Perpustakaan Digital ITB

Matrix acidizing is a method of stimulating carbonate reservoirs for oil and gas production. Unlike acid fracturing, matrix acidizing creates conductive flow channels, also known as wormholes, which possess much higher conductivity than the reservoir rock. These conductive channels transport reservoir fluids from within the formation matrix directly into the wellbore overcoming both low permeability and near wellbore damage. Understanding wormhole patterns can determine the success of acidizing to a large extent. Due to various influences, such as the reaction rate between the acid and rock, and anisotropy of formation, the shapes of wormholes are quite complex and stochastic. So simulating the wormholes by traditional methods cannot be accurate. A New Diffusion Limited Aggregation (DLA) model of wormholes in dual medium is presented after modifying the traditional DLA model. After the discussion, it is revealed that the bigger injected acid volume and porosity, the longer wormhole can be formed. When the natural fractures patterns are complicated, it is necessary to connect natural fractures and pores in the formation and get bigger fractal dimensions of wormholes, which may lead to a successful acidizing treatment. The effects of transport and reaction on the phenomenon of wormhole formation were investigated for a wide range of fluid systems including strong acids, weak acids, and chelating agents. These fluid systems are influenced by a variety of transport and reaction processes such as the transport of reactants to the surface, the reversible surface reactions, and the transport of products away from the surface. When these transport and reaction processes are taken into account, a common dependence of the dissolution phenomenon on the Damkohler number is observed. There exists an optimum Damkohler number at which a minimum number of pore volumes are required for channel breakthrough. This optimum Damkohler number occurs at approximately 0.29 for all fluid/ mineral systems. It is proven through experimental study investigated through the effect of pH and temperature on number of pore volumes to breakthrough. With known Damkohler number, Peclet number is involved to complete new quantitative wormhole model. With certain physical parameters, the model predicts the wormhole length as a function of acid injection rate and could also accurately predict wormhole breakthrough time. More importantly, the critical injection rate is obtained with the model by differentiating the equation with respect to injection rate. These information are very useful to determine optimum growth which enables field carbonate acid treatments to be more efficient.