Browsing by Subject "Acid Fracturing"
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Item Effect of droplet size on the behavior and characteristics of emulsified acid(Texas A&M University, 2008-10-10) Almutairi, Saleh HaifEmulsified acids have been extensively used in the oil industry since 1933. Most of the available research and publications discussed mainly the application of emulsified acid in the field. A fair number of the published work also discussed in depth some of the emulsified acid properties such viscosity, stability and reactivity. However, all of the available research discussed the emulsified acid without sufficient details of its preparation. Beside their chemical composition, the ways emulsified acids are prepared cause significant differences in their physical properties. The characterization of emulsified acid by its droplet size and size distribution complements its chemical composition and gives the emulsified acid a unique description and thus reproducible properties. No previous study considered the impact of the droplet size on the characteristics and properties of emulsified acid. Therefore, the main objective of this research is to study the effects of the droplet size on various properties of emulsified acid such as viscosity, stability and reactivity. Results showed that the droplet size and size distribution have a strong effect on the stability, viscosity and diffusion rate of the emulsified acid. The results of this work are important because knowledge of the effect of the droplet size on major design parameters will guide the way emulsified acid is prepared and applied in the field.Item Experimental Study of Acid Fracture Conductivity of Austin Chalk Formation(2013-05-01) Nino Penaloza, AndreaAcid fracture conductivity and the effect of key variables in the etching process during acid fracturing can be assessed at the laboratory scale. This is accomplished by using an experimental apparatus that simulates acid injection fluxes comparable to those in actual acid fracture treatments. After acid etching, fracture conductivity is measured at different closure stresses. This research work presents a systematic study to investigate the effect of temperature, rock-acid contact time and initial condition of the fracture surfaces on acid fracture conductivity in the Austin Chalk formation. While temperature and rock-acid contact are variables normally studied in fracture conductivity tests, the effect of the initial condition of the fracture surface has not been extensively investigated. The experimental results showed that there is no significant difference in acid fracture conductivity at high closure stress using smooth or rough fracture surfaces. In addition, we analyzed the mechanisms of acid etching and resulting conductivity creation in the two types of fracture surfaces studied by using surface profiles. For smooth surfaces, the mechanism of conductivity creation seems connected to uneven etching of the rock and roughness generation. For rough surfaces, acid conductivity is related to smoothing and deepening of the initial features on the sample surface than by creating more roughness. Finally, we compared the experimental results with Nirode-Kruk correlation for acid fracture conductivity.Item Laboratory-scale fracture conductivity created by acid etching(2009-05-15) Pournik, MaysamSuccess of acid fracturing treatment depends greatly on the created conductivity under closure stress. In order to have sufficient conductivity, the fracture face must be non-uniformly etched while the fracture strength maintained to withstand the closure stress. While there have been several experimental studies conducted on acid fracturing, most of these have not scaled experiments to field conditions and did not account for the effect of rock weakening and etching pattern. Hence, acid fracture conductivity predictions based on the above works have not been able to match actual results. In order to develop a more appropriate and accurate prediction of acid fracturing treatment outcome, a laboratory facility was developed that is properly scaled to field conditions and enables analysis of etching pattern and rock strength. A systematic experimental study that covered a variety of formations, acid types, and acid contact times was conducted. An acid fracture conductivity correlation was developed based on etched volume, etched pattern, and fracture strength under closure stress. Results suggested that there is an optimal time of acid exposure resulting in maximum fracture conductivity. There were large differences in the conductivity created with the different acid systems tested due to different etching patterns and degree of rock strength weakening. There was an optimal acid system depending on formation type, contact time and overburden stress. The acid fracture conductivities measured did not agree with the predictions of the Nierode-Kruk correlation. The newly developed correlation predicts conductivity much closer as it includes the effect of rock strength and surface etching pattern on resulting conductivity.Item Modeling Acid Transport and Non-Uniform Etching in a Stochastic Domain in Acid Fracturing(2010-10-12) Mou, JianyeSuccess of acid fracturing depends on uneven etching along the fracture surfaces caused by heterogeneities such as variations in local mineralogy and variations in leakoff behavior. The heterogeneities tend to create channeling characteristics, which provide lasting conductivity after fracture closure, and occur on a scale that is neither used in laboratory measurements of acid fracture conductivity, which use core samples that are too small to observe such a feature, nor in typical acid fracture simulations in which the grid block size is much larger than the scale of local heterogeneities. Acid fracture conductivity depends on fracture surface etching patterns. Existing acid fracture conductivity correlations are for random asperity distributions and do not consider the contribution of channels to the conductivity. An acid fracture conductivity correlation needs the average fracture width at zero closure stress. Existing correlations calculate average fracture width using dissolved rock equivalent width without considering the effect of reservoir characteristics. The purpose of this work is to develop an intermediate-scale acid fracture model with grid size small enough and the whole dimension big enough to capture local and macro heterogeneity effects and channeling characteristics in acid fracturing. The model predicts pressure field, flow field, acid concentration profiles, and fracture surface profiles as a function of acid contact time. By extensive numerical experiments with the model, we develop correlations of fracture conductivity and average fracture width at zero closure stress as a function of statistical parameters of permeability and mineralogy distributions. With the model, we analyzed the relationships among fracture surface etching patterns, conductivities, and the distributions of permeability and mineralogy. From result analysis, we found that a fracture with channels extending from the inlet to the outlet of the fracture has a high conductivity because fluid flow in deep channels needs a very small pressure drop. Such long and highly conductive channels can be created by acids if the formation has heterogeneities in either permeability or mineralogy, or both, with high correlation length in the direction of the fracture, which is the case in laminated formations.Item Modeling of Acid Fracturing in Carbonate Reservoirs(2014-06-05) Al Jawad, Murtada sThe acid fracturing process is a thermal, hydraulic, mechanical, and geochemical (THMG)-coupled phenomena in which the behavior of these variables are interrelated. To model the flow behavior of an acid into a fracture, mass and momentum balance equations are used to draw 3D velocity and pressure profiles. Part of the fluid diffuses or leaks off into the fracture walls and dissolves part of the fracture face according to the chemical reaction below. 2H^(+)(aq) + CO((2-)/3) ? H_(2 )CO_(3)(aq) ? CO_(2)(g) + H_(2)O (l) An acid balance equation is used to draw the concentration profile of the acid and to account for the quantity of rock dissolved. An algorithm is developed for this process to generate the final conductivity distribution after fracture closure. The objective of modeling acid fracturing is to determine the optimum condition that results in a petroleum production rate increase. The conductivity value and acid penetration distance both affect the final production rate from a fracture. Treatment parameters are simulated to draw a conclusion about the effect of each on the conductivity and acid penetration distance. The conductivity distribution file from an acid fracturing simulator is imported into the ECLIPSE reservoir simulator to estimate the production rate. Reservoir permeability is the determining factor when choosing between a high- conductivity value and a long penetration distance. For the model to be more accurate, it needs to be coupled with heat transfer and geomechanical models. Many simulation cases cannot be completed because of numerical errors resulting from the hydraulic model (Navier-Stokes equations). The greatest challenge for the simulator before coupling it with any other phenomena is building a more stable hydraulic solution.