Particle Size Distributions Generated By Crushed Proppants And Their Effects On Fracture Conductivity
Authors: Carroll H.B. , Baker B.A. 
Published: December 2007

Department of Energy supported research conducted in the tight gas sands of the Piceance, Uintah, and Green River Basins of Colorado, Utah, and Wyoming is directed toward evaluating massive hydraulic fracturing (MEF) for increasing natural gas production. Research at Bartlesville Energy Technology Center supporting the Western Gas Sands Project consists of examining potential areas of formation damage by MHF fluids and proppants.

Fractures produced by the MHF process are propped open by placement of particulate materials propped open by placement of particulate materials creating zones of high permeability and porosity. In this research, high permeability fractures were simulated by placing 40/60 mesh sand proppant between core halves, and subjecting the cores to increasing overburden pressure. As the proppant was crushed, the resultant particles were transported through the propped fracture by frac fluids. Mean, mode, and propped fracture by frac fluids. Mean, mode, and number per unit volume of the produced particle size distributions were measured and related to overburden pressure. pressure. The effects of particle retention, when pumping similar particle distributions through the propped fracture, were detected by a pressure change across the core. Measured changes in the filtration efficiency, conductivity, and threshold plugging pressure of the propped fracture showed significant particle trapping within the porous media. Pressure versus time plots indicate successive pore plugging and particle breakthrough until the fracture is particle breakthrough until the fracture is ultimately plugged.

Introduction

Department of Energy-supported research conducted in the tight gas sands of the Piceance, Uintah, and Green River Basins of Colorado, Utah, and Wyoming is directed toward evaluating massive hydraulic fracturing (MHF) as a means for increasing natural gas production. Research by engineers and scientists at the Bartlesville Energy Technology Center consists of examining potential areas of damage to formations and fractures by MHF fluids and proppants. proppants. The effects from fracture systems on well production shows that by utilizing deep-penetrating, production shows that by utilizing deep-penetrating, high-flow-capacity fracture systems a low-resistance flow path can be made in large portions of the reservoir. The deeply invading fracture provides an average reservoir the capability of producing large volumes of fluids. Also, it provides large drainage areas into which gas from formations of very low permeability can slowly flow, thus utilizing a permeability can slowly flow, thus utilizing a maximum of the available reservoir energy.

Early experimental work has demonstrated that a hydraulically formed fracture tends to heal or return to its initial state after the parting pressure is released unless the fracture is propped. One of the more commonly used proppants is sand because of the economics, its chemical inertness, and its strength properties. However, with the use of sand there are properties. However, with the use of sand there are several inherrent problems associated with its placement in the fracture. placement in the fracture. To create the fracture, a fluid must be used which is viscous enough to retain the sand in suspension in order to carry it back into the fracture. The sand propped fracture must be permeable enough to allow the fluid to be produced back.

Another problem encountered with sand is its strength characteristics. The sand placed in a fracture may crush when the overburden pressure is released upon it, or it may embed in the fracture face depending upon the formation characteristics.

In addition to the capture of sand particles, the propped fracture is further impaired by residue formed upon degradation of the gelled frac fluid. Cooke found that damage occurs from the residue of the guar polymer presently used in fracturing fluids. However, in his study he found that essentially all the residue-forming material in guar polymer was filtered at the face of the rocks. In this study it was found that the material was rather uniformly distributed throughout the element of propped fracture.

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