Energized fluids are defined as fluids with one or more compressible gas components, such as CO2, N2, or any combination of gases, dispersed in a small volume of liquid. Generally, these fluids offer an attractive alternative to conventional stimulation fluids in many cases such as low reservoir pressure, water-sensitive formations, and/or the need for shorten flowback period. Energized fluids have many challenges such as low stability at high temperature, high friction pressure during pumping, corrosion in the case of using CO2, and the need for specialized surface pumping equipment. The objective of this paper is to describe the typical components of energized fluids and their effect on the fluid performance. Also, lab testing methods used to evaluate energized fluids performance will be discussed in detail. Foam is a class of energized fluid used for different applications including acidizing, hydraulic fracturing, and fluid diversion. For each application, foam should have a minimum acceptable value of viscosity, stability, and/or fluid compatibility. Those values were reviewed from literature and categorized based on reservoir conditions. Also, different rheological models are analyzed to understand foam flow behavior in both tubing and porous media. Finally, the mechanism of foam transport in porous media is reviewed in this report, which gives insight into foam stability and propagation. The most common application of nitrogen is in artificial lifting, while supercritical CO2 is proposed for condensate banking removal. Selection of the right surfactant, like alpha olefin sulfonates, which are thermally more stable than alkyl ether sulfates, is crucial while designing foam treatment, as they produce the most persistent foams at high salinity and elevated temperatures in the presence of synthetic and crude oils. Currently available foam-based fracturing fluid systems in the industry have temperature limitations to 300°F. The crosslinked gelled foam has a better temperature range than the viscoelastic foam fluid system, whereas non-crosslinked biopolymer-based foam fluid showed better proppant pack cleanup characteristics. In a recent report, the addition of 0.1% silica nanoparticles along with cationic surfactant was shown to enhance CO2 foam stability by 13 hours. In this review, all these aspects of energized fluids are well reported from literature. In this paper, we discuss findings from different lab testing and field demonstration of energized fluids. Compositional modelling for hydraulic fracturing with energized fluids is also reviewed to add insight on fracture geometry estimation. This paper provides guidelines and recommendations for selecting the right energized fluids for successful stimulation treatment.

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.

Foamed acid fracturing is gaining importance in maximizing flowback recovery and is particularly applicable when reservoir energy is not sufficient to effectively flow back the well. Laboratory studies and field implementations during the 1980s showed application of foamed acid in addressing three fundamental issues of acid fracturing such as reactivity control, fluid loss control, and conductivity generation but it was evaluated at low temperature and in shallow wells. Recently, foamed acid has been successfully utilized to energize reservoirs to enhance flowback recovery and restore production after treatment. This paper summarizes literature reports from the last 30 years, showing improved use of foamed acid for acid fracturing. Foamed acid offers additional benefits such as retardation, deeper conductivity generation, reduced water consumption, and improved acid diversion. Foamed acid laboratory studies from literature such as foam stability, rheology, reaction kinetics, fluid loss, diversion characteristics, and dynamic acid etching is reviewed. Comparison of CO2 and N2 foamed acid is documented in this paper to define fluid selection criteria for a typical foamed acid treatment. Foamed acid rheology at different quality is also summarized in this paper from previous studies. The dissolution of carbonate rock is controlled by reactivity, which is greatly reduced after foaming for the same acid strength and temperature. Foamed acid having 50-60 quality could retard 60-70% acid reactivity. Excessive fluid loss is one of the challenges in acid fracturing. Conventionally, fluid loss is mitigated by using synthetic polymers to viscosify acid that controls leakoff by depositing a low permeability filter cake on the face of formation leading formation damage concerns. Foamed acid does not build filter cake and showed excellent leakoff control. Proper reactivity and fluid loss control regulates conductivity generation in acid fracturing. Conductivity generation depends on kinetic parameters — such as acid type/strength, temperature, reaction time, and flow regime. These parameters affect the amount of rock removed during the acidizing process. Case histories from different regions where recent application of foamed acid is documented show placement strategies and lessons learned. A horizontal well in one case study was treated with N2 foamed acid to achieve a 2.5 fold increase in production. N2 and CO2 foam was used as foam diverter in acid fracturing, and the productivity index increased to 38% with the use of N2 foam while in other fields the productivity index increased to 3.25 fold with the use of CO2 foam. Laboratory studies available in the literature are not adequate to design foamed acid treatment for high-temperature, high-pressure wells. This paper summarizes published literature showing improved use of foamed acid for acid fracturing.

Gas production can be enhanced by the unloading of liquid accumulated in the wellbore. Conventionally, it is addressed by dropping soap sticks into a gas well. The foamability of soap sticks tends to decrease in the presence of condensate. Alternativity, well can be kicked-off by using N2 lifting but it is an expensive method that involves coil tubing operation. In this paper, an innovative and simple method of unloading a condensate-bearing gas well using dry ice is described. Gas wells accumulated with liquid or condensate can be unloaded by displacing it with CO2 gas. It also helps to reduce hydrostatic pressure during kick-off well. Dry ice pellets can be inserted inside the wellbore, which can be settled down by gravity and CO2 gas formation inside the wellbore due to dry ice sublimation. The dry ice sublimation rate can be restricted by encapsulating it with self-degradable polymers that can be hydrolyzed inside the wellbore. Cylindrical dry ice pellets from the food industry having a half-inch diameter and a couple of inches long were used in this work. Dry ice is the solid form of CO2 having an expansion ratio of 1 to 554 for solid to gas at sublimation point −78.5 °C and atmospheric pressure. The density of dry ice is 1.562 gm/cm3. A series of lab experiments were conducted to show CO2 gas generation from dry ice in the water. After inserting a dry ice pellet into the water column, it settled down at the bottom and started releasing CO2 gas with a sudden expansion in volume. CO2 foam was also generated by inserting dry ice pallets with foaming agents inside the water column. The release of CO2 gas in the wellbore and foam generation can assist in decreasing hydrostatic pressure and lifting liquid inside the wellbore. At the well site, a simple modification is required to insert dry ice into the wellbore. The cylindrical chamber needs to be installed above the master value of the Christmas tree. This is described in the paper with the procedure to follow during the operation. A mathematical tool has been developed to estimate the amount of dry ice pallets required for a given well geometry. For 4.5 inch, 1000 ft long production tubing, 1000 kg dry ice can release 51.7 bbl of CO2 gas, which can generate a 495 psi increase in pressure. Well intervention operations are complex and expensive processes. It is preferred to use simpler, quicker, safer, and more cost-effective methodologies. The use of dry ice to unload gas well is simple, cheaper and an innovative solution. The release of CO2 gas from dry ice can offer additional benefits such as better and faster cleanup and the removal of condensate blockage in the near-wellbore area.

Dealing with tight high pressure/high temperature (HPHT) sour gas reservoirs encounters many challenges. One challenge associated with these reservoirs is the development of hard and heavy scale mixture in the production tubing, causing flow and accessibility restrictions. To restore full accessibility, a mechanical de-scaling operations using special milling and cleanout assemblies is the best current solution to this problem, due to the fact that chemical dissolving methods do not deliver the desired results. Another challenge is conventional perforation in some tight wells gives limited penetration, which does not establish the required wellbore reservoir communication. In this case, utilizing the abrasive jetting tool will offer the best solution to overcome the casing string, cement, formation damage achieve optimum penetration which will optimize the stimulation design and enhance the well productivity. In recent years, using coiled tubing (CT) equipped with fiber optics with aforementioned coil tubing intervention operations, have become a common practice in gas wells. Using this system provides the ability to acquire on-job real time data such as pressure, temperature and gamma ray depth correlation. Furthermore, the incorporation of a new rugged fiber optics system into the intervention strategy has enabled increasing operational success rate and results in robust control on the operation parameters, minimizing the risk of gas influx, reducing coil tubing runs and improving decision making process during the operations. This paper describes the challenges in mechanical de-scaling and slot cuttings operations, overview of different applications using CT with fiber optics system, provides a comparison between the rugged and standard fiber optics systems and lessons learned of recent implementation of the rugged CT fiber optic system.