Material and Completion-Equipment Selection for an HP/HT Sour-Gas-Field Development in Indonesia
Authors: Denney Dennis 
Published: February 2015

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 136163, ’Material and Completion-Equipment Selection for HP/HT Sour-Gas-Field Development in Indonesia: Case Study,’ by Gustioro Purwagautama, SPE, and Rizky Andika, SPE, MedcoEnergi, and David McCalvin, SPE, and Dmitry Pleshkov, SPE, Schlumberger, prepared for the 2010 IADC/SPE Asia Pacific Drilling Technology Conference and Exhibition, Ho Chi Minh City, Vietnam, 1-3 November. The paper has not been peer reviewed.

The Lematang Block in South Central Sumatra has estimated total reserves of 330 Bscf, with an expected production life of 10 years. Wells in this field contain 32% CO2 and 100 ppm H2S, have a bottomhole pressure (BHP) of 10,500 psi, and have a bottomhole temperature (BHT) of 408°F. The initial two wells were completed by the previous operator using 22Cr tubulars and 13Cr accessories. However, operational difficulties from material deterioration were identified. Optimization of completion durability considering economics was of high concern when selecting materials and completion-tool designs. 

Introduction

The direct costs of completion hardware and long-term product performance to ensure durability for the life of each well were studied in detail before selections were confirmed. This study required the use of metallurgical and reservoir experts to provide opinions on material selection and required completion specialists to select the specific products to ensure that desired results were obtained. The workflow used to select the correct material and equipment culminated in a complex decision tree. Various analyses then were performed to support the selection of materials and the downhole equipment.

Background

To meet the growing demand for natural gas in the Far East, exploration and appraisal drilling was conducted on the Singa field in South Sumatra, Indonesia. This field has estimated gross reserves of more than 200 Bscf in a carbonate reservoir at 11,900 ft with a BHP of 10,500 psi and BHT of 408°F. Appraisal wells were drilled in 1997 and 1998. Both well tests showed similar results: 10,500-psi reservoir pressure, traces of H2S, and 32% CO2 with no water production. In 2003, the second well was completed with 22Cr tubulars, a packer, and a safety valve. After 1 year of production, the annulus pressure began to increase, indicating completion-equipment-integrity failure. Further development of the field by drilling and completing two additional wells was planned for 2008.

Critical factors, including cost, corrosion rate, life of the field, equipment lead time, gas composition, pressure, and temperature, must be assessed before finding an optimum solution. Besides the 22Cr tubular that had been used, tubular-material candidates for future wells in this field were 13Cr-HP2 and 15Cr-UHP. The operator simulated the corrosion effects on the material and searched for the optimum material to use. To optimize performance and reduce the overall completion cost, a detailed study and a series of tests were performed.