| Sulige gas field is located in the north of Yishan slop in the Ordos basin, with a total area about 4×104 km2. The main structure form is a wide and slow western-leaning monocline and the whole structure tends to be gentle. With the gas field’s effective development, how to further improve the single well production and gas recovery efficiency, to enhance the level of gas field development and exploitation efficiency, is a great challenge of Sulige gas field. Study on sedimentary facies and geological modeling of tight sandstone reservoir are essential to establish effective underground reservoir distribution model, which combined with dynamic data, can be used to form a 3D visualization model of seepage field under geological conditions. It can improve the production of wells in tight gas reservoir, and then optimize gas well working system. Based on the previous studies about tectonic evolution in Ordos basin and geological conditions of Su14 area, we selected 8th member of Shihezi formation and the 1st member of Shanxi formation as the research object. At the same time, we choice the infill well area of Su14 area for more detailed geological research.The target layer of this study is 8th member of Shihezi formation and the 1st member of Shanxi formation. Its unique fluvial facies deposition makes each facies belt distribute very wide in the plane. And the differences in sand bodies are obvious. Stratigraphic erosion and loss is very common. Sedimentary microfacies and lithology change rapidly in the space and the limited log resolution increased the contradiction between lithology profile and base level cycle. Therefore, it is needed to integrate a variety of geological information under the long-term base level cycle control. Use high resolution stratigraphic correlation method as the theoretical guidance, in the recognition of sequence boundaries and sequence division of the basis, combined with the tectonic setting of the Su 14 Area, comprehensive applied thickness, height method and repeated use strata contrast, Shanl and He8 layers can be divided into three long-term cycles, seven medium-term base level cycles,14 short-term base level cycle. Layered data digitization, import into geological modeling software, and full use the high resolution model, through the layer of interpolation and stacking, we can get the 3D structural model of Su14 area. The research area is a large lower monoclinal structure, which is similar to the background to the structure characteristic of Sulige area.Based on outcrop, core and well log data, we analysis the sedimentary facies marks and sequence, finding that the 1st member of Shanxi formation and the upper 8th member of Shihezi formation layer the typical characteristics of meandering river sedimentary. The lower 8th member of Shihezi formation is braided river which develop diara. According to the characteristics of lithology and well log and combined with the exploration practice in the study area, the target layer can be divided into eight microfacies types, such as sandy diara, sandy and gravelly diara, marginal bank, and channel fill sedimentary. Studies have shown that reservoir sand is mainly channel detention, marginal bank in meandering river and diara deposit in braided river. In order to establish the geological database of Su 14 area, we analyse single channel and composite channel sand, and establish low accommodation space braided river deposition and high accommodation space meandering river sedimentary model, and accurately describe sedimentary microfacies and single sand body. Using a variety of logging data and geological data, we can draw the outline of 7 middle term cycles which correspond to the stratigraphic units of sedimentary facies and transform the geological data into quantitative data. Then we can use sedimentary facies to set constraint conditions on porosity, permeability and gas saturation model.For the special fast swing of the continental river sedimentary model in this study area, the prediction process is often full of uncertainty. Therefore, we use the "phase constraint modeling" method, and combine deterministic modeling with stochastic modeling to establish 3D geological model.Firstly, on the issue of how to choose stochastic simulation algorithm, we must not only know the advantages and disadvantages of the algorithm, but also have to test different algorithms in the modeling process, thus selecting the most suitable algorithms for various models. With the algorithms s we can reasonably predict the unknow regions between wells. Secondly, taking sedimentary microfacies, controle structure and sequence stratigraphic frame as the control, we use the deterministic method to establish the assignment method model and Kriging model and used sequential Gaussian simulation method to establish the exponential model and spherical model. Ultimately, we optimize model by comparing the accuracy of these models. Research has shown that under the channel constraints, the spherical mode through sequential Gaussian methods is the optimal model.. Whether in the storage layer attribute parameter plane distribution or the complex prediction in the section of interwel, it has the highest accuracy.In the process of establishing porosity model, permeability model and containing gas saturation model, we find gas often distribute in the dominant facies with effective sand and high porosity and permeability zone. Because gas bearing capacity is controlled by physical properties, while physical properties are affected by lithology. There is a good correlation between sedimentary facies and sand, porosity, permeability and gas (water) saturation. Therefore, facies model can be used as the constraint conditions to establish sand model, facies controlled porosity model, facies controlled permeability model and saturation model. In the same way, according to the positive correlation between permeability, gas saturation and porosity, the porosity model can be used as second variables to establish the model of permeability and gas saturation.Through logging sedimentary facies and effective sand logging interpretation, we found that logging sedimentary facies sand (point bar/channel bar) and effective sand is almost one to one correspondence. So the channel sand in the sedimentary facies model can be separated to establish effective sand body model. The lowest limit value of physical properties of gas bearing sandstone is that the shale content is less then 0%, the porosity is greater than 5%, the gas saturation is greater than 30%, and the permeability is greater than 0.1mD. Through the lowest limit (30%) of the sand body model, the final distribution law of the gas reservoir is obtained. The 3D fine geologic modeling technology of tight sandstone gas reservoir is formed by the attribute model and the effective sand body model, which provides the geological basis for the establishment of the underground seepage field and the evaluation of reservoir. |
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