Offshore Sandstone Reservoir Perforating Practices Used in Saudi Arabia
Authors: Benedyczak Chris , Al-Towailib Abdul Azeem A. 
Published: December 2007

Offshore Sandstone Reservoir Perforating Practices Used Perforating Practices Used in Saudi Arabia

Perforating wells for production has been a widely Perforating wells for production has been a widely accepted industry practice for nearly 50 years. Today, many producing wells are completed with metal casings cemented across hydrocarbon-bearing zones to control oil, gas, water, and solid particle entry into the wellbores. Reservoir fluid flow into wellbores is obtained through perforation tunnels made in casings, cement sheaths, and reservoir rock.

Perforation technology and methods of evaluating perforation efficiencies have advanced greatly during the perforation efficiencies have advanced greatly during the past 50 years. The resulting selection of well perforating past 50 years. The resulting selection of well perforating devices and perforating methods is vast. However, few studies have been published that address field assessment of well perforating efficiencies. The inability of many oil-producing wells to flow naturally to surface hampers evaluation of their perforation effectiveness.

Saudi Arabian offshore oil production is obtained from naturally flowing wells. This situation readily lends itself to analysis of well production profiles and perforation flow efficiencies.

This paper examines perforation efficiencies of jet guns in high-production flowing wells. Perforation interval flow profiles, wellbore pressure buildups and productivity index (PI) tests were evaluated for comparison productivity index (PI) tests were evaluated for comparison of well perforation efficiencies. Effects of drilling operations and the quality of primary cementation on the well perforation efficiencies were evaluated also. perforation efficiencies were evaluated also. Introduction

Safaniya field is located on the northeast coast of Saudi Arabia. The field was discovered in 1951 with the drilling of Sanfaniya Well No. 1.

Safaniya field structure is an unfaulted anticline of the Cretaceous Age containing a number of hydrocarbon-saturated zones. Currently, the bulk of production is being obtained from two sandstone reservoirs.

During the past 31 years, most wells located in the Safaniya field have been perforated with jet guns. Since the first Safaniya field well completion in May 1951, both the jet gun design and well completion methods have been improved greatly. Today, well perforating practices for the field include the use of jet casing and jet practices for the field include the use of jet casing and jet through-tubing guns.

The primary objectives of perforating Safaniya field wells are (1) obtain undamaged and productive perforations, (2) shoot a smooth round entrance hole in casing perforations, (2) shoot a smooth round entrance hole in casing with minimum damage to casing and cement, and (3) obtain maximum flow rate with minimum number of holes while minimizing sand production.

Many investigators 24 have reported that well productivity can be greatly affected during perforating productivity can be greatly affected during perforating operations. Factors that can highly enhance or reduce a well's producing capability include (1) depth of penetration, (2) producing capability include (1) depth of penetration, (2) wellbore hydrostatic pressure, reservoir pore pressure, and fluids present in the well at the time of perforating, (3) lag time from the moment well was perforated and placed on production, (4) shot density and phasing, (5) placed on production, (4) shot density and phasing, (5) entrance hole diameter and geometry, (6) casing grade and weight, (7) borehole geometry and cement sheath thickness, (8) drilling practices, (9) reservoir rock type and in-situ rock stress, (10) reservoir fluid, and (11) charge and gun design.

Influence of perforating methods and gun performance on the Safaniya field well productivities are examined in this study.

Drilling and Completion Practices

Eleven Safaniya field wells were selected for perforation efficiency evaluation. All 11 wells have been completed within the past 7 years as cased and cemented oil producers. producers. Drilling histories of the 11 wells indicate that no specific problems were encountered while penetrating the productive horizons. All wellbores were cut to the bit diameter over the productive zones. Reservoir exposures to the drilling mud ranged from 51 to 162 hours. Well completion practices consisted of setting 7-in. [17.8-cm) casings across the pay zones and cementing them with API Class G cement slurries. One selected well, Well G, was cased with a 4 1/2-in. [11.4-cm) liner.

Two perforating methods, overbalance and under-balance, were used to shoot across casing and cement sheaths. Four wells were perforated overbalance by using casing guns, while seven wells were perforated underbalance by using through-tubing guns.

Perforating gun data and gun performance summaries are listed in Table 1. Particular wellbore conditions at the perforating time and the resulting production capabilities of the 11 wells are shown in Table 2.

JPT

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