Neutron-gamma gas reservoir identification method based on physical properties and formation water salinity correction

Abstract

The invention discloses a neutron gamma gas reservoir identification method based on the physical property and correction of formation water salinity, and belongs to the field of oil and gas exploration and development. The method comprises the steps that S1, logging data, gas testing result data and formation water analysis data as well as mud resistivity and mud salinity at 18 DEG C of researchblocks are collected; S2, a stable mudstone section of each well is determined, neutron gamma logging values of all sampling points in the sable mudstone sections are read, and the average value of the neutron gamma logging values is taken as a single-well neutron gamma basic value; S3, according to the neutron gamma logging value and porosity of each layer, the neutron gamma difference value in the unit porosity is calculated; S4, the formation water salinity of each layer is calculated; S5, a gas reservoir identification chart is established; and S6, a target layer is evaluated through the gas reservoir identification chart. By establishing a formation water salinity-unit porosity neutron gamma difference value coordinate system, the influence of the physical property and the formation water salinity on neutron gamma logging gas reservoir identification can be eliminated, and the accuracy of gas reservoir identification is advantageously improved.

Description

technical field [0001] The invention relates to the technical field of petroleum and natural gas exploration and development, and relates to a neutron-gamma logging fluid identification method, in particular to a neutron-gamma gas layer identification method based on physical properties and formation water salinity correction. Background technique [0002] With the deepening of exploration and development of oil and gas fields, unconventional oil and gas resources such as low porosity and low permeability, tight sandstone reservoirs, and low resistivity oil and gas layers account for an increasing proportion of oil and gas reserves, and the exploration and development of unconventional reservoirs has achieved more and more progress. more and more attention. However, due to the small storage space of low-porosity and low-permeability tight sandstone reservoirs, the contribution of fluid to the logging response is small, and the rock mineral composition is complex, the pore ty...

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Problems solved by technology

[0004] However, the conventional neutron gamma gas layer identification method has the following two problems in practical application: 1) The neutron gamma count rate is greatly affected by the porosity. There is also a large difference in the count rate; 2) The capture interface of chlorine element is relatively large. When the salinity of the formation water is high, the chlorine content in the water layer is obviously greater than that in the oil and gas layer, resulting in a higher neutron gamma count rate. easily misjudged as an air layer

[0005] At present, neutron gamma logging and neutron gamma shift logging are used to identify gas layers, mostly directly using the change of curve amplitude, without considering the correction of the influence of physical properties and salinity of formation water, which affects low porosity, low permeability and formation water. Gas layer identification effect in areas with large salinity changes

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