Overview of Formation Damage

A comprehensive review of the various types of formation damage problems encountered in petroleum reservoirs is presented. The factors and processes causing these problems are described in detail. The design of a team effort necessary for understanding and controlling of the formation damage problems in the field is explained. The motivation for the writing of this book and the specific objectives are stated. The approach taken in the presentation of the materials in this book is explained. A brief executive summary of the topics covered in the book is given. The roles played by different professionals, such as the petroleum and chemical engineers, chemists, physicist, geologists, and geochemists, are described.

Keywords

Petroleum; petroleum reservoirs; formation damage; deformation; remediation

Summary

A comprehensive review of the various types of formation damage problems encountered in petroleum reservoirs is presented. The factors and processes causing these problems are described in detail. The design of a team effort necessary for understanding and controlling of the formation damage problems in the field is explained. The motivation for the writing of this book and the specific objectives are stated. The approach taken in the presentation of the materials in this book is explained. A brief executive summary of the topics covered in the book is given. The roles played by different professionals, such as the petroleum and chemical engineers, chemists, physicist, geologists, and geochemists, are described.

1.1 Introduction

Formation damage is a generic term that refers to the impairment of the permeability of petroleum-bearing formations by various adverse processes. Formation damage is an undesirable operational and economic problem that can occur during the various phases of oil and gas recovery from subsurface reservoirs, including drilling, production, hydraulic fracturing, and workover operations (Civan, 2005a,b,c,d). As expressed by Amaefule et al. (1988): “Formation damage is an expensive headache to the oil and gas industry.” Bennion (1999) described formation damage as: “The impairment of the invisible, by the inevitable and uncontrollable, resulting in an indeterminate reduction of the unquantifiable!” Formation damage assessment, control, and remediation are among the most important issues to be resolved for efficient exploitation of hydrocarbon reservoirs (Energy Highlights, 1990). Formation damage may be caused by many factors, including physico-chemical, chemical, biologic, hydrodynamic, and thermal interactions of porous formation, particles, and fluids, and the mechanical deformation of formation under stress and fluid shear. These processes are triggered during the drilling, production, workover, and hydraulic fracturing operations.

Ordinarily, the mineral matter and fine particles loosely attached to the pore surface are at equilibrium with the pore fluids. However, variations in chemical, thermodynamic, and stress states may create nonequilibrium conditions and induce the salinity, velocity, and thermal shock phenomena, as well as particle detachment and precipitate formation. When the equilibrium condition existing between the pore surface and the fluids is disturbed during reservoir production by primary, secondary, and enhanced recovery processes, the mineral matter may dissolve and generate many different ions in the aqueous phase, and the fine particles are unleashed from the pore surface into the fluid phases. Once these ions and particles are introduced into the fluid phases, they become mobile. Thus, a condition is created, like a bowl of soup of the mobile ions and fine particles in the pore space, which may interact freely with each other in many intricate ways to create severe reservoir formation damage problems.

Formation damage indicators include permeability impairment, skin damage, and decrease in well performance. As stated by Porter (1989): “Formation damage is not necessarily reversible” and “what gets into porous media does not necessarily come out.” Porter (1989) called this phenomenon “the reverse funnel effect.” Therefore, it is better to avoid formation damage than to try to restore the formation. A verified formation damage model and carefully planned laboratory and field tests can provide scientific guidance and help develop strategies to avoid or minimize formation damage. Properly designed experimental and analytic techniques, and the modeling and simulation approaches can help with the understanding, diagnosis, evaluation, prevention, remediation, and controlling of formation damage in oil and gas reservoirs.

The consequences of formation damage are the reduction of the oil and gas productivity of reservoirs and noneconomic operation. Therefore, it is essential to develop experimental and analytic methods for understanding and preventing and/or controlling formation damage in oil- and gas-bearing formations (Energy Highlights, 1990). The laboratory experiments are important steps in reaching an understanding of the physical mechanisms of formation damage phenomena. “From this experimental basis, realistic models which allow extrapolation outside the scalable range may be constructed” (Energy Highlights, 1990). These efforts are necessary to develop and verify accurate mathematic models and computer simulators that can be used for predicting and determining strategies to avoid and/or mitigate formation damage in petroleum reservoirs (Civan, 1994a,b,c,d,e, 1996a, 2007b,c).

Confidence in formation damage prediction using phenomenologic models cannot be gained without field testing. Planning and designing field test procedures for verification of the mathematic models are important. Once a model has been validated, it can be used for accurate simulation of the reservoir formation damage and designing effective measures for formation damage mitigation. Current techniques for reservoir characterization by history matching do not consider the alteration of the characteristics of reservoir formation during petroleum production. In reality, formation characteristics vary (Civan, 2001a,b,c, 2002a,b,c,d,e,f) and a formation damage model can help incorporate this variation into the history-matching process for accurate characterization of reservoir systems and, hence, an accurate prediction of future performance.

Formation damage is an exciting, challenging, and evolving field of research. Eventually, the research efforts will lead to a better understanding and simulation tools that can be used for model-assisted analysis of rock, fluid, and particle interactions and the processes caused by rock deformation and scientific guidance for development of production strategies for formation damage control in petroleum reservoirs. In the past, numerous experimental and theoretic studies have been carried out for the purpose of understanding the factors and mechanisms that govern the phenomena involving formation damage. Although various results were obtained from these studies, a unified theory and approach still do not exist. In spite of extensive research efforts, development of technologies and optimal strategies for cost-effective mitigation of formation damage is still as much art as science.

Civan (1996a) explains:

As J. Willard Gibbs stated in a practical manner: “The purpose of a theory is to find that viewpoint from which experimental observations appear to fit the pattern” (Duda, 1990).

Civan (1996a) states:

As stated by Civan (1996a):