Abstract

Drilling of horizontal oil and water injection wells in Saudi Aramco is rapidly increasing. Ensuring the optimum completion for all types of wells, and in particular water injectors, is essential for rigless intervention work such as stimulation, logging using Coiled Tubing (CT) and installation of mechanical downhole isolation barriers for rigless wellhead repair. A typical horizontal water injection well is usually completed with 3000' to 7000' open hole horizontal section and a tubing string that extends below the last casing. The tubing string is packerless and is installed as a CT guide for intervention work to bypass washouts below the casing shoe. This completion introduces well control challenges in case of rigless wellhead repairs especially in high reservoir pressure areas, where the minimum requirement for well control is two isolation barriers. The standard completion can not accommodate this requirement. The only alternative for the rigless wellhead repair is mobilizing a rig to perform the required work. This option is very expensive. An innovative completion for horizontal water injection wells has been recommended and implemented to achieve two main objectives: first to alleviate well control issues by allowing at least two shutoffs to execute rigless wellhead repair or replacement and second to facilitate accessing the wellbore, in case of formation washouts below the last casing shoe, with CT for intervention work. This paper covers completion background for horizontal injectors and challenges to optimize downhole completions to overcome limitations. Also, discussion of the collaborative work among various Saudi Aramco organizations and Service Companies in deploying this innovative completion will be presented. This success story of using this modified completion will illustrate Saudi Aramco's determination to overcome challenges and introduce best completion practices.

Introduction

The design of horizontal Power Water Injector (PWI) completion has been through various improvements since Saudi Aramco started drilling horizontal wells in the early of 1990s. The main objective of the improvement is to ensure that the completion is providing CT intervention accessibility and also the ability to perform rigless wellhead repair and replacement safely at a low cost. Initially, the horizontal PWI wells were completed as an open hole with 13 3/8″ & 9 5/8″ casings and a 7″ liner set at the top of injected zone. Also, a kill string without packer was run to the top of the injected zone to bypass the anhydrite washouts which usually separates the injected formation from the above zones. Refer to fig.1. The kill string is often called a Coiled Tubing (CT) guide. Also some PWIs have been completed tubeless. The completion with kill string has shortcomings when there is a need to repair or replace defective wellhead rigless due to the inability to install the required two isolation barriers to control the wellbore pressure. The only alternative for the rigless wellhead change out is using a rig which is costly. Also the tubeless completion will not allow easy access of the horizontal open hole for running logging or performing acid stimulation with CT due to the exposed washouts. After thorough evaluation of the existing horizontal power water injection wells, it was decided to modify the completion design for the horizontal water injectors to overcome all the accessibility problems and enable safe rigless wellhead change out at a lower cost.

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