Sandstone matrix acidizing knowledge and future development

To meet rising global demands for energy, the oil and gas industry continuously strives to develop innovative oilfield technologies. With the development of new enhanced oil recovery techniques, sandstone acidizing has been significantly developed to contribute to the petroleum industry. Different acid combinations have been applied to the formation, which result in minimizing the near wellbore damage and improving the well productivity. A combination of hydrofluoric acid and hydrochloric acid (HF:HCl) known as mud acid has gained attractiveness in improving the porosity and permeability of the reservoir formation. However, high-temperature matrix acidizing is now growing since most of the wells nowadays become deeper and hotter temperature reservoirs, with a temperature higher than 200 °F. As a result, mud acid becomes corrosive, forms precipitates and reacts rapidly, which causes early consumption of acid, hence becoming less efficient due to high pH value. However, different acids have been developed to combat these problems where studies on retarded mud acids, organic-HF acids, emulsified acids, chelating agents have shown their effectiveness at different conditions. These acids proved to be alternative to mud acid in sandstone acidizing, but the reaction mechanism and experimental analysis have not yet been investigated. The paper critically reviews the sandstone acidizing mechanism with different acids, problems occurred during the application of different acids and explores the reasons when matrix stimulation is successful over fracturing. This paper also explores the future developing requirement for matrix acidizing treatments and new experimental techniques that can be useful for further development, particularly in developing new acids and acidizing techniques, which would provide better results and information of topology, morphology and mineral dissolution and the challenges associated with implementing these “new” technologies

A preliminary screening and characterization of suitable acids for sandstone matrix acidizing technique: a comprehensive review

Matrix acidizing is a broadly developed technique in sandstone stimulation to improve the permeability and porosity of a bottom-hole well. The most popular acid used is mud acid (HF–HCl). It is a mixture of hydrofluoric acid and hydrochloric acid. However, one of the conventional problems in sandstone acidizing is that mud acid faces significant issues at high temperature such as rapid rate of reaction, resulting in early acid consumption. This downside has given a negative impact to sandstone acidizing as it will result in not only permeability reduction, but can even extend to acid treatment failure. So, the aim of this study is to provide a preliminary screening and comparison of different acids based on the literature to optimize the acid selection, and targeting various temperatures of sandstone environment. This paper has comprehensively reviewed the experimental works using different acids to understand the chemical reactions and transport properties of acid in sandstone environment. The results obtained indicated that fluoroboric acid (HBF4) could be useful in enhancing the sandstone acidizing process, although more studies are still required to consolidate this conclusion. HBF4 is well known as a low damaging acid for sandstone acidizing due to its slow hydrolytic reaction to produce HF. This would allow deeper penetration of the acid into the sandstone formation at a slower rate, resulting in higher porosity and permeability enhancement. Nevertheless, little is known about the effective temperature working range for a successful treatment. Considering the pros and cons of different acids, particularly those which are associated with HF and HBF4, it is recommended to perform a comprehensive analysis to determine the optimum temperature range and effective working window for sandstone acidizing before treatment operation. Prior to sandstone acid stimulation, it is essential to predict the feasibility of acid selected by integrating the effects of temperature, acid concentration and injection rate. Therefore, this manuscript has thrown light into the research significance of further studies

Application of emulsified acids on sandstone formation at elevated temperature conditions: an experimental study

Emulsified acid has attracted considerable attention of the oil and gas industry due to its delayed nature that allows deeper penetration of acid into the formation which essentially facilitate further enhancing the well productivity, and at the same time minimizes the corrosion issues. However, emulsified acid has only been extensively studied and applied on carbonate formations. Considering more than half of the reservoirs worldwide are sandstone reservoirs, studying the effects of emulsified acid on sandstone under high-temperature conditions would unlock the potential of emulsified acid and help generate more value for the oil and gas industry by improving the well productivity from sandstone reservoirs. To ensure the applicability of the emulsified acid on the real sandstone reservoir, which usually has a temperature higher than ambient conditions, the stability of emulsified acids is investigated under 300 °F. Then, the stable emulsified acid samples are developed and their impact on the properties of Berea sandstone core samples, including porosity, pore-size distribution, permeability and wettability, are investigated. The core samples have undergone pre-flush (10% HCl:5% CH3COOH) before the main flush (emulsified acid). The emulsified acids are prepared using hydrofluoric acid, hydrochloric acid, phosphoric acid, cationic surfactant and chelating agent. Fourteen core samples are saturated with different emulsified acids under vacuum conditions for 3 days to ensure maximum saturation. The porosity, permeability and wettability of each core sample are measured before and after the reaction with acid. Nuclear magnetic resonance analysis has been applied to evaluate the change in pore size distribution. This study has demonstrated that the emulsified acids are capable of improving the porosity and permeability of Berea sandstone core sample. The pore size distribution has also been affected by the application of emulsified acid, where more large pores have been evolved to the core samples due to the reaction of acids with the sandstone which ultimately helps in improving the productivity of hydrocarbons. This indicates less precipitation of the secondary reaction products resulting better enhancement in sandstone flow properties. These results demonstrate the potential of emulsified acid during sandstone acidizing as emulsified acid significantly improved the sandstone properties which can essentially enhance the well productivity

A numerical modelling and simulation of core-scale sandstone acidizing process: a study on the effect of temperature

A wide and comprehensive understanding of the chemical reactions and mechanisms of HBF4 is crucial as it significantly influences its performance in stimulating a sandstone formation. In general, it is well-known that HBF4 is able to provide a deeper penetration into the sandstone matrix before being spent due to its uniquely slow hydrolysis ability to produce HF. In the present study, a 3D numerical modelling and simulation were conducted to examine the capability of HBF4 in enhancing the porosity and permeability of the sandstone matrix. The model is built in COMSOL® Multiphysics commercial software of computational fluid dynamics (CFD) to simulate the acid core flooding process on sandstone core. The model had been validated against the experimental data in the literature. The results matched with the measured plot data very well. The effect of temperature on the performance HBF4 sandstone acidizing is evaluated in this study. The simulation results indicated that at low temperature of 25 °C, HBF4 is not very effective, as justified in its poor porosity and permeability increments of only 1.07 and 1.23, respectively. However, at elevated temperatures, the porosity and permeability enhancement also become increasingly more significant, which showed 1.26 and 2.06, respectively, at 65 °C; and 1.67 and 7.06, respectively, at 105 °C. Therefore, one can conclude that HBF4 acid treatment performed better at elevated temperatures due to increased hydrolysis rate, which is a governing function in HBF4 sandstone acidizing. Overall, this model had provided a reliable alternative to optimize various other parameters of HBF4 acid treatment

Generalized PVO‐based dynamic block reversible data hiding for secure transmission using firefly algorithm

In this paper, we proposed a novel generalized pixel value ordering–based reversible data hiding using firefly algorithm (GPVOFA). The sequence of minimum and maximum number pixels value has been used to embed the secret data while prediction and modification are held on minimum, and the maximum number of pixel blocks is used to embed the secret data into multiple bits. The host image is divided into the size of noncoinciding dynamic blocks on the basis of firefly quadtree partition, whereas rough blocks are divided into a larger size; moreover, providing more embedding capacity used small flat blocks size and optimal location in the block to write the information. Our proposed method becomes able to embed large data into a host image with low distortion. The rich experimental results are better, as compared with related preceding arts

Generalized Structures for Switched-Capacitor Multilevel Inverter Topology for Energy Storage System Application

The apparent advantages of Multilevel Inverter (MLI) topologies in handling medium and high power with less loss in switching and lower harmonic distortion in an output voltage waveform makes it better than the conventional inverter. However, the MLI topologies utilize a large number of DC power supplies and power semiconductor devices. They also have a higher value of total standing voltage (TSV). Moreover, capacitor voltage balancing problems, self-voltage boosting inability, and complex control techniques require a relook and improvement in their structure. More recently, Switched-Capacitor Multilevel Inverter (SCMLI) topologies have been proposed to overcome the shortcomings of MLIs. In this paper, a generalized structure for a single-phase switched capacitor multilevel inverter (SCMLI) with self-voltage boosting and self-voltage balancing capability is proposed. A detailed analysis of a general structure of SCMLI is presented. The comparative analysis of the structures is carried out with recently reported topologies to demonstrate superiority. An optimized low-frequency modulation controls the output voltage waveform. The simulation and experimental results are included in the paper for single-unit symmetric (9-level voltage) and asymmetric (17-level voltage) configurations

Cephalexin Adsorption by Acidic Pretreated Jackfruit Adsorbent: A Deep Learning Prediction Model Study

Cephalexin (CFX) residues in the environment represent a major threat to human health worldwide. Herein we investigate the use of novel approaches in deep learning in order to understand the mechanisms and optimal conditions for the sorption of cephalexin in water onto an acidic pretreated jackfruit peel adsorbent (APJPA). The interaction between the initial concentration of CFX (10–50 mg/100 mL), APJAP dosage (3–10 mg/100 mL), time (10–60 min), and the pH (4–9), was simulated using the one-factor-at-a-time method. APJPA was characterized by FESEM images showing that APJPA exhibits a smooth surface devoid of pores. FTIR spectra confirmed the presence of -C-O, C–H, C=C, and -COOH bonds within the APJPA. Maximum removal was recorded with 6.5 mg/100 mL of APJAP dosage, pH 6.5, after 35 min and with 25 mg/100 mL of CFX, at which the predicted and actual adsorption were 96.08 and 98.25%, respectively. The simulation results show that the dosage of APJAP exhibits a high degree of influence on the maximum adsorption of CFX removal (100%) between 2 and 8 mg dose/100 mL. The highest adsorption capacity of APJAP was 384.62 mg CFX/g. The simulation for the effect of pH determined that the best pH for the CFX adsorption lies between pH 5 and 8