ABSTRACT
Formation damage is an undesirable operational and economic problem that can occur in many phases of field development including drilling, completion, workover, production, stimulation, waterflooding and enhanced oil recovery. In fact, it is among the major causes of a well productivity reduction in petroleum reservoirs. Proper understanding of the factors causing these damages is therefore of utmost important. A model for petroleum reservoir formation damage by chemical precipitation and fines migration is presented. Single type of particle (calcium carbonate) was assumed to exist in the porous system. Hydrodynamic force was modeled as the possible cause of fines mobilsation. Pore body deposition was considered as the basic phenomenon for permeability impairment while pore throat blocking was neglected in the modeling process. Macroscopic mass balance approach was used for the particle, fluid and chemical species. A complete formation damage model was obtained by modeling different rock-fluid interactions by kinetic laws and/or empirical relations. Thomas numerical scheme was applied for the model solution using Visual Basic programming language. The simulation results were compared with existing literature data. A reasonable match was observed despite the limited literature data available. The disagreement that was seen to exist at a later stage of the simulation between the present work and the reported literature was attributed to the omission of pore throat plugging in the model. One other factor that was believed to be the cause of this mismatch is the lack of exact correspondence in the modeling phenomena for this work and the compared literature work. However, the model was found to be a useful tool for predicting formation damage caused by inorganic deposition and fines migration during two phase flow of oil and water. In fact, it can be said with high degree of confidence that this is the first type of formation damage model that incorporated geochemical reactions and fines migration during two phase flow.
CHAPTER ONE
INTRODUCTION
1.1 Problem Statement
Formation damage 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 in many phases of field development including drilling, completion, workover, production, stimulation, waterflooding and enhanced oil recovery. In fact, it is among the major causes of a well productivity reduction in petroleum reservoir. Proper understanding of the factors causing these damages is therefore of utmost important. Formation damage indicators include permeability impairment, skin damage and decrease of well performance.
Formation damage can be caused by factor such as fine particle transportation in porous media. Fines enter the formation as suspensions during drilling and completion operations. They can also be generated due to fluid-fluid and fluid-rock interactions. When they enter the formation, they get entrapped in the pore openings, fill and plug the pore spaces of the formation. Sedimentary rocks also contain loosely attached fines. When injection fluids are incompatible with formation fluids, these fines can be released from the rock surface, migrate and plug at pore constrictions. The end result is severe permeability reduction.
It is therefore essential to develop experimental and analytical 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 understanding of the physical basis of formation damage phenomena. From this experimental basis realistic models which allow extrapolation outside the scaleable range may be constructed (Energy Highlights, 1990). These efforts are necessary to develop and verify accurate mathematical models and computer simulators that can be used for predicting and determining strategies to avoid and/ or mitigate formation damage in petroleum reservoirs (Civan, 1994).
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