Jet-Vac Differential Pressure Perforating
Authors: Maier L.P. , Nelner S.H. 
Published: March 2010

Laboratory data confirmed by field results have shown that perforations can be seriously plugged when there is a pressure differential toward the formation at the time of perforating, As a result there has been a trend toward through-tubing completion, so that the wells can be perforated dry or with a reduced hydrostatic head, resulting in differential pressure toward the wellbore, By using the through-lubing charges, particularly the through-tubing hollow carrier type, accompanying sacrifices in depth of penetration, smaller entrance hole size and possible cement bond damage are the results.

The "Jet-Vac" perforating system has been developed whereby the deep penetration of the large casing guns can he combined with the efficient clean-out of negative differential pressure perforating. The perforations are isolated from the hydrostatic pressure in the well Upon perforating the implosion into the hollow gun chamber of the products of combustion, mud filtrate, formation fluids and crushed formation allows each perforation to be swept clean to allow maximum capacity for flow or injection.

Laboratory and field data are pre-sented showing the benefits (If this new perforating system.

Introduction

DURING the past 10 to 15 years, numerous investigations have been carried out and papers presented(1) to confirm the indications and results from the field that perforating are frequently damaged by plugging at the time of perforating. The plugging is particularly serious when a differential pressure toward the formation exists at the time of perforating. Even with clean fluid ill the well bore, perforation efficiency is often reduced due to the formation matrix plugging with formation fines and perforating debris. Gas wells are particularly subject to this type of plugging.

Recognition of the plugging problem led to CPCT (Controlled Pressure Completion Technique) (2).

dry shooting and many variations of these two methods. Tables 1 and 2 show the dramatic increase in clean-hole volume and Well Flow Index: when cores were shot with differential pressure toward the formation. These perforating- tests were performed on API Berea targets, with the procedures as recommended in API RP 48 First Edition. Increased productivity of wells shot with CPCT or its variations confirmed the laboratory results.

When perforating with CPCT, a number of compromises are necessary because in most cases the wells must he shot through tubing. These are:small-diameter guns must be used, sacrificing depth of penetration and hole size;the casing must absorb the shock of detonation; (3)the productivity of the well must be contained and controlled while the gun and the cable are still in the hole;where H,S or other hazardous liquids or gases will be produced, the operation is unsafe.

Development And Operation

In order to expand the benefits of perforating with a differential pressure into the wellbore, the Jet-Vac System was designed(4) to allow the use of a hollow carrier casing gun. An additional advantage is that the well is not swabbed down and thus is designed to be under control at all times while perforating.