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Stimulating carbonate reservoirs by injecting acids results in channels within the rock called wormholes. This study reveals the stability of wormholed chalk and limestone samples under high confining pressure using a triaxial cell. The experiments were conducted on four Austin chalk (AC) and four Indiana limestone (IL) core samples (1.5 inches × 3 inches). The samples were characterized by their petrophysical (i.e., porosity and permeability) and elastic properties (i.e., Young's modulus). Two of each rock type were acidized to generate wormholes using a core flooding setup. Then the samples were subjected to a high confining pressure of up to 88 MPa using a triaxial/acoustic cell. In addition, the permeability of the samples under increasing confining pressure was reported. Medical CT scan images were taken for the wormholed samples before and after subjecting them to high confining pressures. The CT scan images and rock properties were imported to COMSOL finite element to simulate the deformation under high stresses. The results revealed that wormholes closed under confining in the chalk samples while it was mechanically stable in the IL samples. This was attributed to the rigidity of limestone as compared to weak chalk samples. Fractures were observed in one of the chalk samples, while no fractures were noticed in the limestone. The finite element simulations confirmed the experimental outcomes and showed that the wormhole branches were more susceptible to deformation and closure. Highlights: Wormholes in weak carbonate rocks are subject to closure under high confining pressures Wormhole branches tend to close faster due to the higher stress concentration Permeability of the wormhole is a strong function of the confining pressure [ABSTRACT FROM AUTHOR]

Estimating the performance of acid fracture in naturally fractured formation is a complex and computationally expensive process. Therefore, machine learning was utilized in this research to simplify a complex physics-based acid fracture model in naturally fractured dolomite formations. The physics-based model integrates fracture propagation, reactive transport, heat transfer, and reservoir productivity model. The performance of acid fracture depends strongly on acid design parameters (i.e., injection rate, acid concentration, etc.) and reservoir/natural fractures properties (i.e., reservoir permeability, natural fractures spacing, etc.). A parametric study was conducted, and based on a statistical analysis of 4900 simulation scenarios, we found that the acid volume, reservoir permeability, and natural fracture spacing are the most significant parameters. Also, the injection rate and fluid rheology are of paramount importance. A model based on machine learning tools such as support vector machine, fuzzy logic system, and Artificial neural network (ANN) was developed. The artificial neural network model outperforms the other two tools and has a prediction error of 3.3%. Finally, an empirical equation has been obtained from the ANN model. [ABSTRACT FROM AUTHOR]

Matrix acidizing is one of carbonate reservoirs' most efficient and widely implemented stimulation techniques. It improves productivity and flow capacity by creating new conductive flow channels called wormholes. The propagation of these channels has been a topic of interest as many researchers tried to investigate this phenomenon experimentally, theoretically, and numerically. Among various models, the two-scale continuum (TSC) model is the most common and reliable model due to its ability to predict better results as it combines Darcy and pore scales to capture the phenomenon. However, the main disadvantage of using the TSC model is its high computational cost. This highlights the need for a computationally efficient model that reduces that cost while maintaining solution accuracy. Also, examining wormhole propagation in 3D perforation is untouched yet. In this paper, we developed a numerical model in-house using MATLAB® software to simulate the wormhole generation considering the perforation in three-dimensional space based on the two-scale continuum mathematical model. The model performance is optimized to be a time-efficient simulation model that considers thermal energy transfer beside flowing and reactive mass transfer. Computation efficiency is achieved using the Darcy equation, vectorizing code operations, and implementing a proposed iterative algorithm that is based on the GMRES method. The associated tuning parameters and a proper preconditioner are obtained, which improved the model efficiency by more than 90%. The model used typical data reported in experimental acidizing work. [ABSTRACT FROM AUTHOR]

The occurrence of wellbore mechanical failure is a consequence of the interaction among factors such as in situ stress, rock strength, and engineering procedures. The process of hydrocarbons production, causing reduction of pore pressure, alters the effective stresses in the vicinity of a borehole, leading to borehole instability issues. Estimating the rocks' elastic modulus and compressive strength is essential to comprehend the rock matrix's mechanical response during drilling and production operations. This study aimed to assess the practicality of Diammonium Hydrogen Phosphate (DAP) application as a chemical for strengthening chalk in hydrocarbon reservoirs, to make it resistant to high stresses and failure during drilling and production. The mechanical and physical properties of Austin chalk rock samples treated with DAP under mimicked reservoir conditions were studied. The results showed that DAP is a highly effective carbonate rock consolidating agent that improves the mechanical strength of the chalk. Compressive test measurements conducted on rocks treated at two different temperatures (ambient and 50 °C) showed that DAP effectively strengthened the rock matrix, resulting in an increase in its compressive strength (22–24%) and elastic modulus (up to 115%) compared to the untreated sample. The favorable outcomes of this research suggest that the DAP solution holds promise as a consolidation agent in hydrocarbon reservoirs. This contributes to the advancement of knowledge regarding effective strategies for mitigating mechanical failures of the wellbore during drilling and production. [ABSTRACT FROM AUTHOR]

This research investigates the impact of different rock, acid, and reaction dynamic properties on the pore volume to breakthough (PVBT) at different acid injection rates using in-house developed two-scale continuum simulation model. We analyzed the parameters relation and developed a reliable machine learning model to accurately predict the PVBT at similar range of investigated parameters. In the simulation, it was found that different acid concentrations result in the same optimum injection velocity but at large contrast in PVBT between low and high acid concentration. However, other parameters such as diffusion coefficient and reaction rate exhibited an inverse PVBT behavior across optimum injection velocity due to change in acid transport and reaction behavior. After that, different reliable machine learning algorithms were employed to predict the optimum PVBT for carbonates matrix acidizing. The utilized machine learning models undergone multiple optimizations and comparison to obtain the most accurate prediction performance. The artificial neural network model with 2 hidden layers outperforms the other optimizations with 11.27% estimation error, 0.96 R2 and 0.98 correlation coefficient for the testing data set. Finally, an empirical correlation was developed to accurately estimate PVBT at a low cost and very short time compared to lab experiments and numerical simulation models. The novelty of this research stems from examining PVBT curves behavior by varying five matrix acidizing parameters independently, analyzing the correlation between these parameters and developing machine learning model for handy and reliable optimum PVBT estimation. [ABSTRACT FROM AUTHOR]

Calculation of REV (representative elementary volume) properties of geological porous media refers to the process of creating a 3D digital representation of a rock sample, typically obtained from imaging techniques such as X-ray microtomography. This technique allows for a detailed analysis of the internal structure and the properties of rocks, as well as precise calculation of various flow parameters. However, one major challenge with calculation of REV properties of geological porous media is the high computational cost required to generate accurate results, especially for large and complex samples. In this study, we constructed 3D digital cores of dune sand and fractured shale using CT scanning technology, and then used two image processing techniques, namely digital core image resampling and cutting, to reduce the computational cost of calculating digital core permeability. Next, a fast permeability calculation method is employed to reduce the complexity of permeability calculation. Finally, we summarized the applicability of different image processing methods to different rock samples, and provided prerequisites for high computational cost digital core permeability calculation. [ABSTRACT FROM AUTHOR]

Matrix acidizing is vital to enhance the production of tight carbonate formations. In weak carbonate rocks or acid over-dissolution, the rock is prone to failure upon developing wormholes. Strengthening agents can play a significant role in mitigating failure and supporting more extended productivity. In this study, we tested 0.1 M and 0.2 M zinc sulfate (ZnSO4) and 0.5 M diammonium phosphate ((NH4)2HPO4) as strengthening agents, which change the dominant host mineral into harder ones. Both agents were tested on two different types of acidized (i.e., wormholed) carbonate rocks, specifically Austin chalk and Indiana limestone. The impulse hammer and acoustics measurements evaluated the carbonate rocks' mechanical properties before and after the treatment. In addition, scanning electron microscopy energy-dispersive X-ray spectroscopy (SEM–EDS) and scanning electron microscopy (SEM) were used to affirm the change of rock mineralogy into harder minerals after the treatment. The chemical treatment caused no noticeable change in the wormhole size and shape, as revealed by the scanned micro-computed tomography (micro-CT) images. The chemical treatment of the samples was conducted by core flooding the plugs at high pressure and temperature with 4–5 pore volumes of the chemicals and leaving them in the treatment solution for 72 h. As a result of the formation of harder minerals, the mechanical properties after the treatment showed improvement. Zinc sulfate raised the surface rock hardness of limestone by 16%, while diammonium phosphate showed a 30% increase when evaluated with the same technique. The most noticeable improvement happened to chalk after treatment with diammonium phosphate. Chalk impulse hammer hardness almost quadrupled with the diammonium phosphate. The acoustics measurements showed a similar result to the impulse hammer through an increase in the dynamic Young's modulus and a decrease in Poisson's ratio. [ABSTRACT FROM AUTHOR]

Overbalanced drilling is the most common drilling technique; nevertheless, it has several disadvantages such as formation damage, mud losses, and stuck pipes; challenges that are common in high permeability zones and highly fractured formations. To overcome those issues, the underbalanced drilling method could be implemented. The underbalanced drilling (UBD) technique is widely utilized in hard, under pressure, depleted, and fractured/vuggy formations. Low-density drilling fluids are usually used in UBD operations and could be categorized into a gas (i.e., air, nitrogen, and natural gas) or two-phase (i.e., mist and foam). Although foamed fluid attracted attention in enhanced oil recovery and hydraulic fracturing operations, it is ideal for UBD operations due to its low density and efficient transport capacity. This paper highlights the applications, limitations, advantages, and disadvantages of UBD operations. It also discusses the drilling foam chemistry, structure, characterization, and rheological properties. Finally, this paper highlights a few successful UBD operations utilizing foamed drilling fluids worldwide. [ABSTRACT FROM AUTHOR]

The diversion efficiency measures the acid capacity to change its flow direction to the lower permeability reservoir sections. A good acid diverter creates a tortuous (zigzagged) wormhole within the acidized core sample in a laboratory setup. Here, we studied two different acid diverters compared to the conventional hydrochloric acid (HCl) to investigate their efficiency in changing the wormhole direction inside the rock core. Nuclear magnetic resonance (NMR) can be used to measure the 3D tortuosity of a rock sample; hence, we propose it as a tool to measure acid diversion efficiency because it can be applied in the field and in the laboratory. Two acid systems were utilized: straight 15 wt.% HCl acid and gelled acid consisting of 15 wt.% HCl acid and polyacrylamide polymer (PAM). Four coreflooding experiments were conducted on 1.5 inch-diameter × 3 inch-length Indiana limestone samples, two with straight HCl acid and two with gelled HCl acid at different PAM concentrations. NMR was utilized to measure the T2 distribution of the rock samples and diffusion tortuosity in two orthogonal directions. Also, X-ray computed tomography (CT) of the acidized samples was taken to visualize the wormholes. Results showed that the polymer-based acid-created zigzagged paths, and more acid volume was consumed to create the wormholes using CT. NMR diffusion tortuosity measurements showed that the tortuosity was reduced along the wormhole direction in all experiments. Nevertheless, the gelled acid treatments showed a significant reduction of the tortuosity orthogonal to the main wormhole path. The diversion efficiency of the 50 lbm/ 1000 gal PAM-gelled acid was 35% higher compared to the straight HCl acid. On the contrary, the 30 lbm/ 1000 gal PAM-gelled acid gave only 10% improvement in the diversion. The index could screen quantitatively which diverting acid is more efficient. We introduced a new diversion index based on the NMR diffusion measurements in this study to quantify the diversion capacity of an acid system in carbonate rock. [ABSTRACT FROM AUTHOR]

Brittleness Index (BI) is among the key parameters used to evaluate zones of interest or "sweet spots" before drilling and hydraulic fracturing in unconventional reservoirs. Several methods can be used to calculate the BI, including mineral-based, log-based, and elastic-based approaches. This work presents a new approach that can provide a fast, accurate, and continuous profile of the brittleness index, which would significantly aid unconventional resource characterization and identification. Different artificial intelligence tools were utilized in this work to come up with the best model for evaluating the rock brittleness based on elemental data acquired using x-ray fluorescence instruments. Artificial neural networks, support vector machines, and fuzzy logic techniques were used to develop new models that can provide continuous profiles of quartz, calcite, and clay minerals using profiles of few elements. After that, the mineral-based brittleness index (MBI) was estimated using the predicted profiles of quartz, calcite, and clay minerals. Moreover, a new model was developed to assess the MBI profile based on the elemental compositions (Na, Al, Si, K, and Ca), without a need to determine the rock mineralogy. The results showed that the developed models could provide accurate predictions for the mineralogical profiles and brittleness index, with R2 higher than 0.90. The proposed equation can be used to estimate the rock brittleness based on the logging data. [ABSTRACT FROM AUTHOR]

This study aimed to optimize the acidizing efficiency during stimulation treatments with chelating agents. The performance of hydroxylethylethylenediaminetriacetic acid (HEDTA), diethylenetriaminepentaacetic acid (DTPA), and ethylenediaminetetraacetic acid (EDTA) in stimulating carbonate rocks were investigated. In this paper, the effect of injection rate, chemical type, pH, and concentration on the stimulation performance was studied. Also, the optimum treatment conditions were identified utilizing the acid volume and treatment time. Different measurements were carried out, including solubility tests, coreflooding experiments, and CT scan analysis. Solubility tests were performed to study the impact of solution concentration and pH on the performance of the chelating agent. Coreflooding experiments were carried out at high-pressure, high-temperature conditions to assess the performance of chelating agents in different treatment situations. In addition, CT scan analysis was carried out before and after the acid injections to capture the changes induced in the carbonate matrix due to the stimulation treatment. The success of acidizing treatment was identified by the creation of the dominant wormholes. The pressure-drop profiles and the CT scan analysis were used to confirm the generation of wormholes. Finally, the normalized volume and time to breakthrough were utilized to identify the optimum treatment conditions. In this work, chelating agents successfully created dominant wormholes (WHs) in carbonate rocks at different injection rates and treatment conditions. However, applying an injection rate between 0.7 and 1 cm3/min significantly improved the acidizing performance and reduced the acid volume that was required to create wormholes. EDTA and HEDTA chelating agents showed better performance at low pH. Using a solution pH of 4.5 resulted in reducing the acid volume by 30% compared to using a solution pH of 10 at the same conditions. However, DTPA chelating agent showed better performance at high pH, and dominant WHs were created at a pH of 12 using less acid volume. Finally, the optimum acidizing treatment can be achieved by using EDTA chelating agent with a concentration of 9.25 wt.% and pH of 4.5. Applying the optimum treatment parameters can reduce the acid volume by 40% and the chemical cost by a factor of 6, on average. Overall, this study indicates that chelating agents' solution can be injected at optimum conditions in terms of chemical concentration, pH, and injection rate, to maximize the treatment efficiency and reduce the cost. [ABSTRACT FROM AUTHOR]

Hydraulic fracturing operations target enhancing the productivity of tight formations through viscous fluid injection to break down the formation and transport proppant. Crosslinked polymers are usually used for desired viscoelasticity of the fracturing fluid; however, viscoelastic surfactants (VES) became a possible replacement due to their less damaging impact. To design a fracturing fluid with exceptional rheological and thermal stability, we investigated mixing zwitterionic VES with carboxymethyl cellulose (CMC), hydroxyethylcellulose (HEC), or a poly diallyl dimethylammonium chloride (DADMAC) polymers. As a base fluid, calcium chloride (CaCl2) solution was prepared with either distilled water or seawater before adding a polymer and the VES. A Chandler high-pressure, high-temperature (HPHT) viscometer was used to conduct the viscosity measurements at a shear rate of 100 1/s. It has been found that adding 1% CMC polymer to 9% (v/v) VES increases the viscosity more compared to 10% (v/v) VES at reservoir temperatures of 143.3 °C. On the other hand, adding only 1.0% of HEC to 9% (v/v) VES doubled the viscosity and proved more effective than adding CMC. HEC, nevertheless, reduced the system stability at high temperatures (i.e., 148.9 °C). Adding DADMAC polymer (DP) to VES increased the system viscosity and maintained high stability at high temperatures despite being exposed to saltwater. CaCl2 concentration was also shown to affect rheology at different temperatures. The improved viscosity through the newly designed polymer can reduce chemical costs (i.e., reducing VES load), making it more efficient in hydraulic fracturing operations. [ABSTRACT FROM AUTHOR]

Carbonate rock strengthening techniques are widely used in cultural heritage preservations. Recently, there has been a growing interest in their application in the oil and gas sector to improve the hardness and stability of fracture surfaces compared to the predominant host mineral. In this study, two rock lithologies were treated (chalk and limestone) at ambient temperature using 0.9 M NaF and 0.1 M ZnSO4 solutions with the aim of improving the hardness of the rock surfaces by transforming their mineralogy. The carbonate rocks were characterized before and after treatment using various techniques to establish changes in their mineralogical compositions (using x-ray diffraction (XRD), scanning electron microscopy energy-dispersive X-ray spectroscopy (SEM–EDS), and X-ray photoelectron spectroscopy (XPS) techniques) and petrophysical/mechanical properties (using Brinell test, impulse hammer, scratch test, steady-state gas injection). The reaction rates were monitored using inductively coupled plasma optical emission spectrometry and ion chromatography (ICP-OES) over a period of 2–5 days at 4–6 h intervals. It was found that the NaF treatment yielded a 4% and 6% improvement in indentation resistance of limestone and chalk, respectively. The ZnSO4 treatment produced the most notable improvement in rock hardness (presented by Young's modulus), with a 21% improvement for chalk and a 17% improvement for limestone, respectively. The novel findings in this study suggest that NaF and ZnSO4 are potential carbonate rock strengthening agents that can be utilized in various industrial applications, such as, for example, solving conductivity reduction problems arising in hydraulic fractures due to rock softening. [ABSTRACT FROM AUTHOR]

This study offered a detailed review of data sciences and machine learning (ML) roles in different petroleum engineering and geosciences segments such as petroleum exploration, reservoir characterization, oil well drilling, production, and well stimulation, emphasizing the newly emerging field of unconventional reservoirs. The future of data science and ML in the oil and gas industry, highlighting what is required from ML for better prediction, is also discussed. This study also provides a comprehensive comparison of different ML techniques used in the oil and gas industry. With the arrival of powerful computers, advanced ML algorithms, and extensive data generation from different industry tools, we see a bright future in developing solutions to the complex problems in the oil and gas industry that were previously beyond the grip of analytical solutions or numerical simulation. ML tools can incorporate every detail in the log data and every information connected to the target data. Despite their limitations, they are not constrained by limiting assumptions of analytical solutions or by particular data and/or power processing requirements of numerical simulators. This detailed and comprehensive study can serve as an exclusive reference for ML applications in the industry. Based on the review conducted, it was found that ML techniques offer a great potential in solving problems in almost all areas of the oil and gas industry involving prediction, classification, and clustering. With the generation of huge data in everyday oil and gas industry activates, machine learning and big data handling techniques are becoming a necessity toward a more efficient industry. [ABSTRACT FROM AUTHOR]

Multistage hydraulic fracturing is a technique to extract hydrocarbon from tight and unconventional reservoirs. Although big advancements occurred in this field, understanding of the created fractures location, size, complexity, and proppant distribution is in its infancy. This study provides the recent advances in the methods and techniques used to diagnose hydraulic fractures in unconventional formations. These techniques include tracer flowback analysis, fiber optics such as distributed temperature sensing (DTS) and distributed acoustic sensing (DAS), tiltmeters, microseismic monitoring, and diagnostic fracture injection tests (DFIT). These techniques are used to estimate the fracture length, height, width, complexity, azimuth, cluster efficiency, fracture spacing between laterals, and proppant distribution. Each technique has its advantages and limitations, while integrating more than one technique in fracture diagnostics might result in synergies, leading to a more informative fracture description. DFIT analysis is critical and subjected to the interpreter's understanding of the process and the formation properties. Hence, the applications of machine learning in fracture diagnostics and DFIT analysis were discussed. The current study presents an extensive review and comparison between different multistage fracture diagnostic methods, and their applicability is provided. The advantages and the limitations of each technique were highlighted, and the possible areas of future research were suggested. [ABSTRACT FROM AUTHOR]

Freshwater scarcity is a highly pressing and accelerating issue facing our planet. Therefore, there is a great incentive to develop sustainable solutions by reusing wastewater or produced water (PW), especially in places where it is generated abundantly. PW represents the water produced as a by-product during oil and gas extraction operations in the petroleum industry. It is the largest wastewater stream within the industry, with hundreds of millions of produced water barrels per day worldwide. This research investigates a reuse opportunity for PW to replace freshwater utilization in well stimulation applications. Introducing an environmentally friendly chelating agent (GLDA) allowed formulating a PW-based fluid system that has similar rheological properties in fresh water. This work aims at evaluating the rheological properties of the developed stimulation fluid. The thickening profile of the fluid was controlled by chelation chemistry and varying different design parameters. The experiments were carried out using a high-pressure, high-temperature (HPHT) viscometer. Variables such as polymer concentration and pH have a great impact on the viscosity, while temperature and concentration of the chelating agents are shown to control the thickening profile, as well as its stability and breakage behaviors. Furthermore, 50 pptg of carboxymethyl hydroxypropyl guar (CMHPG) polymer in 20 wt.% chelating solution was shown to sustain 172 cP viscosity for nearly 2.5 h at 150 °F and 100 S−1 shear rate. The newly developed fluid system, solely based on polymer, chelating agent, and PW, showed great rheological capabilities to replace the conventional stimulation fluids based on fresh water. The newly developed fluid can also have economic value realization due to fewer additives, compared with conventional fluids. [ABSTRACT FROM AUTHOR]

The process of well cleanup involves the removal of an impermeable layer of filter cake from the face of the formation. The inefficient removal of the filter cake imposes difficulty on fracturing operations. Filter cake's impermeable features increase the required pressure to fracture the formation. In this study, a novel method is introduced to reduce the required breakdown pressure to fracture the formation containing the water-based drilling fluid filter cake. The breakdown pressure was tested for five samples of similar properties using different solutions. A simulated borehole was drilled in the core samples. An impermeable filter cake using barite-weighted drilling fluid was built on the face of the drilled hole of each sample. The breakdown pressure for the virgin sample without damage (filter cake) was 6.9 MPa. The breakdown pressure increased to 26.7 MPa after the formation of an impermeable filter cake. Partial removal of filter cake by chelating agent reduced the breakdown pressure to 17.9 MPa. Complete dissolution of the filter cake with chelating agents resulted in the breakdown pressure approximately equivalent to the virgin rock breakdown pressure, i.e., 6.8 MPa. The combined thermochemical and chelating agent solution removed the filter cake and reduced the breakdown pressure to 3.8 MPa. Post-treatment analysis was carried out using nuclear magnetic resonance (NMR) and scratch test. NMR showed the pore size redistributions with good communication between different pores after the thermochemical removal of filter cake. At the same time, there was no communication between the different pores due to permeability impairment after filter cake formation. The diffusion coupling through NMR scans confirmed the higher interconnectivity between different pores systems after the combined thermochemical and chelating agent treatment. Compressive strength was measured from the scratch test, confirming that filter cake formation caused added strength to the rock that impacts the rock breakdown pressure. The average compressive strength of the original specimen was 44.5 MPa that increased to 73.5 MPa after the formation of filter cake. When the filter cake was partially removed, the strength was reduced to 61.7 MPa. Complete removal with chelating agents removed the extra strength that was added due to the filter cake presence. Thermochemical and chelating agents resulted in a significantly lower compressive strength of 25.3 MPa. A numerical model was created to observe the reduction in breakdown pressure due to the thermochemical treatment of the filter cake. The result presented in this study showed the engineering applications of thermochemical treatment for filter cake removal. [ABSTRACT FROM AUTHOR]

Hydraulic fracturing consumes massive volumes of freshwater that is usually scarce and costly. Such operation is not sustainable, and hence seawater could be used as an alternative. Nevertheless, seawater has high total dissolved solids (TDS), affecting the fracturing fluid rheology and providing a damage potential to the subterranean hydrocarbon reservoirs. Resolving these issues requires fracturing fluid systems with many additives, which results in an expensive and non-eco-friendly system. This study proposes eco-friendly and biodegradable chelating agents that could replace many additives such as scale inhibitors and crosslinkers. The study aims to optimize the rheology of seawater fracturing fluids using a chelating agent and polymer. By optimizing N,N-Dicarboxymethyl glutamic acid (GLDA) conditions, high viscosity was achieved using a standard industry rheometer. The GLDA was mixed with carboxymethyl hydroxypropyl guar (CMHPG) polymer and tested in both deionized water (DW) and seawater (SW). The polymer was examined first, where the rheology did not show a time-dependent behavior. The polymer in SW showed a slightly higher viscosity than in DW. The GLDA and CMHPG were tested at different temperatures, pH, and concentrations. These sets showed a time-dependent viscosity behavior, which can be utilized in various fracturing steps. Results showed that the solution pH and GLDA concentration significantly impacted the fluid viscosity magnitude and behavior. The developed formulation is shear thinning, where the viscosity declines as the shear rate increases. The temperature negatively impacted the viscosity and caused the formulation to break. The study provided an understanding of how to optimize the rheology of SW fracturing fluid based on GLDA chelating and CMHPG polymer. [ABSTRACT FROM AUTHOR]

The desire to improve hydraulic fracture complexity has encouraged the use of thermochemical additives with fracturing fluids. These chemicals generate tremendous heat and pressure pulses upon reaction. This study developed a model of thermochemical fluids' advection-reactive transport in hydraulic fractures to better understand thermochemical fluids' penetration length and heat propagation distance along the fracture and into the surrounding porous media. These results will help optimize the design of this type of treatment. The model consists of an integrated wellbore, fracture, and reservoir mass and heat transfer models. The wellbore model estimated the fracture fluid temperature at the subsurface injection interval. The integrated model showed that in most cases the thermochemical fluids were consumed within a short distance from the wellbore. However, the heat of reaction propagated a much deeper distance along the hydraulic fracture. In most scenarios, the thermochemical fluids were consumed within 15 ft from the fracture inlet. Among other design parameters, the thermochemical fluid concentration is the most significant in controlling the penetration length, temperature, and pressure response. The model showed that a temperature increase from 280 to 600 °F is possible by increasing the thermochemical concentration. Additionally, acid can be used to trigger the reaction but results in a shorter penetration length and higher temperature response. [ABSTRACT FROM AUTHOR]

The distribution of acid over all layers of interest is a critical measure of matrix acidizing efficiency. Chemical and mechanical techniques have been widely adapted for enhancing acid diversion. However, it was demonstrated that these often impact the formation with damage after the acid job is completed. This study introduces, for the first time, a novel solution to improve acid diversion using thermochemical fluids. This method involves generating nitrogen gas at the downhole condition, where the generated gas will contribute in diverting the injected acids into low-permeability formations. In this work, both lab-scale numerical and field-scale analytical models were developed to evaluate the performance of the proposed technique. In addition, experimental measurements were carried out in order to demonstrate the application of thermochemical in improving the acid diversion. The results showed that a thermochemical approach has an effective performance in diverting the injected acids into low-permeability rocks. After treatment, continuous wormholes were generated in the high-permeability rocks as well as in low-permeability rocks. The lab-scale model was able to replicate the wormholing impact observed in the lab. In addition, alternating injection of thermochemical and acid fluids reduced the acid volume 3.6 times compared to the single stage of thermochemical injection. Finally, sensitivity analysis indicates that the formation porosity and permeability have major impacts on the acidizing treatment, while the formations pressures have minor effect on the diversion performance. [ABSTRACT FROM AUTHOR]