Analyzing fracture stratigraphy

1. A computer-implemented method for identifying fracture stratigraphy based on microseismic data, the method comprising:

receiving microseismic event data associated with a fracture treatment of a subterranean zone, the subterranean zone including a plurality of subsurface layers;

using a filter to select a subset of the microseismic event data, the selected subset of the microseismic event data associated with a particular subsurface layer in the subterranean zone, wherein the filter includes filter parameters that define a specified region within the particular subsurface layer, wherein using the filter to select the subset of the microseismic event data includes identifying microseismic events in the specified region;

generating, by data processing apparatus, a plurality of fracture planes based on the selected subset of microseismic event data associated with the identified microseismic events in the specified region within the particular subsurface layer;

calculating, by data processing apparatus, a fracture stratigraphy for the particular subsurface layer, wherein the fracture stratigraphy is calculated from the fracture planes generated using the selected subset of the microseismic event data associated with the identified microseismic events in the specified region within the particular subsurface layer; and

correlating the calculated fracture stratigraphy with mechanical stratigraphy for the particular subsurface layer, wherein correlating the calculated fracture stratigraphy with mechanical stratigraphy for the particular subsurface layer comprises comparing spatial variations in the calculated fracture stratigraphy with spatial variations in mechanical properties of rock in the particular subsurface layer of the subterranean zone; and

controlling an injection treatment based on the calculated fracture stratigraphy.

2. The method of claim 1 , wherein using the filter to select the subset of the microseismic event data includes identifying microseismic events associated with fracture planes intersecting the specified region, and the fracture stratigraphy is calculated for the specified region based on the identified microseismic events associated with fracture planes intersecting the specified region.

3. The method of claim 2 , wherein at least one of the fracture planes intersects the specified region and at least one other subsurface layer, and the identified microseismic events include at least one microseismic event in the other subsurface layer.

4. The method of claim 1 , wherein the filter parameters define the specified region as a range of vertical depth.

5. The method of claim 1 , further comprising:

generating a user interface that includes a graphical representation of the particular subsurface layer of the subterranean zone and locations of microseismic events; and

receiving, through the user interface, a user selection of the filter parameters.

6. The method of claim 1 , wherein calculating fracture stratigraphy comprises at least one of:

generating a statistical description of fracture orientations for fracture planes associated with the particular subsurface layer;

generating a statistical description of fracture spacing for fracture planes associated with the particular subsurface layer; or

generating a statistical description of fracture dip angles for fracture planes associated with the particular subsurface layer.

7. The method of claim 1 , wherein the selected subset of the microseismic event data includes all microseismic events in the particular subsurface layer.

8. The method of claim 1 , wherein the selected subset of the microseismic event data includes a less than all microseismic events in the particular subsurface layer.

9. The method of claim 1 , wherein the selected subset of the microseismic event data includes all fracture planes in the particular subsurface layer.

10. The method of claim 1 , wherein the selected subset of the microseismic event data includes a less than all fracture planes in the particular subsurface layer.

11. A non-transitory computer-readable medium encoded with instructions that, when executed by data processing apparatus, perform operations comprising:

receiving microseismic event data associated with a fracture treatment of a subterranean zone, the subterranean zone including a plurality of subsurface layers;

using a filter to select a subset of the microseismic event data, the selected subset of the microseismic event data associated with fracture planes in a particular subsurface layer in the subterranean zone, wherein the filter includes filter parameters that define a specified region within the particular subsurface layer, wherein using the filter to select the subset of the microseismic event data includes identifying microseismic events in the specified region;

generating a plurality of fracture planes based on the selected subset of microseismic event data associated with the identified microseismic events in the specified region within the particular subsurface layer;

calculating a fracture stratigraphy for the particular subsurface layer, wherein the fracture stratigraphy is calculated from the fracture planes generated using the selected subset of the microseismic event data associated with the identified microseismic events in the specified region within the particular subsurface layer; and

correlating the calculated fracture stratigraphy with mechanical stratigraphy for the particular subsurface layer, wherein correlating the calculated fracture stratigraphy with mechanical stratigraphy for the particular subsurface layer comprises comparing spatial variations in the calculated fracture stratigraphy with spatial variations in mechanical properties of rock in the particular subsurface layer of the subterranean zone; and

controlling an injection treatment based on the calculated fracture stratigraphy.

12. The computer-readable medium of claim 11 , wherein the filter includes parameters that define a specified region within the particular subsurface layer, using the filter to select the subset of the microseismic event data includes identifying microseismic events associated with fracture planes intersecting the specified region, and the fracture stratigraphy is calculated for the specified region based on the identified microseismic events.

13. The computer-readable medium of claim 11 , wherein calculating fracture stratigraphy comprises at least one of:

generating a statistical description of fracture orientations for fracture planes associated with the particular subsurface layer;

generating a statistical description of fracture spacing for fracture planes associated with the particular subsurface layer; or

generating a statistical description of fracture dip angles for fracture planes associated with the particular subsurface layer.

14. A system comprising:

a computer-readable non-transitory medium that stores microseismic event data associated with a fracture treatment of a subterranean zone, the subterranean zone including a plurality of subsurface layers; and

data processing apparatus operable to:

use a filter to select a subset of the microseismic event data, the selected subset of the microseismic event data associated with a particular subsurface layer of a plurality of subsurface layers in the subterranean zone, wherein the filter includes filter parameters that define a specified region within the particular subsurface layer, wherein using the filter to select the subset of the microseismic event data includes identifying microseismic events in the specified region;

generate a plurality of fracture planes based on the selected subset of microseismic event data associated with the identified microseismic events in the specified region within the particular subsurface layer;

calculate a fracture stratigraphy for the particular subsurface layer, wherein the fracture stratigraphy is calculated from the fracture planes generated using the selected subset of the microseismic event data associated with the identified microseismic events in the specified region within the particular subsurface layer; and

correlate the calculated fracture stratigraphy with mechanical stratigraphy for the particular subsurface layer, wherein correlating the calculated fracture stratigraphy with mechanical stratigraphy for the particular subsurface layer comprises comparing spatial variations in the calculated fracture stratigraphy with spatial variations in mechanical properties of rock in the particular subsurface layer of the subterranean zone; and

control an injection treatment based on the calculated fracture stratigraphy.

15. The system of claim 14 , wherein the data processing apparatus is further operable to generate a user interface that includes a graphical representation of the subsurface layers of the subterranean zone and locations of microseismic events, and the system further comprises a display device operable to:

display the user interface; and

receive a user selection of parameters of the filter.