In this study, a novel numerical approach is proposed to characterize the dissolution of rock minerals and wormhole propagation in carbonate rocks using the Darcy scale model. Accordingly, only the spatial variables of the governing partial differential equations are discretized, while the time variable remains continuous. Consequently, the partial differential equations are turned into ordinary ones, which are then numerically solved by high-order Runge-Kutta methods. The proposed approach is verified against the analytical solution in a 1D core model. Afterwards, it will be utilized to investigate the effect of multiple transport and reaction phenomena on the Matrix acidizing in 2D carbonate formations. Also, the staggered grid technique is employed to accurately predict the wormhole patterns during several injection regimes. Compared to the previous studies, the proposed numerical approach is less complicated and straightforward. Furthermore, the computational cost is more affordable.

Well stimulation by means of acidizing has been extensively conducted for enhancing the productivity or inject ability of producing and/or abandoned wells in southern Iranian oilfields, and Matrix acidizing is considered as the major stimulation method in this region. Permeability improvement and consequently reaching a negative skin is the main objective of this type of stimulation. The aim of this research is to evaluate the performance of the carried out Matrix acidizing and put forward some alternative methods to improve this kind of operation. The post production results of acidizing show an inefficient outcome of the majority of these operation in the investigated oilfield. The history of performed Matrix acidizing operation in some of the southern Iranian oilfields in recent years has been introduced in this study. By employing Pansys software, the evaluation of pre and post stimulation jobs has been applied to nine wells. Also, Nodal analysis has been performed by Pipesim software in the investigated oil wells to study the production systems of these nine oil wells. By utilization of the results of this study and assessment the literature review of the related studies, Matrix acidizing operation will be discussed in detail in this paper. The results show that among the nine oil wells studied in this research, wells 20, 22, and 38 are the best candidate for Matrix acidizing operation. Finally because of the associated difficulties with Matrix acidizing and in order to bypass various types of formation damage, the authors of this paper recommend Iranian upstream industry to considering Hydraulic Fracturing operation as a replacement stimulation method.

Matrix acidizing refers to one of the two well stimulation processes in which acid penetrates the rock pores at pressures below the fracturing pressure. During Matrix acidizing, the acid dissolves sediments and mud solids which reduce the rock permeability. This process enlarges the natural pores of the reservoir that stimulates the flow of hydrocarbons. In this article, different mechanisms of acidizing process in carbonate and sandstone reservoirs and the relevant reactions are studied. Moreover, various simulation techniques of acidizing in carbonate reservoirs are studied, including the dimensionless model, capillary tube model, network model, and continuum model. Moreover, numerical silulation of sandstone acidizing is also discussed. Also, optimization of the acidizing process is described. In each of the sections, field studies have been investigated based on the type of subject.

Matrix acidizing is a method for improving well inflow performance. In this operation, acidic solution is injected into the carbonate formation to increase near wellbore permeability by rapid creation of irregularly shaped channels named “wormholes”. Other common carbonate stimulation techniques include: hydraulic fracturing, acid fracturing, hydro-blasting and combination of acidizing and cased-hole perforation. In this research, we aim to calculate wormhole propagation in a horizontal carbonate later (bed dip=0) during acidizing a directionally drilled well which is open-hole or cased-hole and thus modeling skin factor evolution with time. For this purpose, Buijse-Glasbergen semi-empirical field scale wormhole propagation model based on regression with acid efficiency curve, a model for unsteady-state pressure distribution in the formation caused by a directionally drilled well and a model for single phase Newtonian fluid flow in the wellbore considering inflow/outflow from wellbore wall are coupled which by solving them simultaneously, wormhole propagation in each time step can be calculated. Based on the obtained results, wormhole propagation decreases with reservoir layer depth due to the fact that by starting acidizing job, permeability of the upper portions of the layer will increase more than the lower parts as a result of the sooner contact of the acid with them. Thus, these parts will receive larger volumes of acid and greater wormhole penetration depths. Also, wormhole propagation radius will be increased in a cased-hole completion in comparison with the open-hole and thus carbonate reservoirs acidizing results will be improved. It is required to consider optimum number of sublayers used in simulation based on reasonable precision and runtime to obtain accurate results. Increasing wellbore inclination causes wormhole propagation to be increased to a specific depth, but it does not necessarily improve overall acidizing results and reducing skin factor. Minimum skin factor occurs in a specific inclination which must be considered in planning directional wells which their reservoirs will require acidizing certainly.

The aim of the present study was the histological evaluation of Enamel Matrix Derivative (EMD) effectiveness for regeneration of periodontal defects. EMD activates cementum synthesis, PDL and bone during the maturation stage of follicole. In this research, EMD was used in surgical defects of premolar teeth in four adult sheep. Muccoperiosteal flap was reflected in buccal site of teeth. The buccal bone plate was removed from mesial to distal in 4 mm depth. After eliminating the cementum by bur and its etching, EMD was applied on exposed dentine and flap was sutured. In opposite sites of those teeth (control sites) the same process was performed without etching. After 100 days, sheep were sacrificed and histological study through light microscopic was performed on black sections of operation sites. The results showed that in test sites, regeneration of cementum and bone was 62/5% and 42/5-50% respectively. But in control sites regeneration of cementum and bone was 37.5% and 32/5-42/5% respectively. Also the migration of junctional epithelium in control sites was 8-10% more than test sites. The important point is that in test sites, cementum was completely attached to undermining dentine. But, in control sites, the gap between cementum and dentine was visible. As a result, this study suggests that EMD promotes periodontal regeneration, and EMD application is a successful achievement in regenerative periodontal therapy.

During the acidizing process in oil and gas reservoirs, the injected acid reacts with the rock grains, changes the rock pore structure and affects the flow conditions. Due to the presence of a concentration gradient at the vicinity of the rock grains and the continuous changes in rock-fluid interfaces, the continuum assumption of the effective local mass transport coefficient and porosity-permeability relation in the continuum scale modeling of this process has been remained debatable. Therefore, the need for pore scale modelling is evident. The novelty of this study relies in adapting the grid refinement method on reactive flow modeling that implements the Lattice Boltzmann method to compute the effective local mass transport coefficient on the pore scale and in changing porous media. Quadtree grid refinement method is a multiscale mesh refiner that adjusts the grid resolution based on recursive subdivisions, and it is able to reduce the computational load while keeping the desired precision. The simulation results with one-and two-level refinements show that quadtree is two to three times faster relative to uniform fine grid model. Meanwhile, this study uses the constructed model to regenerate the experimental results of wormhole dissolution pattern and discusses the variation in the porosity-permeability relation and the mass transport coefficient due to rock dissolution at different flow conditions that are characterized using the dimensionless numbers of Damkohler, Peclet and Sherwood. The simulation results demonstrate the relation between the dissolution and the Sherwood number and indicate that accurate investigation of the variation in porosity-permeability relation can be performed through analyzing the Kozeny-Carman relation in different flow conditions. Therefore, grid refinement method provides a Pore-Darcy scale bridging tool by achieving larger simulation domains on the pore scale.

Carbonate acidizing modeling presents an effective tool to determine dynamic behavior trends during Matrix acidizing treatment. A successful Matrix acidizing process requires a minimum volume of injected acid while creating highly conductive wormholes. In this work, the two-scale continuum model was used to simulate carbonate acidizing using finite difference approach. This model describes the reactive transport of acid at the Darcy scale and determines the local permeability, porosity, pore radius, and solid-fluid interfacial area changes at the pore-scale through structure-property relationships. In this study, a two-dimensional model was employed with constant flow rate inlet boundary condition, constant pressure outlet boundary condition, and no flow boundary condition on the lateral sides. To perform a grid independent verification, the normalized acid concentration was plotted versus mesh elements which, then, results in determining the optimum number of grid blocks. To solve governing equations, finite difference approach was used by employing initial and boundary conditions. The results of the two-dimensional homogeneous model revealed that there is a uniform acid concentration profile with a reduction trend during the model length. A sensitivity study on acid injection velocity in a heterogeneous model showed that there is an optimum injection velocity of 0. 33 to 1. 5 cm/s in which deep wormholes with a minimal amount of acid are created. Moreover, as time passes, the reactive dissolution process takes place and results in a dynamic change in the model porosity. This model indicated a good capability to qualitatively capture the experimentally observed wormhole propagation and growth.

SummaryA numerical code based on the finite element method in MATLAB software has been developed to investigate the effect of joint shear rate on the hydraulic behavior of joints in pre/post-acidizing conditions. IntroductionEvaluation of permeability and fluid flow behavior in rock joints is one of the most critical and fundamental issues in many rock engineering projects. In recent years, changes in the permeability of rock joints and mechanical deformations of the rock mass with the effects of chemical reaction have been studied by H-M-C process. Shear-flow coupling tests are generally performed under conditions where the flow direction is either parallel to the cutting direction or radially from the center of the joint sample due to the limitations of difficult laboratory conditions. One of these difficulties is the complete insulation of the sample to create a one-dimensional linear flow in the direction of the shearing. Numerical simulations can eliminate laboratory difficulties with flow sealing conditions. In this paper, the influence of chemical agents on fluid flow while the shearing process is applied. Due to the difficulties of implementing this issue, modeling has been done by developing a computational code using the finite element method. Methodology and ApproachesDesigning a coupling process with simultaneous effect of hydro-mechanical-chemical phenomena, numerical modeling based on the finite element method has been used to study the effect of shear displacement on fluid flow rate when fracture surfaces are degraded. The hydraulic head pressure (equal to one meter of water) is applied to the flow's input, and zero pressure is applied to the flow's outflow to simulate and quantify the flow rate from the fracture's left to right. The upper and lower boundaries of the fracture are also sealed. In the next step, because the fluid flow is to be examined separately in the X and Y directions, then, in each step, the flow in the conduct of outlets must be opened in the desired direction and closed in the other directions. To apply the effect of shear displacement on the flow rate, a secondary code based on the changes in the elements due to shear displacement was used and added it to the computational process of the developed primary code. The aperture values in each step are calculated and returned to the original code to calculate the flow rate step by step. Results and ConclusionsThe results show that with increasing the shearing rate in both conditions before and after acidizing, the flow rate has an increasing trend. Also, the fluid flow pattern goes channelized with an increasing shear rate. After acidizing the joint surface, the difference between the roughness coefficient and the linear roughness of the two fracture surfaces increases, which increases the initial hydraulic conductivity of the fracture, and flow changes shows a lower trend compared with the conditions in the pre-acid state. In some cases, the trend of discharge rates in the conditions after acidizing does not follow the general pattern of discharge rates. It seems it’s caused by closures which are created by shear displacement in the fluid flow path, forcing the fluid to change direction and find a new path to pass through the joint.