ISA model: A constitutive model for soils with yield surface in the intergranular strain space

In this article, a new constitutive model for soils is proposed. It is formulated by means of plasticity, but in contrast to the precedent works, it presents a yield function describing a surface within the intergranular strain space. This latter is a state variable providing information of the recent strain history. An expression for the plastic strain rate has been proposed to guarantee the stress rate continuity. Under the application of medium or large strain amplitudes, the constitutive equation becomes independent of the intergranular strain and delivers a mathematical structure similar to some Karlsruhe hypoplastic models. Some simulations of monotonic and cyclic triaxial test are provided to evaluate and analyze the model performance. Copyright © 2015 John Wiley & Sons, Ltd.     

Analysis of shaft resistance of jacked piles in sands

In recent years, pile jacking has become a viable alternative installation method for displacement piles. Pile jacking produces minimal noise, vibration and air pollution during installation. In addition, it is possible, at the end of jacking, to have a good estimate of the ultimate static capacity of the pile. In this paper, the shaft resistance of piles jacked into sand is studied using one‐dimensional finite element analysis. The finite element simulations, using a two‐surface plasticity model, demonstrate the effects of relative density and confinement on the unit shaft resistance of piles jacked in sand. The impact of the number of jacking strokes on the unit shaft capacity is also assessed. Based on the numerical results, we developed equations for shaft resistance quantifying the effects of relative density, initial confinement and number of jacking strokes. Predictions using these equations are compared with data obtained from centrifuge tests and field tests. Copyright © 2010 John Wiley & Sons, Ltd.     

济阳坳陷古近系泥页岩成因相划分

系统岩心观察和高密度薄片鉴定等分析测试资料研究结果显示,济阳坳陷沙三下-沙四上泥页岩成分组成及构造类型主要受沉积作用控制,岩石结构特征主要受成岩作用控制。根据泥页岩中方解石成因及重结晶程度,结合岩石成分及构造特征,将济阳坳陷沙三下-沙四上泥页岩划分为沉积主控型、沉积-成岩双控型及成岩主控型三大成因相。沉积主控型分布最为广泛,岩相类型多样,构造特征反映成因环境;沉积-成岩双控型主要见于纹层状岩相,由泥质纹层与显晶粒状方解石纹层互层构成;成岩主控型以柱状、柱纤状方解石垂直层面呈脉状、透镜状产出为特征。成岩主控型和沉积-成岩双控型泥页岩与页岩油气关系密切,是重要的有利成因相类型。     

新疆春风油田石炭系火山岩岩性特征及测井识别方法

不同岩性的火山岩其储集性能差异甚远,准确识别火山岩岩性对于火山岩储层的研究具有重要意义。研究区春风油田石炭系储层以火山岩为主,过渡类型较多,岩性较为复杂。利用岩心观察、薄片鉴定、地化分析等方法确定研究区发育火山熔岩类和火山碎屑岩类两类火山岩,其中,火山熔岩包括玄武岩、安山玄武岩、玄武安山岩以及安山岩,火山碎屑岩有凝灰岩和火山角砾岩等。通过识别出的岩性标定测井,分析每种岩性的测井响应特征,利用交会图法和星形图法,建立了不同岩性的识别标准。     

Application research of enhanced in-situ micro-ecological remediation of petroleum contaminated soil

Experimental study of enhanced in-situ micro-ecological remediation of petroleum contaminated loess soil was carried out in Zhongyuan oil production areas, and the enhanced in-situ micro-ecological remediation technique includes optimistic in-situ microbial communities, physical chemistry methods, alfalfa planting and regulation of soil environmental elements. Experiments showed that the oil content in the contaminated soil with oil content about 2 898.25 mg/kg can be reduced about 98.61% after in-situ micro-ecological remediation for 99 days, which demonstrated the effectiveness of in-situ micro-ecological remediation methods for petroleum contaminated soil in central plains of China, and explored the practical and feasible application of these methods.     

Controls on reservoir heterogeneity of tight sand oil reservoirs in Upper Triassic Yanchang Formation in Longdong Area,southwest Ordos Basin,China: Implications for reservoir quality prediction and oil accumulation

Compared to conventional reservoirs, pore structure and diagenetic alterations of unconventional tight sand oil reservoirs are highly heterogeneous. The Upper Triassic Yanchang Formation is a major tight-oil-bearing formation in the Ordos Basin, providing an opportunity to study the factors that control reservoir heterogeneity and the heterogeneity of oil accumulation in tight oil sandstones.The Chang 8 tight oil sandstone in the study area is comprised of fine-to medium-grained, moderately to well-sorted lithic arkose and feldspathic litharenite. The reservoir quality is extremely heterogeneous due to large heterogeneities in the depositional facies, pore structures and diagenetic alterations. Small throat size is believed to be responsible for the ultra-low permeability in tight oil reservoirs. Most reservoirs with good reservoir quality, larger pore-throat size, lower pore-throat radius ratio and well pore connectivity were deposited in high-energy environments, such as distributary channels and mouth bars. For a given depositional facies, reservoir quality varies with the bedding structures. Massive- or parallel-bedded sandstones are more favorable for the development of porosity and permeability sweet zones for oil charging and accumulation than cross-bedded sandstones.Authigenic chlorite rim cementation and dissolution of unstable detrital grains are two major diagenetic processes that preserve porosity and permeability sweet zones in oil-bearing intervals. Nevertheless, chlorite rims cannot effectively preserve porosity-permeability when the chlorite content is greater than a threshold value of 7%, and compaction played a minor role in porosity destruction in the situation. Intensive cementation of pore-lining chlorites significantly reduces reservoir permeability by obstructing the pore-throats and reducing their connectivity. Stratigraphically, sandstones within 1 m from adjacent sandstone-mudstone contacts are usually tightly cemented (carbonate cement > 10%) with low porosity and permeability (lower than 10% and 0.1 mD, respectively). The carbonate cement most likely originates from external sources, probably derived from the surrounding mudstone. Most late carbonate cements filled the previously dissolved intra-feldspar pores and the residual intergranular pores, and finally formed the tight reservoirs.The petrophysical properties significantly control the fluid flow capability and the oil charging/accumulation capability of the Chang 8 tight sandstones. Oil layers usually have oil saturation greater than 40%. A pore-throat radius of less than 0.4 μm is not effective for producible oil to flow, and the cut off of porosity and permeability for the net pay are 7% and 0.1 mD, respectively.     

Geological control factors of micro oil distribution in tight reservoirs

Understanding the oil distribution characteristics in unconventional tight reservoirs is crucial for hydrocarbon evaluation and oil/gas extraction from such reservoirs. Previous studies on tight oil distribution characteristics are mostly concerned with the basin scale. Based on Lucaogou core samples, geochemical approaches including Soxhlet extraction, total organic carbon (TOC), and Rock-Eval are combined with reservoir physical approaches including mercury injection capillary pressure (MICP) and porosity-permeability analysis, to quantitatively evaluate oil distribution of tight reservoirs on micro scale. The emphasis is to identify the key geological control factors of micro oil distribution in such tight reservoirs. Dolomicrites and non-detrital mudstones have excellent hydrocarbon generation capacity while detritus-containing dolomites, siltstones, and silty mudstones have higher porosity and oil content, and coarser pore throat radius. Oil content is mainly controlled by porosity, pore throat radius, and hydrocarbon generation capacity. Porosity is positively correlated with oil content in almost all samples including various lithologies, indicating that it is a primary constraint for providing storage space. Pore throat radius is also an important factor, as oil migration is inhibited by the capillary pressure which must be overcome. If the reservoir rock with suitable porosity has no hydrocarbon generation capacity, pore throat radius will be decisive. As tight reservoirs are generally characterized by widely distributed nanoscale pore throats and high capillary pressure, hydrocarbon generation capacity plays an important role in reservoir rocks with suitable porosity and fine pore throats. Because such reservoir rocks cannot be charged completely. The positive correlation between hydrocarbon generation capacity and oil content in three types of high porosity lithologies (detritus-containing dolomites, siltstones, and silty mudstones) supports this assertion.     

江汉平原古生界构造结构特征及油气勘探方向

江汉平原古生界具有北西—南东向分为三块、北东—南西向分为三带及纵向上多层楼的构造结构特征。三个区块为当阳—京山构造区、荆州—仙桃构造区及鄂城—大冶构造区,每个区块均可划分出三个次级构造带,并在全区形成三个构造变形分带。这三个分带在变形强度、构造样式等方面具有特征性差异:北东侧的构造分带受东秦岭—大别山造山运动产生的挤压应力的直接作用,显示以逆冲推覆结构为主要特征;南西侧的构造分带在三个构造区有差别,在当阳—京山构造区形成斜坡稳定带,在另两个构造区则以推覆叠瓦构造为特征;中部构造分带一般显示前缘断褶或复合叠加构造。当阳—京山构造区东部和鄂城—大冶构造区应以逆冲推覆体为勘探对象;荆州—仙桃构造区的仙桃地区应以上古生界油气藏为勘探目标;当阳—京山构造区西部宜昌稳定带和荆州—仙桃构造区的珂理—簰洲地区则应以下古生界油气藏为勘探目标。     

油藏地球化学原理及其在油气勘探与油藏评价中的应用

综合评述了近年来油藏地球化学基础研究方面的主要进展,包括油气藏内流体非均质性成因、烃充注成藏及混合作用模式、储层内流体与岩石相互作用、油藏内烃的地球化学变化等,阐述了烃族群划分及其地球化学意义。结合实例介绍了油藏地球化学在油气勘探、油藏评价与油田生产管理中的主要应用领域与研究现状。在油气勘探领域的应用主要包括烃运移方向的地球化学研究、烃成藏时间及期次的确定、古油水界面的判别等;在油藏评价和油田生产管理方面的应用主要有油藏流体的连通性和分隔性研究、混合开采油藏单层产能贡献研究以及油、水、干层的地球化学识别等。     

泥质砂岩复电阻率的频散特性实验

不同孔隙流体特性的岩石复电阻率频散实验,是复电阻率测井资料评价水淹层和低阻油层的岩石物理基础。通过水驱水、水驱油、油驱水的岩石复电阻率频散特性的实验研究,发现泥质砂岩的复电阻率频散特性受含油饱和度的影响较大,受地层水矿化度的影响较小,尤其是异相电阻率,受地层水矿化度的影响更小;与含水泥质砂岩相比,含油泥质砂岩的相角相对较大,且随着含油饱和度的增加而增大;含水岩石和含油岩行在频散特性上存在着较大差异。实验研究结果表明,利用基于岩石频散特性发展起来的复电阻率测井技术,可以有效地识别油水层。