Thermo-sensitive polymer nanospheres as a smart plugging agent for shale gas drilling operations

Emulsifier-free poly（methyl methacrylate-styrene） [P（MMA-St）] nanospheres with an average particle size of 100 nm were synthesized in an isopropyl alcoholwater medium by a solvothermal method. Then, through radical graft copolymerization of thermo-sensitive mono- mer N-isopropylacrylamide （NIPAm） and hydrophilic monomer acrylic acid （AA） onto the surface of P（MMA- St） nanospheres at 80 ℃, a series of thermo-sensitive polymer nanospheres, named SD-SEAL with different lower critical solution temperatures （LCST）, were prepared by adjusting the mole ratio of NIPAm to AA. The products were characterized by Fourier transform infrared spectroscopy, transmission electron microscopy, thermogravimetric analysis, particle size distribution, and specific surface area analysis. The temperature-sensitive behavior was studied by light transmittance tests, while the sealing performance was investigated by pressure transmission tests with Lungmachi Formation shales. The experimental results showed that the synthesized nanoparticles are sensitive to temperature and had apparent LCST values which increased with an increase in hydrophilic monomer AA. When the temperature was higher than its LCST value, SD- SEAL played a dual role of physical plugging and chemical inhibition, slowed down pressure transmission, and reduced shale permeability remarkably. The plugged layer of shale was changed to being hydrophobic, which greatly improved the shale stability

Stress redistribution in multi-stage hydraulic fracturing of horizontal wells in shales

Multi-stage hydraulic fracturing of horizontal wells is the main stimulation method in recovering gas from tight shale gas reservoirs, and stage spacing deter- mination is one of the key issues in fracturing design. The initiation and propagation of hydraulic fractures will cause stress redistribution and may activate natural fractures in the reservoir. Due to the limitation of the analytical method in calculation of induced stresses, we propose a numerical method, which incorporates the interaction of hydraulic fractures and the wellbore, and analyzes the stress distri- bution in the reservoir under different stage spacing. Simulation results indicate the following： （1） The induced stress was overestimated from the analytical method because it did not take into account the interaction between hydraulic fractures and the horizontal wellbore. （2） The hydraulic fracture had a considerable effect on the redis- tribution of stresses in the direction of the horizontal wellbore in the reservoir. The stress in the direction per- pendicular to the horizontal wellbore after hydraulic frac- turing had a minor change compared with the original in situ stress. （3） Stress interferences among fractures were greatly connected with the stage spacing and the distance from the wellbore. When the fracture length was 200 m, and the stage spacing was 50 m, the stress redistribution due to stage fracturing may divert the original stress pat- tern, which might activate natural fractures so as to generate a complex fracture network.

A rock physics model for the characterization of organic-rich shale from elastic properties

Kerogen content and kerogen porosity play a significant role in elastic properties of organic-rich shales. We construct a rock physics model for organic-rich shales to quantify the effect of kerogen content and kerogen porosity using the Kuster and Toks6z theory and the selfconsistent approximation method. Rock physics modeling results show that with the increase of kerogen content and kerogen-related porosity, the velocity and density of shales decrease, and the effect of kerogen porosity becomes more obvious only for higher kerogen content. We also find that the Poisson＇s ratio of the shale is not sensitive to kerogen porosity for the case of gas saturation. Finally, for the seismic reflection responses of an organic-rich shale layer, forward modeling results indicate the fifth type AVO re- sponses which correspond to a negative intercept and a positive gradient. The absolute values of intercept and gradient increase with kerogen content and kerogen porosity, and present predictable variations associated with velocities and density.

Simulation and visualization of the displacement between CO2 and formation fluids at pore-scale levels and its application to the recovery of shale gas

This article reports recent developments and advances in the simulation of the CO2-formation fluid displacement behaviour at the pore scale of subsurface porous media. Roughly, there are three effective visualization approaches to detect and observe the CO2-formation fluid displacement mechanism at the micro-scale, namely, magnetic resonance imaging, X-ray computed tomography and fabricated micromodels, but they are not capable of investigating the dis- placement process at the nano-scale. Though a lab-on-chip approach for the direct visualization of the fluid flow behaviour in nanoscale channels has been developed using an advanced epi-fluorescence microscopy method combined with a nanofluidic chip, it is still a qualitative analysis method. The lattice Boltzmann method （LBM） can simulate the CO2 displacement processes in a two-dimensional or three-dimensional （3D） pore structure, but until now, the CO2 displace- ment mechanisms had not been thoroughly investigated and the 3D pore structure of real rock had not been directly taken into account in the simulation of the CO2 displacement process. The status of research on the applications of CO2 displacement to enhance shale gas recovery is also analyzed in this paper. The coupling of molecular dynamics and LBM in tandem is proposed to simulate the CO2-shale gas displacement process based on the 3D digital model of shale obtained from focused ion beams and scanning electron microscopy.

Influence of gas transport mechanisms on the productivity of multi-stage fractured horizontal wells in shale gas reservoirs

In order to investigate the influence on shale gas well productivity caused by gas transport in nanometer- size pores, a mathematical model of multi-stage fractured horizontal wells in shale gas reservoirs is built, which considers the influence of viscous flow, Knudsen diffusion, surface diffusion, and adsorption layer thickness. A dis- crete-fracture model is used to simplify the fracture mod- cling, and a finite element method is applied to solve the model. The numerical simulation results indicate that with a decrease in the intrinsic matrix permeability, Knudsen diffusion and surface diffusion contributions to production become large and cannot be ignored. The existence of an adsorption layer on the nanopore surfaces reduces the effective pore radius and the effective porosity, resulting in low production from fractured horizontal wells. With a decrease in the pore radius, considering the adsorption layer, the production reduction rate increases. When the pore radius is less than 10 nm, because of the combined impacts of Knudsen diffusion, surface diffusion, and adsorption layers, the production of multi-stage fractured horizontal wells increases with a decrease in the pore pressure. When the pore pressure is lower than 30 MPa, the rate of production increase becomes larger with a decrease in pore pressure.

Preparation of Single Phase Na-X Zeolite from Oil Shale Ash by Melting Hydrothermal Method

A single phrase Na - X zeolite was synthesized from pretreated oil shale ash by alkaline fusion and hydrotherreal treatment. Eff3cts of the NaOH concentration, crystallization time ant temperature on the formation of Na-X zeolite were studied in detail. The single phase Na- X zeolite powders can. be prepared by alkaline fusion o.f pretreated oil shale ash at 600 ℃ .for 1 h, and crystalli-zation at 80 - 100 ℃ .for 8 - 10 h with NaOH concentration of 3 -3. 5 tool · L-1. Na - A zeolite appears when decreasing NaOH concentration, crystallization time or temperature, ant an unnamed zeolite emerges when prolonging crystallization time or raising crystalli-zation, temperature. SEM micrographs suggest that the aggregates of Na-X zeolite particles have perfect dispersity and uniform granular with about 1.5 μm in size, and most of the Na-X zeolite crystals display a regular octahedral structure with the size of about 500 nm. The specific surface area of the powders with single Na-X zeolite phase reaches the maximum value of 488. 163 2 m2· g -1, larger than that of multiple zeolite powders.

改进的砂泥岩地层中断裂封闭性评价SGR法及应用

SGR法评价断裂在砂泥岩地层中侧向封闭性时,通常采用统计得到的常数作为下限值,导致评价结果与勘探实践存在着较大的偏差。针对上述问题,采用断裂倾角、断层岩压实成岩时间、目的储层泥质含量和压实成岩时间,确定断裂在砂泥岩地层中侧向封闭所需的最小断层岩泥质含量。研究表明:最小断层泥质含量是基于封闭机理所求的一个变值,解决了SGR法统计采用常数值存在偏差的问题,有效提高了侧向封闭性评价的准确性。将该方法应用于海拉尔盆地贝尔凹陷西部呼和诺尔构造带F3断裂在南二段砂泥岩储层的侧向封闭性评价,获得了测点5、7、8和12—15处F3断裂在南二段砂岩储层内侧向封闭,而其余测点处侧向不封闭的重要认识。该认识与油气主要分布在测点7、8、12、14处的情况吻合。研究成果对含油气盆地砂泥岩地层断层型油气藏分布特征及指明油气勘探方向具有重要借鉴意义。

Nanopore structure comparison between shale oil and shale gas:examples from the Bakken and Longmaxi Formations

In order to analyze and compare the differences in pore structures between shale gas and shale oil formations, a few samples from the Longmaxi and Bakken Formations were collected and studied using X-ray diffraction, LECO TOC measurement, gas adsorption and field-emission scanning electron microscope. The results show that samples from the Bakken Formation have a higher TOC than those from the Longmaxi Formation. The Longmaxi Formation has higher micropore volume and larger micropore surface area and exhibited a smaller average distribution of microsize pores compared to the Bakken Formation. Both formations have similar meso-macropore volume. The Longmaxi Formation has a much larger meso-macropore surface area, which is corresponding to a smaller average meso-macropore size. CO_2 adsorption data processing shows that the pore size of the majority of the micropores in the samples from the Longmaxi Formation is less than 1 nm, while the pore size of the most of the micropores in the samples from the Bakken Formation is larger than 1 nm. Both formations have the same number of pore clusters in the 2–20 nm range, but the Bakken Formation has two additional pore size groups with mean pore size diameters larger than 20 nm. Multifractal analysis of pore size distribution curves that was derived from gas adsorption indicates that the samples from the Longmaxi Formation have more significant micropore heterogeneity and less meso-macropore heterogeneity. Abundant micropores as well as mesomacropores exist in the organic matter in the Longmaxi Formation, while the organic matter of the Bakken Formation hosts mainly micropores.

Pore structure and tracer migration behavior of typical American and Chinese shales

With estimated shale gas resources greater than those of US and Canada combined, China has been embarking on an ambitious shale development program. However, nearly 30 years of American experience in shale hydrocarbon exploration and production indicates a low total recovery of shale gas at 12 %-30 % and tight oil at 5 %-10 %. One of the main barriers to sustainable devel- opment of shale resources, namely the pore structure （ge- ometry and connectivity） of the nanopores for storing and transporting hydrocarbons, is rarely investigated. In this study, we collected samples from a variety of leading hydrocarbon-producing shale formations in US and China. These formations have different ages and geologic char- acteristics （e.g., porosity, permeability, mineralogy, total organic content, and thermal maturation）. We studied their pore structure characteristics, imbibition and saturated diffusion, edge-accessible porosity, and wettability with four complementary tests： mercury intrusion porosimetry, fluid and tracer imbibition into initially dry shale, tracer diffusion into fluid-saturated shale, and high-pressure Wood＇s metal intrusion followed with imaging and ele- mental mapping. The imbibition and diffusion tests use tracer-bearing wettability fluids （API brine or n-decane） to examine the association of tracers with mineral or organic matter phases, using a sensitive and micro-scale elemental laser ablation ICP-MS mapping technique. For two molecular tracers in n-decane fluid with the estimated sizes of 1.39 nm x 0.29 nm x 0.18 nm for 1-iododecane and 1.27 nm ~ 0.92 nm ~ 0.78 nm for trichlorooxobis （triph- enylphosphine） rhenium, much less penetration was observed for larger molecules of organic rhenium in shales with median pore-throat sizes of several nanometers. This indicates the probable entanglement of sub-nano-sized molecules in shales with nano-sized pore-throats. Overall findings from the above innovative approaches indicate the limited accessibility （several millimeters from sample edge） and connectivity of tortuous nanopore spaces in shales with spatial wettability, which could lead to the low overall hydrocarbon recovery because of the limited frac- ture-matrix connection and migration of hydrocarbon molecules from the shale matrix to the stimulated fracture network.

Multiple-stacked Hybrid Plays of lacustrine source rock intervals：Case studies from lacustrine basins in China

Hydrocarbon-producing lacustrine basins are widely developed in the world, and China has a large number of lacustrine basins that have developed since the early Permian. The organic-rich shale-dominated heterogeneous source rock intervals in Chinese lacustrine basins generally contain frequent thin interbeds of stratigraphically associated sandstone, siltstone, marl, dolomite, and limestone. The concept of ‘‘Hybrid Plays＇ ＇ as put forth in this article recognizes this pattern of alternating organicrich shale and organic-lean interbeds and existence of mixed unconventional and conventional plays. Hybrid Plays in lacustrine source rock intervals present a unique closed petroleum system hosting continuous hydrocarbons.The interbedded organic-lean siliciclastic and/or carbonateplays are efficiently charged with hydrocarbons via short migration pathways from the adjacent organic-rich shale that is often also a self-sourced play. We assert ‘‘Hybrid Plays＇ ＇ provide the most realistic exploration model for targeting multiple-stacked and genetically related very tight shale, tight and conventional plays together in the entire source rock interval rather than individual plays only. The Hybrid Play model has been proven and works for a wide variety of lacustrine rift, sag and foreland basins in China.

砂页岩赤红壤磷肥活化效果及其机理研究

应用不同活化剂处理不同性质的磷肥,并对其在砂页岩赤红壤中的生物效应及作用机理进行了研究。结果表明,在砂页岩赤红壤上,施用供试的几种经活化剂处理的磷肥均能显著提高蔬菜生物量。砂页岩赤红壤中的铁、锰质量分数与磷素的有效性有密切的关系,且在还原条件下,土壤铁、锰对磷的固定作用更大;硅、钙可促进土壤中磷的释放。供试活化剂不仅可促进难溶磷的释放,还可控制水溶性磷的释放,使土壤供磷性能平稳;有机活化剂的用量,用于难溶性磷促释时其质量分数为3%,用于水溶性磷控释时其质量分数约为14%。在土壤-植物体系中,活化剂对磷的促释和控释机理是它通过对土壤铁、锰、铝质量分数的调节而实现对磷的活化。

砂页岩山地土壤粒级侵蚀规律的研究

通过对试验实测值的分析研究,认为砂页岩山地土壤粒级侵蚀是有选择性的侵蚀,1～0.25、0.25～0.05和<0.005mm的土壤粒级是侵蚀的高峰粒级。研究结果表明:砂页岩山地土壤有选择性的粒级侵蚀引起土壤沙化和土壤退化。

大丽铁路三叠系松桂组页岩型隧道特征及施工对策

研究目的:大丽铁路三叠系松桂组页岩型隧道具有特定构造环境下的工程条件,破碎页岩遇水软化膨胀等原因易引起初期支护变形,给隧道施工带来较大困难,因此,有必要研究该类围岩特性及隧道施工对策。研究结论:根据页岩(砂质页岩、炭质页岩)的结构特征,提出了相应的施工对策,如对开挖外轮廓进行调整、增大预留变形量、采用三台阶法施工、设置全环工18工字钢架、调整系统锚杆长度、加强监控量测等,这些措施较好地抑制了初期支护变形。

砂页岩山地土壤侵蚀性降雨因子的研究

本文通过对试验小区观测值的分析和研究,认为砂页岩山地土壤侵蚀性降雨因子,主要为降雨量的大小和10min时的瞬时降雨强度。随着降雨量和10min时的瞬时雨强的增大,土壤侵蚀量增加。试验结果表明:砂页岩山地土壤侵蚀的强弱,取决于10min时的瞬时雨强的大小。

沙田柚树施用活化磷肥的效果及机理研究

通过田间试验与室内模拟试验相结合,用相应活化剂处理水溶性P并配成沙田柚专用肥,进一步对其在广东梅县沙田柚产区施用的效果及机理进行研究。结果显示:(1)在沙田柚产区施用含活化P肥的专用肥,能有效改善柚树各生育期的P营养,从而能显著提高柚果产量和品质。(2)在梅县砂页岩赤红壤条件下,土壤中的Fe、Mn与P素有效性关系密切;Si可促进土壤中P的释放,适量的Ca可增加P的活性。(3)供试活化剂可控释水溶性P的释放,使土壤供P性能平稳。(4)在砂页岩赤红壤 植物体系中,活化剂对P的控释机理与不同地带性和不同母质的玄武岩砖红壤一样,是通过对土壤Fe、Mn、Al含量的调节而实现对P的活化。

砂页互层岩坡群锚室内模型实验研究

文章以岩屑粉砂岩夹页岩路基边坡作为模型实验的对象,采用室内模型实验,对均质粉砂岩与粉砂岩夹页岩两种不同岩体的模型试件的群锚效应进行了对比研究,初步分析了群锚极限承载力和变形情况,并对群锚参数的合理选择进行了初步探讨,最后还提出了对实验的局限性及需改进的地方,为进一步的实验打下较为坚实的基础。

羊鸡冲小流域主要雨型对砂页岩坡耕地土壤侵蚀的影响

根据羊鸡冲小流域坡耕地野外径流小区径流泥沙观测数据及降雨特征资料,研究主要雨型对砂页岩坡耕地土壤侵蚀的影响,结果表明:侵蚀性降雨主要发生在6—9月,尤其7月的降雨量、产沙量、降雨侵蚀力最大;依据降雨量、降雨历时、雨强划分的3类雨型,聚类效果较好,3类雨型降雨频率呈C雨型>B雨型>A雨型,单位面积侵蚀量呈B雨型>C雨型>A雨型;B雨型单位面积侵蚀量与雨强、最大30 min雨强呈幂函数关系,C雨型单位面积侵蚀量与降雨量呈幂函数关系;A雨型单位面积侵蚀量与径流系数呈线性相关,C雨型单位面积侵蚀量与径流深呈幂函数关系。

SHALE程序改进及在二维弹塑性流计算中的应用

简要介绍ALE方法。参考SHALE程序，用线积分差分格式代替SHALE程序中的面积积分差分格式，添加了Grüneisen状态方程、弹塑性模型，编制了HEPALE程序。用HEPALE程序对平面碰撞一维问题和圆柱体碰撞固壁二维问题进行了计算，平面碰撞一维问题的计算结果与用冲击波关系式计算得到的值符合得很好；圆柱体碰撞固壁的二维计算图像合理，与用LS-DYNA计算的结果一致。结果表明HEPALE程序对碰撞问题的计算是可行的。