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WATER JET CONFERENCE - Waterjet Technology Association

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<strong>WATER</strong> <strong>JET</strong> CLEANING SPEEDS - THEORETICAL DETERMINATIONS<br />

Casper William Zublin, Consulting<br />

Bakersfield, California 93308<br />

ABSTRACT<br />

In an effort to improve state-of-theart water jet cleaning techniques as used in<br />

oilwells, a study was undertaken in 1980, to evaluate certain known parameter and their<br />

relationships. Using theoretical, observed, and empirical field data, a statement based on<br />

rotary applications was developed. Cleaning speeds and effectiveness were increased, and<br />

job results, in economic terms, were significantly improved in most cases. This paper<br />

deals not so much with the results of that development, as it does with the suggested use<br />

of those relationships to a linear application.<br />

BACKGROUND<br />

Oilwell water jet cleaning is a patented process (Hutchison, 1973 & Zublin, 1982)<br />

whereby directionally controlled hydronic energy is applied through very small jet<br />

nozzles to clean liner slots or perforations, and well screens that are partially or<br />

completely plugged.<br />

During normal operations the jets are rotated, as well as pulled up or lowered,<br />

through the interval to be cleaned. The resulting overlapping spiral track created by the<br />

jet streams removes most of the plugging material contacted.<br />

DEVELOPMENT<br />

In early 1971 tank tests were performed (Hutchison, 1973) that clearly<br />

demonstrated the effective cleaning width of a water jet with respect to nozzle size ("D")<br />

and standoff distance ("X"). It was shown that for a range of short dwell times or single<br />

pass operations, effective cleaning was not accomplished for "X/D" ratios in excess of 10.<br />

Limited jet sizes and narrow ranges of pressure drops across the jets were explored.<br />

Track cleaning speeds (the reciprocal of dwell time) covered a goodly range and were not<br />

considered critical.<br />

In utilizing this information and other related data, this author explored the results<br />

and concluded that dwell time needed to be evaluated further. Additionally it was<br />

expected that dwell time for effective cleaning, with respect to differing deposited<br />

plugging materials, would be different. The following analysis furnished an<br />

understanding of travel rate requirements for effective cleaning under varying field<br />

conditions.<br />

Fluid Rate and Velocity<br />

Early workers (Pittman, Harriman and St. John, 1961) developed a relationship<br />

between the flow rate, jet diameter pressure drop and fluid density as follows:<br />

Q = 69 D^2(P/e)^1/2 (1)<br />

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