Method for identifying low-permeability gas-water layer while drilling

Abstract

The invention discloses a method for identifying a low-permeability gas-water layer while drilling. The method comprises the following steps: S1, calculating movable gas saturation; S2, determining aT2 cut-off value of formation water, and calculating movable water saturation and irreducible water saturation; S3, calculating a movable gas-water ratio index; S4, establishing an interpretation chart by taking the movable gas-water ratio index as a vertical coordinate and the irreducible water saturation as a horizontal coordinate; and S5, projecting the irreducible water saturation and the movable gas-water ratio index of a layer to be interpreted onto the interpretation chart, and interpreting according to an interpretation region where a drop point is positioned. According to the method,the problem of identification while drilling of a tight gas reservoir is effectively solved; and the method is easy to operate, low in cost, accurate in interpretation and wide in application prospect.

Description

technical field [0001] The invention relates to the technical field of interpretation and evaluation of oil and gas layers, in particular to a method for identifying low-permeability gas water layers while drilling. Background technique [0002] Tight gas reservoirs are characterized by low porosity, low permeability, low abundance, and complex gas-water relationship. The identification while drilling mainly relies on gas logging technology. Since the gas logging data is greatly affected by drilling conditions, it is difficult to identify formations. Water content and reservoir effectiveness lead to a low coincidence rate of gas logging interpretation; nuclear magnetic resonance logging technology can effectively identify the water content and availability of reservoirs, but because the measurement is carried out under normal temperature and pressure conditions on the surface, the gas The number of hydrogen-containing molecules is low, and no gas-containing signal can be det...

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Problems solved by technology

[0002] Tight gas reservoirs are characterized by low porosity, low permeability, low abundance, and complex gas-water relationship. The identification while drilling mainly relies on gas logging technology. Since the gas logging data is greatly affected by drilling conditions, it is difficult to identify formations. Water content and reservoir effectiveness lead to a low coincidence rate of gas logging interpretation; nuclear magnetic resonance logging technology can effectively identify the water content and availability of reservoirs, but because the measurement is carried out under normal temperature and pressure conditions on the surface, the gas The number of hydrogen-containing molecules is low, and no gas-containing signal can be detected by NMR; mud logging evaluation personnel compare the saturated sample with the fresh sample T 2 The amplitude difference between the spectra is defined as the gas-bearing area. This assumption lacks scientific basis, because the gas has strong compressibility, even if there is gas in the pores, it is impossible to know the gas-bearing abundance; On the premise of the number of hydrogen molecules or gas fullness, it is also inaccurate to evaluate the gas saturation

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