Downhole optical chemical compound monitoring device, bottom hole assembly and measurements-while-drilling tool comprising the same, and method of optically monitoring chemical compound downhole during drilling

A bottom hole assembly of a drilling system comprising a mandrel having a recess positioned on a mandrel circumference, the recess being arranged to receive a downhole optical chemical compound monitoring device comprising:

• an analysis cell part comprising an open cavity into which a drilling fluid is free to flow;
• a first optical probe coupled to a light source and arranged to transmit a light energy into the open cavity;
• and
• a second optical probe coupled to a detector and arranged to produce in use a signal resulting from an interaction of the drilling fluid present in the open cavity with said light energy, indicative of a quantity of chemical compound present in the drilling fluid;
• wherein:
• each of said optical probes is mounted through a wall of the analysis cell part in a sealed manner and has a tip, the tip being needle shaped and having an external diameter less than 1 mm;
• and
• the first optical probe and the second optical probe are arranged such that the first and second tips of the respective optical probes project into the open cavity and such that the first tip of the first optical probe faces the second tip of the second optical probe at a defined distance ranging from 10 μm to 10 mm.

A measurements/logging-while-drilling tool of a drilling system comprising a recess positioned on an external surface, the recess being arranged to integrate a downhole optical chemical compound monitoring device comprising:

• an analysis cell part comprising an open cavity into which a drilling fluid is free to flow;
• a first optical probe coupled to a light source and arranged to transmit a light energy into the open cavity;
• and
• a second optical probe coupled to a detector and arranged to produce in use a signal resulting from an interaction of the drilling fluid present in the open cavity with said light energy, indicative of a quantity of chemical compound present in the drilling fluid;
• wherein:
• each of said optical probes is mounted through a wall of the analysis cell part in a sealed manner and has a tip, the tip being needle shaped and having an external diameter less than 1 mm;
• and
• the first optical probe and the second optical probe are arranged such that the first and second tips of the respective optical probes project into the open cavity and such that the first tip of the first optical probe faces the second tip of the second optical probe at a defined distance ranging from 10 μm to 10 mm.