Method for monitoring downhole casing strain by using optical fibre sensor

Abstract

The invention relates to a method for monitoring the stress of a casing in a well by applying optical-fiber sensors, which mainly solves the problem that the existing research field of the casing erosion of an oil field and oil-water well does not have a direct method for monitoring the stress loading process of the casing in the well and the morphological characters of the casing erosion. The method is characterized in that: optical-fiber grating sensors are circumferentially arranged along the outer surface of the casing; a ground optical-fiber grating demodulation instrument connected with the optical-fiber grating sensors is utilized to monitor the circumferential strain Epsilon Theta of the casing and obtain the circumferential strain data of the casing; meanwhile, Brilliouin optical-fiber sensors are axially arranged along the outer surface of the casing; a ground Brilliouin optical-fiber demodulation instrument connected with the Brilliouin optical-fiber sensors is utilized to monitor the axial strain Epsilon Z of the casing and obtain the axial stain data of the casing; and the obtained circumferential strain Epsilon Theta and the axial strain Epsilon Z of the casing are utilized to obtain the stress of the outer layer of the casing in the well according to a ground stress explanation model. The method is characterized by being capable of permanently monitoring the deformation of the casing and obtaining corresponding stratum pressure under the condition without knowing the casing erosion and the stratum pressure.

Description

Technical field: [0001] The invention relates to a method for monitoring the force of downhole casing in the field of oil field casing damage research, in particular to a method for monitoring the force of downhole casing by using an optical fiber grating sensor and an optical fiber Brillouin sensor. Background technique: [0002] At present, the research on casing damage of oil and water wells in oilfields only analyzes the influence of clay minerals, injection water quality and ground stress on casing damage from the mechanism, but there is no direct monitoring method for the stress process of downhole casing and the shape characteristics of casing damage. Invention content: [0003] In order to solve the problem of the lack of direct monitoring methods for the stress process of downhole casing and the shape characteristics of casing damage in the field of oil and water well casing damage research in the existing oil field, the present invention provides a method for moni...

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Problems solved by technology

[0003] In order to solve the problem of the lack of direct monitoring methods for the stress process of downhole casing and the shape characteristics of casing damage in the field of oil and water well casing damage research in the existing oil field, the present invention provides a method for monitoring downhole casing using fiber grating sensors and fiber optic Brillouin sensors. Using this method, the circumferential strain and axial strain of the casing can be measured, and according to the theory of the ground stress interpretation model, the casing deformation can be permanently monitored and the corresponding formation pressure can be obtained under the condition of unknown casing damage and formation pressure in advance. provide a basis for oilfield development casing damage monitoring and targeted system pressure adjustment measures

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