A method for evaluating the microscopic pore structure of tight reservoirs and classifying them

Abstract

The invention provides a micro-pore structure evaluation and reservoir classification method for tight reservoirs. The method comprises steps as follows: the origin and the petrologic features of each reservoir are analyzed, and the phase type, the content and the like of each reservoir are determined; physical features of each reservoir are analyzed; features of a reservoir space of each reservoir are observed, and the pore type, the surface porosity and the like are determined; pore structure parameters of the reservoirs are measured with a high-pressure mercury intrusion method and a nitrogen adsorption method; the diagenesis is researched, and compaction, cementation and corrosion sequences are determined; physical property control factors of the reservoirs are analyzed; the reservoirs are classified. The method mainly has the effects as follows: the diagenesis and the influences of the diagenesis on the reservoirs are comprehensively reflected through cathode luminescence and micro-area mineral quantitative analysis; micro pores of the tight reservoirs are researched elaborately through fluorescent casting and field emission scanning electron microscopy; the microscopic features of the tight reservoirs are determined accurately through high-pressure mercury intrusion experiments and the nitrogen adsorption experiments; the parameters are optimized for classification and evaluation of the reservoirs, and the method has a great significance in further prediction of beneficial developing stratums or zones.

Description

technical field [0001] The invention relates to a method for evaluating the microscopic pore structure of tight reservoirs and classifying the reservoirs, and belongs to the technical field of geological research in the field of petroleum exploitation. Background technique [0002] my country's low-permeability reservoirs have a wide range of distribution and great resource potential, and have become the focus of oil and gas exploration today. For low-porosity and low-permeability sandstone reservoirs such as the Triassic Xujiahe Formation in the front of the Longmen Mountains in the west of Sichuan Basin, the Triassic Yanchang Formation in the Ordos Basin, and the Jurassic-Cretaceous in the Kuqa Depression at the northern margin of the Tarim Basin, previous per capita A large number of studies have been carried out, and a series of evaluation methods have been established. However, the early research objects are often reservoirs with relatively developed pores and relative...

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Problems solved by technology

[0006] However, the technique of observing porous casting thin sections with ordinary transmitted light polarizing microscope has the following defects: firstly, due to the extremely small throats and poor permeability in tight reservoirs, it is difficult to inject the die-casting liquid into the pores during the die-casting process After the film production is completed, through the ordinary transmitted light polarizing microscope, it will be found that the existence of the casting body can hardly be observed in the thin slice, that is, the pores cannot be found; secondly, even if the die casting liquid can be injected during die casting, the resolution of the ordinary transmitted light polarizing microscope The power is limited, and the image is not clear enough when magnified to 400 times, and it is difficult to observe the characteristics of micro-nano pores

[0010] However, the mercury injection method has the following disadvantages: it needs to fill the pores with mercury, and the minimum pore size that can be measured is related to the maximum mercury injection pressure used in the experiment. The pore size range that can be measured by the mercury injection method at 100 MPa is 14nm to 400μm , that is, the pore size smaller than 14nm cannot be measured; at the same time, due to the extremely poor permeability of tight reservoirs, it is difficult to press mercury into the pores of the sample during the experiment, and the measured mercury saturation may not exceed 50%, so conventional methods cannot be used Calculate the median value of pore throat radius and other parameters

However, the lower limit of the actual measurable permeability is 0.1×10 -3 μm 2

Dense samples take a long time to reach steady state and flow measurements are rather inaccurate

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