| With the depth of oil exploration and development or the improvement and perfection of various process technology, the objectives of exploration and development transfer from the original tectonic reservoirs with high porosity, high permeability and high amplitude to the reservoirs which is low porosity, low permeability, complex lithology and complex reservoir space. Exploration and development of the low porosity and permeability sandstone reservoir has become an important part of the global oil industry. Because the low porosity and permeability reservoirs have complicated causes, pore complex structure, poor physical properties and strong heterogeneity, these give rise to difficult logging interpretation and evaluation. If the conventional methods are used to evaluate low porosity and low permeability reservoir, that would cause serious error. So it is very urgent to making sense of the causes, mechanism and characteristics of the low porosity and permeability reservoirs, carrying out petrophysical study of low porosity and permeability reservoir, clarifying the factors and mechanisms of electrical responses and low porosity and permeability reservoir and the evaluation logging method of it.Low porosity and permeability reservoir are so complexity that it makes conventional logging evaluation methods difficult to calculate reservoir parameters and reservoir fluid properties accurately. And the result of the log interpretation results or testing and production testing are not consistent. Quan4Fuyu reservoir which is in Qianan oilfield belongs to continental fluvial-deltaic deposit. It also belongs to layered structure constructed, low porosity and permeability sandstone reservoirs which result from fracture. From the angle of reservoir geological features and logging features, this article study "four properties relations" based on understanding the geology of the region. In order to effectively identify oil, gas and water layers, we adapt "core calibration logging" technology by using collected data and experimental analysis data. What we do are that analyzing experimental data and the logging response characteristics of low porosity and permeability reservoir, extracting the microscopic pore structure characteristic parameters of sandstone reservoir, researching "four properties relations". Aim at different formation water salinity and mud salinity, we should determine that if the mud invasion correction is needed for numerical simulated different pore structure formation resistivity which effects by mud invasion regular analysis. We can establish porosity, permeability, oil saturation logging interpretation model base on different region and lithology using reservoir classification ideological; Considering the influence of lithology, heavy mineral, using oiliness data, well testing and pre-production data by the technology "oil production calibrating log", establishing interpretation criteria of reservoir logging to identify different lithology oil, gas, water layer. Applying the theory and methods of displacement accumulation, we can analyze the relationship between reservoir displacement force and saturation (resistivity). And what’s more, we can study the cause of formation of oil layer or oil and water in the same layer, and summary the distribution of low porosity and low permeability reservoir saturation in the area. Through researching the article, we get the following results and understanding:1. By studying the "four properties relations" of the reservoir, we can understand the lithology, physical property, electric property and oiliness of low porosity and permeability of research blocks more deeply, specially we can get the conclusion about their general rule changes:Along with the more coarse the lithology is, the better physical property is, the better electric property is, and the higher oil level is. The minimum standard of lithology of this area is argillaceous siltstone, so we can determine the minimum standards of reservoir physical property:the minimum standard of reservoir porosity is6%, and that of permeability is0.04×10-3μm22. Capillary pressure curve can reflect the pore throat distribution of the rock and determine the reservoir types and reservoir performance. Using mercury intrusion analysis test means, we can analyze the influence factors of Qianan Oilfield Quan4Fuyu reservoir pore structure of reservoir. And the Qianan Oilfield Quan4Fuyu reservoir can be divided into three kinds through parameters such as porosity and permeability. After classifing the lithology of the reservoir, homogeneous reservoir rocks have the similar characteristics which show the similar rock power relations and the logging response characteristics, so the formation heterogeneity problem can be changed to the relative homogeneity problem.3. Based on the four properties’ relations analysis of reservoir, it has been known that the lithologies which contain oil are mainly fine-grained sandstone, siltstone, argillaceous siltstone in Qianan oil field. By using the cross plot of GR-AC, the lithologies of70wells is obtained, and the correct rate is83%, the lithology identification is solved well by this method in this erea.4. The low compositional maturity, low structure maturity, big change of each component content, strong reservoir heterogeneity of sandstone are the main factors which lead to complex structure, low permeability of sandstone.We can establish porosity model of low porosity low permeability reservoir in the study area by using neural network, regression analysis, The density of the fitting, principal component analysis (pca), Acoustic wave fitting. The Absolute error less than0.5%, and The relative error is less than3%; using "core scale logging", the neural network method can establish the permeability model in the study area. The range of error is in the scope of one order. The effect of establishing model of data processing of the application is better.5. Using the Archie equation and capillary pressure data to calculate initial oil saturation. Because the planar distribution of formation water salinity in Qianan Oilfield Quan4Fuyu Reservoir has big changes, and the oil storage of lithologies are different. Combining with testing data, we can establish the corresponding reservoir plates based on different lithologies and different formation water salinity. Contrast with testing reservoir level, comprehensive interpretation is rate reached82.8%, increased by nearly25percent, basically solved the puzzles which block oil and water layer identification difficult6. Carrying out the mechanism of the layer which was oil and water are in the same layer in the condition of low porosity and permeability. And we can get the cause that why water and oil in the same layer:hydrocarbon source rocks are above the Qing1period, and the expulsion force driven hydrocarbons migrated into the below of the reservoir, in the mean time, the oil and gas buoyancy is the first one that need to overcome; when hydrocarbons migrate into the bottom of the reservoir, the remaining expulsion force (displacing force) need to overcome capillary forces so that they can go into the pores of the reservoir and be stored; because of the thin reservoir lithology, poor porosity and permeability, when oil in the displacement process, they need higher displacement force:when the water of large pores are just in the minority and the capillary force is small, the displacement force are easy to remove, but the water in small pores of can not be completely flooding, that can lead to the condition that the oil filling is not enough, and in the result, that can form more layers which are water and oil in the layer. |
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