With proper scaling, the large scale laboratory hydraulic fracturing tests can be an effective way to provide parametric justification for the fracturing design. The tests can also be used to validate hydraulic fracturing models, considering the significant cost reduction via the laboratory tests in lieu of the field tests. Similarly, numerical simulation may act as a virtual test to imitate the laboratory test for achieving improved flexibilities at further reduced cost. In this paper, the result of numerical simulation of the hydraulic fracturing using 3-D model is presented and compared with the measurements from the large scale laboratory hydraulic fracturing tests. The excellent match between the numerical simulation and the experimental tests validates both processes. Further pressure analysis offers an in-depth study on transient fracture propagation and contrasting pressure responses based on the relative positions from the perforation, as well as offers certain validation for the zone of fluid lag near the fracture tip area.
Hydraulic fracturing techniques have been considered as one of the most effective reservoir stimulation technologies since its initial application during late 1940s. With the advances of the measurements and monitoring technologies, the field hydraulic fracture can now be assessed by using: 1) tiltmeter for determining the primary fracture orientations (e.g. azimuth), 2) microseismics for determining the fracture area extent, 3) cross-well micro-seismics for determining the fracture cross-section scope, and 4) bottom hole pressure for determining the fracture width and leakoff quantities. The ultimate aims of these techniques are to determine the evolving fracture geometries as it develops during the fracturing, and the terminal fracture geometries as the fracturing operation is completed. It should be emphasized, however, that the measurement of fracture geometry via these field techniques is rather indirect and qualitative. Frequently, the interpretation of the measuring results becomes more or less subjective as the acquired data can be blurred by the background noises [1].
As an alternative to the field measurement technologies, laboratory testing of hydraulic fracturing in a large scale block rock for determining the fracture geometries becomes more and more appealing. First of all, laboratory tests can imitate the field operation with proper scaling, and with substantially reduced costs. Secondly, the evolving fracture geometries as it propagates can be assessed relatively with ease using pre-embedded pressure probes and with continuing measurement, while the fracture final shape and geometry can be directly observed and measured by splitting the tested block after the test ceases. Thirdly, parametric investigation of a hydraulic fracturing via laboratory large scale block tests can be quite handy, since boundary conditions (e.g. stress and confining pressure), fluid properties (e.g. density, viscosity, etc.) and injection schedule (e.g. injection rate and volume, etc.) can be easily altered as needed during the testing period. Past successful tests can be traced back to early 1990?s when the unique large scale polyaxial stress frame was employed to determine the proper fluid properties for solving fracture initiation and mud circulation problems [2, 3, 4].
