Summary Millimeter-sized (10 μm–mm) preformed particle gels (PPGs) have been used successfully as conformance-control agents in more than 5,000 wells. They help to control both water and CO2 production through high-permeability streaks or conduits (large pore openings), which naturally exist or are aggravated either by mineral solution or by a high injection pressure during the flooding process. This paper explores several factors that can have an important impact on the injectivity and plugging efficiency of PPGs in these conduits. Extensive experiments were conducted to examine the effect of the conduit inner diameter and the PPG strength on the ratio of the particle size to the opening diameter, injectivity index, resistance factor, and plugging efficiency. Five-foot tubes with four internal diameters were designed to emulate the opening conduits. Three pressure taps were mounted along the tubes to monitor PPG transport and plugging performance. The results show that weak gel has less injection pressure at a large particle/opening ratio compared to strong gel. PPG strength affected injectivity more significantly than did particle/opening ratio. Resistance factor increased as the brine concentration and conduit inner diameter increased. PPGs can significantly reduce the permeability of a conduit, and their plugging efficiency depends highly on the particle strength and the conduit inner diameter. The particle size of PPGs was reduced during their transport through conduits. Experimental results confirm that the size reduction was caused by both dehydration and breakdown. On the basis of the laboratory data, two correlations were developed to quantitatively calculate the resistance factor and the stable injection pressure as a function of the particle strength, particle/opening ratio, and shear rate. This research provides significant insight into designing better millimeter-sized particle-gel treatments intended for use in large openings, including open fractures, caves, worm holes, and conduits.
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.
Cement sheath is considered an important barrier throughout the life cycle of the well. The integrity of the cement sheath plays a vital role in maintaining the integrity of wells. Cement’s ability to seal the annular space or a wellbore, also known as cement sealability, is an important characteristic of the cement to maintain the well integrity. It is believed that placing cement in the annular space or wellbore can totally prevent any leakage; however, that is debatable. The reason why cement cannot completely prevent fluid leakage is that cement is considered as a porous medium, and also flaws in cement, such as microannuli, channels, and fractures, can develop within the cement sheath. Furthermore, the complexity of casing/cement and cement/formation interaction makes it very difficult to fully model the fluid migration. Hence, fluid can migrate between formations or to the surface. This article presents a numerical model for gas flow in cement sheath, including the microannulus flow. A parametric study of different variables and their effect on the leakage time is carried out, such as the microannulus gap size, cement matrix permeability, cement column length, and cement porosity. In addition, it presents leakage scenarios for different casing/liner overlap length with the existence of microannulus. The leakage scenarios revealed that the cement matrix permeability, microannulus gap size, and cement length can highly impact the leakage time; however, cement porosity has a minimal effect on the leakage time. In addition, modeling results revealed that the casing/liner overlap length should not be less than 300 ft, and the casing pressure duration should be beyond 30 min to detect any leak.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.