Killing of a Gas Well: Successful Implementation of Innovative Approaches in a Middle-Eastern Carbonate Field - A Field Case
Authors: Salehi Saeed , Hareland Geir , Azar J.J. 
Published: November 2008

A casing collapse occurred in a gas producing well with about 2.5 million cubic meters per day gas flow rate at a depth of 216 ft due to tectonic movements. As a result, the well blew out and different serious procedures were put into play to kill the well (Figure 1). This paper aims to review the practical and innovative approach that was used to secure and extinguish the well.

Initially attempts to kill the well included pumping water and or cement into the well to kill and secure it but it was not successful. Two directional relief wells, Kanagan-23A and Kanagan-23B were drilled to secure the well, the latter one was successful. The 23B well was drilled down to total depth of 2500m and entered into drainage area of Kangan-23 gas well. Different directional surveys were tried according to geophysical and geological data for entering the target area. The well relief and intersection was done by combining the new wellpath with the old well and injecting different pills and acidizing the new well to generate connectivity between the two wells. This type of innovative techniques has never been used in killing a well successfully before. This paper presents the unique thinking and practical approach used for securing this well including the failures as well as successes. The successful procedure may be used in killing future wells under similar condition.

Introduction

The case history herein describes a relief well planning and execution for a shallow blow out in a middle-eastern carbonate gas field. The reason for the sheared failure of the casing was detected to be the tectonic movements. One successful deviated well with four legs were used to kill this well. Key achievements included designing a secure program utilizing the injection of pills and acid. This is the first paper describing a killing program for relief operation of this kind in a middle-eastern gas fields.

The Kangan anticline is located in coastal Fars, southwest of Nar and west of the western Assaluyeh anticlines and north of Kangan harbor in Busher province. This structure is extended in the northwest-southeast direction and divided into 4 parts of A, B, C and D. The Kangan anticline is nearly asymmetric and the base on a structural map shows a 55Km length and 6Km width. The youngest and the oldest formations on surface are Bakhtiyari (Pliocene) and Sarvak (Cenomanian) respectively.

The highest dip angles of 30 and 40 degrees were defined for north and south flanks of Kangan anticline respectively and two reverse faults cut these flanks parallel to structure elongation.

The well Kangan-23 is located on the southern flank of the Kangan structure with the distance around 1.1 km from the well Kangan-22 and 1.8 km from the well Kangan-3 with the Lambert coordinate of: Easting: 2, 201, 400 m, Northing: 677, 512 m. Figure 2shows the location of this well. The Kangan-23 well was expected to have collapse problem at shallow depth from the observed seepages around the well. The Kangan-23 was a gas producer well with 1900 psi flowing wellhead pressure and shut in tubing pressure was 2800 psi. The flowing wellhead pressure suddenly dropped from 1900 psi to 880 psi on the 9th of October, 2005, and an immediate decision was made to close the well. After two days the well pressures had dropped even more as reported in Table 1.

After investigating the evidence showed there was severe casing damage from 60m-300m. The 7" tubing and the casing in the well was damaged and connected to each other and to the formation behind the casing. This caused the underground blowout and the gas from tubing flowed in the shallow formations. Sketches of the well before and after the collapse are illustrated respectively in Figure 3 and Figure 4.