Mechanisms governing the direct removal of wastes from the Waste Isolation Pilot Plant repository caused by exploratory drilling

Abstract

Two processes are identified that can influence the quantity of wastes brought to the ground surface when a waste disposal room of the Waste Isolation Pilot Plant is inadvertently penetrated by an exploratory borehole. The first mechanism is due to the erosion of the borehole wall adjacent to the waste caused by the flowing drilling fluid (mud); a quantitative computational model based upon the flow characteristics of the drilling fluid (laminar or turbulent) and other drilling parameters is developed and example results shown. The second mea'hanism concerns the motion of the waste and borehole spall caused by the flow of waste-generated gas to the borehole. Some of the available literature concerning this process is discussed, and a number of elastic and elastic-plastic finitediffelence and finite-element calculations are described that confirm the potential importance of this process in directly removing wastes from the repository to the ground surface. Based upon the amount of analysis performed to date, it is concluded that it is not unreasonable to expect that volumes of waste several times greater than that resulting from direct cutting of a gauge borehole could eventually reach the ground surface. No definitive quantitative model for waste removal as a result of the second mechanism is presented', it is concluded that decomposed waste constitutive data must be developed and additional experiments performed to assess further the full significance of this latter mechanism.

Historical background on performance assessment for the Waste Isolation Pilot Plant

“…Concurrent with the 1992 PA (but not part of the 1992 PA), the quantity of waste particulate released through the spalling of the borehole wall was estimated, i.e., waste released due to the movement of high-pressure gas generated from degradation of containers and organic material to the borehole when the repository was penetrated (Berglund, 1992). Several types of calculations were made and an experimental program was begun to more thoroughly understand the phenomenon.…”

Computational implementation of a systems prioritization methodology for the Waste Isolation Pilot Plant: a preliminary example

“…The value of the shear stress acting on the borehole wall can then be determined from Equation (8). Using an iterative procedure similar to that for the laminar flow problem, the fluid shear stress can be forced to equal the repository shear resistance to erosion (zfaa) to obtain the final eroded borehole radius (Berglund, 1992).…”

“…The calculations performed by Berglund(1992) and preliminary results from 1D experiments conducted in late 1993 and early 1994 (Berglund and Lenke 1994) on gas pressurized porous granular media have indicated that if a drillbit inadvertently penetrates a gas pressurized WIPP disposal room, failure (spall) of the waste adjacent to the drillbit can occur followed by the compression of the waste against the drillstring surface. The compressed waste is likely to cause either sticking of the drillstring assembly or to exacerbate erosion adjacent to the drillpipe and consequently cause a quantity of waste to reach the ground surface.…”

“…k=lx10-13m*) and high gas pore pressure (14.8 MPa), gas will flow into the hole at approximately O.lm3/(m2of exposed waste area)/s (Berglund, 1992). This volume increases by a factor of 86 as it rises in the annulus and the rate of gas inflow into the drilling mud at the waste elevation is further exacerbated by the drop of hydrostatic pressure as the mud is displaced out of the hole and the length of the fluid column decreases. This is a classic blowout condition.…”

“…The three nonlinear integral equations represented by Equations (3) generally must be solved numerically, a process which is described in detail in Berglund (1992). In that report, the final eroded diameter is determined through an iterative process that equates the fluid shear stress adjacent to the waste to a measure of the erosion resistance of the waste.…”