Method for evaluating invasion degree and influence of mud invading into ultra-low-permeability oil layer

Abstract

The invention relates to a method for evaluating the invasion degree and influence of mud invading into an ultra-low-permeability oil layer. The method includes the steps that according to geologicallogging, experimental analysis, fracturing test mining and other data, on the basis of dynamic analysis, a seepage theory, a material balance principle and combination of dynamic analysis and static analysis, production dynamics of the ultra-low-permeability oil layer are divided into two stages including the initial production stage and the stability stage according to fracturing test mining curve features; the mud invasion degree of the ultra-low-permeability oil layer is determined according to differences of the initial fluid throughput amount of strata, and properties of the oil layer arejudged according to the fluid throughput amount of the strata and the mud invasion depth in combination with quantification of the fracturing curve features; a relationship chart between the resistivity and mud invasion depth of the oil layer is compiled to quantitatively evaluate the mud invasion influence. The invasion volume and invasion radius of a mud filtrate in the ultra-low-permeability oil layer can be determined simply, accurately and quantitatively, correspondingly the mud invasion influence and causes of the low-resistance oil layer are analyzed, the properties of the oil layer are identified and evaluated, and the causes of the low-resistance oil layer are determined.

Description

technical field [0001] The invention relates to the technical field of evaluation of low-resistivity oil reservoirs, in particular to an evaluation method for the degree of mud invasion in an ultra-low permeability oil layer and its influence. technical background [0002] Low porosity and ultra-low permeability sandstone reservoirs and oil layers are widely developed in the Mesozoic Yanchang Formation in the Ordos Basin. This type of reservoir has great differences in microstructure, strong heterogeneity, various types of pore throats, developed natural micro-fractures, and widely distributed low-resistivity oil layers. Low-resistivity oil and gas layers refer to a type of oil and gas layers whose resistivity value is lower than that of adjacent water layers, which makes the interpretation of oil and water layers difficult. It is usually defined by the resistance increase rate of less than 2 or 3. [0003] Micro-fractures are not only the main type of natural fractures in ...

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Problems solved by technology

Not only do these factors often co-exist, but it is also difficult to specifically distinguish and quantify the degree of influence of a single factor

More importantly, the factors of the reservoir itself are often difficult to reasonably explain the simultaneous development of normal oil layers and low-resistivity oil layers under the same geological conditions in the same block.

[0005] So far, the research on the identification and evaluation of low-resistivity oil layers is still widely concerned and valued by the academic community; combined with seepage theory and experimental simulation, using logging parameter processing and interpretation technology to identify and evaluate oil and gas layers, and discuss the degree of mud invasion and its impact. It is not only the main method content of logging reservoir evaluation, but also the main problem faced by logging analysis technology; although previous research has accumulated many achievements, theories and methods, it is clear that mud invasion is an important factor causing low-resistivity oil layers. The degree of filtrate invasion and its impact is an important way to identify and evaluate low-resistivity oil layers, but no attempt has been made to analyze and evaluate the degree of mud invasion and its impact in ultra-low permeability oil layers using oilfield production performance data

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