Backsurging and Abrasive Perforating To Improve Perforation Performance

Abstract

Compared with conventional completions, backsurged completions in this group of wells on the Louisiana Gulf Coast show permanently improved productivity. To a lesser extent, abrasive perforating also improves productivity. To a lesser extent, abrasive perforating also improves well completions, particularly in zones that are less than 30 percent depleted. Introduction One of the major problems associated with conventional completion practices in unconsolidated sands is that of obtaining unimpaired perforations prior to sand control installation. Debris resulting from crushed formation material and explosion products often remains in perforations, producing severe restrictions to fluid flow. Zones that would be expected to have productivity indices of 2 to 4 B/D/psi based on permeability estimates in fact often exhibit productivity indices less than one-tenth of these values. This is particularly true in Shell's South Pass Blocks particularly true in Shell's South Pass Blocks 24 and 27 fields, where nearly all completions require sand control before sustained production can be established. Any debris remaining in perforations when sand control is installed can perforations when sand control is installed can become "locked-in," resulting in a permanent impairment that cannot be corrected by conventional stimulation techniques. Suman studied perforation debris and proposed several methods to increase perforation efficiency. We shall discuss here the effectiveness of two of those methods backsurging and abrasive perforating. The Backsurge Tool The backsurge tool consists of an atmospheric chamber formed by two valves spaced in the work string above a squeeze packer (Fig. 1). After conventionally perforating, the assembly is run and set above the perforating, the assembly is run and set above the perforations to be treated. The lower valve is then perforations to be treated. The lower valve is then opened to expose the perforations to the atmospheric pressure in the chamber. The resulting surge flows pressure in the chamber. The resulting surge flows perforating debris and crushed formation material perforating debris and crushed formation material into the wellbore where it can be reversed out or allowed to settle into the rat hole. The well is then ready for installation of a sand control. When plastic consolidation is used, the well may be treated through the tool without unseating the packer, thus the perforations need not be exposed to annular fluids until perforations need not be exposed to annular fluids until the plastic has cured. Bottom-hole pressure bombs can be run below the tool and inside the chamber to monitor pressures throughout the treatment. Backsurging was first introduced in the South Pass Block 27 field in July, 1969. Initial results were impressive, and in Dec., 1969, backsurging was adopted as a standard procedure. Through Aug., 1970, more than 80 zones had been backsurged; 70 of these are oil-producing zones on which data are complete enough to be meaningful and are included in the study. Fifty-two backsurge treatments were performed on "new" zones not previously open; 11 were performed on "new" zones not previously open; 11 were in "old" zones in which an additional interval was perforated during workover; and seven were in old perforated during workover; and seven were in old zones in which the perforated interval was not altered; i.e., seven were workovers to replace sand control. All but five new zone completions were gravel packed. These five were given sand consolidation treatments. The Abrasive-Perforating Tool The abrasive-jetting process uses sand carried in salt water or acid pumped through jetting nozzles at high velocity to abrade perforations through the casing and cement sheath. JPT P. 1207