Title: Formation Logging Tools for Microholes
Participants - Texaco, Halliburton, Chevron, Strata Production, Los Alamos and Lawrence Livermore National Laboratory
Background. Los Alamos is pioneering the miniaturization of coiled-tubing drilling technology for the purpose of achieving a very substantial reduction (ultimately, 80-90%) in the cost of exploration drilling.
Figure A- An experimental drilling rig that Los Alamos is using to evaluate components for "micro" drilling 1-3/8 to 1-3/4 inch wells. The development of microdrilling at Los Alamos has been supported by a combination of DOE Partnership and Defense Programs funding, and most recently by a collaboration of oil companies (the DeepLook Collaboration). Los Alamos has also demonstrated that through the use of modern electronics and state-of-the-art sensors, small diameter microholes will pose no fundamental obstacle for logging. This latter effort, however, has been restricted to instrumentation for acquisition of seismic data (See Figure B).
Figure B. Microhole seismic tool developed through a DOE Partnership Project alongside a wooden yardstick. Tool diameter is 0.5 inch.
Statement of Problem
While rapid progress is being made in developing a microdrilling capability, the development of a basic suite of formation logs has yet to begin. A further gap in the technology is the absence of the simple capability to survey microholes. If our past experience is a guide, when effective use of commercially mass produced micro-electronic components and state-of-the-art sensors is made, the unit manufacturing cost and the cost of using microhole logging tools will be greatly reduced. The ultimate combination of drilling microholes and use of a new generation of logging tools will lead to a revolutionary decrease in the cost and a dramatic increase in the use of drilling for direct exploration for hydrocarbon reserves.
Technical Approach
We propose a multi-year project for the design, testing, and evaluation of a suite of miniaturized logging tools for formation property wireline measurements in microholes. The project will begin with the prototyping of wireline tools that will be ultimately adaptable to a measurement-while-microdrilling system, to measure the following: borehole trajectory (a surveying tool); natural and spectral gamma; and resistivity (an electrode, focussed current, or induction device or simple combination thereof). The tools will be patterned after non-proprietary designs of conventional tools obtained through the project's industrial participants and subcontractors. The tools will incorporate, where applicable, state-of-the-art technologies available at Los Alamos and in the industrial sector. The resistivity tool will be designed to take advantage of the capability to drill underbalanced microholes with very low volume "designer" drilling fluids that would enhance the resistivity contrast of target formations. In successive years, these tools will be incorporated into the microhole drilling bottomhole assemblies. Other conventional logging tools will be considered for miniaturization and prototyping. Environmental testing of the tools will occur in existing small pressure vessels and conventional wells. Verification of the measurement performance of the logging tools will be conducted in microholes drilled in close proximity to wells for which conventional logs are available. Once miniaturized, we expect, based on our experience to date, that the unit cost of a tool that is developed in this project will be a small fraction of the cost of its full-size equivalent.
Tasks and Contributions
Los Alamos will lead the project and be responsible for design and fabrication of the microhole logging tools. In this regard, Los Alamos has a 25-year history of designing, fabricating and operating specialty logging tools, recently including microhole seismic instrumentation, in environments ranging from oil to geothermal wells. Los Alamos will apply its expertise in developing radiation monitoring devices to the development of the micro-gamma tool. In addition, Los Alamos currently operates a deep hot well and microhole test facilities at a site 40 miles west of Los Alamos. Los Alamos will be responsible for all microhole drilling and microtool logging associated with the project. The Lawrence Livermore National Laboratory contribution will be the design of telemetry subassemblies for the various packages under development. Industrial Service Sector participants (Halliburton) and Oil Company Participants (Texaco, Chevron, Strata Production Company) will provide overall technical guidance and assistance in the form of access to engineering personnel, nonproprietary existing designs, selective parts, test and calibration facilities, and logs from conventional-sized wells at locations where a microhole can be drilled and logged.
Deliverables (FY99-00).
- Surveying device. A microtool surveying tool, comprised of miniature inclinometer magnetic bearing sensors, will be designed, fabricated and evaluated in the field.
- Gamma logging tool. Calculations of the expected performance (count rate versus logging rate, etc.) of the proposed microhole tool in a microhole in comparison to a conventional 3-5/8-inch tool in an 8-inch wellbore will be made. A new scintillation counter with appropriate changes in the electronics package and mechanical design will be developed to optimize the performance of the tool. A prototype with uphole signal processing will be fabricated and initial tests conducted in a microhole. Final testing will consist of comparisons of logs taken in an adjacent microhole and conventional well.
- Resistivity tool conceptual design. Novel measurement combinations and synergisms can be expected when one realizes that much smaller hole size, readily achieved underbalanced drilling conditions, and controlled fluid resistivity schedules are now possible through microdrilling. We will explore the new possibilities created through "measurements-while-micro-drilling" and propose a design for a tool flexible enough to take advantage of these unique measurement opportunities.
Microhole Drilling and Instrumentation Publications
Albright, J.N., Woo, D.W., Fairbanks, T.D., Rutledge, J.T., Thomson, J.C., Howlett, D., and Barge, D. (1998),"Development and testing of a 0.5-inch microhole geophone package," Proceedings of the SEG Annual Meeting, September 14-17, New Orleans, La.
Dreesen, D.S., and Cohen, J.H. (1996), "Investigation of the Feasibility of Deep Microhole Drilling," 1997 ASME/API Energy Week Conference, January 28-30, 1997, Houston.
