Laboratory Flow Characteristics Of Gun Perforations

Abstract

Flow rates through gun perforations calculated for radial-flow conditions and confirmed in laboratory tests indicated perforation efficiencies substantially lower than those observed in API RP 43 tests with linear-flow test targets. Observed perforation efficiencies were also strongly influenced by differential pressure: below, the API RP 43 standard of 200 psi, efficiencies were significantly decreased. Introduction From the inception of the gun perforating technique in 1932, the ultimate test of perforator effectiveness has been well productivity. As a result, much attention has been devoted to laboratory testing of perforators as a means of predicting and improving well perforators as a means of predicting and improving well performance. Laboratory procedures have evolved performance. Laboratory procedures have evolved over the years from simple single-shot penetration tests in steel to multishot tests in large cement targets using actual field guns. Shots at atmospheric pressure have been supplemented with tests under pressure and temperature environments simulative of down-hole conditions. Interest in laboratory flow properties of perforations entered the picture in 1953 with the perforations entered the picture in 1953 with the introduction of the laboratory flow test. This test, refined in 1956, culminated in the standard API RP 43 procedure in 1962. The API procedure until recently procedure in 1962. The API procedure until recently used Well Flow Index (WFI) as a means of comparing flow performance of perforations in the linear flow system employed. However, no true indication of the productive capacity of a perforation in the more nearly radial flow system that is encountered down hole could be derived from the WFI measurement. In an effort to provide more meaningful data, the API procedure was revised in 1971 to introduce Core Flow Efficiency (CFE) as the indicator of laboratory performance in the linear target. CFE is the ratio of flow from an actual perforation to flow from an ideal perforation of the same diameter and depth in the same target. While CFE represents a better basis than WFI for comparing perforation performance in the laboratory, the linear nature of flow in the API target still has raised questions as to the validity of applying CFE to down-hole conditions. Consequently, studies were undertaken to better define the liquid-flow characteristics, and particularly the flow efficiencies, of perforations under conditions more simulative of those down hole. Calculated flow and pressure distributions surrounding single perforations in linear laboratory targets were compared perforations in linear laboratory targets were compared with those existing around single perforations in a simplified down-hole model. Perforation-flow efficiencies for the down-hole model were calculated and confirmed in simulative experimental tests. Pressure and Flow Distributions - Ideal Perforations Pressure and Flow Distributions - Ideal Perforations Mathematical models of the linear target and a simplified down-hole system were developed to facilitate investigation of the flow and pressure distributions in the two systems. Initial work was done on ideal perforations since their flow rates are the basis for perforations since their flow rates are the basis for calculating perforation-flow efficiencies. The mathematical approach employed in analyzing the linear target is commonly referred to as the finite-difference technique. The target model is divided into a series of concentric segments as shown in Fig. 1. JPT P. 1095