Simulation Of Acidified Acid Etching Pupil Growth In Carbonate Matrix

In the production of carbonate reservoirs, matrix acidizing and acid fracturing are the most commonly used methods in well transformation and stimulation. Acid fracturing is expected to form fractures through squeeze fracturing fluid and acid alternately into target formation, to enhance the permeability of the formation, making it more conductive. Matrix acidizing, however, is widely applied as a block remover to ease the damage in the immediate vicinity of wellbore. By generating wormholes with deep penetration, high fracture conductivity channels are formed, connects to the original formation, and reduces the skin factor, and thus, production performance is promoted.In matrix acidizing, the accurate morphological characteristics of wormholes and its growing process are the basic issues in the research of well stimulation in carbonate reservoirs. The current situation is, domestic and oversea reseachers had tried a variety of methods, but yet, have never succeeded to demonstrate the 3D growing characteristics of wormholes. In addition, reports related to domestic research of acid etched wormholes using large physical stimulation methods are rare to see. Therefore, it is particularly important to establish more accurate models of the growing wormholes in the research of well stimulation by matrix acidizing.On the basis of previous researches, this paper intends to study morphological characteristics of wormholes, and its influencing factors in matrix acidizing jobs in carbonate reservoirs. Knowledge and methods in the field of Petroleum Engineering, Mechanical Engineering, Chemical Reaction Engineering, Probability and Statistics, Fractal Theory are used to reveal the objective laws and main controlling factors of how wormholes form and expand. The main work and contributions achieved can be summarized in the followings:(1) Analyzed the mechanism of wormholes'formating and its influencing factors, and proposed the necessity to establish models in the wellbore scale, combining macro and micro factors;(2) Using the principle of similarity criterion, links between physical simulation and engineering parameters are established. Also, a wellbore scale 3D physical simulation device for wormholes study is developed, and with preliminary tests completed;(3) Five parameters have been chosen as the indicators to analyze the growth characteristics of wormholes, which are breakthrough pore volume multiple, primary wormhole diameter, secondary branch wormhole number, fractal dimension and multi fractal spectrum width respectively. Acid concentration, displacement, along with temperature are selected as influential factors.In addition, orthogonal design was utilized to arrange and carry out the three-factor and three-level in total nine core flow experiments. Besides, the growth parameters of wormholes were analyzed using 3D CT reconstruction and X-ray imaging technology, obtained the main control factors influencing the growth and morphological characteristics of wormholes;(4) Taking advantage of VB.net, computer programs are written to perform the acid wormhole 3D growth process, which contributes better relevance between stimulation results and physical simulation experiments.