Rapid calculation method for porosity of coal seam fracture

Abstract

The invention relates to a rapid calculation method for the porosity of a coal seam fracture. In the method, a fracture development occurrence identification part and a fracture porosity calculation part are utilized. In the fracture development occurrence identification part, according to the method, a deep lateral apparent resistivity difference is utilized and is particularly combined with the distribution condition of the resistivity of coal seam bed rocks, so as to be used for observing the development condition of a horizontal fracture, a vertical fracture and the combination thereof. In the fracture porosity calculation part, two groups of orthogonal or heterotropic fracture characteristics are mainly developed according to a coal seam; and the according to the method, three groups of computational formulas the number of which is 9 in total of the porosity of the fracture according to a fracture development occurrence identification result and a distribution range of the coal seam resistivity are determined. According to the method provided by the invention, by aiming at the characteristic of large resistivity difference or variation range of the coal seam, the method for determining the porosity of the coal seam fracture by utilizing double lateral loggings, which is established according to a resistivity distribution range, is extremely high in pertinence; and the method has the advantage of stronger practical applicability.

Description

technical field [0001] The invention belongs to the technical field of geophysical exploration of unconventional oil and gas resources, and is mainly used for the identification of the fracture development degree of coalbed gas reservoirs and the calculation of the fracture porosity. Background technique [0002] Well logging is an important field of earth science and one of the important engineering technologies for oil and gas exploration and development of coalbed methane and other unconventional oil and gas resources. In the exploration and development of coalbed methane, the determination of the development degree of coalbed fractures and its parameters is of great significance. It not only involves the production of coalbed methane, water yield, etc., but also has important guiding significance for the later transformation of coalbeds and the production process of coalbed methane. However, due to the complex anisotropy and heterogeneity of coalbed methane formations an...

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Problems solved by technology

However, due to the complex anisotropy and heterogeneity of coalbed methane formations and the generally poor drilling environment, the existing calculation methods for the fracture porosity of coalbed methane reservoirs are extremely inaccurate

[0003] 1. The conventional use of neutron, density and sonic logging is greatly affected by the borehole environment. Therefore, the method of using the combination of neutron, density and sonic logging to determine fracture porosity cannot obtain the technical guarantee of logging quality;

[0004] 2. The currently commonly used calculation of fracture porosity based on dual laterolog is established for fractured carbonate rock formations, which are quite different from coal seams, and it mainly uses the range of deep and shallow resistivity The difference reflects the fracture porosity, which is inconsistent with the fact that the amplitude difference mainly depends on the occurrence of fracture development, and this method has limitations in practical application;

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