【作者】 王晓梅；

【导师】 王震亮；

【作者基本信息】 西北大学 ， 矿产普查与勘探， 2013， 博士

【摘要】 鄂尔多斯盆地是我国重要的能源生产基地,其上古生界天然气资源主要来自煤系地层,多属致密砂岩气藏范畴。近年来的勘探、开发实践表明,在多个天然气开发区见到不同程度的产水现象,气、水分布规律复杂,流体的赋存特征、成藏机制研究尚需进一步深化。故本研究既可探索致密砂岩中流体的赋存规律,也为揭示天然气成藏机制提供了重要依据,具有较为重要的理论和实践意义。论文将储层的微观孔隙结构与油气的动态成藏过程相结合,选择盆地西部的鄂托克旗、东部的榆林-子洲地区作为解剖对象,并进行了对比研究。根据1000余口井的地质、测井、试气及动态资料,采用岩心观察、水化学成分分析、压汞测试和相对渗透率参数等分析测试手段,剖析、讨论了影响流体分布的宏观和微观地质因素,在此基础上探讨了鄂尔多斯盆地上古生界天然气藏的形成机制。研究表明,鄂尔多斯盆地上古生界内流体的宏观分布具有明显的差异性。下部成藏组合产气区主要在伊陕斜坡东部连片分布,伊盟隆起和产气区西南部主要产水；中部成藏组合产气区主要分布在伊陕斜坡西部,在伊盟隆起和产气区西部主要产水；上部成藏组合产气区主要在伊陕斜坡西部小范围分布。该盆地上古生界产出水以正常地层水为主。氢、氧同位素和溴的研究显示,盆地西部鄂托克旗地区地层水源于经过强烈水-岩作用和蒸发浓缩作用的陆相成因水。该区地层水封闭条件好,有利于天然气聚集和保存。结合盖层分析,该区地层水主要是弱动力成藏过程中的残余地层水。分析了天然气和地层水所在砂岩在沉积相、成岩相、地层压力和储层微观孔隙结构等方面的差异性。东部子洲地区山2段天然气主要赋存在孔隙结构中等的储层内,中值孔喉半径平均为0.51μm,个别优质储层孔喉半径大但分选性差；地层水主要赋存在中值孔喉半径平均为1.0μm、分选性好的主河道构造下倾部位,产出水类型以自由水为主。西部鄂托克旗地区盒8段产气井储层的中值孔喉半径、孔隙度和渗透率与气水同产井相似,产气区内储层物性越好,含气饱和度越高；产水井主要表现为气水同产,产出水类型以毛细管水为主。盆地上古生界不同含气组合均具有垂向运移成藏的特征。盆地东部下部含气组合山2段源储剩余压力差达5.99MPa,油气充注动力大且孔隙结构较好：盆地西部鄂托克旗地区盒8段源储剩余压力差为4.76MPa,天然气充注动力较弱且孔隙结构较差,决定了两个地区流体分布特征迥异。更多还原

【Abstract】 The Ordos basin is one of the main bases for energy production in China. The natural gas resource in this basin is mainly derived from the Upper Paleozoic coal-bearing strata, which is mainly belonged to tight sandstone gas reservoir. According to exploration and production practical in recent years, the distribution and occurrence characteristics of natural gas in this basin is very complicated, for water production phenomenon is common in many production areas, so it’s difficult to clarify the distribution of natural gas and formation water underground. The phenomenon of high formation water production not only seriously constrains the improvement of natural gas production, but also blocks the arrangement of exploration disposition. Seeking for the occurrence rule of fluids in tight sandstone is one of the hot topics in the field of petroleum geology, which can provide key evidences for exposing the mechanism of natural gas accumulation. Therefore, this study is important either in practical aspect or in theoretical aspect.The idea to combine the dynamic accumulation processes and static microcosmic pore framework of reservoir is employed in this study. Two case study areas i.e. Otog gas field in the west and Yulin-Zizhou gas field in the eastern Ordos basin are chosen to anatomizing and comparing study. The main technical data include drilling, wire-line logging, gas test and dynamic data based on more than1000boreholes, as well as core description, water geochemistry analysis, physical parameters examination for rock and so on. Macro and micro distribution characteristics of different type of fluids in natural gas reservoir, as well as the factors affecting the distribution of fluid are analyzed. As a result the forming mechanism of natural gas reservoir in Upper Paleozoic in the Ordos basin is discussed.It’s concluded that the fluids distribution in the Upper Paleozoic reservoirs show obvious heterogeneity in macro aspect. For the lower accumulation association, the gas-producing area is mainly continuously distributed in the eastern Yishan slope, while the major water-producing areas are located in the Yimeng uplift and to the southwest of the main gas-producing area. For the middle accumulation association, the main gas-producing area is located in the western Yishan slope, while the major water-producing areas are located in the Yimeng uplift and to the west of the main gas-producing area. The main gas-producing area in the upper accumulation association is sparsely distributed in the western Yishan slope.It’s showed that the water production derived from the Upper Paleozoic in the Ordos basin mainly belongs to normal formation water. Combined the hydrogen and oxygen isotope examination and the rare bromine element analysis, it’s indicated that the formation water in the Otog Banner of the western Ordos basin, is derived from continental origination, which experienced intense water-rock interaction and evaporation-concretion processes. The characteristics of formation water chemistry reveal that the formation water in this area has good closed condition and is propitious to natural gas accumulation and conservation. Combined with the analysis of hydrocarbon accumulation elements, the formation water type in the Otog Banner area mainly belongs to residual formation water forming in the weak accumulation processes.Compared the differentiation of hosted sandstones for natural gas and formation water in aspects of sedimentary facies, diagenesis facies, strata pressure and micro pore framework of reservoir, two conclusions are showed as follow. With respect to the second member of Shanxi Formation in Zizhou area, eastern Ordos basin, natural gas mainly hosted in pore framework with medium size. The mean pore throat radius is0.51μm. A few reservoirs have large pore throat radius while bad sizing. The formation water is mainly hosted in the down-dip part of major channel sand bodies with mean pore throat radius of1.Oμm and well sizing. The type of formation water is mainly belonged to free water and served as edge-bottom water. With respect to the eighth member of Lower Shihezi Formatin, in Otog area, western Ordos basin, there has similarity between the gas-producing wells and water-producing wells in aspects of medium pore throat radius, porosity and permeability. In the gas-producing areas, the better physical properities are corresponded with higher gas saturation. The water-producing wells are usually found to produce gas and water together in which the capillary water is considered to be the major water-producing type.It’s indicated that the characteristics of vertical migration and accumulation are widely developed in various gas-bearing accociations. There is as high as5.99MPa overpressure difference between the source rock and reservoir in the second Member of Shanxi Formation in lower gas-bearing association in the east. There are strong filling power combined with better pore framework in this area. With respect of the Eighth Member of Lower Shihezi Formation in Otog area in the western Ordos basin, there is only4.76MPa overpressure difference between the source rock and reservoir. The relative lower filling power accompanied with worse pore framework in reservoir. Therefore the variety between filling power and reservoir physical properities result in the difference of fluid distribution between two case study areas.更多还原