Evaluation Of Aerated Drilling Fluids Used At The Nevada Test Site
Authors: Hammer Wallace L. , Walker Joe A. 
Published: December 2007

The use of rotary-drilled holes at the Nevada Test Site for emplacement of instrument hardware requires drilling techniques that provide for optimum hole stability. To meet these requirements with minimum costs, five types of aerated drilling fluids using direct and dual-string reverse circulation were evaluated. Results show that air-low water loss bentonite mud (A-LWB) using integral dual-string reverse circulation is the preferred drilling fluid to achieve acceptable hole conditions with lowest costs.

Introduction

As of Dec. 27, 1978, 3,877 rotary holes have been drilled at the Nevada Test Site. Hole diameters range from 0.076 m (0.25 ft) to 4.06 m (13.33 ft) mad to a depth or 4,172 m (13,686 ft). The majority (83.4%) of these holes were drilled since the Nuclear Test Ban Treaty of 1963. There are five basic classifications of holes.Utility holes are required for water supply, mining ventilation, and pull test facilities.Exploratory holes are drilled to obtain geological and hydrological information.Instrument holes are used to obtain data during nuclear testing.4 Post shot holes are drilled after a nuclear test to recover samples in the cavity.5 Emplacement holes are used for containment of a nuclear device.

The capability of the Nevada Test Site operations for rotary drilling and completion of large-diameter holes includes the following projects.Holes drilled to 1,524 m, cased with 1.22 m ID steel casing end cemented in place. Underreamed chambers as large as 6.68-m diameter by 3.96 m in height excavated at 1,452 m in depth, which is 610 m below the static water table.A string of 1.22-m ID steel casing, weighing 1,542,200 kg, set and cemented to surface.A large hole of 2.44-m diameter presently is drilled from 37 to 366 m deep in 12 days. This compares to 1.22-m diameter holes drilled to 183-m depth in 1963. The drill cuttings removed fro a 244-m diameter hole to 366-m depth are 1,537 m compared with 214 m for a 1.22-m diameter hole to 183 m in depth. The material removed from a 2.44-m diameter hole to 366-m depth is equivalent in volume to seventy-five 0.31-m diameter holes to 366m depth.

This study is directed to evaluating performance data of aerated circulating fluids for performance data of aerated circulating fluids for drilling holes of 1.31-m to 7.05-m (52-in. to 96-in.) diameter from 93 to 761 m (305 to 2496 ft) in depth. This paper compares type of circulating method and fluid vs hole size and depth. No consideration is given to changes in other drilling parameters such as specific fluid velocity, bit parameters such as specific fluid velocity, bit weight, rate of rotation, or geological conditions. A total of 59 holes were used in this evaluation, representing a random selection of emplacement holes drilled since 1971. The geologic sequence of formations drilled are alluvium and rhyolitic volcanics.

THEORY

Conventional mud and circulating systems did not meet hole criteria integrity and were cost prohibitive. This was due to numerous lost prohibitive. This was due to numerous lost circulation intervals encountered. Air-Form, using direct circulation, was the first method used to correct the problem. This practice evolved to the present technology of using aerated fluids with present technology of using aerated fluids with integral dual-string reverse circulation.

This method is the most efficient for removal of cuttings to obtain acceptable hole stability presently developed at the Nevada Test Site. The presently developed at the Nevada Test Site. The ultimate goal is to reduce the hydrostatic pressure on the formation with minimum hole erosion.