Abstract: The application describes methods and apparatus for seismic monitoring using fiber optic distributed acoustic sensing (DAS). The method involves interrogating a first optical fiber (102) deployed in an area of interest to provide a distributed acoustic sensor comprising a plurality of longitudinal sensing portions of fiber and also monitoring at least one geophone (107) deployed in the area of interest. The signal from the at least one geophone is analyzed to detect an event of interest (105). If an event of interest is detected the data from the distributed acoustic sensor acquired during said event of interest is recorded. The geophone may be co-located with part of the sensing fiber and in some embodiments may be integrated (307) with the sensing fiber.

Abstract: A method of producing a hydrocarbon fluid from a subsurface formation, wherein use is made of a directionally sensitive Distributed Acoustic Sensing (DAS) fiber optical assembly having adjacent lengths of optical fiber (A,B) with different directional acoustic sensitivities, which are used to detect the direction (?) of acoustic signals relative to the lengths of optical fiber (A,B).

Abstract: A directionally sensitive Distributed Acoustic Sensing (DAS) fiber optical assembly comprises adjacent lengths of optical fiber (A,B) with different directional acoustic sensitivities, which are used to detect the direction (a) of acoustic signals relative to the lengths of optical fiber (A, B).

Abstract: A distributed acoustic sensor, comprises a housing having a longitudinal bore therethrough, an optical fiber supported in the bore; and an inertial member supported within the bore, wherein the fiber is mechanically coupled to the inertial member. The inertial member may include a weight and may provides isotropic stiffness such that it deforms more readily in a first direction normal to the bore than it does in a second direction that is normal to both the bore and the first direction. The sensor may include a plurality of axially-spaced centralizers in the bore, and at least one of the inertial member and the centralizers may comprise swellable material.

Abstract: The application describes methods and apparatus for seismic monitoring using fibre optic distributed acoustic sensing (DAS). The method involves interrogating a first optical fibre (102) deployed in an area of interest to provide a distributed acoustic sensor comprising a plurality of longitudinal sensing portions of fibre and also monitoring at least one geophone (107) deployed in the area of interest. The signal from the at least one geophone is analysed to detect an event of interest (105). If an event of interest is detected the data from the distributed acoustic sensor acquired during said event of interest is recorded. Th geophone may be co-located with part of the sensing fibre and in some embodiments may be integrated (307) with the sensing fibre.

Abstract: A distributed acoustic sensor, comprises a housing having a longitudinal bore therethrough, an optical fiber supported in the bore; and an inertial member supported within the bore, wherein the fiber is mechanically coupled to the inertial member. The inertial member may include a weight and may provides isotropic stiffness such that it deforms more readily in a first direction normal to the bore than it does in a second direction that is normal to both the bore and the first direction. The sensor may include a plurality of axially-spaced centralizers in the bore, and at least one of the inertial member and the centralizers may comprise swellable material.

Abstract: A directionally sensitive Distributed Acoustic Sensing (DAS) fiber optical assembly comprises adjacent lengths of optical fiber (A,B) with different directional acoustic sensitivities, which are used to detect the direction (a) of acoustic signals relative to the lengths of optical fiber (A, B).