Surface response to fracture growth (as measured by an array of tilt meters) is now being analyzed jointly with formation pressure response data to more accurately determine the result of fracture growth during stimulation treatments and for fracture closure after shut-in.
Previously, interpretations of fracture growth behavior during and after injection have depended primarily on observed trends of the treating pressure (or net pressure) response vs time. For some wells, this analysis is improved by prefrac pump-in tests and analysis of pressure decline following shut-in. However, as with well test analysis, determination of fracture parameters from a single pressure record in the wellbore will yield no nu nique solutions. Moreover, important parameters such as azimuth and inclination of the induced fracture plane cannot be interpreted from treating pressure data.
In recent years, determinations of fracture azimuth and dip have been achieved by fracture mapping based on measuring surface displacement with arrays of high gain tilt sensors. Now, more accurate fracture mapping can occur because the tilt data are being jointly analyzed with the net treating pressure response during the fracturing operation. This has yielded more highly constrained three dimensional projections of fracture growth and geometric parameters.
This paper will discuss such fracture mapping applications and present several field examples.