Permeability characteristics of lime treated marine clay

An attempt has been made to investigate the lime induced permeability changes in the permeability and engineering behavior of different lime column treated soil systems. Lime columns treated marine clay shows an increase in permeability up to a maximum value of 15–18 times that of untreated soil with time. The shear strength of the treated soil systems show an increment up to 8–10 that of untreated soil within a period of 30–45 days curing. In the case of lime injection systems, the permeability has been increased up to 10–15 times that of untreated soil, whereas the strength of the soil has been higher by 8–10 times that of untreated soil. Further, consolidation tests show a reduction in the compressibility up to 1/2–1/3 of original values. The test results revealed that both lime column and injection techniques could be used to improve the behaviour of underwater marine clay deposits.     

一种缝洞型碳酸盐岩储层胶结指数m计算新方法

碳酸盐岩储集空间类型多样、孔隙结构复杂,具有很强的非均质性,使得传统的阿尔奇公式应用效果不佳,主要原因之一在于胶结指数m的无法准确确定.基于多孔介质理论,在深入分析不同孔隙空间对储层导电贡献外,进一步考虑了孔隙形态对导电性能的影响,尤其是裂缝倾角,进而给出了全新的计算胶结指数m的方法,并深入剖析组成碳酸盐岩复杂孔隙空间的各部分对胶结指数m的影响.认为对于物性较差的缝洞型储层,裂缝倾角对胶结指数m的影响很大,当裂缝角度较小时,裂缝会使胶结指数m变小,而当裂缝角度较大时,裂缝反而会使胶结指数m变大;当储层物性很好时,裂缝倾角的影响则可以忽略.实际应用表明,利用基于裂缝倾角的多孔介质模型得到的胶结指数m所计算的含水饱和度精度相比传统方法有较大提高,且该方法适用于任何类型的储层,具有很好的应用性.     

油气充注对成岩作用的影响

油气充注对成岩作用的影响有三个方面 :抑制石英和伊利石的胶结作用、油气中所有机酸对深部孔隙的溶蚀改造作用、油气超压对压实的缓冲作用。英国北海Miller油气藏等的资料显示 ,油气充注较早时 ,油区的石英胶结速率比水区的明显要低 ,石英的胶结丰度比一般预测值低 ,而孔隙度比一般的预测值要高。我国渤海湾盆地东营凹陷油田资料显示 ,无论浅部或深部 ,凡是含油砂岩 ,其长石类及碳酸盐类矿物的溶解都十分强烈 ,次生孔隙很发育 ,而不含油的砂岩 ,其矿物溶解及次生孔隙发育一般较差 ;油层的方解石、白云石含量一般比水层低 ,深层尤为明显。干酪根生成油气时的流体体积增加 ,可大大增加孔隙流体压力 ,产生超压 ,并可传递到储集层 ,因而大大增加对压实作用的抵抗能力。上述三方面实质上都为深部油气成藏改善了储层基础 ,对深部油气勘探具有非常现实的意义。     

Physical chemical analysis of marine sediment cementation from the Gulf of Guinea

This study aims at investigating the cementation of marine sediments from the Gulf of Guinea by using physicochemical analysis. In order to highlight the presence of cementation in the sediments, three conventional consolidation tests were conducted on intact and remoulded samples. Mercury intrusion porosimetry analyses were then carried out on the specimens taken from samples after consolidation tests. Several physicochemical experimental techniques were used to analyze these cementations, such as cation exchange capacity analysis, batch test, scanning electron microscope imaging coupled with EDS chemical analysis, and thermal analysis. The results seem to indicate that the cementation of these sediments is predominated by the presence of smectite gel between clay aggregates (clusters). Finally, a conceptual sediment microstructural model is proposed to describe the cementation.     

Authigenic dolomite cementation in the Upper Cretaceous Phosphate Formation, Western Desert, Egypt

The Upper Cretaceous Phosphate Formation in the Western Desert of Egypt displays a characteristic facies association that includes marine phosphorites interbedded with black shales and glauconitic sandstones. The upper part of the formation is characterized by the presence of thin phosphatic beds, which are filled-extensively-with disordered and non stoichiometric (mean MgCO₃ = 41.4 ± 0.34 mol%) authigenic dolomite cement. SEM and the back scattered images of these coarse crystalline dolomite cements reveal that they display planar euhedral crystal boundaries, polymodal crystal size distribution and variable inclusion pattern. The relatively low and wide ranged δ¹⁸O (− 0.87 to − 4.15‰ VPDB) values of the dolomite cements coupled with their depleted Sr (mean = 187 ± 26 ppm) and high iron and manganese values (mean = 6851 ± 554 ppm and 11599 ± 229 ppm respectively) invoke that they were formed from mixed hypo-saline fluids within a mixing marine-meteoric zone probably during a low stand period at the vicinity of the Maastrichtian/Early Tertiary unconformity. Meanwhile, their negative δ¹³C (− 1.31 to − 3.56‰ VPDB) values argue for a possible involvement of isotopically light carbon, derived from degradation of organic matter, during their precipitation.     

Microfabric, chemical and mineralogical study of Indian marine clays

Marine clay deposits are encountered in the coastal regions of the world. They are soft in consistency with low shear strength and are highly compressible. The properties of these deposits are complex and diverse, and they mainly depend on the minerals present and microstructural arrangement of constituent particles. In the present investigation, the physico-chemical properties of the sediment samples obtained from marine deposits of east and west metropolitan coastal cities of India are discussed, and the test results obtained are compared with the synthetic samples such as bentonite and kaolinite. Mineralogical and fabric studies were carried out using scanning electron microscopy and x-ray diffraction techniques. Several consolidation and strength tests were carried out to study the engineering behaviour of these deposits. The strength and compressibility (Cc) values of these deposits varies from 27 to 45 kN/m² and 0.37 to 0.81 respectively. XRD studies confirm the presence of highly compressible clay minerals such as smectite, vermiculite, chlorite and traces of the low swelling mineral, kaolinite. The fabric studies indicate that the constituent particles were arranged in an open network, or flocculated structure resulting in a high void ratio.     

磷块岩的胶结作用

磷块岩胶结物有泥质、硅质、磷质和碳酸盐质4种,共形成19种胶结结构,其中尤以磷泥晶环边结构、等厚纤状环边结构、似重力式结构、磷质纤状环边叠加云质亮晶充填结构特征突出,具有指示沉积成岩环境的意义。4种类型的胶结物在剖面和平面上的演变与水体深度和沉积成岩环境有关,而胶结作用的地球化学特征,既是磷块岩的环境指示,又反映微生物的影响状况。     

The mechanical behaviour of synthetic, poorly consolidated granular rock under uniaxial compression

In order to isolate the effect of grain size and cementation on the mechanical behaviour of poorly consolidated granular rock, we prepared synthetic rock samples in which these two parameters were varied independently. Various proportions of sand, Portland cement and water were mixed and cast in a mold. The mixture was left pressure-free during curing, thus ensuring that the final material was poorly consolidated. We used two natural well-sorted sands with grain sizes of 0.22 and 0.8 mm. The samples were mechanically tested in a uniaxial press. Static Young's modulus was measured during the tests by performing small stress excursions at discrete intervals along the stress–strain curves. All the samples exhibited nonlinear elasticity, i.e., Young's modulus increased with stress. As expected, we found that the uniaxial compressive strength increased with increasing cement content. Furthermore, we observed a transition from grain size sensitivity of strength at cement content less than 20–30% to grain size independence above this value. The measured values of Young's modulus are well explained by models based on rigid inclusions embedded in a soft matrix, at high cement content, and on cemented grain-to-grain contacts, at low cement content. Both models predict grain size independence in well-sorted cemented sands. The observed grain size sensitivity at low cement content is probably due to microstructural differences between fine- and coarse-grained materials caused by small differences in grain sorting quality.     

碳酸盐岩储层孔隙结构对电阻率的影响研究

碳酸盐岩储层孔隙类型多样,各种孔隙的尺寸变化范围可以跨越几个数量级,孔隙结构非常复杂,这种复杂孔隙结构和不均匀分布的多元孔隙空间使得储层电性呈现明显非阿尔奇特性.为了了解影响电阻率变化的控制因素,本次研究选取中三叠世雷口坡组的8块全直径碳酸盐岩岩样,开展了核磁共振、岩电实验、孔渗实验、压汞实验及薄片等实验,并利用数字图像分析法定量分析了孔隙结构特征.研究结果表明：①孔隙度是影响电阻率高低的重要因素,但并非唯一因素,除孔隙度以外,孔隙尺寸和数量、孔隙网络复杂程度远比吼道大小对电阻率的影响大;②在孔隙度一定的条件下,胶结指数m随储层中孤立大孔隙占比的增多而增大,当孔隙度增大到一定程度后,胶结指数m又随大孔隙占比的增多而减小,微裂缝起重要沟通作用;③在给定孔隙度时,以简单大孔隙为主的岩样表现为胶结指数m值较大,而以复杂孔隙网络、细小孔隙为主的岩样表现为胶结指数m值较小,具分散、孤立大孔隙的岩样,胶结指数m值最高;④依据孔隙几何参数与电阻率和胶结指数之间的关系,可以利用测井资料间接判别储层类型,从而提高储层有效性和含水饱和度评价精度.