A method for identifying low-permeability gas-water layers while drilling

Abstract

The invention discloses a method for identifying a low-permeability gas water layer while drilling. The steps are: S1, calculating the movable gas saturation; S2, determining the T of formation water 2 Cutoff value, calculate the movable water saturation and irreducible water saturation; S3, calculate the movable air-water ratio index; S4, take the movable air-water ratio index as the ordinate, and the irreducible water saturation as the abscissa, establish an explanation chart; S5 1. Project the irreducible water saturation and the movable air-water ratio index of the layer to be explained onto the interpretation chart, and perform interpretation according to the interpretation area where the landing point is located. The method of the invention effectively solves the difficult problem of identifying tight gas reservoirs while drilling, and has the advantages of simple operation, low cost, accurate interpretation and wide 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...

AI Technical Summary

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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