ODP Technical Note 10


A. Introduction

A packer is defined as a device that produces a hydraulic seal in a borehole (Fig. IV-1). If the integrity of this hydraulic seal is properly maintained, the hydrologic properties of the formation can be tested by applying differential fluid pressures to the isolated section. Formation properties that can be measured using a packer include pore pressure, transmissivity, from which permeability can be derived, and (less accurately) storage coefficient, which is related directly to formation porosity. In addition, it may be possible to sample fluids from the section of borehole isolated by a packer; if the formation is permeable enough, the sample may contain a component of formation fluids.

A drill-string packer is designed to be part of the BHA; the wireline packer deployed on Leg 133 was a separate tool lowered on a conducting cable into open hole, like a logging tool. A drillstring packer or a wireline packer can be configured as a straddle packer, which incorporates two hydraulic seals and allows the zone between the seals to be tested or sampled. In contrast, a single element packer isolates the zone between the packer seal and the bottom of the hole.

One packer is presently available in ODP: a nonrotatable drill-string packer that can be configured as a single packer or a straddle packer, originally supported by an NSF grant to K. Becker and now maintained and run by ODP/TAMU. This packer was used successfully during Legs 109, 111, 118, 139, 144, 146, and 148 and is available for use in reentry holes that penetrate stable formations.

At various times, three additional packer tools have been deployed from the Resolution, although none was run successfully. Like the successfully deployed straddle packer, these three unsuccessful packer tools were manufactured by TAM International of Houston, Texas. The first of these tools was a rotatable drill-string packer built and operated by ODP and intended for use in less stable formations where a rotational capability may be required for safety reasons. This packer was tested during Leg 110, subsequently modified, and run again during Legs 123 and 131. It was sometimes called the TAM drilling packer, or "TDP". The third packer-type tool run from the Resolution was the wireline sampler built and operated by the Borehole Research Group at LDEO. As the name suggests, this instrument was built primarily for fluid sampling but also was intended to be capable of limited formation testing. The wireline packer was deployed once during Leg 133 but suffered from several design and construction flaws. The fourth packer tool was called the Geoprops probe, a third-party tool initially funded and developed with an NSF grant by D. Karig; Geoprops was deployed for the first time for field testing during Leg 146.

The failures of the rotatable packer, wireline sampler, and Geoprops probe are revealing in terms of the effort required for downhole-tool development and the nature of drilling in ODP. All three tools were intended for use in less than optimal borehole conditions (open, possibly large holes, semi-stable formations) and suffered from fundamental design flaws (see Chapter VIII for more details). These tools have all been retired for now, and none is presently scheduled for use or available during ODP cruises as part of regular operations.

The use of the drill-string straddle packer is discussed briefly in this chapter. A more complete treatment of packer testing is available as Technical Note 14 (Becker, 1990a).

To Drill-string Packers, Section B.
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