RIASSUNTO
Abstract
In oil producing regions like the US Mid-Continent, there are a large number of mature conventional oil fields that have reached or are approaching their production limit by conventional techniques, however, current strong oil prices and security issues justify additional EOR/IOR efforts. Air injection-based techniques (fireflooding or in situ combustion) have been demonstrated to provide commercially successful recovery from medium and light oils reservoirs. While the history of air injection-based EOR is littered with the perception of failed projects, many of the failures were associated with low oil prices. In other cases, failures were due to compressor problems, or incorrect concepts of how air injection processes operate. Ineffective ignitions, failure to inject enough air, and applications in reservoirs that had no hope of success explain the trouble with many past projects.
This paper reviews some of the successful air injection projects in higher gravity oil reservoirs and discusses the elements that are critical for success. These include the ability to ignite and continuously burn a fraction of the oil at reservoir conditions, the suitability of the reservoir for a gas-injection based recovery process, the availability and suitability of pre-existing infrastructure, and a reasonable prediction of how much air should be injected and how much oil recovery could be expected. The paper also discusses possible options for taking advantage of the product gas stream.
The purpose of this paper is to arm the petroleum engineer with the relevant information and the right set of questions to ask when considering the application of air injection in a given field.
Introduction
Around the world, there are many oil reservoirs that have had a long production history and are reaching or have reached the end of their economic life; yet significant quantities of oil remain in the pools, beyond the reach of conventional recovery techniques. These stranded oil reserves are the subject for a variety of enhanced oil recovery (EOR) techniques, which have the objective of prolonging the life of the fields and increasing recoverable reserves. The U.S. Mid-Continent is one example of such reserves. With initial discoveries in the late 1800s and significant development in the early 1900s, the region has been well developed. In a 2006 report to the United States Department of Energy (DOE), Advanced Resources International estimated in the region consisting of Arkansas, Kansas, Oklahoma and Nebraska, 14.3 billion m3 (90 billion barrels) of initial resources, of which, to date, 3.8 billion m3 (24 billion barrels) have been produced, leaving some 10.5 billion m3 (66 billion barrels) of oil, which would become stranded without significant EOR (A.R.I. 2006). The U.S. Mid-Continent resources have the advantage of being owned and operated by both large and small operators who are generally experienced and entrepreneurial. As a result, many EOR techniques have been applied, including in situ combustion, which has seen some successes, but has not become a significant recovery process, despite its compelling theoretical potential.
This paper attempts to address many of the common questions which the authors receive from companies considering air injection for application in US Mid-Continent and other reservoirs. The information provided is not intended to be exhaustive and it is recognized that any advice given to potential operators needs to be reservoir specific.