The Accumulation Mechanisms Of Fractured Mudstone Reservoirs

Taking the Dongying Sag source rocks in Eogene as the example, the main task of this article is to discuss the accumulation mechanisms of fractured mudstone reservoirs by researching on the characters of source rocks and the evolution of hydrocarbons; the characters. formation and the distribution of source rocks fracture; the mechanisms of migration of oil and gas in source rocks. The main conclusions of this paper are that:Source rocks in the upper part of the forth section and the middle-lower part of the third section of Shahejie Formation of Dongying Sag is main melanocratic mudstone and shale, half deep-deep lake facies, high abundance of organic carbon and main I, assistance II1, II2 organic matter type. Source rocks in Eogene evolute from organic matter to oil and gas during bury. subsidence and increasing temperature in Tertiary and Quaternary. The magma of Tertiary period has significant effect on the evolution of Tertiary organic matter.The Es4 source rocks of Dongying Sag began to evolute from organic matter tohydrocarbon in Esj and all evolute in Quaternary. The Es3 and Es3 source rocks began to evolute in Ng and between well Shi 14. Tuo 1. Li . Bin 4. Gao 2. Chun 2 in Quaternary. The effect range of magma of Tertiary period to evolution of Tertiary source rocks is main in magma development area of Tertiary-the south and west of Dongying Sag. The complement in horizon caused by the evolution related to bury and the evolution related to magma made almost all source rocks produced hydrocarbon.According to the relationship to sediment statum, fracture which widely distribute in source rock statum include vertical fracture, oblique fracture and horizontal fracture. According to origin, fracture include fracture caused by magma. vertical differential load fracture and plasticity rocks mass upper bend fracture.The fracture caused by magma in E34 -Ess2-3 source rocks mainly distribute in magma development area of Tertiary in south and west of Dongying Sag.The vertical differential load fracture in Es4'-î–¹32"3 source rocks mainly distribute like annulus. The rest are all development area of vertical differential load fracture besides the area of Li. He80 of west Liangjialou oil field and the area of west Fan2. Fan5.The plasticity rocks mass upper bend fracture mainly distribute in plastical rock mass upper zone between well Dongfeng 8. Ying 2. Tuo 3. Li K Bin 110. Shi 104. He2. Niu43. Lai 48.The three kinds of fractures are complemental. The fracture wide-ranging development in the rest of Dongying Sag excluding the between well Liang 2. Shi 4. Lil.The oil saturation in source rocks enhances with increasing buried depth thatprovide the material basis to form fractured mudstone reservoirs.The development of fracture caused by magma. vertical differential load fracture and plasticity rocks mass upper bend fracture provide the beneficial migration pathway and storage room. In fracture, pressure differential and buoyant can promote oil to migration upward slope. Even if oil float on the upper sandstone and accumulation due to the source faults in overlying formation, there are many residual oil be left in the source rocks. The area of oil and gas accumulating is mainly in the area of the updip direction top of the structure and fracture belt.