Pore & Fracture Development And Oil & Gas Accumulation Of Shahejie Continental Shale Of The Liaohe Western Sag

In order to study the accumulation space for shale oil and gas in deep and reveal the rules of them in the shale layer. Through core description, section observation,focused ion beam-scanning electron microscope(FIB-SEM), low field nuclear magnetic resonance(NMR) and X-CT computer tomography technology, from macroscopic to microcosmic,the reservoir space and physical property of continental shale which is represented by the western sag of Liaohe Depression were studied. On the basis of the study, the accumulation process of shale oil and gas in the reservoir space were discussed.The results show that sedimentary primary pore, diagenesis secondary pore and hydrocarbon generation pore has been developed of Es3-4 in the Western sag of Liaohe Depression. The sedimentary primary intergranular pore has been preserved to a certain degree. The size of diagenetic dissolution pore distributes for a wide range,from the naked eye visible cm, mm level to the electron scanning microscope nanometer level, and this is in favor of the accumulation and migration of shale oil. At the same time, some μm level of organic pore in the part of organic matter can be found.The sedimentary bedding fissure, diagenetic shrink fracture, tectonic fracture and hydrocarbon expulsion fracture is developed in the study interval. And shrink fracture can be developed around the organic matter edge and inside the clay mineral.The extensive development of organic internal cracks is actually the main difference between continental low maturity shale and southern high maturity marine shale, and it plays an important role in the communication between the internal of organic matter and the intergranular pore.Because of the strong heterogeneity of the pore distribution of shale in the study area, the porosity and permeability of different samples are very different. Porosity is distributed in 0.8%~18.1%(average 5.8%) and the permeability is distributed in0.0032mμm2 ~0.8524 mμm2( average 0.876 mμm2). Low field nuclear magneticresonance tests show two types of pore are contained in the shale, the aperture is mainly about 10 nm, less distributed between 100nm~1 m. About the CT scan of the shale sample, the three-dimensional pore model is established, which accounts for44.4% of the connected pores, shows that the pores and fractures in the shale connect well.The generation and accumulation of oil and gas in the shale is gradually occurring According to the difference in phase of oil and gas, modes of occurrence and space of accumulation, the accumulation process of shale oil and gas in the shale layer can be divided into four stages. The first stage is mainly bio-gas accumulation,the second stage is the oil and gas accumulation in micro pore of shale, the third stage is the oil and gas gathering in the fracture and big pore of the shale, the fourth stage is that the oil and gas enrich the interval with large amount of hydrocarbon generation.The layer which has high gray and dolomite content or strong tectonic experience is better for the accumulation of shale oil and gas. The different scale of pores and fractures in the shale layer leads to shale oil and gas accumulating effectively within it.