UAE Case Study Highlights Challenges of a Mature Gas-Condensate Field
Authors: Carpenter Chris 
Published: December 2018

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 188422, “Well-Integrity Management: Challenges in Extending Life of a Mature Gas-Condensate Field—A Case Study,” by S. Jain, M.A. Al Hamadi, H. Saradva, SPE, and J. Asarpota, Sharjah National Oil Company, and S.J. Sparke, SPE, M. Volkov, and H. Abu Rahmoun, TGT Oilfield Services, prepared for the 2017 Abu Dhabi International Petroleum Exhibition and Conference, Abu Dhabi, 13–16 November. The paper has not been peer reviewed.

Three onshore fields in the Emirate of Sharjah, United Arab Emirates, have more than 30 years of production history from more than 50 gas-condensate wells. While existing resources could be recovered by drilling additional wells, the most economical solution would be to confirm that existing well stock has sufficient well integrity to allow the continued use of these wells safely.

Introduction

The Sajaa asset consists of three retrograde condensate onshore fields. All wells are naturally flowing, with support from wellhead compression to reduce the effect of liquid loading on these mature gas producers. The reservoir was blown down to produce gas associated with rich condensate, water, and liquefied petroleum gas. With the reservoir’s long production history, its pressure has been greatly reduced.

Through use of a highly simplified upstream production technique, the wells continue to produce condensate-rich gas with the low-pressure regime. But, because of the reservoir-pressure decline, the production rate remains reduced. Therefore, surface gas compression is required to reduce backpressure and pump the gas to a nearby production facility for separation and, ultimately, custody transfer and sale.

Mature Well Status

The asset wells were completed with 5-in. tubing along with a nominal 7-, 9-, and 13-in. completion scheme. For production-optimization purposes, 10% of the wells produce directly up the production casing, while all the wells are completed packerless. The main purpose of the open annulus completion was to avoid the extensive problems and costs encountered previously with packer completions in the hostile environment and allow for chemical corrosion inhibition along the conduit of the A annulus (Fig. 1).

The cement behind the casing is generally accepted as accomplishing vertical isolation, though not radial isolation, with the natural pore pressure being applied laterally through the cement as a worst case. Collapse is considered to be more critical as a parameter than burst during production, even more so in mature reservoirs with cemented barriers that support against burst conditions. Actual well-integrity failures in a well stock do not always imply a situation in which uncontrolled flow of fluids reaches the surface. Individual barrier failures in a specific well group depend on a variety of factors, such as geographical area, operator, drilling era, well type, and maintenance quality. Gas is expected to be the primary fluid lost when a multibarrier failure occurs.

The Sajaa asset features comprehensive active and passive barrier systems. Cemented-to-surface annuli and heavy-duty wellheads account for the passive barriers; continuous remote monitoring of the annuli and weekly visits to the well location are effective active barriers.