Patent ID: 8611703

Claim:
A method for measuring a physical parameter at a plurality of spaced apart locations in a subterranean formation where the temperature is in excess of 200 degrees Celsius, the method comprising: a. inserting into a well extending into the subterranean formation an elongated sensing element, the elongated sensing element including: i. an outer jacket having a coefficient of thermal expansion CTE jacket ; ii. an optical fiber in the jacket defining an optical path through the plurality of locations, the optical fiber having an excess fiber length EFL at 20 degrees Celsius of at least 0.35%, the optical fiber having a coefficient of thermal expansion CTE fiber , a ratio CTE jacket /CTE fiber being greater than 1.0; b. injecting an optical signal in the optical fiber, the optical fiber producing a measurable response to the optical signal, the measurable response being dependent on” a dimensional change induced in the optical fiber as a result of thermal expansion or contraction of the optical fiber; c. processing the measurable response to derive physical parameter information at the plurality of spaced apart locations.