Engineering Success into Wireline Operations in High Pressure Gas Wells
Authors: Ismail Abdul Malek , Clancey Byron Michael , Mercer Larry , Sorem William A. , Riebe Chuck 
Published: December 2009

The RasGas Company Limited (RasGas) North Field wells are typically completed with a sail angle of up to 70o. The field is developed with both 7-in. monobore and 9-5/8-in. optimized big-bore (OBB) wells designed to handle produced gas containing H2S and CO2, and HCl acid stimulation respectively. The wells must also accommodate high flow rates and through-tubing intervention.

RasGas completion operations in the North Field are wireline intensive and are often complex in nature. The staged approach of perforating, stimulating, and testing (PST) in conjunction with production profile evaluation requires multiple high-pressure through-tubing wireline interventions in each well. The scope of wireline intervention includes electric line (E-line) for perforating and cased-hole logging, and mechanical wireline for deploying and retrieving retrievable bridge plugs. These frequent interventions for the staged PST campaign increase risk exposure for wireline failures.

In recent years, wireline has parted in several instances and thus resulted in complex live well fishing operations. Fishing operations in the OBB well design are challenged by the tapered tubing string, requiring multiple tool string configurations to fish inside 9-5/8-in., 7-5/8-in., and 7-in. tubulars.

This paper describes the development and use of wireline equipment and downhole fishing tools with specifications developed specifically for the harsh, high-pressure North Field environment, that exceed general industry standards. The paper also discusses the planning considerations, fishing procedures and methods, and real-time implementation of lessons learned that enabled successful recovery of approximately 11,000 ft of wireline in a recent fishing operation.

Introduction

The North Field is located offshore, northeast of Qatar in the Arabian Gulf. It is the world's largest non-associated gas field with reported reserves of more than 900 Tcf. The sour, slightly over-pressured natural gas is contained in the Khuff carbonate formation.

Two different types of production wells have been drilled by RasGas in the last six years; a 7-in. monobore well design completed with 7-in. tubing and liner sections, and an OBB well design featuring 9-5/8 x 7-5/8-in. tapered production tubing and a 7-in. liner section. Nominal design capacity of these wells is 125 MMscfd for the 7-in. monobore, and 200MMscfd for the 9-5/8-in. OBB design. Deviations of these wells are from vertical up to ~70o.

As summarized in Fig. 1, the PST operations required for initial completion of the long, heterogeneous, Khuff carbonate interval during initial completion ranges from a two to four stage acid stimulation program for each well. Up to twenty E-line runs may be required to perforate production intervals greater than 1000-ft measured depth (MD). To reduce the number of perforating runs, larger diameter and higher strength 0.32-in. cable was introduced to replace the previous 0.23-in. E-line. This change enabled lengthening of the 2-7/8-in. perforating gun assembly from 40-ft to 60-ft, reducing overall perforating time and exposure to wireline risks by 33%. Additionally, the introduction of electronic addressable switches for selective perforating further optimized perforating operations and contributed to reduced time. However the introduction of 0.32-in. cable required development of modified procedures and techniques to address higher inherent cable torque and greater propensity for gas infusion into the cable.