As reserves dwindle and exploration/development cost escalates particularly in frontier regions, the need for effective prevention and/or treatment of formation damage to maximize well productivity, has become apparent to prudent operators. This paper discusses economic implications, reviews various origins and forms, and provides methods for recognition of formation damage. Geological and engineering tests for proper assessment of the problem, and optimization schemes for effective solution are also described.
Formation damage is a condition which occurs when barriers to flow develop in the near-wellbore region to give rise to a lower than expected production rate from or injection rate into a hydrocarbon bearing reservoir rock. This problem has been recognized for several decades as a major contributor to anomalous production and/or abnormal decline in productivity or injectivity in hydrocarbon reservoirs. Many potential pay zones have been misdiagnosed as nonproductive, and payout on investment has been delayed because or formation damage. Understanding formation damage requires a multidisciplinary approach that involves such diverse specialty fields as inorganic/organic chemistry, physical chemistry, colloid and interfacial sciences, chemical kinetics, mineralogy, diagenesis and fluid transport through porous media. Unfortunately, the primary interest of the various field groups involved in reservoir definition and exploitation often seem to be in conflict. For instance, the driller is typically interested in reaching the targeted depth quickly(increased ROP), and safely (overbalance pressure condition), while maintaining a gauged bole. Avoidance of formation damage when appears to be of secondary concern. However, if a project team is formed at the outset to include drillers, mud engineers, geologists, production and reservoir engineers, then proper objectives of a safe drilling program can be set to protect the formation and to ensure that the reservoir will be exploited to its maximum productive capacity to generate a maximum return on investment.
Once, formation damage has occurred, proper assessment and Treatment will require the cooperative efforts of geologists and engineers both in the field and in the laboratory. This synergistic approach is necessary to develop effective solutions to this expensive problem. Better understanding of the mechanism of formation damage is required in order to develop effective preventive and mitigative procedures. With recent advances in technology, laboratory geological and engineering measurementscan provide the necessary insights into the mechanism, prevention and effective treatment of formation damage.
Formation damage is a very expensive headache to the oil and gas industry. Before the drill bit penetrates the reservoir domain, the reservoir rock and its constituents minerals and resident fluids ore essentially in a state of physico-chemical and thermodynamic equilibrium. This equilibrium is disturbed during the drilling process when extraneous mud solids/fluids are introduced into the wellbore giving rise to pressures in excess of the reservoir pore pressure. The resultant differential pressure, usually referred to as overbalance pressure, promotes the invasion of fine colloidal materials and filtrates into the near-wellbore region of the formation where they reduce the intrinsic permeability. An artistic rendition of a wellbore model with associated mud and filtrate invaded zones is shown on Figure 1.