MODIFICATIONS EXTEND LOG TOOL RUNS AT 25,500 FT

Modification of a conventional logging tool has resulted in successful, longer continuous runs in deep, high temperature wells. With the tool modified by Los Alamos National Laboratory (LANL), Los Alamos, N.M., one operator estimates a potential savings of $2040,000/well. The retrofitted tool reached critical temperatures more slowly, was able to resist the downhole temperatures three times as long as the conventional high temperature tool, and was still operating at the end of the run.

March 4, 1991

5 min read

Modification of a conventional logging tool has resulted in successful, longer continuous runs in deep, high temperature wells.

With the tool modified by Los Alamos National Laboratory (LANL), Los Alamos, N.M., one operator estimates a potential savings of $2040,000/well.

The retrofitted tool reached critical temperatures more slowly, was able to resist the downhole temperatures three times as long as the conventional high temperature tool, and was still operating at the end of the run.

Exxon Co., U.S.A. has historically experienced significant costs associated with tool failures and resultant additional electric line runs, tool repairs, and rig time on deep, high temperature wells.

Before using the modified tool in the Anadarko basin in December 1991, Exxon had employed numerous well logging companies in several divisions. Repeated runs were usually required because the tools failed in too short a time to obtain the required formation measurements.

Exxon and Royal Wireline Inc., Mercedes, Tex., contacted LANL to provide design and technical consultation and upgrade the logging instruments.

LANL used technologies developed in its laboratories in design of deep well logging instrumentation for operation in geothermal wells drilled for the U.S. Department of Energy's Hot Dry Rock program and electronic circuitry designed to meet requirements for satellite projects.

TOOL MODIFICATION

LANL's modification to the existing tool required changes in the geometry of electronic components and upgrading of industry components to military specifications.

It modified Royal's conventional neutron-gamma ray and collar locator tools for use in the Hazel Howell well, being completed in late 1990 early 1991 in Northeast Mayfield field, Beckham County, Okla.

Bottomhole temperatures in the area, 25 miles west of Elk City, are about 400 F.

Existing high temperature logging tools can be readily modified for higher temperature ratings using the technology discussed below. These include open hole density, neutron-gamma ray, dual induction, and sonic log tools.

The most stringent requirement was to ensure that internal components of the tool, when modified, occupied no more space than was available in the original tool pressure housing.

The heat sink, electronic circuits, dewar flask, and neck insulation subsystems were reproportioned to make the entire system more heat efficient (Fig. 1).

An important aspect of heat management included modifications to the electronics by replacing discrete components with flight qualified integrated circuits and parts screened to operate at about 250 F.

The new electronic circuits were high density power efficient chips mounted on flight qualified printed circuit boards.

Reconfiguration and miniaturization of the electronics using the space age technology reduced the original volume 25%.

DEALING WITH HEAT

LANL also improved heat conduction paths and developed heat storage devices.

One essential modification was to provide adequate heat conduction paths for the internally generated heat and heat transferred to the dewar from the external environment.

The internal heat is generated by the power dissipation of the electronic circuits.

Metal covers were designed to encase the electronic components. These provided both a heat storage device and sufficient conductive paths to the heat sinks to eliminate hot spots inside the dewar flask.

Heat pipes transfer heat 50,000% more efficiently than a solid metal tube (Fig. 2).

Heat pipes are small diameter pipes, 1/8 to 1/4 in. outside diameter; filled with a wick, usually a steel mesh; partially filled with some liquid, water or alcohol; and closed at each end.

The liquid inside boils from the bottom to the top of the tube. Capillary action then forces the condensed liquid back to the bottom.

This circulation serves to transfer heat very fast and very efficiently in the closed system.

The heat pipes convey the heat buildup from electrical components very efficiently from the tool into the heat sinks above and below it. The entire assembly is enclosed in a dewar flask that is inserted into the carrying case.

The designers developed heat sinks, brass and copper containers filled with a solid eutectic alloy, Cerrobend, that melts at the prescribed temperature of about 250 F.

The sinks use the latent heat of fusion of the Cerrobend metal to keep the tool at a steady 250 F. Heat pipe/heat sink technology is used to cool nuclear reactors in satellites, wing leading edges in supersonic aircraft, and nuclear reactor cores.

TOOL COMPARISONS

The original and upgraded neutron-gamma ray instruments were thermally tested in the laboratory to obtain comparable results prior to field test. Before modification, internal temperature in the electronics compartment exceeded 250 F. in 4 hr. The modified tool took 22 hr to reach that temperature.

Two standard industry temperature resistant logging sondes were run from surface to 25,525 ft at the 1 Howell well Dec. 27, 1990.

The neutron sonde failed after 2 hr in the well, the gamma ray tool after 4 hr.

The LANL modified neutron-gamma ray sondes were run Dec. 30, 1990.

Two consecutive logging runs were made for a total of 12 hr in the well. The tool performed as expected with no failures. Test results confirmed 8 hr of continuous operation at the specified temperature, far exceeding the original goal of 5 hr (Fig. 3).

Exxon estimated that the upgraded tool might operate efficiently for 9-12 hr in a deep gas well.

Further improvements could extend the temperature range of the neutron-gamma ray tool if time were available for a complete redesign of both the mechanical and electronic components, the companies believe.