1. INTRODUCTION To increase hydrocarbon recovery in the subsurface, it is desirable to produce fractures with high surface area to release the maximal amount of naturally stored oil and gas. The larger the surface area created by fractures in a finite space, the higher the potential of the system to recover hydrocarbons, because more flow channels are produced. Such a system is called an open, complex hydraulic fracture network. We investigate the creation of an open complex fracture network via laboratory experiments using a range of fracturing fluids and stress conditions. In this paper, we focus on fracture within homogenous samples, to better understand how complex networks initially develop. Once a baseline of data of fracture pressure per fluid has been made, the initial conditions can be manipulated for future experiments to create fractures of increased surface area. 2. EXPERIMENTAL PROCEDURE Experiments were conducted in the Rock and Sediment Laboratory at the Pennsylvania State University. 2.1 Specimen and Preparation A standard homogenous material used in hydraulic fracture experiments is Polymethyl methacralate (PMMA) [1, 2, 3]. We used PMMA because it has known physical properties and supports stresses on order of tens of MPa, comparable to that of rock. PMMA is transparent such that facture propagation can be analyzed during and after fracturing experiments. Here, we report results for hydraulic fracture of homogeneous cubes 101 mm (4 in) and 121 mm (5 in) on a side. A model borehole was drilled into the PMMA cube, and set with acrylic adhesive to seal a high-pressure tube fitting and preserve the sample integrity. Boreholes were 3.66 mm (0.144 in) in diameter and tube fittings were 3.175 mm (0.125 in) in diameter. Samples were subject to biaxial and triaxial stress states, and boreholes were oriented parallel to the least principal stress direction σ 3 . ARMA 12-678 Exploring the physicochemical processes that govern hydraulic fracture through laboratory experiments Alpern, J. S., Marone, C. J. and Elsworth, D. College of Earth and Mineral Sciences, The Pennsylvania State University, University Park, PA 16802 Belmonte, A. Department of Mathematics and of Material Sciences & Engineering, The Pennsylvania State University, University Park, PA 16802 Connelly, P. Chevron Exploration Technology Company, Houston, TX 77002 Copyright 2012 ARMA, American Rock Mechanics Association This paper was prepared for presentation at the 46 th US Rock Mechanics / Geomechanics Symposium held in Chicago, IL, USA, 24-27 June 2012. This paper was selected for presentation at the symposium by an ARMA Technical Program Committee based on a technical and critical review of the paper by a minimum of two technical reviewers. The material, as presented, does not necessarily reflect any position of ARMA, its officers, or members. Electronic reproduction, distribution, or storage of any part of this paper for commercial purposes without the written consent of ARMA is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgement of where and by whom the paper was presented. ABSTRACT: Hydrocarbon recovery is potentially maximized with an open, complex fracture network of large surface area to volume ratio that penetrates the reservoir. We study the hydraulic rupture of a solid, homogenous cube of Polymethyl methacrylate (PMMA) containing model boreholes as an analog to hydraulic fracturing with various fracture-driving fluids. The transparency of PMMA allows for the visualization of fracture propagation using high-speed video. The cubes are constrained by prescribed triaxial far-field stresses with the borehole-parallel stress set to zero. The cube is ruptured by overpressuring the borehole at controlled rates with fluids present as both liquids and gases pre- and syn- failure. We measure the fracture breakdown pressure, rates of fracture propagation and the physical characteristics of the resulting fractures and how they vary between fluid types. Further research extends these experimental methods to bluestone and granite, with additional tests that determine the permeability of these materials and its effect on creating a complex fracture network.