Fracture Geological Modeling Of Keshen 8 Gas Field In The Kuche Depression

The reservoir of Keshen 8 Gas filed contains a high gas production,the buried depth of these reservoirs is over 6000m.Due to the strong compaction and cementation,the physical properties of rock matrix are usually very poor,so the fractures are the key factor to improve the seepage capacity of tight sandstone reservoir.Constrained by the poor quality seismic data and a little core data,the distribution characteristics of fractures,the main controlling factors for the development of fractures and the formation stages were analyzed using the field outcrop observation,core observation,imaging logging,and core casting thin section.Through attribute modeling,the development characteristics of matrix and structural fractures were studied,then the reservoir fractures of K₁bs Formation in the study area were comprehensively characterized.The basic parameters and spatial distribution characteristics of fractures in the study area were identified and described by using similar outcrop,core observation,imaging logging and thin section observation.Primarily four characteristics of fractures were summaried,the structural shear fracture,the high angle fractures,the half filled-unfilled fractures,and the most of the fillings are gypsum or calcite.The relative fracture linear density is mainly in 0.41-0.76/m.In plane view,the dominant strike of fracture is mainly concentrated on NNW-SSE and NEE-SWW.The fracture aperture is mainly distributed in 0.1mm-0.4mm,indicating high value in the east structural high point.Due to the high fracture aperture and low fracture filling in the anticline core,oil and gas are easy to be accumulated in the core of anticline,showing a favorable area for exploration.Vertically,the small difference of fracture strike was interpreted between East and West structure.By decreasing the distance to the controlling fault,the fractures are well developed.The fractures were significantly influenced by the main faults,followed by the secondary fault.The reservoir is mainly formed in fresh water diagenetic environment.With the increasing of sandstine and mudstone thickness,the fracture linear density decreased.Based on the fluid inclusion testing,three tectonic movements were interpreted in the study area,the Late Cretaceous（K₂）-Paleocene（E₁）,the Neogene Miocene（N₁）,the Neogene Pliocene（N₂）.During the three tectonic fracturing periods,the Neogene Pliocene（N₂）was characterized with the strongest tectonic movement and the most developed fractures.Through the construction of physical parameters and fracture discrete network model,the porosity firstly decreases and then increases with the deepening of formation depth.Compared with the anticline wing,the anticline core showed a strong deformation.The core showed the stronger connectivity than the limbs,so the porosity is higher than the two wings.The increasing and decreasing trend of permeability is the same as that of porosity.Fractures in the core than that in the limb,in the core are more effective.Through the weighted summation of stress field,distance from fault,lithofacies,structural principal curvature,formation thickness and sedimentary microfacies geological model of Keshen 8 gas field,the attribute volume characteristics of fracture development strength between wells is constructed,which can provide constraints for the construction of discrete fracture network model in later stage and improve the reliability of the model.By using the methods of multi factor constraint,multi-scale combination,deterministic and stochastic modeling,the discrete fracture network model with high reliability is established,which can describe the reservoir fractures more accurately.