Laser-based monitoring tool

A method for wellbore monitoring comprising:

• providing, in a wellbore, a laser beam generator to provide a laser beam in the infrared or near-infrared spectrum;
• providing an optical element that is part of the optical path, the optical element for receiving the laser beam from the one or more optical transmission media and for outputting the laser beam;
• providing a detector configured and positioned to receive the laser beam output from the optical element to detect light intensity of the laser beam;
• providing a first chamber enclosing the optical element and the detector;
• providing a second chamber in a fluid connection with the first chamber, the second chamber having a fluid inlet and a fluid outlet;
• providing a gas-permeable membrane positioned across the fluid connection such that the gas-permeable membrane forms an interface between the first chamber and second chamber;
• receiving, by the second chamber, wellbore fluid through the fluid inlet;
• retrieving a solid sample and storing the sample in a sample collection device, where the second chamber is or comprises the sample collection device;
• receiving, by the first chamber, gas permeating through the gas-permeable membrane from the second chamber into the first chamber;
• subjecting the gas to the laser beam output by the optical element;
• receiving, by the detector, the laser beam output by the optical element;
• receiving, by a processing unit, intensity data from the detector;
• determining, by a processor of the processing unit, an amount of absorption of light of the laser beam by the gas;
• and
• releasing, by the second chamber, wellbore fluid through the fluid outlet.