Download or read book Experimental Investigation on the Effect of Permeability on the Optimum Acid Flux in Carbonate Matrix Acidizing written by Jordan Ruby Etten and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Determination of optimal acidizing conditions through laboratory experimental study is crucial for designing matrix acid stimulation jobs in the field. Optimum interstitial velocity, v[subscript i-opt] (the velocity of injected fluid that yields the minimum volume of acid needed to propagate wormholes) can be determined though curve fitting of experimental data. This optimum interstitial velocity coincides with the minimum volume of acid required for wormhole breakthrough, and therefore, the most efficient stimulation design. Optimum interstitial velocity determines the injection rate for a treatment, and the optimum pore volume to breakthrough, PV[subscript bt-opt], suggests the total volume of acid needed. Studies of carbonate matrix acidizing have focused on the role of many parameters, such as acid concentration, acid type, temperature, and core dimensions. However, under the same experimental conditions, different limestone rocks exhibit different optimal conditions. It is important to explore how changes in rock properties, such as permeability and pore structure, can also impact the efficacy of matrix acidizing techniques. In this work, a series of linear coreflood experiments on relatively homogenous Indiana limestone and Desert Pink limestone cores were performed at ambient temperature. Cores of 1.5-in. diameter by 8-in. long were acidized using 15% hydrochloric acid. The average permeabilities of the cores tested were 6, 11, 33 and 239 mD with varied porosity. The effects of permeability and porosity were isolated using thin section analysis to study pore structure. Based on experimental results, a detailed explanation of the pore structure and permeability effects on optimum interstitial velocity is presented. The coreflood acidizing results show that at low permeabilities, optimum interstitial velocity increases with permeability. When permeability of the rock reaches a certain value, the effect of permeability on the optimum injection condition diminishes. In addition, the optimum pore volume to breakthrough increases across the entire range of permeabilities tested. This work also briefly quantifies the differences in pore structure of the samples, leading to recommendations for future work. The implications and applications of this work are far-reaching; better understanding of optimal acidizing conditions based on the studied rock properties has significant potential economic and operational impact. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/155227

Download or read book Experimental Investigation for the Effect of the Core Length on the Optimum Acid Flux in Carbonate Acidizing written by Kai Dong and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Matrix acidizing is commonly used to stimulate wells in carbonate reservoirs. Large amounts of lab tests indicate an optimum acid interstitial velocity (Vi-opt, injection rate over flow area and porosity) exists, which results in the minimum volume of acid required for wormhole propagation and best stimulation results. Previous tests showed that the Vi-opt increased with increasing core length, but it is not clear if the Vi-opt can be independent of the core length when the core length reaches a certain value. In this work, a series of core flood experiments with different core lengths was carried out to determine the Vi-opt. Results showed that the Vi-opt became a constant when the core length reached a certain length. The finding of this study can guide lab researchers to use proper core lengths when determining the Vi-opt.

Download or read book Experimental Investigation for the Effects of the Core Geometry on the Optimum Acid Flux in Carbonate Acidizing written by Xiao Jin and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Previous matrix acidizing experimental research showed that there exists an optimum acid interstitial velocity (V[subscript i-opt]) that results in the minimum volume of acid used while providing the best stimulation results. There are already several upscaling models that translate experimental results into field conditions. By finding the optimum core geometry to use for matrix acidizing experiments, a great amount of time and money will be saved in selecting the correct size core for future experimental work. Laboratory experiments have already indicated that the optimum acid interstitial velocity can be independent of the core length when the core length is long enough. In this thesis, further core flood experiments were done using four inches diameter cores that varied in length. The lengths of the cores are 4 inches, 6 inches, and 8 inches long. The acid concentration used for these experiments was 15 wt% HCl. A pressure drop plot was created as the acid penetrates through the core sample. By looking at the pressure drop plot, the start of acid penetration, the early stages of wormhole competition, the later stages of a dominant wormhole forming, and the time when the acid breaks through the core can all be recorded. Theoretical works were done to correlate experimental results with previously published work. It can be concluded that when the core reaches a certain length, the optimum interstitial velocity becomes independent of the core length due to the dominant wormhole being formed. Also, when the core length reaches a certain value, the optimum acid injection rate is independent of the core radius given that the core radius is large enough to comprise the early effects of wormhole competition. One inch diameter cores should never be used because it only shows the dominant wormhole being formed. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/151623

Download or read book Multiphase flow behavior in complex and critical environments written by Zhiyuan Wang and published by Frontiers Media SA. This book was released on 2022-12-29 with total page 146 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Applied Matrix Acidizing of Carbonate Reservoir written by Ehsan Khamehchi and published by Springer Nature. This book was released on with total page 229 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Modeling and Optimization of Matrix Acidizing in Horizontal Wells in Carbonate Reservoirs written by Hậu Trần and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: In this study, the optimum conditions for wormhole propagation in horizontal well carbonate acidizing was investigated numerically using a horizontal well acidizing simulator. The factors that affect the optimum conditions are rock mineralogy, acid concentration, temperature and acid flux in the formation. The work concentrated on the investigation of the acid flux. Analytical equations for injection rate schedule for different wormhole models. In carbonate acidizing, the existence of the optimum injection rate for wormhole propagation has been confirmed by many researchers for highly reactive acid/rock systems in linear core-flood experiments. There is, however, no reliable technique to translate the laboratory results to the field applications. It has also been observed that for radial flow regime in field acidizing treatments, there is no single value of acid injection rate for the optimum wormhole propagation. In addition, the optimum conditions are more difficult to achieve in matrix acidizing long horizontal wells. Therefore, the most efficient acid stimulation is only achieved with continuously increasing acid injection rates to always maintain the wormhole generation at the tip of the wormhole at its optimum conditions. Examples of acid treatments with the increasing rate schedules were compared to those of the single optimum injection rate and the maximum allowable rate. The comparison study showed that the increasing rate treatments had the longest wormhole penetration and, therefore, the least negative skin factor for the same amount of acid injected into the formations. A parametric study was conducted for the parameters that have the most significant effects on the wormhole propagation conditions such as injected acid volume, horizontal well length, acid concentration, and reservoir heterogeneity. The results showed that the optimum injection rate per unit length increases with increasing injected acid volume. And it was constant for scenarios with different lateral lengths for a given system of rock/ acid and injected volume. The study also indicated that for higher acid concentration the optimum injection rate was lower. It does exist for heterogeneous permeability formations. Field treatment data for horizontal wells in Middle East carbonate reservoirs were also analyzed for the validation of the numerical acidizing simulator. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/149428

Download or read book Reactive Flow in Vuggy Carbonates written by Omer Izgec and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Carbonates invariably have small (micron) to large (centimeter) scale heterogeneities in flow properties that may cause the effects of injected acids to differ greatly from what is predicted by a model based on a homogenous formation. To the best of our knowledge, there are neither theoretical nor experimental studies on the effect of large scale heterogeneities (vugs) on matrix acidizing. The abundance of carbonate reservoirs (60% of the world?s oil reserves) and the lack of a detailed study on the effect of multi-scale heterogeneities in carbonate acidizing are the main motivations behind this study. In this work, we first present a methodology to characterize the carbonate cores prior to the core-flood acidizing experiments. Our approach consists of characterization of the fine-scale (millimeter) heterogeneities using computerized tomography (CT) and geostatistics, and the larger-scale (millimeter to centimeter) heterogeneities using connected component labeling algorithm and numerical simulation. In order to understand the connectivity of vugs and thus their contribution to flow, a well-known 2D visualization algorithm, connected component labeling (CCL), was implemented in 3D domain. Another tool used in this study to understand the connectivity of the vugs and its effect on fluid flow is numerical simulation. A 3D finite difference numerical model is developed based on Darcy-Brinkman formulation (DBF). Using the developed simulator a flow-based inversion approach is implemented to understand the connectivity of the vugs in the samples studied. After multi-scale characterization of the cores, acid core-flood experiments are conducted. Cores measuring four inches in diameter by twenty inches in length are used to decrease the geometry effects on the wormhole path. The post acid injection porosity distribution and wormhole paths are visualized after the experiments. The experimental results demonstrate that acid follows not only the high permeability paths but also the spatially correlated ones. While the connectivity between the vugs, total amount of vuggy pore space and size of the cores are the predominant factors, spatial correlation of the petro-physical properties has less pronounced effect on wormhole propagation in acidiziation of carbonates. The fact that acid channeled through the vugular cores, following the path of the vug system, was underlined with computerized tomography scans of the cores before and after acid injection. This observation proposes that local pressure drops created by vugs are more dominant in determining the wormhole flow path than the chemical reactions occurring at the pore level. Following this idea, we present a modeling study in order to understand flow in porous media in the presence of vugs. Use of coupled Darcy and Stokes flow principles, known as Darcy-Brinkman formulation (DBF), underpins the proposed approach. Several synthetic simulation scenarios are created to study the effect of vugs on flow and transport. The results demonstrate that total injection volume to breakthrough is affected by spatial distribution, amount and connectivity of vuggy pore space. An interesting finding is that although the presence and amount of vugs does not change the effective permeability of the formation, it could highly effect fluid diversion. We think this is a very important observation for designing of multi layer stimulation.

Download or read book Investigating the Effect of Oil Saturation on Acid Propagation During Matrix Acidization of Carbonate Rocks written by Rahul Pradeep Kumar and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The existence of an optimum injection rate for wormhole propagation, and face dissolution at low injection rates during matrix acidizing are well established. However, little has been documented that describes how the presence of residual oil affects carbonate acidizing. This study demonstrates the impact of oil saturation on wormholing characteristics while acidizing field and outcrop cores under reservoir conditions (200°F). Knowledge of the effect of different saturation conditions on acid performance will contribute towards designing more effective acid treatments. Coreflood experiments at flow rates ranging from 0.5 to 20 cm3/min were performed to determine the optimum injection rate for wormhole propagation when acidizing homogeneous calcite and dolomite reservoir cores, and low permeability Indiana limestone cores of dimensions 3 and 6 in. length and 1.5 in. diameter. Absolute permeability of the cores ranged from 1 to 78 md. The study involved acidizing cores saturated with water, oil, and waterflood residual oil using 15 wt% HCl. The viscosity of the crude oil used was 3.8 cP at 200°F. CAT scans were used to characterize wormholes through the cores. The concentrations of the dissolved calcium and magnesium ions were measured using Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES) and the effluent samples were titrated to determine the concentration of the acid. HCl was effective in creating wormholes with minimal branches for cores with residual oil (Sor=0.4-0.5) at injection rates 0.5 to 20 cm3/min. Compared to brine and oil saturated cores, waterflood residual oil cores took less acid volume to cause breakthrough. Additionally, the wormholing efficiency of regular acid improved with increases in acid injection rates in the presence of residual oil. A decrease in acid pore volumes to breakthrough for oil saturated cores was noted at high acid injection rates, which could be attributed to viscous fingering of acid through oil. Unlike brine saturated and oil saturated cores, waterflood residual oil cores showed no face dissolution at low acid injection rates. Conclusions from this work aid in the designing of better acid jobs by highlighting the impact of oil saturation on wormholing characteristics of acid while acidizing carbonate rocks. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/152452

Download or read book The Effect of Viscoelastic Surfactants Used in Carbonate Matrix Acidizing on Wettability written by Oladapo Adejare and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Carbonate reservoirs are heterogeneous; therefore, proper acid placement/diversion is required to make matrix acid treatments effective. Viscoelastic surfactants (VES) are used as diverting agents in carbonate matrix acidizing. However, these surfactants can adversely affect wettability around the wellbore area. Lab and field studies show that significant amounts of VES are retained in the reservoir, even after an EGMBE postflush. Optimizing acid treatments requires a study of the effect of VES on wettability. In a previous study using contact angle experiments, it was reported that spent acid solutions with VES only, and with VES and EGMBE are water-wetting. In this thesis, we studied the effect of two amphoteric amine-oxide VES', designated as "A" and "B" on the wettability of Austin cream chalk using contact angle experiments. We extended the previous study by using outcrop rocks prepared to simulate reservoir conditions, by demonstrating that VES adsorbs on the rock using two-phase titration experiments, by studying the effect of temperature on wettability and adsorption, and by developing a detailed procedure for contact angle experiments. We found that for initially oil-wet rocks, simulated acid treatments with VES "A" and "B" diversion stages and an EGMBE preflush and postflush made rocks water-wet at 25, 80, and 110 degrees C. Simulated acid treatments with a VES "A" diversion stage only made rocks water-wet at 25 degrees C. Our results suggest that both VES formulations cause a favorable wettability change for producing oil. The two-phase titration experiments show that both VES "A" and "B" adsorb on the rock surface. From our literature review, many surfactant wettability studies use contact angle measurements that represent advancing contact angles. However, wettability during stimulation is represented by receding contact angles. Results of static receding contact angles may be misinterpreted if low oil-acid IFT's cause oil droplets to spread. Spreading could be a reflection of the effect of the surfactants on the fluid-fluid interface rather than the rock-fluid interface. The new procedure shows the effect of VES and EGMBE on the rock-fluid interface only, and so represents the actual wettability.

Download or read book SPE Journal written by and published by . This book was released on 2000 with total page 524 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Experimental High Velocity Acid Jetting in Limestone Carbonates written by Christopher Charles Holland and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Acid jetting is a well stimulation technique that is used in carbonate reservoirs. It typically involves injecting acid down hole at high flow rates through small orifices which cause high velocities of acid to strike the borehole wall. The combination of high kinetic energy and chemical reaction of the acid removes drilling mud filter cake from the borehole wall and produces long conductive channels, called wormholes, into the formation, therefore improving well performance. Studies have shown that injecting fluid down hole at high velocities can mitigate damage to wellbore caused by drilling mud filter cake. Both water and acid have shown positive results in such cases. However, there are no laboratory results on how high velocity acid impacts the borehole wall and the formation of wormholes. The purpose of this study is to investigate how the high velocity acid affects the acidizing treatments. The experiments are conducted on 4" diameter by 16" length Indiana limestone cores with acid injected at the velocity of 106 ft/s, 150 ft/s, and 200 ft/s. The experiments are conducted with a constant pressure differential across the core. 15%wt Hydrochloric acid is injected at room temperature at various flux rates. The results show that the higher the velocity of jetted acid, the further it penetrates into the formation. The 200 ft/s acid penetrates furthest into the core, thus potentially lowering the skin factor the greatest. A large cavity is formed into the core from the high velocity acid. This large cavity creates a pathway for acid to divert into the core to create wormholes. Acid jetting cannot be directly compared with matrix acidizing because of the formation of these large cavities. The Buijse-Glasbergen model that is used to predict the formation of wormholes does not accurately match the acid jetting data due to the formation of these large cavities, so the optimum flux and pore volume to breakthrough cannot be accurately determined. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/152722

Download or read book The Effect of Heterogeneity on Matrix Acidizing of Carbonate Rocks written by Ryan Scott Keys and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: In matrix acidizing, the goal is to dissolve minerals in the rock to increase well productivity. This is accomplished by injecting an application-specific solution of acid into the formation at a pressure between the pore pressure and fracture pressure. A hydrochloric acid solution is used in carbonate reservoirs, which actually dissolves the calcite rock matrix in the form of conductive channels called wormholes. These wormholes propagate from the wellbore out into the reservoir, bypassing the damaged zone. In matrix acidizing of carbonates, there are four parameters that affect performance: the concentration of calcite present, injection rate of the acid, reaction type, and heterogeneity. Of these parameters, this paper will focus on how rock heterogeneity affects performance. To do this, a coreflood and acidizing apparatus was used to acidize heterogeneous limestone core samples. Rock characterizations and volumetric measurements were considered with the results from these experiments, which made it possible to correlate and quantify the results with rock and volume parameters. It was found that the core samples with more and larger heterogeneities generally required less acid (measured in pore volumes) to achieve breakthrough, that is, a wormhole created axially from one end of the core to the other. This value for pore volumes to breakthrough was one to two orders of magnitude less than more homogeneous samples. The general procedure and best practices for acidizing the core samples is also detailed in this thesis. This procedure was followed for preparation, coreflooding, and acidizing for all core samples.

Download or read book Investigating the Effects of Core Length on Pore Volume to Breakthrough PVBT Behavior in Carbonate Core Samples During Matrix Acidizing with Hydrochloric Acid written by Mohamed Nour Nour and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Most literature contains Hydrochloric acid (HCl) carbonate acidizing experiments performed on short (2 - 6 inch) cores. These cores do not accurately represent reservoir conditions, as spent acid is not propagated for any appreciable distance along the length of the sample. In this work, HCl injection experiments are performed on both short (6 inch) and long (20 inch) calcite cores to investigate the pore volume to breakthrough (PVBT) behavior. PVBT is defined as the volume of acid necessary to propagate the wormhole network from the inlet to the outlet of the core sample, divided by the pore volume of the core. HCl (5 and 15 percent by weight) injection core flood experiments were performed on 6 inch and 20 inch calcite (Indiana Limestone) cores. The cores were CAT scanned before and after acid injection to observe wormhole propagation. Core outlet effluent samples were collected and their calcium concentration was measured using Inductively-Coupled Plasma. Results from core flood experiments show an increased PVBT for 20 inch cores compared to the 6 inch samples. Results from CAT scan experiments show enlarged worm-holing and face dissolution on the 20 inch cores compared to the 6 inch cores, due to increased acid spending at the same acid concentration, flow rate, and injection temperature. Results from experiments performed at various flowrates indicate the existence of an optimum injection rate for 20 inch cores, just as in 6 inch cores. This study summarizes and explains the results obtained from the aforementioned experiments. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/152518

Download or read book A New Organic Acid to Stimulate Deep Wells in Carbonate Reservoirs written by Ahmad F Al-Douri and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Carbonate acidizing has been carried out using HCl-based stimulation fluids for decades. However, at high temperatures, HCl does not produce acceptable results because of its fast reaction, acid penetration, and hence surface dissolution, and its high corrosion rate. As a result, alternatives to HCl have been investigated including organic acids. In this work, the reaction of a new organic acid with calcite was investigated using the rotating disk apparatus and coreflood setup. The organic acid was obtained using both a phosphorous-based and iron-based catalyst. The rate of reaction of a 10 wt% solution of the new organic acid was measured using the rotating disk apparatus at temperatures up to 250°F. Low-permeability Indiana limestone (1-5 md) samples of 1.5 in. diameter and 0.75 in. length were used. The effect of disk rotational speed (100-1,500 rpm) was investigated. Samples of the reacted fluid were collected periodically and calcium and iron concentrations were measured using Inductively-Coupled Plasma, and used to determine the acid-rock reaction rate and to study the possibility of precipitation. Also, coreflood experiments at different injection rates and a temperature of 300°F were performed to study the effect of the acid on wormhole propagation in calcite. Low-permeability Indiana limestone (1-10 md) cores used in these experiments have a diameter of 1.5-in. and a length of 6 in. For the phosphorus-based acid, experimental results showed that the rate of calcite dissolution at 205°F was controlled only by the rate of mass transfer of the acid to the surface. However, at 250°F, the reaction was controlled by both mass transfer and by the kinetics of the surface reaction. At 205°F, the reaction rate varied from 7.79E-07 to 4.47E-06 gmol/cm2.s, while at 250°F, the range was between 5.82E-07 and 2.72E-06 gmol/cm2.s. In coreflood experiments, the phosphorus-based acid caused calcium phosphate precipitation at 300°F, while the iron-based acid achieved breakthrough. Also, the optimum injection rate of the iron-based acid was determined to be 2.0 cm3/min. This study summarizes the results obtained and recommends the use of the new organic acid for field applications in calcite reservoirs. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/152449

Download or read book Numerical Modeling of Matrix Acidizing in Carbonate and Sandstone Reservoirs written by Wan Wei and published by . This book was released on 2020 with total page 452 pages. Available in PDF, EPUB and Kindle. Book excerpt: Matrix acidizing is a stimulation technique to improve productivity/injectivity in the near-wellbore region in carbonate and sandstone reservoirs. Carbonate reservoir is heterogeneous in mineralogy, primary porosity, and secondary porosity such as fractures. Optimally through acidizing treatment, wormholes are generated in carbonate reservoirs to improve the permeability and bypass the damaged zone. A two-scale continuum model is implemented in a radial coordinate system to simulate acidizing process in the near-wellbore geometry. The model is extended from single-phase to two-phase by considering mobility change due to water-oil displacement and defining a new criterion for acidizing breakthrough applicable to two-phase flow. The requirement of acid consumption is lower with the existence of oil prior to acidizing treatment. This indicates that for field treatment, maintaining a higher oil saturation can enhance acidizing efficiency. To consider varying mineral compositions in carbonates, the acidizing model is implemented in the UTCOMP-IPhreeqc coupled software to model homogeneous and heterogeneous reactions among acid and minerals. Different acid pore volumes are predicted for limestone, dolostone, and partially dolomitized formation due to the difference in reaction rate and dissolution structures generated. To consider fracture effect in carbonates, the acidizing model in UTCOMP-IPhreeqc is extended to consider reactions on the fracture surface with the aid of EDFM (Embedded Discrete Fracture Model). The fracture with a high conductivity will receive most acid and slow down the wormhole propagation in the matrix. To improve computational efficiency, the acidizing model is also implemented in the semi-parallel version of UTCOMP-IPhreeqc, with the parallelized geochemical calculation. Besides, speedup techniques through defining a tolerance on the relative amount change of geochemical elements to reduce IPhreeqc calls are also applied. Parallel computing saves up to 85% of the total computational time when using 16 processors. And speedup techniques obtain about 50% improvement for the wormhole pattern. The acidizing model in UTCOMP-IPhreeqc is also extended to simulate acidizing process in sandstone reservoirs through modifying IPhreeqc database to include primary and secondary reactions. A largest possible injection rate is recommended to achieve best performance mitigating formation damage caused by precipitation

Download or read book Study Towards Improving the Efficiency of Matrix Acidizing in Oil bearing Carbonate Formations written by Mohamed Mustafa Elmabruk Elsafih and published by . This book was released on 2021 with total page 157 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Existence of an optimum injection rate in carbonate acidizing and the effect of rock heterogeneity on wormhole patterns written by Yimei Wang and published by . This book was released on 1993 with total page 246 pages. Available in PDF, EPUB and Kindle. Book excerpt: