Abstract

This paper highlights the differences between an Alkali-Surfactant-Polymer (ASP) Flood project and traditional Exploration and Production (E+P) developments from an Engineering and Operations perspective. It lists the common problems encountered, drawing on published and unpublished sources, and describes their root causes. It proposes strategies for avoiding the problems in future ASP flood applications.

Introduction

A number of Shell-affiliated operating companies have identified Enhanced Oil Recovery by chemical injection as an option for accessing the remaining oil in place and extending field life. Several pilots have been implemented and more are under development. Currently the most advanced of these is a full-scale Polymer Flood that will soon start in Marmul in the Sultanate of Oman.

In general these companies are working to meet the challenges typical of late-life field production, namely: handling increasing water production, minimizing chemical usage, prioritizing well interventions, optimizing equipment maintenance strategies and assuring technical integrity and plant availability. The organisation and the skill set of the staff running these fields reflect this focus.

Implementing a chemical flood requires special skills and a different focus. The project is somewhat experimental because of the unknowns about how the chemicals will behave in the reservoir. The process line-up and equipment list include items not seen in a typical Exploration and Production company. The standard of cleanliness and the degree of sampling and monitoring are more like those seen in a specialty chemicals or food processing plant. This paper summarizes what is different about chemical EOR for the surface engineering and operations team and it provides an overview of the skills and the team culture needed to succeed.

What is ASP flooding?

This paper considers Alkali-Surfactant-Polymer (ASP) flooding, as this encompasses a broad range of chemicals and technologies. Most of the challenges associated with, for example, polymer flooding, are a subset of those for ASP flooding. In an ASP flood, a series of chemical slugs sweeps the reservoir from injection wells to producing wells. The sequence of injection is:

  1. Softened water. This provides a buffer in the reservoir between the existing water (which, in late field life, will be a mixture of connate water and water flood water) and the following ASP slug. Generally this existing water is hard and without this buffer the Alkali in the ASP slug would precipitate the divalent ions as scale. These divalents also precipitate the surfactant, which is usually anionic, and interact with polymer to reduce its viscosity.

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