Method for improving water saturation evaluation precision of complex oil and gas layer by using digital core analysis

Abstract

The invention discloses a method for improving water saturation evaluation precision of a complex oil and gas layer by using digital core analysis, and belongs to the technical field of oil and gas exploration. The method includes the following steps: (1) preparing a test sample; (2) performing backscattered electron and secondary electron imaging on the test sample; (3) preforming pore volume segmentation and statistics on secondary electronic imaging to obtain pore shape parameters; (4) performing automatic mineral analysis on the fine imaging to collect a characteristic atomic spectrogram and perform automatic mineral analysis on the characteristic atomic spectrogram to obtain additional conductive mineral content; (5) determining electrical parameters of saturated rock, and establishing the conversion relationship between the pore shape parameters and m and the conversion relationship between additional conductive minerals and n; (6) calculating the water saturation of the complexoil and gas layer to achieve the purpose of accurately quantifying the water saturation value by extracting the distribution of smaller pores which affect the saturation evaluation and the content ofkey additional conductive minerals.

Description

technical field [0001] The invention belongs to the technical field of oil and gas exploration, and in particular relates to a method for improving the evaluation accuracy of water saturation in complex oil and gas layers by using digital core analysis. Background technique [0002] In the process of oil and gas exploration and development, the calculation of water saturation is the most critical oil and gas layer evaluation parameter. At present, the most widely used in the industry is to use the Archie formula to calculate it. The Archie formula is as follows: [0003] [0004] The formula shows that the formation water saturation is almost directly proportional to the formation water resistivity Rw, and is almost inversely proportional to the formation resistivity Rt. At the same time, it is affected by the rock porosity Pore ​​structure factor m, saturation factor n. [0005] In the archie formula, a is an adjustment coefficient related to the shale composition, con...

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Problems solved by technology

However, due to the differences in the sedimentation of each layer, the actual lithoelectric parameters of each layer vary greatly, resulting in sometimes water layers with high resistivity, and sometimes oil layers with low resistivity, which are very different from the actual oil and gas characteristics, which directly affects the use of the Archie formula. Accuracy of calculating water saturation

[0010] In order to overcome the above defects, many improvements have been made on the basis of the Archie formula, such as the Indonesian formula, the Sumatra formula, the two-water model, etc., but the results are not very satisfactory, and it is impossible to obtain the formation water saturation objectively and quantitatively. Especially in recent years, oil and gas exploration and development have transitioned from conventional oil and gas reservoirs to complex reservoirs (low-porosity and low-permeability reservoirs, tight reservoirs, shale gas, low-resistivity oil layers, etc.), and the calculation of quantitative saturation has become a constraint for complex reservoirs. evaluation bottleneck

[0011] The whole oil field coring is costly and time-consuming, and it is impossible to take coring layer by layer. However, with the improvement of technology, at present, the oilfield site can be carried out at a relatively low cost, and the wellbore coring can be carried out in each key layer. At the same time, the oilfield There is also a large amount of cuttings data on site, which are important materials for fine evaluation of reservoir saturation in the later stage. However, due to mud flushing and mechanical impact during the coring process, it is impossible to directly use borehole coring to determine the original water content. Calculation of saturation

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