Abstract

This paper presents the Mobil Oil Indonesia experience associated with cementing the 9-5/8 inch casing through the abnormally pressured and water sensitive sand/shale Baong formation in the Arun field, North Sumatra.

The paper will discuss how the cement slurries and cementing procedures for the 9-5/8 inch casing have been modified to overcome two major problems. The first being the inability to fully displace the cement due to swelling of sensitive shales, the second being severe annular flow after cementing.

This paper will further examine the changes made to slurry design after the recent discovery that circulating temperatures during 9-5/8 inch cementing operations are considerably lower then predicted by the API schedules. Because of these low temperatures, the slurries used in the pest were greatly over retarded which contributed to the long and costly afterflow periods. periods

Introduction

The Arun gas field is located in Aceh Province, North Sumatra (Figure 1). The field was initially discovered in 1971 when the Pertominc-Mobil Arun a well was drilled. The field is now being developed by directional wells drilled from four clusters as shown in Figure 1. To date, c total of 29 producing wells and 8 gas injection wells have been drilled. producing wells and 8 gas injection wells have been drilled. This paper will concern itself with the cementing of the 9-5/8 inch casing in directional producing wells. These directional wells hove been responsible for the majority of the problems associated with cementing casing through the abnormally pressured and sensitive Baong sand/shale formation.

During the early stage of development drilling, unsuccessful cement jobs resulted from the inability to fully displace the cement due to hole packing by sensitive shales in the Baong formation. This was remedied by packing by sensitive shales in the Baong formation. This was remedied by the addition potassium salt and synthetic cellulose to the cement slurry.

Once it become possible to place a full column of cement to surface, it was discovered that the slurry would not control flow from the high pressure salt water sands in the Baong formation. Modifications to the slurry and the addition of an anti-migration additive have eliminated or significantly reduced the severity of the cement afterflow.

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