TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe use of high energy material to stimulate production has been practiced in the oilfield since early in the industry's history. While the materials used for stimulation have progressed from explosive materials to propellants, the basic concept remains the same. A highly energetic material is burned in the wellbore and the gasses and energy released cause the rapid pressurization and breakdown of the formation. This breakdown is capable of generating multiple fractures with certain geometric properties.To investigate and confirm the generation of propellant induced fractures in low permeabililty formations, a large scale laboratory test was designed and conducted at the TerraTek, Inc. laboratories in Salt Lake City, Utah. The test was conducted on a 30"x30"x36" Colton Sandstone block that was loaded in a poly-axial stress frame to predetermined reservoir conditions. A scaled wellbore, drilled in the center of the block, contained the propellant charge. After the block was properly stressed, the propellant charge was deflagrated. The block contained several pressure probes imbedded in the block and located in the wellbore that were capable of sampling at extremely high rates (milliseconds) to capture the full response of the propellant burn.Upon completion of the deflagration, the block was removed from the test frame and cut horizontally to examine the fracture pattern generated by the propellant burn. Each half was later split along the primary fracture to examine the height growth and fracture lengths generated by the propellant stimulation.This paper discusses the test design and execution, the resulting fracture geometries and analyzes the pressure responses witnessed during the propellant deflagration. The results show laboratory verification of some propellant fracture theories and provide insight to the effects of propellant deflagration in field applications.

Unconventional tight gas reservoirs are made economical through effective stimulation techniques. Hydraulic fracture mapping combined with an in-depth knowledge of reservoir geology and geomechanics can give a better understanding to the effectiveness of reservoir stimulation. Massive hydraulic fractures from two wells in the Rocky Mountain region were mapped in real time with a 3-D stimulation viewer software package. One well employed techniques standard to the area -while some experimental fracture techniques were tested on the other. A general east-west orientation of planar fracture geometry was found with a maximum fracture event length of 800 feet. The planer fracturing scheme is consistent with low amounts of acoustic anisotropy recorded. Increasing treating and bottom hole pressures with time observed in this study indicate fracture length growth for each stage. 11 and 12 stages were chosen for the two well completion program based on data from an open hole logging and geomechanics.Some experimental fracturing techniques were tested including longer pump times, larger sand volumes, high viscosity fracture fluids, re-fracturing for re-orientation, using temporary, degradable fiber plugs between stages, and plugging of stages with ball sealers. Perforation entry by stage was effective and some stages could possibly be eliminated to save cost. There is not a direct correlation between pump time, sand volume, and stage height. Ball sealers were not an optimum method for closing off a stage for fracturing, but there is evidence that degradable fiber plugs could be a cost saving option between stages. This paper outlines in more detail the observations from hydraulic fracture mapping in this area. Regional BackgroundThis area of study includes 3000 vertical feet of fluvial and marine sands located in the Rocky Mountain region of the United States. (Figure 1) The formation contains natural fractures, laterally restricted lenticular sandstones, and tight brittle sands. The main natural gas reservoir interval is from 5000 to 8500 feet. The productive sands have an average porosity of about 7% and permeability is in the micro-Darcy range. The first well was drilled in this region of the Rocky Mountains in 1955. In the late 1990's the discovery of increased production by fracturing lenticular sands has made this a profitable area. Due to the nature of these tight sands -wells can be located in closer proximity without lowering the production rates of neighboring wells. Wells are currently drilled on 10 acre density. Much of the area uses directional drilling from pad wells to reduce surface damage.