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).
Most of the previous work on formation damage dealt with single-phase
flow of fluids or filtrates. Several models have been developed that
characterized fines migration in single-phase flow. In reality,
multiphase flow is commonly encountered in petroleum bearing formations
than single-phase flow. There is scarce information in the literature
about formation damage during multiphase flow. The present work seeks to
develop a mathematical simulation model for formation damage due to
chemical precipitation and particulate processes in the presence of oil
and water.
1.2 Objectives
The objectives of this work are as follows:
1. To develop a mathematical model for the simulation of
formation damage due to chemical precipitation and particulate processes
in two-phase flow of oil and water.
2. To obtain the numerical simulation of the developed model.
3. To compare the results obtained from the simulation with real experimental data available in the literature.