An Overview of Formation Damage Mechanisms Causing a Reduction in the Productivity and Injectivity of Oil and Gas Producing Formations

Abstract

Introduction Formation damage is a hot topic these days-with justifiable reason, as more operating companies move to the exploitation of more and more challenging oil and gas reservoirs in tighter, deeper, and more depleted conditions. Disappointing production or injection 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 poor inherent natural reservoir quality characteristics, others about mechanical considerations surrounding the condition and type of the wellbore obtained, and still others under the nebulous catch-all 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. This is due to the inability of the reservoir engineer to retrieve exact samples and conduct detailed measurements on the area of interest, usually represented by 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 allowing the use of the available information to obtain a much better indication f the type and degree of damage which different reservoirs may be sensitive to, thereby adjusting operating practices to attempt to minimize or reduce these permeability reducing factors. This data would include information such as production and pressure data, pressure transient data, log analysis, fluid and PVT data and core, cuttings, and special core analysis data. The subject of this brief article is to provide a synopsis of some of the 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? A technical definition of formation damage 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." Although the drilling process often bears the brunt of the blame, formation damage can occur at any time during the life of a well including 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 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.