Measuring horizontal stress in an underground formation

1. A diagnostic wellbore testing method comprising:

forming a diagnostic wellbore in a subterranean zone comprising one or more formations, the wellbore extending from a surface of the subterranean zone through a portion of a formation having a maximum horizontal stress extending in a first direction and a minimum horizontal stress extending in a second direction perpendicular to the first direction;

forming a pair of notches on a circumference of the wellbore, the pair of notches diametrically opposite each other and extending away from the circumference of the wellbore in the second direction;

applying fluidic pressure to the wellbore at the pair of notches in the second direction while avoiding applying fluidic pressure in the first direction by fluidically isolating the portion of the formation in the first direction from a remainder of the formation, and fluidically isolating the portion of the formation in the first direction comprises disposing one or more packers adjacent the portion of the formation in the first direction, the one or more packers diverting the fluidic pressure away from the portion of the formation in the first direction, wherein fractures propagate from the pair of notches responsive to the fluidic pressure;

measuring a closure pressure of the wellbore; and

providing the closure pressure as the maximum horizontal stress of the formation.

2. The method of claim 1 , wherein forming the pair of notches comprises lowering a notching tool into the wellbore after forming the wellbore and orienting the notching tool to form the pair of notches in the second direction.

3. The method of claim 2 , wherein forming the pair of notches comprises forming at least one of a pair of U-shaped notches, a pair of V-shaped notches, or a pair of O-shaped notches.

4. The method of claim 2 , wherein forming the pair of notches comprises jetting a fluid through the notching tool.

5. The method of claim 2 , wherein orienting the notching tool comprises rotating the notching tool about a longitudinal axis of the wellbore.

6. The method of claim 1 , wherein measuring the closure pressure comprises sealing the wellbore and increasing the fluidic pressure in the sealed wellbore.

7. A diagnostic wellbore testing method comprising:

forming a diagnostic wellbore in a subterranean zone comprising one or more formations, the wellbore extending from a surface of the subterranean zone through a portion of a formation having a maximum horizontal stress extending in a first direction and a minimum horizontal stress extending in a second direction perpendicular to the first direction;

forming a pair of notches on a circumference of the wellbore at a downhole location, the pair of notches diametrically opposite each other and extending away from the circumference of the wellbore in the second direction;

sealing the first direction at the downhole location from fluidic pressure;

applying the fluidic pressure to the wellbore at the pair of notches in the second direction while the first direction is sealed from the fluidic pressure by fluidically isolating the portion of the formation in the first direction from a remainder of the formation, and fluidically isolating the portion of the formation in the first direction comprises disposing one or more packers adjacent the portion of the formation in the first direction, the one or more packers diverting the fluidic pressure away from the portion of the formation in the first direction;

measuring a closure pressure of the wellbore; and

providing the closure pressure as the maximum horizontal stress of the formation.

8. The method of claim 7 , wherein forming the pair of notches comprises lowering a notching tool into the wellbore after forming the wellbore and orienting the notching tool to form the pair of notches in the second direction.

9. The method of claim 8 , wherein forming the pair of notches comprises forming at least one of a pair of U-shaped notches, a pair of V-shaped notches, or a pair of O-shaped notches.

10. The method of claim 8 , wherein forming the pair of notches comprises jetting a fluid through the notching tool.

11. The method of claim 8 , wherein orienting the notching tool comprises rotating the notching tool about a longitudinal axis of the wellbore.

12. The method of claim 7 , wherein measuring the closure pressure comprises sealing the wellbore and increasing the fluidic pressure in the sealed wellbore.

13. A wellbore testing tool comprising:

a jetting compartment fluidically coupled to a pipe configured to receive fluid from a surface of a wellbore, the jetting compartment configured to be disposed within the wellbore at a subterranean zone comprising one or more formations, the wellbore extending through a portion of a formation having a maximum horizontal stress extending in a first direction and a minimum horizontal stress extending in a second direction perpendicular to the first direction, the jetting compartment comprising two nozzles, each nozzle disposed in opposite sides of the jetting compartment, the nozzles configured to jet fluid away from the jetting compartment to form a pair of notches on a circumference of the wellbore, the pair of notches diametrically opposite each other and extending away from the circumference of the wellbore in the second direction;

a first pair of mechanical packers configured to constrain fluid flow along a longitudinal axis of the wellbore, each mechanical packer of the pair of mechanical packers disposed at respective upstream and downstream ends of the jetting compartment, the upstream end opposite the downstream end; and

a second pair of mechanical packers, each mechanical packer of the second pair of mechanical packers disposed at opposite sides of the jetting compartment between the nozzles, the second pair of mechanical packers configured to prevent fluid from applying fluidic pressure along the first direction, the second pair of packers configured to constrain fluid flow along the second direction such that applying fluidic pressure by the jetting compartment comprises applying fluidic pressure at the notches to cause fractures to propagate from the pair of notches responsive to the fluidic pressure, and such that a closure pressure of the wellbore can be provided as the maximum horizontal stress of the formation.

14. The wellbore testing tool of claim 13 , wherein each mechanical packer of the second pair of mechanical packers comprises a semicircular cross-sectional shape, each mechanical packer comprising a circumference that follows the circumference of wellbore 104 .

15. The wellbore testing tool of claim 13 , further comprising a general purpose inclinometry tool (GPIT) and a rotating motor communicatively coupled to the GIPT, the rotating motor and GPIT disposed upstream of the jetting compartment between the jetting compartment and the pipe, the motor configured to rotate the wellbore testing tool based on information received from the GPIT.

16. The wellbore testing tool of claim 13 , wherein the nozzles are arranged to form at least one of a pair of U-shaped notches, a pair of V-shaped notches, or a pair of O-shaped notches.