This presentation will give some recent developments in the hydraulic fracturing
design, application and evaluation procedures in the oil and gas industry.
Depending on the reservoir, hydraulic fracture treatments have as a goal either to
bypass damaged permeability close to the well, or to create additional contact area
between the reservoir and the well. While for the first goal the key is to maximize
the fracture conductivity and thus the fracture width in the vicinity of the
wellbore, the second goal requires large fractures, preferably connecting to an
already existing network of natural fractures. Typically, such massive hydraulic
fractures are placed in low-permeability reservoir.
The successful placement of a propped hydraulic fracture depends critically on the
quality of the design input data. Such data contain knowledge about the in-situ
stresses, the reservoir permeability, the elastic parameters, and the fracture
propagation criteria. Minifrac tests are designed to disclose such parameters. To
this end, the time-dependent behaviour of the pressure after a short injection test
above the fracture pressure is analysed with specially designed software. Further
important knowledge is the containing capacity of different layers in the
subsurface, as these determine the height / length ratio of the fracture. A profile
of the parameters, required to assess this, is still often difficult to obtain.
Even with good design input data and a properly operated fracturing treatment, the
results are not always in line with the predictions. Knowledge is usually built up
in specific areas during subsequent hydraulic fracturing treatments and their
careful evaluation. One method that can help considerably in this evaluation is
tiltmeter mapping, by which the non-seismic displacements during the fracturing
operation are measured and inverted determine the dimensions of the created fracture.