Formation Damage-The Impairment of the Invisible, By the Inevitable And Uncontrollable, Resulting In an Indeterminate Reduction of the Unquantifiable!

Abstract

Introduction Formation damage is a a hot topic these days-with justifiable reason as we move to the exploitation of more and more challenging oil and gas reservoirs in tighter, deeper, and more depleted conditions. As the title of the article suggests, disappointing results from an oil or gas well can be related to a number of factors which may be difficult to diagnose. Some of these may center about inherent reservoir quality characteristics, others about mechanical considerations surrounding the condition and type of the wellbore obtained and still others about the nebulous catchall of "formation damage" which often (and sometimes unjustly) absorbs the majority of the blame for the poor results of many projects. Formation damage in oil and gas wells is difficult to quantify in many cases, due to the inability of the reservoir engineer to retrieve exact samples and conduct detailed measurements on the area of interest, which usually represents a volume of rock surrounding the wellbore, which is generally several thousand meters below the surface of the earth. However, ongoing research over the years has allowed the development of a variety of techniques which allow the use of the information which is available to us, such as production and pressure data, pressure transient data, log analysis, fluid and PVT data and core, cuttings and special core analysis techniques. These methods provide one a much better indication of the type and degree of damage which different reservoirs may be sensitive to, and, thereby, allow one to adjust operating practices to attempt to minimize or reduce these permeability reducing factors. The subject of this article is to provide a synopsis of some of types of formation damage which commonly present themselves as problems for many oil and gas producing projects, and review some of the associated technology being used to overcome these problems. How Much of a Concern is Formation Damage Anyway? A more technical definition of formation damage than that given in the title would be: Any Process that Causes a Reduction in the Natural Inherent Productivity of an Oil or Gas Producing Formation, or a Reduction in the Injectivity of a Water or Gas Injection Well. Formation damage can occur at any time during the life of well: during drilling, completion, production, stimulation, kill or workover operations. Often the problem is ignored due to a combination of ignorance and apathy with the common rationale that-"We don't care about formation damage in this reservoir-we can always fracture through it." Surprisingly this pretense may make sense in certain situations, particularly when the formation is of such low inherent quality that it is obvious that the flow area and driving differential pressure available for production present in a normal cased and perforated or open hole completion are insufficient to sustain economic production rates, even with a totally "non damaged" well.