospheric level down to the millibar range) and for dry and wet conditions. The results of the low pressure measurements may become relevant in view of possible applications on other planetary bodies, like at the surface of the planet Mars, which will be explored in the coming decade by in situ geotechnical methods.     

Particle simulation of thermally-induced rock damage with consideration of temperature-dependent elastic modulus and strength

Based on the particle simulation method, a thermo-mechanical coupling particle model is proposed for simulating thermally-induced rock damage. In this model, rock material is simulated as an assembly of particles, which are connected to each other through their bonds, in the case of simulating mechanical deformation, but connected to each other through thermal pipes in the case of simulating heat conduction. The main advantages of using this model are that: (1) microscopic parameters of this model can be directly determined from the related macroscopic ones; (2) the temperature-dependent elastic modulus and strength are considered in an explicit manner, so that thermally-induced rock damage can be realistically simulated in a thermo-mechanical coupling problem. The related simulation results from an application example have demonstrated that: (1) the proposed model can produce similar behaviors to those observed in experiments; (2) the final failure is initiated from the outer surface of the testing sample and propagates toward the borehole; (3) microscopic crack initiation and propagation processes can be reasonably simulated at the cooling stage.     

Convolution-based particle tracking method for transient flow

A convolution-based particle tracking (CBPT) method was recently developed for calculating solute concentrations (Robinson et al., Comput Geosci 14(4): 779–792, 2010). This method is highly efficient but limited to steady-state flow conditions. Here, we present an extension of this method to transient flow conditions. This extension requires a single-particle tracking process model run, with a pulse of particles introduced at a sequence of times for each source location. The number and interval of particle releases depends upon the transients in the flow. Numerical convolution of particle paths obtained at each release time and location with a time-varying source term is performed to yield the shape of the plume. Many factors controlling transport such as variation in source terms, radioactive decay, and in some cases linear processes such as sorption and diffusion into dead-end pores can be simulated in the convolution step for Monte Carlo-based analysis of transport uncertainty. We demonstrate the efficiency of the transient CBPT method, by showing that it requires fewer particles than traditional random walk particle tracking methods to achieve the same levels of accuracy, especially as the source term increases in duration or is uncertain. Since flow calculations under transient conditions are often very expensive, this is a computationally efficient yet accurate method.     

The Effect of Specimen Size on Strength and Other Properties in Laboratory Testing of Rock and Rock-Like Cementitious Brittle Materials

The effect of specimen size on the measured unconfined compressive strength and other mechanical properties has been studied by numerous researchers in the past, although much of this work has been based on specimens of non-standard dimensions and shapes, and over a limited size range. A review of the published literature was completed concentrating on the presentation of research pertaining to right cylindrical specimens with height:diameter ratios of 2:1. Additionally, new data has been presented considering high strength (70 MPa) cement mortar specimens of various diameters ranging from 63 to 300 mm which were tested to failure. Currently, several models exist in the published literature that seek to predict the strength–size relationship in rock or cementitious materials. Modelling the reviewed datasets, statistical analysis was used to help establish which of these models best represents the empirical evidence. The findings presented here suggest that over the range of specimen sizes explored, the MFSL (Carpinteri et al. in Mater Struct 28:311–317, 1995) model most closely predicts the strength–size relationship in rock and cementitious materials, and that a majority of the empirical evidence supports an asymptotic value in strength at large specimen diameters. Furthermore, the MFSL relationship is not only able to model monotonically decreasing strength–size relationships but is also equally applicable to monotonically increasing relationships, which although shown to be rare do for example exist in rocks with fractal distributions of hard particles.     

Initial assessment of the infiltration and overland flow for different rainfall events in land constituted of sandstones of the Botucatu Formation (Guarani Aquifer), State of São Paulo, Brazil

This study was carried out in the Córrego do Vaçununga basin constituted of eolic sandstones of Botucatu Formation and residual unconsolidated materials (>90%), considered the most important unconfined aquifer in Brazil, in the city of Luiz Antonio, State of São Paulo, Brazil. Laboratory and in situ tests were performed to characterize the unconsolidated materials in terms of basic physical properties, potential infiltration rate, suction and hydraulic conductivity. The results for infiltration and overland flow depths were obtained according to Morel-Seytoux and Khanji (Water Resour Res 10(4):795–800, 1976) and Chu (Water Resour Res 14(3):461–466, 1978) adaptation of the Green and Ampt [J Agr Sci 4(Part 1):1–24, 1911] model for steady and transient rainfalls, respectively. Rainfall data were collected from January of 2000 to December of 2002, and 12 scenarios were defined considering the intensity and durations. Rather than high homogeneity in terms of the texture of unconsolidated materials, the infiltration and overland flow ratio depends on the type of land use and associated management practices. The results showed that rainfall with high intensity and short duration do not produce high overland flow ratio as we have observed for transient scenarios with long duration and low intensities.     

Surface temperature history determination from borehole measurements

All methods proposed to date for the determination of surface temperature history from temperature profiles measured in boreholes are based on the assumption that the borehole is a hole in a semiinfinite homogeneous earth of constant diffusivity , and more or less ignore the fact that the mathematical formulation for this problem is improperly posed. This assumption, which frequently represents a gross oversimplification of the situation, was originally introduced as a computational expedient. We propose a computational procedure which is independent of this assumption and takes the improperly posed nature of the problem into account. The essence of the method is: (a) determine the set of borehole profiles corresponding to a given set of linearly independent surface temperature history functions, and then (b) take the coefficients of the least-squares fit of these borehole profiles to the given borehole data as the coefficients in the linear combination of surface temperature history functions which defines the required approximation to the surface temperature history. An analogous procedure can be used to determine the lower boundary condition for the heat-flow problem if the surface-temperature history is assumed to be known. Results of numerical experimentation are used to indicate the extent to which the method is viable in practice.     

Emission reduction technology and application research of surface borehole methane drainage in coal mining-influenced region

Windblown methane is an important gas resulting in atmospheric greenhouse effect. Therefore, reduction in windblown methane is one of the important measures to mitigate atmospheric greenhouse effect. In China, weak coal seam of low permeability is common in coal mines, so it is beset with difficulties to decrease the methane emission rate by means of gas drainage from the virgin coal seam, further to decrease the windblown mine gas. Utilizing the pressure relief and permeability and fluidity improvement effect in coal mining an approach to release methane emission through surface borehole was established, for example establishing a comprehensive deformation fracture model of surface borehole in extraction area based on quantitative rule of overlying rock movement in pit and forming a technology to select the surface borehole arrangement site in extraction area on the basis of deformation of bore frame structure and distribution characteristics of extraction flow field. And optimization technology of shape and structure of surface borehole in extraction area on the basis of ultimate stress analysis of surface borehole casing was given. The technology overcomes effectively the problem that surface borehole casing is vulnerable to premature fracture due to impact of strata movement on the surface borehole, and further increases the drainage result of the surface borehole. The technology has been test in China Shanxi Jincheng Sihe Coal Mine, achieving good results, including 12,000 Nm³/d pure methane drainage rate from single borehole, 85% methane concentration and 1.1 million Nm³ accumulative methane drainage, which demonstrate practicability and advanced performance of the technology.     

从钻孔温度看气候变化──方法介绍及实例

地壳浅层的地温分布与过去一定时期的地表温度变化之间有着内在的联系，地温场记录着地表温度变化的历史。由于地表温度是描述气候变化的重要参数，通过对钻孔地温数据进行分析处理，可以达到研究古气候变化的目的。美国东北部、加拿大东南部和中国四川攀西地区若干钻孔地温剖面的反演结果一致表明，这些区域在过去数百年间地表温度均有不同程度的升高。与研究古气候的其他方法相比，地热方法具有理论基础牢固和现成数据基础庞大的突出特点，这一研究方法在世界范围的广泛应用必将有助于揭开全球气候变化的奥秘。     

Seismic liquefaction analysis of a reservoir dam foundation in the South–North Water Diversion project in China. Part I: Liquefaction potential assessment

In this paper, the dynamic characteristics of a liquefiable silt substratum within the foundation soil of a reservoir dam in the Tianjin area are investigated by means of standard penetration resistance and dynamic triaxial tests. Properties including N-values, factors influencing liquefaction as a cyclic stress, consolidation pressure, structure, and particle composition are considered in this research. Parameters used to evaluate liquefaction potential are obtained through testing. A comprehensive program based on the Chinese code and standard for geological investigation (Ministry of Water Resources of China 1999a; Ministry of Construction of China 2001a) and Seed’s simplified method (Seed and Idriss 1971; in J Geotech Eng Div ASCE 109(3): 458–482, 1983) was carried out to evaluate the potential of liquefaction within the reservoir dam foundation. Liquefaction potentials were also assessed in response to the Chinese codes for seismic design (Hydropower Research Institute of China 2000; Ministry of Construction of China 2001b). The evaluation shows that saturated surface silt in the reservoir dam foundations is vulnerable to liquefaction at seismic intensities of VII and above. The two assessment methods are in good agreement with each other, and the research results can provide useful information for the safe construction and normal operation of the reservoir.     

Supersaline and metal-rich brine obtained from the Quaternary Kakkonda Granite by NEDO WD-1a in the Kakkonda geothermal field, Japan

A supersaline, metal-rich brine (ca. 40 weight% total chloride salt) was extracted from 3708 m depth of well WD-1a in the Kakkonda Granite by reverse circulation after a standing time about 196 hours. The estimated borehole temperature exceeds 500 °C near the bottom. Tritium content and the relationship between δD and δ¹⁸O show that the injected borehole fluid (river water) evidently mixed with an isotopically heavy and ancient fluid. The phase analysis showed that a gas phase separated from a brine and that a brine concentrated in the borehole as the borehole temperature recovered after cooling by drilling fluids. We think the original fluid was trapped in the Kakkonda Granite and mixed with the borehole fluid through fine fractures induced by thermal stress. Received: 15 May 1997 / Accepted: 24 September 1997