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Micro-characteristics Of Tight Sandstone Reservoir Of Yanchang Formation In Ordos Basin

Posted on:2016-03-04Degree:DoctorType:Dissertation
Country:ChinaCandidate:D Z RenFull Text:PDF
GTID:1220330470469381Subject:Oil and Gas Field Exploration and Development
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The Chang 63 reservoir in Huaqing oilfield in Longdong region of Ordos Basin is typical tight sandstone reservoir, and typical practice in domestic and overseas. As the conventional and single experiment data and method hardly realize and evaluate the micro reservoir characteristic of tight sandstone oil reservoir, it always restrict the exploration development process and theoretical anderstanding of the Chang 63 tight sandstone reservoir.Based on the physical property, casting thin slice, X-ray, the SEM,3D CT scanning, high pressure mercury injection, constant-speed mercury injection, nuclear magnetic resonance, oil-water relative permeability, real sandstone water-oil displacement and so on, the author makes a detail research on the diagenesis, lithogenous phase, porosity evolution, micro-pore structure, the occurrence characteristic of movable fluid, oil-water relative permeability, physical property, movable fluid saturation and the influence on oil-water seepage characteristic. With the combination of the practical dynamic production data, the author discusses about the exploration characteristic of tight sandstone reservoir on the perspective of micro-pore structure. Based on the research we get the following achievements:(1) Carbonate cementation and compaction machinery is the main diagenetic evolution characteristics of reservoir’s dense evolution. Nowadays, the reservoir diagenetic stage mainly belongs to the middle-late period of A phase during the middle diagenetic stage.And part of the reservoir has entered into the early stage of B the middle diagenetic stage.(2) The reservoir can be devided into seven diagenetic facies which are chlorite cementation membrane-intergranular pore facies,Illite with chlorite cementation membrane-intergranular pore facies, illite cementation-intergranular pore facies, illite with chlorite cementation -dissolution, illite cementation-dissolution facies, illite cementation facies and dense carbonate cementation respectively. And the properties of chlorite cementation membrane-intergranular pore facies, illite with chlorite cementation -dissolution and the illite cementation-intergranular pore facies is much better.(3) The porosity evolution calculation results show that the unconsolidated sandstone reservoir porosity of Chang 63 reservoir is 38.33%. Porosity lose 22.49% in the compaction process, early cementation, Porosity lose 4.54% in the early cementation-replacement process. Porosity lose 6.62% in the middle-late cementation-replacement process.However, the dissolution generated the porosity of 4.16%.The calculated porosity is 9.16%. By comparing the maximum compaction rate, maximum rate of cementing, dissolution rate, the biggest development of the intergranular pore, the porosity evolution path of the different diagenetic facies belt, which find out the differences causes that led into the dense reservoir property.(4) The porosity evolution analysis shows that the fluid properties and temperature is the direct response factor of porosity evolution through the L126 well.And the same time, burial depth, the stratigraphic age and the different types of the cemention content is the main parameter during the porosity evolution. The total porosity decreases to 9.51% in L126 well during the process of comprehensive evolution, which indicate that the function and effect simulation method has calculated the porosity evolution’ consistency. Oil and gas’filling critical porosity is 10.26% and the critical permeability is 0.796×10-3μm2.(5) The main pore of the reservoir is the intergranular hole, and the feldspar, dissolved pore is given priority to the intergranular hole.The 3d shapes of pore types mainly are bundle, banded, ball.The pore throat redius which have ability of permeability contribution mainly are tiny throat and micro-fine throat.(6) The throat radius size, distribution and sorting characteristics is the main controlling factors of raising different, similar or equivalent permeability, and differences of the sample permeable ability of the average throat radius which are similar or same.At the same time, there is a phenomenon that the mainstream of the throat radius with dense reservoir and high expulsion pressure is smaller than the average throat radius.The ability of unimodal seepage is better than double modal and multimodal for the range of similar or identical pore throat radius, but it is not on behalf of the seepage ability of pore system.(7) The high pressure mercury injection has high identification accuracy especially for the pore system which is less than 0.1μm, and the Constant speed mercury intrusion has high identification accuracy especially for the pore system which is more than 0.1μm.The combination of these two can characterize the microscopic pore reservoir’s structural features in a quantitative and effective way.(8) The saturation of movable fluid in the Reservoir is low, the average is 27.48%. The T2 spectrum curve is given priority to the twin peaks before centrifugal. T2 spectrum curve form is mainly unimodal after centrifugal. The movable fluid saturation Has certain independence which is out of the space position control. Filling of clay minerals content and pore types are important factors of complicated pore structure.Throat radius size.The key to influence the occurrence characteristics of movable fluid is distribution characteristics, sorting and areal porosity.The occurrence of remaining oil are the pore space of T2 which is less than 100ms.(9) Study samples have high bound water, and the residual oil saturation is greater than the width of oil and watersaturation.Oil phase permeability, water phase permeability and oil-water relative permeability is low. No water displacement efficiency contribution is huge that it should be given more attention and research.The curve and parameter of oil-water relative permeability has a good consistency with the actual production data. The increase of confining pressure reduce the oil-water displacement efficiency.The change of the curve of oil-water relative permeability decrease the heterogeneity of microscopic pore structure.(10) Controlled by the throat radius,distribution characteristic and sorting factor, different permeability, similar permeability, same permeability and different oil-water relative permeability curve pattern corresponds to different seepage characteristic and displacement efficiency. While the average throat radius is less than 0.4μm and the permeability is less than 0.15×10-3μm2, it is difficult to explore the oil reservoir. Besides, there is a negative correlation between physical property, throat radius and displacement efficiency.According to the above analysis, the anisotropism of the micro-pore structure is the crux of the reservoir exploration efficiency. Aiming at the reservoir which keeps well sorted pore-throat and weak micro anisotropism, its exploitation efficiency is better than the relative high-permeability reservoir whose micro anisotropism is strong.
Keywords/Search Tags:tight sandstone reservoir, Huaqing Oilfield, Chang 63 reservoir, physical property, porosity evolution, micro pore structure, movable fluid saturation, seepage characteristic
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