Asphaltene is a component of crude oil that has been reported to cause severe problems during production and transportation of the oil from the reservoir. It is a solid component of the oil that has different structures and molecular makeup which makes it one of the most complex components of the oil. This research provides a detailed review of asphaltene properties, characteristics, and previous studies to construct a guideline to asphaltene and its impact on oil recovery. The research begins with an explanation of the main components of crude oil and their relation to asphaltene. The method by which asphaltene is quantified in the crude oil is then explained. Due to its different structures, asphaltene has been modeled using different models all of which are then discussed. All chemical analysis methods that have been used to characterize and study asphaltene are then mentioned and the most commonly used method is shown. Asphaltene will pass through several phases in the reservoir beginning from its stability phase up to its deposition in the pores, wellbore, and facilities. All these phases are explained, and the reason they may occur is mentioned. Following this, the methods by which asphaltene can damage oil recovery are presented. Asphaltene rheology and flow mechanism in the reservoir are then explained in detail including asphaltene onset pressure determination and significance and the use of micro-and nanofluidics to model asphaltene. Finally, the mathematical models, previous laboratory, and oilfield studies conducted to evaluate asphaltene are discussed. This research will help increase the understanding of asphaltene and provide a guideline to properly study and model asphaltene in future studies.

h i g h l i g h t sPermeable gel-pack was formed in the large fluid channels by gel particles. A better gel blocking efficiency gained by optimizing gel strength and particle size. Gel pack permeability was a few hundred millidarcies before the load pressure. PPG is compressible and its compressibility was between 0.0003 psi À1 and 0.003 psi À1 . PPG formed internal channels when subjected to a continuous load pressure. a b s t r a c tA newer trend in gel treatments is using preformed particle gel (PPG) to reduce fluid channels through super-high permeability streaks/fractures and thus to decrease water production and increase sweep efficiency for mature oilfields. The success of a PPG treatment mainly depends on whether or not the PPG can effectively reduce the permeability of the channels to an appropriate level. This work sought to determine what factors significantly influence the blocking efficiency of PPG in fluid channels. A transparent filtration model was designed to observe the compression of gel particles in fluid channels at several differential pressures and to study the effect of various parameters, such as brine concentrations and particle sizes, on PPG blocking efficiency. The results suggested that rather than fully blocking the channel, a permeable gel pack was formed in the fluid channel by gel particles, and its permeability was dependent on the gel strength, particle size, and load pressure. The gel pack permeability decreased as the gel strength, particle size, and load pressure increased. Thus, the blocking efficiency of the particle gel on a channel is increased if large sizes or/and strong particles are used. The gel pack permeability was a few hundred millidarcies before the load pressure was applied; it decreased to less than 10 md when the load pressure rose. The results also indicated that the PPG pack was compressible and its compressibility decreased as the load pressure increased. These results can be effectively used to optimize a PPG design. A gel pack that has a desired permeability can be devised by selecting the proper gel strength and particle size corresponding to the reservoir pressure. This is essential for a successful gel treatment so as to reduce the permeability to a manageable preplanned degree.

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In recent times, particularly in the 21st century, there has been an alarming increase in the demand for global energy, along with continuous depletion in conventional oil reservoirs. This necessity has incentivized interested scholars and operators worldwide to seek alternative oil resources. To secure such accelerating energy demand, considerable effort has been directed toward the development of previously unconventional oil formations that, in past decades, had remained sidelined. Although shale oil reservoirs have seen tremendous success over the past decade, the continued challenges of rapidly declining oil flow rates and oil retention in the pores continuously persist. Substantial attempts have been made to improve shale-bypassed oil recovery; however, there is little data about the accessibility on recovery mechanisms, especially in the oil field. Furthermore, approachesparticularly, Huff-n-Puff (H-n-P) experiments using conventional proceduresfail to properly represent field conditions and they generate deceptive findings, because the utilized cores are not simulated under realistic reservoir conditions, leaving the significance of critical factors unclear. Therefore, this review study comprehensively and specifically discusses the feasibility of enhanced oil recovery (EOR) methods in unconventional oil reservoirs. Beside addressing the validity of the currently applied H-n-P technology in shale/tight oil reservoirs and underlining some critical gaps regarding laboratory results, modified technology is proposed in this paper for a better field future performance. The study is divided into sections, and each section analyzes the role of one specific H-n-P portion in detail, such as preferable injected solvents, their mechanisms, and critical factors affecting H-n-P recovery. The exceptions to this are the first and second sections, which provide a brief introduction about shale and tight oil reservoirs, a history of applied technology, and the method’s current problem statement. In the Introduction section, the authors will justify why this Review fills a critical gap in the field. Within the assessment study, great focus is given to the H-n-P technique, its parameters, and effective processes. In the final sections, carefully chosen experimental results and tools are reviewed to highlight the controversy and state “the gap”.