Equipment For Drilling And Fracturing Hot Granite Wells
Authors: Williams R. Edward , Rowley John C. , Neudecker Joseph W. , Brittenham Terry L. 
Published: December 2007

Drilling and fracturing requirements for deep, deviated geothermal hells in very hot granite creates several severe equipment problems. These problems result from the very high temperatures and problems result from the very high temperatures and extremely hard rock of the geothermal reservoir under development. Previous drilling of two wells to 10,000 feet (3 km) depths and 400 degrees F (200 degrees C) at the Fenton Hill, NM, Hot Dry Rock (HDR) geothermal experimental site have defined these problems and directed efforts toward solutions. These problems and directed efforts toward solutions. These solutions have required extensions of current drilling methods and development of new tools and hardware.

This paper describe the requirements for the hot hole tools, the new equipment, and status of tests of the tools that have been developed for drilling and open-hole fracturing operations for use in 14,500 foot (4.4 km) deep, 527 degrees F (275 degrees C) bottom hole temperature wells. The relationships and potential applications of these drilling equipment advances to drilling of natural (hydrothermal) geothermal reservoirs are presented. presented. The high temperature equipment, services, and operations described include turbodrill performance, special hybrid core bits, gyro surveys, hot hole directional drilling steering, rock bit performance and life, Shock absorbers, and packers performance and life, Shock absorbers, and packers for open-hole fracturing and testing.

Introduction

Geothermal Drilling Trends

The National Energy Act (October 1978) provided a 22% depletion allowance, and tax incentives provided a 22% depletion allowance, and tax incentives in the form of intangible gilling cost write-offs and investment credits for geothermal development. These provisions and the rising world prices for oil have served to accelerate geothermal leasing, exploration, and drilling activities. The U.S. DOE has sponsored research and development support for needed technology improvements, established a loan guaranty program, and funded geothermal demonstration projects.

In addition to projects intended to promote hydrothermal (steam and hot water) resource development, programs to evaluate the potential of geopressured and hot, dry rock geothermal resources have been initiated. Geothermal developments, both private and government funded, ultimately require drilling to prove, evaluate, mad produce the resources. Drilling problems and costs produce the resources. Drilling problems and costs are a major influence in commercial decisions in geothermal development. For the Los Alamos Scientific Laboratory's (LASL) Hot Dry Rock (HDR) geothermal program, solution to some drilling problems is central to successfully performing the required scientific feasibility experiments, reservoir formation operations, and heat extraction demonstrations.

Hot Dry Rock Geothermal Concepts

The hot, dry rock concept is based on the fact that geothermal heat is present and stored in rocks at depth even when natural geothermal fluids and/or permeability are absent. The direct evidence for permeability are absent. The direct evidence for this is the significant number of "dry" but hot, wells that have been drilled in search of hydrothermal reservoirs. It seems clear that the heat contained in hot, relatively impermeable (" dry") rock is widely spread and if a technically feasible and practical method of extraction can be devised, this energy source may, in time, contribute to our energy supply. The HDR program has as its prime objective the development of the methods and technology to form artificial reservoirs in hot impermeable rock formations and demonstrate practical techniques for heat extraction.