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.     

杨氏模量和泊松比反射系数近似方程及叠前地震反演

杨氏模量和泊松比等岩石弹性参数是表征页岩气储集体岩石脆性、评价储层含气特征的重要特征参数,而叠前地震反演是从地震资料中获取此类参数的有效途径.地震波反射系数方程是叠前反演的基础.首先,在平面波入射等假设条件下推导了基于杨氏模量(Y)、泊松比(σ)和密度(D)的纵波反射系数线性近似方程(YPD反射系数近似方程),该方程建立了地震纵波反射系数与杨氏模量反射系数、泊松比反射系数和密度反射系数的线性关系;其次,对该方程的精度和适用条件进行了分析,模型分析表明,在入射角为40°时,该方程具有较高的计算精度;最后,建立了一种稳定获取杨氏模量和泊松比的叠前地震直接反演方法.模型试算和实际资料试处理表明,基于新方程的反演方法能够稳定合理的直接从叠前地震资料中获取杨氏模量和泊松比参数,提供了一种高可靠性的页岩气"甜点"地震识别方法.     

阴离子交换柱分离—火焰原子吸收法测定铜精矿中微量金

王水分解后的铜精矿试液中,Ａｕ（Ⅲ）与Ｃｌ－形成稳定的络阴离子。选定顶杯式小型阴离子交换柱,在６０～８０目２０１×７阴离子交换树脂上富集Ａｕ的络阴离子,树脂经灰化处理后用原子吸收光谱仪测定Ａｕ。经标样分析验证,结果与标准值相符。对于ｗ（Ａｕ）在１０－６水平的试样,７次测定的相对标准偏差为１．５％～２．２％。     

Seismic quality factors across a bottom simulating reflector in the Makran Accretionary Prism, Arabian Sea

The hydrate-bearing sediments above the bottom simulating reflector (BSR) are associated with low attenuation or high quality factor (Q), whereas underlying gas-bearing sediments exhibit high attenuation. Hence, estimation of Q can be important for qualifying whether a BSR is related to gas hydrates and free-gas. This property is also useful for identifying gas hydrates where detection of BSR is dubious. Here, we calculate the interval Q for three submarine sedimentary layers bounded by seafloor, BSR, one reflector above and another reflector below the BSR at three locations with moderate, strong and no BSR along a seismic line in the Makran accretionary prism, Arabian Sea for studying attenuation (Q⁻¹) characteristics of sediments. Interval Q for hydrate-bearing sediments (layer B) above the BSR are estimated as 191 ± 11, 223 ± 12, and 117 ± 5, whereas interval Q for the underlying gas-bearing sediments (layer C) are calculated as 112 ± 7, 107 ± 8 and 124 ± 11 at moderate, strong and no BSR locations, respectively. The large variation in Q is observed at strong BSR. Thus Q can be used for ascertaining whether the observed BSR is due to gas hydrates, and for identifying gas hydrates at places where detection of BSR is rather doubtful. Interval Q of 98 ± 4, 108 ± 5, and 102 ± 5, respectively, at moderate, strong and no BSR locations for the layer immediately beneath the seafloor (layer A) show almost uniform attenuation.     

苏里格气田苏54区块储层孔隙结构特征研究

鄂尔多斯盆地苏里格气田是我国最大的气田,但是储层岩性较为致密,已成为制约天然气勘探开发的主要因素,因此,开展储层孔隙结构特征研究对于该区天然气生产具有重要意义。通过扫描电镜、薄片鉴定、压汞、铸体薄片等分析测试方法对苏里格气田苏54区块储层微观孔隙结构进行了深入分析。结果表明：该区储层由北到南主要发育岩屑砂岩、岩屑质石英砂岩和石英砂岩;喉道半径普遍较小,孔喉分选较差,且以细孔径为主,孔喉连通性中等;孔渗普遍偏低,属低孔低渗,孔渗明显受沉积相带的控制,高孔渗区呈贯穿南北的条带状分布,与河道展布特征近似。研究表明物性高值区连片分布,东部好于西部,盒8下物性最好。     

Mud volcanic natural phenomena in the South Caspian Basin: geology,fluid dynamics and environmental impact

The South Caspian sedimentary basin is a unique area with thick Mesozoic-Cenozoic sediments (up to 30–32 km) characterized by an extremely high fluid generation potential. The large amount of active mud volcanoes and the volumes of their gas emissions prove the vast scale of fluid generation. Onshore and offshore mud volcanoes annually erupt more than 10⁹ cubic meters of gases consisting of CH₄ (79–98%), and a small admixture of C₂H₆, C₃H₈, C₄H₁₀, C₅H₁₂, CO₂, N, H₂S, Ar, He. Mud volcanism is closely connected to the processes occurring in the South Caspian depression, its seismicity, fluctuations of the Caspian Sea level, solar activity and hydrocarbon generation.The large accumulations of gas hydrates are confined to the bottom sediments of the Caspian Sea, mud volcanoes crater fields (interval 0–0.4 m, sea depth 480 m) and to the volcanoes body at the depth of 480–800 from the sea bottom. Resources of HC gases in hydrates saturated sediments up to a depth of 100 m and are estimated at 0.2×10¹⁵–8×10¹⁵ m³. The amount of HC gases concentrated in them is 10¹¹–10¹² m³.The Caspian Sea, being an inland closed basin is very sensitive to climatic and tectonic events expressed in sea level fluctuations. During regressive stages as a result of sea level fall and the reducing of hydrostatic pressure the decomposition of gas hydrates and the releasing of a great volume of HC gases consisting mainly of methane are observed.From the data of deep drilling, seismoacoustics, and deep seismic mud volcanic activity in the South Caspian Basin started in the Lower Miocene. Activity reached its highest intensity at the boundary between the Miocene and Pliocene and was associated with dramatic Caspian Sea level fall in the Lower Pliocene of up to 600 m, which led to the isolation of the PaleoCaspian from the Eastern ParaTethys. Catastrophic reduction of PaleoCaspian size combined with the increasing scale of mud volcanic activity caused the oversaturation and intoxication of water by methane and led to the mass extinction of mollusks, fishes and other groups of sea inhabitants. In the Upper Pliocene and Quaternary mud volcanism occurred under the conditions of a semi-closed sea periodically connected with the Pontian and Mediterranean Basins. Those stages of Caspian Sea history are characterized by the revival of the Caspian organic world.Monitoring of mud volcanoes onshore of the South Caspian demonstrated that any eruption is predicted by seismic activation in the region (South-Eastern Caucasus) and intensive fluid dynamics on the volcanoes.     

海上高分辨率地震实例研究

在莺歌海盆地油气勘探中,应用高分辨率地震资料评价ＤＦ１一１气田,探明了储集层顶面的水道冲蚀,给出了正确的气田地质模式;并应用高分辨率地震资料做气藏描述,比较准确地估算了储集层的厚度与孔隙度,减少了评价井数．应用高分辨率地震的亮点加平点技术,在原认为是空构造的ＬＤ８一１构造发现了高产天然气。理论和实践都表明,若要得到高分辨率的地震资料,提高地震子波的频率是很重要的,但保护低频比提高高频更重要。高分辨率地震波阻抗剖面比地震偏移剖面更直接、更清晰地反映地下地质情况,直接用波阻抗剖面做地震解释和油藏描述可得到更好的效果。     

谱睿在线除氯技术检测高氯水样中的阴离子

采用戴安公司谱睿(Pre)在线样品前处理技术,使用高容量在线Ag柱和Na柱,开发出了一种柱前去除高氯基体中氯离子的在线分析方法。操作简便,且适用样品范围广;不更换Ag柱可耐受10 g/L NaCl基体,25μL连续进样400针,氯离子去除效率可保持在99%以上。系统选用高容量IonPac AS11-HC氢氧根体系阴离子交换色谱柱,在线淋洗液自动发生装置进行梯度淋洗,用抑制型电导检测。对食盐、分析纯氯化钠等不同基体进行检测,可实现样品在线除氯,并可检测其中不高于10μg/L的溴酸根、氯酸根、亚硝酸根、硝酸根和硫酸根等离子。不同离子校准曲线相关系数均在99.8%以上,加标回收率为80%~110%。该技术具有操作简单、可重复性强、方法新颖等特点,解决了以往高氯基体检测成本过高、适用范围有限、前处理操作复杂等问题。     

南海神狐峡谷群海底沉积物摩擦特性

海底滑坡区沉积物的摩擦特性对滑坡发育具有控制作用, 是海底边坡稳定性评估、滑坡过程中温压场演化及与滑坡相关的水合物成藏规律研究的基础参数.我国南海北部陆坡区不仅赋存着丰富水合物资源, 而且在地质历史上也曾多次发生滑坡作用, 目前仍是潜在的海底滑坡区.为了尽可能了解南海北部滑坡区沉积物的原位摩擦特性, 本文在围压P_c=20 MPa、孔隙压P_p=10 MPa及温度T≈20 ℃条件下, 对采自南海神狐峡谷群的4个沉积物样品开展了三轴准静态摩擦滑动实验.实验结果表明神狐峡谷群浅层沉积物: (1) 均呈现速度强化及位移强化特征; (2) 最大静摩擦系数μ_max为0.460~0.510, 稳态摩擦系数μ_ss为0.455~0.554, 二者的变化趋势较一致; (3) 内聚力c为0.30~0.57 MPa、摩擦角φ为24.5°~27.0°.而神狐峡谷群地形坡度较缓(＜6.8°).现今神狐峡谷群仅在沉积物自重作用下不会发生失稳, 总体上比较稳定.结合峡谷群多期次的滑坡特征以及滑坡体与水合物稳定域底界(通常与似海底反射层(Bottom simulating reflector, 简写BSR)重叠)、气烟囱等构造的空间分布关系, 我们推测: 神狐峡谷群滑坡的形成主要是由于BSR附近地层孔隙压升高、强度降低, 进而导致失稳.BSR附近地层孔隙压升高则可能是由于深部热成因游离气的聚集、BSR附近的水合物在地震等对其温、压场的扰动下分解所致.

     

Quantitative gas saturation estimation by frequency‐dependent amplitude‐versus‐offset analysis

Seismic amplitudes contain important information that can be related to fluid saturation. The amplitude‐versus‐offset analysis of seismic data based on Gassmann's theory and the approximation of the Zoeppritz equations has played a central role in reservoir characterization. However, this standard technique faces a long‐standing problem: its inability to distinguish between partial gas and “fizz‐water” with little gas saturation. In this paper, we studied seismic dispersion and attenuation in partially saturated poroelastic media by using frequency‐dependent rock physics model, through which the frequency‐dependent amplitude‐versus‐offset response is calculated as a function of porosity and water saturation. We propose a cross‐plotting of two attributes derived from the frequency‐dependent amplitude‐versus‐offset response to differentiate partial gas saturation and “fizz‐water” saturation. One of the attributes is a measure of “low frequency”, or Gassmann, of reflectivity, whereas the other is a measure of the “frequency dependence” of reflectivity. This is in contrast to standard amplitude‐versus‐offset attributes, where there is typically no such separation. A pragmatic frequency‐dependent amplitude‐versus‐offset inversion for rock and fluid properties is also established based on Bayesian theorem. A synthetic study is performed to explore the potential of the method to estimate gas saturation and porosity variations. An advantage of our work is that the method is in principle predictive, opening the way to further testing and calibration with field data. We believe that such work should guide and augment more theoretical studies of frequency‐dependent amplitude‐versus‐offset analysis.