Abstract

A literature survey of both improved oil recovery ("IOR") methods, and offshore oil operations, has been performed. The survey of IOR methods examined both current field applications (commercial and pilot operations), and "horizon" research investigations. The survey of offshore oil operations has focused upon the European North Sea, to understand the implications for marginal field development there, and also in the Canadian East Coast.

It is believed that oil recovery can be increased above a base waterflood development. This would be accomplished by earlier application of improved oil recovery methods, rather than the application of same late in the life of a watered-out field. The specific IOR method would require very early studies to design and tailor a method that is appropriate for the unique qualities of a given reservoir.

In this paper, a "Type Field", hypothetical, but representative of a marginal field or isolated fault block, is used to illustrate this philosophy. Evaluation of various operational enhancements are performed via numerical simulation. Cases compared are a base waterflood, and IOR operations utilizing Gravity Assisted Immiscible Gas Injection ("GAIGI"). A novel operational scheme has been developed and is termed"Coupled Dual Phase Displacement" ("CDPD"). The oil recovery factor obtained for certain models using CDPD is 58%. This compares to a base waterflood recovery factor of 44% for the same models, giving an incremental recovery of 14% oil initially in place.

Hurdles that must be overcome are early characterization of the reservoir prior to production, and the identification of the optimal depletion process. This will require an integrated study team. Nonetheless, novel IOR schemes can be designed in some circumstances that can be insensitive to some forms of geological traps under displacement processes.

The benefits of early IOR applications extend to the deferral of abandonment, which is demonstrated to have positive incremental economics to the corporation.

It is pointed out that although the concept is outlined here for offshore oil fields, the natural extension of these ideas to onshore oil fields should also be considered.

Introduction

A literature survey has been conducted regarding the status of Improved Oil Recovery ("IOR") methods and the historical developments of the North Sea oil industry. This was done in order to understand potential IOR applications for offshore oil production operations. In the context of this survey, IOR was considered to be any process that obtains oil production and recovery incremental to either primary or waterflood pressure maintenance operations. The survey included all major IOR forms, and encompassed the time period up to late-1996. Increases in recovery by mechanical methods, such as infill drilling of new wells, were considered as enhancements to a given process, and not the base IOR operation itself.

There are many reasons why IOR methods should be strongly considered for offshore oil operations. Those issues that are pertinent to this paper are the very high cost of abandonment, large volumes of oil initially in place, and large volumes of remaining oil in place at the end of a waterflood operation.

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