Acid fracturing has been an integral part of reservoir development strategies for carbonate reservoirs as mechanical and chemical means of bypassing formation damage enhances productivity. Over the past few years, acid fracturing has significantly increased targeting more carbonate reservoirs. There is a need to fully address the heterogeneous petrophysical and geomechanical properties of target reservoirs, which adversely affects the stimulation efficiency and production if fluids are not properly designed. When injecting stimulation fluids to fracture the reservoir rock, the fluid is prone to traveling along the path of least resistance, and consequently less permeable zones and high stress reservoir rock receive treatments that could be further improved or enhanced. Accordingly, this drives the industry to continuously develop high performance chemical dynamic diverter systems. To ensure an effective and sufficient acid fracturing is achieved when treating long intervals of perforated clusters or openhole horizontal wells. Recent advancements in diversion technology utilize various forms of degradable particles, where they serve to provide a temporary bridge, which is either inside the existing fracture or the perforation entrance. This allows for intentionally forming a low permeability pack, allowing the pressure inside the fracture to increase and redirect the next stage of fluid to the zone having a higher degree of stress that has not yet been covered by the fracture. The objective is to increase the fracture complexity, particularly in vertical wells where there is big variation in geomechanical properties of the formation. To gain a deeper understanding of the performance of these diverters, a simulation study was conducted to analyze and compare the efficiency of particulate diverters used in two pilot wells. Fracture modelling and sensitivity analysis were also performed to understand the effect of diverters on the fracture geometry. To match the actual treatments, modelling validation and control were achieved through utilization of field data such as production logging, temperature surveys and pressure buildup tests. The study determined that the success of the particulate diverter employed for the fracturing application is heavily dependent and governed by the geomechanical properties of the treated zone and the ability of the diverter to overcome the stress difference in the stimulated interval. Optimization of the diverter design and degradation profile is still needed to improve and achieve the best stimulation efficiency.

Recent development of horizontal well completions and stimulation methods enhanced the development of conventional and unconventional resources. Multistage fracturing allowed oil and gas operators to stimulate long laterals in continuous and efficient operations that increase the reservoir contact, thus increasing the recovery of oil and gas. Oil and gas operators work to improve the efficiency of multistage fracturing treatments by developing and integrating enabler hardware, processes and chemical technologies to enhance the fracturing operations and reduce cost. This paper reviews and discusses the different types of horizontal wells with multistage fracturing completions and stimulation techniques including plug-and-perf, abrasive jetting, just-in-time perforation, sliding sleeve systems, coiled-tubing conveyed fracturing systems and annular isolation methods. The efficiency of the multistage fracturing treatments depends on multiple factors comprising the operational time and cost associated with different type of completions such as plugs and sleeves, different intervention operations such as wireline or coiled-tubing and different stage distribution and pumping designs. Combination of multiple multistage fracturing methods resulted in hybrid cost-effective treatments. In addition, multistage fracturing fluids diversions contribute significantly to the stimulation efficiency. Different types of diversion methods are discussed for each stimulation system. This paper provides a comprehensive summary of the operational practices, fracturing methods, and different multistage fracturing completions in horizontal wells while emphasizing on the recent advancements available in the market. The ability to develop an efficient and effective multistage fracturing operation is based on understanding the reservoir requirements, and identifying logistical and resource challenges at the geological location where the operation is taking place. The developed solutions would be an integration of currently available process, with proper completions, materials and development of innovative enabler technologies to accomplish optimum procedures. In recent years, several enabler technologies were developed to address the challenges within the existing multistage fracturing operations. The electronic monobore sliding sleeve was developed to address the limitation caused by small ball seat (baffle) in ball actuated sliding sleeve completions. Plug-and-perf operation was enhanced by applying the Just-In Time Perforation (JITP) method by developing a new perforation gun assembly that cuts operation time. Development of autonomous completion elements with the ability to navigate and self-destruct after accomplishing the job helped to reduce the number of trips into the well that greatly affected the operation efficiency. Completion elements and diverters built from dissolvable materials eliminated the drill-out and cleanout operations, which reflect positively on the efficiency of the fracturing process. Reviewing current advancements of multistage fracturing completions and treatments can pave the way for further operation optimization and cost reduction.

Well stimulation of carbonate reservoirs is conventionally associated with the using of strong mineral acids such as hydrochloric acid (HCl). However, the heterogeneity of the reservoir as well as the fast reaction rate of HCl with the rock will lead to face dissolution rather than achieving deeper wormholes or longer fractures. A commonly used approach to slow down the acid/rock reaction rate is through the use of acid-in-oil emulsions. Unfortunately, the thermal stability of the emulsified acids is significantly impacted at high temperatures (+300 °F), which will result in poor penetration of the reservoir, thus reducing the treatment effectiveness. This paper showcases the development and successful field application of an enhanced emulsified acid system for stimulating high-temperature carbonate reservoirs. The new system utilizes organically modified nanoparticles with the emulsified acid to form a solid stabilized emulsion. The unique morphology of the nanoparticles along with their selective organic modification facilitates formation of a high temperature stable emulsified acid system with lower viscosity compared to conventional emulsified acids. The low viscosity reduces surface pumping pressures leading to higher pumping rates for deeper reservoir penetration. The new system can work with HCl concentration up to 28% and temperatures up to 325 °F. We present here the systematic developmental study and field trial results for the organo-modified nanoparticles stabilized emulsified acid system, targeting high temperature carbonate gas reservoirs. Several laboratory performance tests were judiciously undertaken to compare the performance of the new emulsified acid with conventional systems. Experimental studies including rheological characterization, thermal stability, corrosion mitigation and formation damage profiling are reported. The new emulsified acid displayed lower viscosity, enhanced stability at high temperatures, corrosion loss within industry acceptable limits, superior stimulation effectiveness and minimal formation damage compared to conventional emulsified acid. Stimulation treatments using the enhanced emulsified acid showcased excellent flowback performance with no reservoir damage. The new organo-modified nanoparticles based emulsified acid system not only demonstrated enhanced temperature stability, but also minimized the surface treating pressure facilitating higher pumping rates and deeper reservoir penetration resulting in excellent stimulation of carbonate reservoirs.

The oil and gas industry has been developing various technologies to increase the productivity and recovery of hydrocarbons from conventional and unconventional reservoirs. Reservoir stimulation is an essential operation used to enhance production in many fields around the world. Hydraulic fracturing and acid treatments are the main stimulation methods. Reservoir tunneling concepts are used to drill branched channels in the formation from the main wellbore. With thousands of tunnels drilled to date, it is a viable technique that can improve the recovery of selected reservoirs. This paper reviews the recent developments in reservoir tunneling technologies and their current applications. These tunneling methods can be categorized mainly into water jetting, abrasive jetting, reactive jetting (acid), and needle and mechanical tunneling (radial drilling). The paper includes reviewing and analyzing these techniques based on documented literature results that include simulation studies, lab and yard experiments, field implementation, candidate selection, operational requirements, technology enhancements, advantages, limitations, and challenges of each technique. The paper provides a comprehensive summary of different tunneling techniques focusing on the operational practices, tunneling mechanisms, tunneling depth, and recent advancements available in the market. The most effective applications of the tunneling techniques are in stimulating low permeability, depleted and thin reservoirs, layers close to water zones, and bypassing near wellbore formation damage. The efficiency of creating tunnels is affected by many factors such as reservoir properties, nozzle, and fluid types, etc. The tunnel shape and trajectory are affected by reservoir geological properties. The combination of the tunneling with other stimulation techniques can result in more effective treatments, which enhance the methods of current stimulation. Reservoir tunneling technologies can pave the way to improve hydrocarbon recovery and enable access to unstimulated formations.

Low-molecular-weight hydrocarbon gases, such as methane and ethane, along with other low-molecular-weight species, such as CO2 and H2S, exist within the gas stream flowing through the pipelines used to transport natural gas and crude oils. Under certain conditions of low temperature and high pressure, and in the presence of free water molecules, gas-hydrate crystals will start to form. These gas hydrate crystals may accumulate and cause partial or complete plugging of the pipeline in the vertical or horizontal sections of the pipe. Methanol was previously found to be the only effective chemical able to clear gas hydrate plugs in many cases. The low flashpoint of methanol makes it unsafe to be pumped or stored in large volumes in hot regions such as in the Middle East. The main objective of the current work is to develop a safer chemical treatment with a higher flashpoint for the dissolution/mitigation of in-place gas hydrate plugs in pipelines. The parameters that make methanol an effective hydrate dissolver were investigated before development of the new hydrate dissolver. Methanol has a very low freezing point (-90°C) and is completely miscible with water. Solvent-based and aqueous-based formulations were chosen while considering parameters such as miscibility with water, freezing point, viscosity, and availability. The performance of these formulations was evaluated using a see-through gas hydrate cell. Pressure and temperature were modified to allow the formation of hydrates at simulated field conditions. Representative gas and water compositions were used in the experiments to form gas hydrate inside the gas hydrate cell. Hydrate formation can be detected either by detecting the change in torque on the stirring shaft or by visual inspection of the cell. The performance of these formulations was evaluated and compared to methanol. Two solvent-based formulations and two aqueous-based treatments met the flashpoint requirement and were effective in dissolving hydrate plugs at similar dosage when compared to methanol. These formulations proved to dissolve gas hydrate plugs in similar or less time than methanol. Two field trials were conducted to test one of the aqueous-based treatments and the outcome showed that the hydrate plug was dissolved in less than 17 minutes from the moment the aqueous solution was injected. The tested formulations have been shown to not only work as a dissolver, but also as an inhibitor to prevent the fresh formation of hydrate downstream. In addition to improving the performance of dissolving gas hydrate plugs in the pipelines, the use of these treatments has enabled safer operations in the field.