A New Approach Toward Elimination of Slug in Shaped Charge Perforating

FEATURE ARTICLE A New Approach Toward Elimination of Slug in Shaped Charge Perforating SOCIETE DE PROSPECTION ELECTRIQUE J. DELACOUR PARIS, FRANCE M. P. lEBOURG SCHLUMBERGER WELL SURVEYING CORP. Downloaded from http://onepetro.org/jpt/article-pdf/10/03/15/2238755/spe-941-g.pdf by guest on 30 September 2021 W. T. BELL HOUSTON, TEX. MEMBERS AIME Abstract ing of shaped charge tools, as applied thoroughly explored, both classically to oilwell perforating, has evolved from and experimentally by Pugh, et al."1.4 Since the advent of the perforation simple surface shooting to tests con In considering the formation of the flow laboratory, increased attention has ducted in a flow laboratory in which jet and the slug, let us refer to a sim been focused on new designs of shaped a study of the charge could be made ple schematic of a conventional, cop charges as applied to ai/well perforat under simulated down-hole conditions'. per-lined shaped charge (Fig. 1). This ing. Data derived from the flow lab In the flow laboratory, pressures and type charge will produce (1) a high oratory, in which charges are subjected temperatures were elevated prior to speed penetrating jet with a velocity to simulated down-hole tests, indicate firing the charge into a target of me approximating 8,000 m/sec, and (2) that serious perforation plugging often dium-hard sandstone material. An a relatively slow moving slug or car exists due to the elltrance of slugs into elaborate system was devised for firing rot, the velocity of which reaches 800 the perforated hole. the charge under various fluids and m/sec, and which may in turn plug The slug or "carrot" is all intrinsic differential pressures. Provisions were the hole produced by the jet. part of the jet ["ocess and its adverse made for a~tually "flowing" the per The charge shown in this classical efJect is inherently characteristic of forated hole under controlled condi illustration consists of a cylinder of many commercial-shaped charges tions. It was at this ooint that the term powerful high explosive which is gen which otherwise exhibit excellent per slug or carrot really emerged into oil erally die-formed or molded to a coni formance properties. well perforating vernacular. While it cal copper liner and primer explosive. Numerous approaches have been had been noted that a slug of charge Copper is commonly used as the liner tried throughout the industry in an ef liner material often entered the per material due to its superior combina fort to prevent this flow-impeding slug foration, these plugged test targets had tion of plasticity and density charac from entering the perforated hole. Yet, drawn little attention. Now in the teristics. Initiation of the explosion is publicly conducted tests indicate that flow laboratory, it was found that this effected at the primer section, after none of these devices are entirely suc obstructing slug reduced the resultant which a detonation wave travels from cessful when applied under the clear flow through the perforation to as lit left to right, sweeping from apex to ance and pressure conditions for which tle as one-half that normally expected! base along the liner. the charges are designed. This paper It was then clear that the slug must be The resulting pressures produced on deals with a new, direct approach either eliminated from the shaped the liner are so large that the copper toward the elimination of the slug or charge entirely or reduced to such pro behaves like a perfect fluid. Such pres carrot in shaped charf]e perforating. portions that it would be ineffective in sures cause the walls of the liner to Herein is described a newly devel plugging the perforated hole. collapse and move inward at high velo oped bimetallic liner for shaped cities nearly perpendicular to their sur- charges, which when fired under pres Slug Formation in the Jet Process sure leaves no slug in the perforated hole and yet maintains the high per MAIN CONICAL To gain an understanding of the CHARGE LINER formance oj the conventional-type slug formation in the jet process, it is PRIMER charge. worthwhile to review basic shaped Introduction charge principles. While it is beyond the scope of this paper to present a During the past few years the test- comprehensive theoretical treatment, the specific phases involved will be Original manuscript received in Society of discussed. Both the mechanisms and Petroleum Engineers office June 6. 1957. Re vised manuscript received Feb. 27. 1958. Paper properties of the jet and slug have been presented at 32nd Annual Fall Meeting of So ciety of Petroleum Engineers in Dallas, Tex., Fie;. 1 - Schematic of copper-lined Oct. 6-9, 1957. 1References given at end of paper. shaped charge ready for detonation. SPE 941-0 MARCH, 1958 15 faces. The collapsing copper retains DETONATION charge containing an ordinary copper practically a conical shape as shown WAVE cone liner. This charge, which is rep in Fig. 2. Point P moves to the right ,------ - .. resentative of those used in commer I along the axis with the collapsing cone I JET cial application, possessed the follow describing the indicated angle, 2f3. iJ-l ing specifications: ( 1) angle at the During this process, the inner part I [ apex = 2 0: = 60°, (2) diameter at L,_.J of the cone is "squeezed out" from the base = 32.6 mm, and (3) mean thick [ inner apex of the liner and forms the L _______ .;. ness liner = 0.65 mm. jet, which travels to the right. To the Substituting maximum and mini left behind the moving apex (P) is SLUG mum values of the angle f3 as observed found a section of collapsed liner con Fig. 2 - Schematic of copper-lined on radiographs, Eqs. 1 and 2 were ap shaped charge after detonation show taining the slug metal from the outer ine; collapse of liner. plied. It was thus determined that the part of the cone. In other words, the slug should weigh between 5.0 and 7.5 metal of the liner divides into two \ Y gm. Actual slugs recovered in shooting parts with the dividing surface between through water weighed 6 gm, which these two parts being a cone lying represents a reasonable check on the somewhere between the inner and theoretical values. outer surface of the original liner. Observations on many test shots in The manner in which the metal of the laboratory on hollow carrier the collapsing liner divides (between charges of various types bring out the the jet and the slug) can be precisely following further facts. Downloaded from http://onepetro.org/jpt/article-pdf/10/03/15/2238755/spe-941-g.pdf by guest on 30 September 2021 determined. Let us assume that the 1. Slugs produced from successive liner (Fig. 3) which is in the process shots with the same type of copper of collapsing under the detonation lined charge may have a wide, random wave is considered from the point of variation in final dimension, but hold view of a moving observer s"tationed to approximately the same weight. The Fig. 3-Formation of slue; and .iet from at the moving junction, P. The liner paint of view of observer stationed at variation in dimensions depends on will thus appear to flow toward P with moving junct'on P. many different factors which vary in a velocity, V, and after passing the the individual charge characteristics. junction, the jet and slug will appear ZINC OUTER 2. Plugging action does occur when to recede with the same velocity. CONE the slug enters the perforated hole. Therefore, in accordance with the 3. Slugs produced by the solid cop principle of conservation of momen per liner are found to plug from a tum, we may equate the horizontal smalI percentage to 100 per cent of the components of momentum before, to perforations, depending on the type those after passing the junction P in of charges and the down-hole shooting the moving coordinate system of Fig. 3, conditions. m V cosf3 = m., V - mj V , (1) 4. Large differential pressures in where m represents the total mass per these cases generally do not dislodge unit length of collapsing liner, m; that the slug. part of m going into the jet, and m., COPPER INNER CONE that going into the slug.' Then, ac Methods Applied in Eliminating the cording to the principle of conserva Slug from Perforations tion of mass, we have Fill:. 4-Bimetallic cone liner. m = m; + m.. , (2) Throughout the industry, numerous and can therefore obtain attempts have been made to eliminate mj = m/2(1 - cosf3) = m sin 'f3/2 the slug. Various approaches have m., = m/2(1 + cosf3) = m cos 'f3/2 been tried. Among these, an effort has (3) been made to stop or "catch" the slug. Mechanical devices such as spe Now, from Eqs. 1, 2, and 3, the size AI of the slug is a function of the design cial porthole covers and washers have and weight of the liner. The slug been employed. Charges have been weight resulting from a given liner can modified to throw the main perform therefore be readily predicted if the ance factors out of balance in an ef various parameters are known. Thicker fort to produce a hole large enough so liners will naturally produce larger and that the carrot would not remain in heavier slugs. Thinner liners, con the perforation. Others have been fitted versely, produce smaller slugs. Unfor with asymmetrical cone liners in an ef tunately, however, experience shows fort to force the carrot to one side of the path of the jet and prevent its en that reduction of liner thickness is ac BI companied by reduction in perform trance into the hole.

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