Abstract

Water injection wells with horizontal openhole completions were successfully drilled and completed to provide enhanced injection capabilities for waste water disposal. The impending start-up of several new RasGas Company Limited (RasGas) LNG mega-trains will significantly increase the requirements for water disposal. Prior injection wells that have been operating for several years are vertical or slightly deviated with cased-hole completions. In order to meet the future injection requirements including increased capacity and sustained higher injectivity, studies indicated that horizontal wells with openhole completions were required.

This paper describes the design, implementation and initial performance evaluation of the new horizontal injection wells. The main topics discussed include well design and construction, acid stimulation, and water injection testing and evaluation. For both wells, a 3,000-ft interval was drilled and completed with a predrilled liner and swellable packers for annular isolation. Various studies were conducted to optimize the well design and successfully execute the drilling and completion operations. The main stimulation objective was to enhance the desired acid placement along the wellbore and provide a more uniform injection profile for maximum and sustained long-term injectivity. Key points of the design approach for the acid stimulation program and execution strategy are described. In addition, a comprehensive water injection testing program was developed to assess initial well performance including capacity and conformance along the openhole interval. The evaluation results demonstrate that the wells were effectively stimulated and provide the required initial injection capacity. The assessment indicates that both of the horizontal injection wells provide initial injection capacity several times that of a vertical well drilled and completed in the same formation.

Introduction

Two new water injection wells were drilled and completed by RasGas Company Limited to provide enhanced injection capabilities in preparation for the impending start-up of several new LNG mega-trains. The gas processed by the LNG trains is produced from the North Field, the world's largest non-associated natural gas field, located offshore Qatar in the Arabian Gulf as shown in Fig. 1. Highly prolific offshore production wells and subsea pipelines deliver the natural gas to onshore processing facilities in Ras Laffan Industrial City. The LNG operations generate a significant volume of water that is disposed into shallow, water-bearing formations using injection wells. Disposal water sources include process water from the facility and condensed water from the produced natural gas. The water injection wells are located onshore near the gas processing facilities. The total rate of water generated by the existing RasGas LNG trains is approximately 7,500 B/D. With the addition of the new LNG mega-trains, the total rate of water may ultimately exceed 30,000 B/D.

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