Well Integrity Issues in Malacca Strait Contract Area

Abstract

Summary The Malacca Straits contract area is located on the east of Sumatera Island between Sumatera and the Malaya Cape. This area started oil production in the early 1980’s, and consist of 175 onshore and offshore oil wells spread over five fields, namely the Kurau, Melibur, Selatan, Lalang, and Mengkapan oil fields. A 7.9 Richter scale earthquake occurred on 12 September 2007. The epicenter of the earthquake was 159 KM south west of Bengkulu, a province in the southern part of Sumatera. Two days later, during a snubbing unit service on the K-02 well, the 9-5/8" casing suddenly dropped down six feet. It was believed that the area had been impacted by the earthquake since another snubbing unit found lateral movement on wellhead while doing workover on nearby well. Following the incident, the well services team inspected the K-02 well and found it had an integrity problem. This finding lead to a wider investigation, which revealed that other wells also suffered integrity problems, including unsecured wellheads, leaking wellheads and christmas trees, severe corrosion of well components, failure of cement bonding, and casing elongation / casing drop due to top soil compaction / reservoir subsidence. At this point, it was decided to initiate a comprehensive well integrity study. The integrity problems are due to several causes: wells exceeding their design life (most wells were constructed in the mid to late nineteen-eighties), exploration wells being used as producers without improvement, environmental degradation from deforestation (drop in the water table causing top soil compaction), and more than twenty years of production (causing formation subsidence). This paper details the well integrity study, including the well assessment, the evaluation of well operation in term of safety, environment and profitability, and recommended effective temporary remedial actions.