Patent ID: 8811776

Claim:
A method for measuring a physical parameter at a plurality of spaced apart locations in a subterranean formation, 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 , the jacket having an internal cross-sectional area A j ; 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 C., the optical fiber having a coefficient of thermal expansion CTE fiber , a ratio CTE jacket /CTE fiber being greater than 1.0, variations in the physical parameter causing localized dimensional changes in the optical fiber at the spaced apart locations; the elongated sensing element having a parameter S = A j E ⁢ ⁢ F ⁢ ⁢ L of at least 1 mm 2 per percent of EFL; b. injecting an optical signal in the optical fiber, the optical fiber producing a response to the optical signal that is dependent on the localized dimensional changes and conveys information about the physical parameter at the plurality of spaced apart locations; processing the response to derive information about the physical parameter at each of the plurality of spaced apart locations.