Wells – Processes – Cementing – plugging or consolidating
Reexamination Certificate
2002-12-03
2004-12-28
Neuder, William (Department: 3672)
Wells
Processes
Cementing, plugging or consolidating
C166S290000, C166S117600
Reexamination Certificate
active
06834720
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to methods and equipment for treatment and remediation of contaminated soil and groundwater, with emphasis on improved in-situ methods and equipment for efficiently delivering of active treatment agents to the contaminated region.
A primary objective of environmental remediation of subsurface contamination is to remove or treat the contamination when possible; and when removal or treatment is not possible, to provide interim containment of mobile hazardous and/or radioactive waste constituents. Examples of contaminants of concern include pesticide-contaminated soil and/or groundwater, benzene vapors, or non-aqueous phase liquids, such as gasoline leaking from a buried storage tank. An underground barrier, whether permeable or impermeable, can be used to contain, remediate, and/or redirect the flow of contaminated groundwater. An impermeable subsurface barrier wall is typically made of a substantially impermeable material that prevents the migration of mobile waste forms through the relatively permeable surrounding ground (soil, sand, etc.). Neat cement-based grout (a well-known mixture of Portland cement and water), mixed with the surrounding soil, is commonly used as a ground-hardening material to fabricate impermeable underground barrier walls. The neat cement is vigorously mixed with the soil to ensure the soil aggregate acts as a binder. The cement/soil mixture can be used to backfill trenches that have been dug (which is limited to a depth of less than 40 feet).
Advancing this technology, the underground barrier wall can be constructed of reactive materials that actively remediate (i.e., remove or transform) contaminants, as opposed to simply blocking movement or confining with impermeable barriers. Conceptually, permeable reactive barriers (PRB's) are used to intercept and remove ground water contaminants in-situ before passing into the wider ecosystem (see FIG.
1
). The barrier can be constructed of benign permeable reactive media (PRM), such as small, solid particles of zero-valent (metallic) iron that are used to breakdown or immobilize contaminants (e.g., by redox reduction) using ordinary chemical, physical, and/or biological means (the word “barrier” is defined herein to include zones that are permeable to the passage of water, other liquids, or gases). Treated, uncontaminated groundwater then exits from the barrier and is returned to the aquifer.
Currently, reactive barrier technology is practically limited to use in excavated trenches at depths of less than 40 feet, due to problems with injecting dry particulate media to greater depths using drill strings. Experimental attempts at greater depth placement have used fluid-based viscosifying agents to inject PRM into subsurface regions. Viscosifying/suspension agents (e.g., organic guar, with a viscosity like molasses) have been used to suspend the often-dense PRM (e.g., iron particles) to facilitate pumping and injection using high-pressure systems. Problems with this method include non-uniformity of the mixture and retention of the viscosifier in the treatment zone, potentially causing permeability reduction problems, biological growth abnormalities, and other problems.
Underground reactive barrier walls (or zones) can be fabricated in-situ using modified (i.e., hybrid) jet grouting techniques. The term “jet grouting” refers to the use of one or more high-pressure jet spray nozzles, which are located on a jet grout injector sub-assembly attached to the end of a drill string, to inject slurry-like materials at relatively high velocity radially outwards into the surrounding soil. The high-velocity jet spray simultaneously masticates and erodes the surrounding soil, while dispersing and blending the injected slurry with the loosened soil. If the slurry is primarily made of cement-based grout, then the mixture of soil and grout subsequently hardens into a solid, substantially impermeable material, sometimes called “soilcrete”. In the case of the advanced technology the jetted reagent material contains PRM's, and the mixture of soil and PRM (or, the replacement of loosened soil with PRM's) forms a permeable reactive barrier zone.
Traditionally, the jet grout injector is rotated during withdrawal (by rotating the drill string), creating a cylindrical column (typically in the vertical direction). On the other hand, if the jet grout drill string is not rotated during withdrawal, then the jet spray creates a relatively thin panel/wall section. Multiple columns or wall panels can be emplaced underground in an overlapping pattern to create a continuous barrier wall or zone.
Conventionally, three different generic types of jet grouting injector sub-assemblies are currently used for injecting neat cement grout i.e., one-fluid, two-fluid, and three-fluid designs. A one-fluid design has a single outlet nozzle that radially sprays a slurry mixture containing grout. A two-fluid design has two coaxial outlet nozzles, where the inner nozzle sprays the grout slurry and the outer nozzle sprays a conical aureole of compressed air, which serves to increase the radial distance of jet cutting action. A three-fluid design has three nozzles. Two of these nozzles are coaxial; with the inner nozzle injecting high-velocity water, and with the outer coaxial nozzle injecting a conical aureole of compressed air. The combined action of the water jet surrounded by the conical aureole of compressed air cuts and masticates the surrounding soil. The third nozzle, located some distance below the upper two coaxial nozzles, injects a relatively low-pressure slurry of grout into the already-masticated, loosened soil. In the two-fluid and three-fluid designs, the use of compressed air increases the radius of influence of the water jet. It also “lightens” the mixture of soil and water in the zone of influence of the jet, thus creating an airlift which pumps excess water and soil fines through the annular space between the borehole wall and the drill string to the surface. However, the single-fluid design is generally preferred for drilling inclined and horizontal holes.
For construction of permeable reactive barrier zones to depths greater than 40 feet, drilling operations use drill bits such as tri-cone, drag, and rock bits mounted on the end of a jet grouting nozzle sub-assembly (“sub” or “monitor”). Drilling bits use air or water or bentonite mud as a bit lubricant/cooling medium, which also serves as a carrier medium to bring cuttings up out of the hole during the drilling operation (i.e., spoils). Down-the-hole (DTH) hammer drill assemblies can also be used, which are driven by compressed air to provide a repetitive, percussive hammering force on the drill bit to increase drilling rates. The compressed air exits the DTHH drill assembly through passages in the attached drill bit, which expels rock cuttings from around the drill bit and flushes them away.
Downhole injection of PRM's mixed with liquid-based suspension agents results in multiple problems and concerns, which center around the practice of using jet grouting nozzles that were designed only for injecting neat cement/grout slurries.
Melegari, in U.S. Pat. No. 5,624,209, teaches that permeable reactive media made of dry aggregate particles can be suspended in a stream of air under relatively low pressure (approx. 20 bar), and then co-injected simultaneously with a separate spray of high-pressure water (approx. 500 bar) using a pair of coaxial radial nozzles, where the high-pressure water is injected through the inner nozzle, and the air/media spray being injected through the outer nozzle. The high-pressure/high-velocity (approx. 200-250 m/s) water jet disintegrates the soil and produces a mixing effect that disperses the injected dry media in the soil. The use of only low-pressure air to suspend the solid particles limits the ability of the device to inject the particulate matter deeply into the soil (in a radial direction).
Melagari explains in related U.S. Pat. No. 5,944,454 that the size of solid particles suspended in h
Dwyer Brian P.
Dwyer Stephen F.
Stewart Willis E.
Vigil Francine S.
Neuder William
Sandia Corporation
Watson Robert D.
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