Strain monitoring system

An apparatus for detecting strains and deformations in subterranean rock formations in the earth comprising:

• a substantially enclosed vessel constructed and arranged to be insertable into a borehole extending into a subterranean formation;
• an elongated tube extending from said vessel and in fluid communication therewith at a first end thereof, said tube having a length so that a second end thereof extends generally to the surface of the earth;
• sensing structure isolated from the atmosphere in an enclosed sealed vessel coupled to said second end of the tube;
• an elongated compensating tube filled with said fluid having a length such that a first end thereof is disposed generally at the surface with a second end thereof disposed generally adjacent said vessel, said second end being closed;
• compensating sensing structure being coupled to said first end of said compensating tube, said compensating sensing structure being isolated from the atmosphere in an enclosed sealed vessel and constructed and arranged to detect a volume change in said compensating tube to compensate for temperature effects between the vessel and the surface;
• and
• a fluid substantially filling the vessel and the tube, said vessel being constructed and arranged such that a deformation of solids surrounding said vessel that is transmitted to said vessel causes a change in volume in said vessel which in turn forces fluid into said tube thereby changing a volume of fluid in said tube, said sensing structure being constructed and arranged to detect a volume change in said tube, thereby detecting the deformation of the solids.

A device for detecting strains and deformations in subterranean rock formations in the earth comprising:

• a substantially enclosed vessel insertable into a borehole extending into a subterranean formation;
• a first tube having a first end connected to an upper portion of the vessel and a second end, said first tube having a length so that said second end is disposed generally at the surface of the earth;
• first sensing structure isolated from the atmosphere in an enclosed sealed vessel coupled to said second end of said tube;
• a fluid substantially filling the vessel and in fluid communication with the interior walls of the vessel and filling the first tube;
• coupling structure constructed and arranged to couple walls of the vessel to walls of the borehole by prestressing the walls of the vessel during installation thereof to transmit deformation of rock and solids surrounding the borehole to the walls of the vessel and to produce volume changes in the vessel;
• a second tube filled with fluid and having first and second ends, said second tube having a length such that said first end thereof may be disposed generally adjacent said upper portion of said vessel with said second end of said second tube being disposed generally at the surface of the earth;
• and
• second sensing structure isolated from the atmosphere in an enclosed sealed vessel coupled to said second end of said second tube, said first end of said second tube being closed;
• said vessel being constructed and arranged such that deformation of solids surrounding said vessel that are transmitted to said vessel causes a change in volume in said vessel which in turn forces fluid into said first tube thereby displacing the volume of fluid in said first tube, said first sensing structure being constructed and arranged to detect a volume displacement in said first tube, thereby detecting the deformation of the solids, said second sensing structure being constructed and arranged to detect a volume displacement in said second tube to compensate for environmental effects between the vessel and the surface.

A method for detecting deformation and strains in subterranean formations in the earth which comprises:

• placing a sensing apparatus into a borehole in a subterranean formation subject to elevated temperatures, said sensing apparatus including a vessel, a first tube having a first end coupled to the vessel and in fluid communication therewith and a second end disposed generally at the surface of the earth, said vessel and said first tube being filled with fluid, said sensing apparatus including sensing structure isolated from the atmosphere housed in sealed hydraulic sump coupled to said second end of said first tube;
• forming a prestressed tight fit between walls of the borehole and exterior walls of the vessel so that deformation of rocks and solids surrounding the borehole is transmitted to the walls of the vessel which in turn produces volume changes in the vessel and fluid displacement in the first tube;
• detecting the fluid volume displaced in the first tube by use of said sensing structure to measure deformation in the subterranean formation;
• and
• compensating for environmental effects of the volume of fluid in said first tube between said vessel and the surface of the earth by providing a second tube closed at its lower end and having substantially the same length, substantially the same volume and being filled with the same fluid as the first tube, compensating sensing structure isolated from the atmosphere in a sealed hydraulic sump coupled to a second end of said second tube to detect volume displacement in said second tube which is compared with volume displacement in said first tube.