Porosity refers to the ratio of the pore volume in a rock (or the volume of space in a rock that is not filled with solid matter) to the total volume of the rock.
The study of porosity is quite different between the continental sequence stratigraphy and the passive continental margin marine sequence stratigraphy. The continental basin sedimentation is controlled by many factors, and the main controlling factors of different types of basins are different. In the continental basin, there are many sedimentary types, fast phase transitions, poor lateral continuity, and large variations in longitudinal upper layer thickness. Frequent lake intrusion and lake retreat makes the vertical rhythm of the lake basin sedimentation change rapidly; therefore, the formation of continental sequence stratigraphy, Structures and models are more complex and research is more difficult. In the research and practice, Chinese scholars have established a depression type that conforms to the sedimentary reality of the Chinese basin based on the boundary characteristics of the continental basin, the boundary characteristics of the system domain, the initial lake surface and the maximum lake surface, and whether there are slope breaks. Sequence stratigraphic framework and model of basins and faulted basins. The factors controlling the development of terrestrial stratigraphic sequence are mainly the change of lake level, structure, climate, datum change and supply of provenance, especially the structure and climate are very important, they directly control the changes of the lake level. The method system of terrestrial stratigraphic sequence research mainly includes outcrop sequence research method, experimental observation and analysis method, log sequence stratigraphic analysis, seismic sequence stratigraphic analysis and numerical simulation method of sequence stratigraphy. Sequence stratigraphy can play an irreplaceable role in the exploration stage, target exploration stage and development stage of oil and gas exploration.
Effective Porosity in Oil and Gas Exploration The ratio of the pore volume to the volume of a material in a natural state is called the porosity of the material. It includes all the pores in the material, whether or not they are connected. However, when studying the porosity of the oil reservoir, the measured porosity is the ratio of the connected pore space to the total volume of the rock, ie the effective porosity. In general, the effective porosity is 5 to 10% less than the total porosity. The porosity of most oil reservoirs varies between 5 and 30%, with the most common being within the range of 10 to 20%. Oil storage with a porosity of less than 5% is generally considered to have no mining value unless there are cracks, cracks and voids that are not seen in the removed core or cuttings. According to the rough porosity estimation in the oil and gas exploration site experience, the reservoir rocks can be divided into:
Porosity 0~5% Non-value porosity 5~10% Poor porosity 10~15% Medium porosity 15~20% Good porosity 20~25% Excellent for reservoir evaluation Porosity is important for reservoir evaluation One of the parameters. Nuclear magnetic resonance (NMR) porosity is only responsive to pore fluids and has advantages over other well logging methods in determining formation porosity. However, in the application of complex continental strata in China, it is often found that there is a difference between the NMR porosity and the actual porosity of the formation, and sometimes the difference is even obvious, which affects the application effect of NMR logging. The theoretical basis of NMR porosity is introduced. Based on the analysis of the influencing factors of NMR porosity, the influence of the existing NMR porosity logging method on the measurement results is investigated, and the large number of artificial rock samples and different: Experimental measurements of natural rock samples have proposed porosity logging methods suitable for China's continental formations, improving the measurement of NMR porosity. In view of the complexity of China's continental strata, it is suggested that different regions should be analyzed according to the specific conditions; the appropriate NMR logging method should be determined to obtain a more accurate NMR porosity.
Porosity is typically measured in the laboratory using small pieces of core or cuttings. In addition, there are several qualitative methods for estimating porosity, such as electrical measurements, radioactive logging, and so on.
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