Unconventional Oil Development Research Articles

Probing the influence of secondary fracture connectivity on fracturing fluid flowback efficiency

A deep understanding of the geometric impacts of fracture on fracturing fluid flowback efficiency is essential for unconventional oil development. Using nuclear magnetic resonance and 2.5-dimensional matrix-fracture visualization microfluidic models, qualitative and quantitative descriptions of the influences of connectivity between primary fracture and secondary fracture on flowback were given from core scale to pore network scale. The flow patterns of oil-gel breaking fluid two-phase flow during flowback under different fracture connectivity were analyzed. We found some counterintuitive results that non-connected secondary fracture (NCSF, not connect with artificial primary fracture and embedded in the matrix) is detrimental to flowbackefficiency. The NCSF accelerates the formation of oil channeling during flowback, resulting in a large amount of fracturing fluid trapped in the matrix, which is not beneficial for flowback. Whereas the connected secondary fracture (CSF, connected with the artificial primary fracture) is conducive to flowback. The walls of CSF become part of primary fracture, which expands the drainage area with low resistance, and delays the formation of the oil flow channel. Thus, CSF increases the high-speed flowback stage duration, thereby enhancing the flowback efficiency. The fracturing fluid flowback efficiency investigated here follows the sequence of the connected secondary fracture model (72%) > the matrix model (66%) > the non-connected secondary fracture model (38%). Our results contribute to hydraulic fracturing design and the prediction of flowback efficiency.

Unconventional Oil Prospects and Challenges in the Covid-19 Era

Fossil fuels will continue to play an important role for the forthcoming decades, including in key hard-to-abate transport and industrial sectors. Unconventional oil (UO) has emerged as a sizeable contributor to meeting the global energy demand in the energy transition period. However, unfavorable circumstances compounded by the Covid-19 pandemic have intensified uncertainties and speculation regarding the future prospects of these resources. This mini-review explores prospects and challenges faced by UO development in the Covid-19 era, focusing on technical, economic, energy security, and environmental sustainability aspects. While UOs have been significantly affected by the pandemic in the short term, limited medium to long-term UO projections exist, with contrasted findings. The review reveals the multiplicity and complexity of interactions between the Covid-19 pandemic and the discussed UO aspects, the diversity of views, and conflicting short- and long-term goals of the energy industry.

Experimental study of oil recovery from pore of different sizes in tight sandstone reservoirs during CO2 flooding

The investigation of tight oil reservoirs has become a significant area of interest in unconventional oil development. CO 2 flooding is considered an effective oil recovery method for tight oil reservoirs as it can significantly increase oil recovery when it reaches supercritical condition and becomes miscible with oil. Although extensive research has been conducted on CO 2 flooding, the oil recovery from pore of different sizes in tight sandstone reservoirs at different pressures has not been thoroughly investigated. In this study, we analyzed the petrology features and the pore structure of a reservoir using casting section and scanning electron microscope (SEM) images. Subsequently, three cores with different permeability from the reservoir were subjected to CO 2 flooding experiments at different pressures. A nuclear magnetic resonance (NMR) spectrometer was used to quantify the oil recovery. Amott-Harvey index was measured to study the effect of CO 2 flooding on core wettability. Results indicate that the total oil recovery and the oil recovery of smaller pores increase as the pressure increasing. The oil recovery of the larger pores does not increase continuously. The oil recovery of the smaller pores is more dependent on pressure than that of the larger pores, and the total oil recovery is related to the oil recovery of smaller pores. Meanwhile, the supercritical and miscible CO 2 has a positive effect on oil recovery. After CO 2 becoming supercritical and miscible, the cores still have potential to produce more oil with the pressure increasing. As the pore structure is playing a significant role in oil recovery, the core with a higher proportion of the volume of larger pores is relatively easy to produce more oil at low pressure. Amott-Harvey index shows CO 2 flooding can significantly reduce the hydrophilicity of cores. This study reveals the mechanism of pressure effect on oil recovery during CO 2 flooding in tight sandstone reservoirs. The results can be used to improve the efficiency of reservoir development. • The features and the pore structure of a tight sandstone reservoir were analyzed using casting section and SEM images. • NMR was used to quantify the oil distribution before and after CO 2 flooding to explain the oil recovery of tight reservoirs. • The oil recovery of tight oil reservoir is strongly related to pore structure as well as CO 2 injection pressure. • CO 2 flooding can significantly reduce the hydrophilicity of cores with the increase of pressure.

Forecasting the use of enhanced oil recovery methods in oilfields of Bashkortostan

Today oil and gas complex in Bashkortostan is characterized by a deterioration in the quality of raw material base, which is associated with a significant degree of highly productive fields. It is a long-term operation, resource increment due to the discovery of fields unconventional oil, which are confined to low-permeable and weakly thick reservoirs oil deposits with extensive underwater gas and waterfowl zones. At the current stage of unconventional oil development of Bashkortostan oilfields, the urgent tasks are to study the experience of their development; identify peculiarities of the influence of geological and technological factors on the development efficiency of productive layers reserves; geological and commercial substantiation of various methods for enhanced oil recovery. The classification of development objects is based on the methods of mathematical statistics. Recommendations to improve the impact effectiveness on residual and unconventional oil reserves are based on the criteria-based analysis of enhanced oil recovery. The paper describes characteristics of reservoir systems and results of object grouping for oilfields development in Bashkortostan. Taking into account the established criteria for effective use of enhanced oil recovery and geological and field conditions of selected groups of objects with similar characteristics, there are some recommendations to increase the efficiency of oil recovery with targeted formation effects technologies.

Salting the Earth: The Environmental Impact of Oil and Gas Wastewater Spills.

Salting the Earth: The Environmental Impact of Oil and Gas Wastewater Spills.

Brine Spills Associated with Unconventional Oil Development in North Dakota.

The rapid rise of unconventional oil production during the past decade in the Bakken region of North Dakota raises concerns related to water contamination associated with the accidental release of oil and gas wastewater to the environment. Here, we characterize the major and trace element chemistry and isotopic ratios ((87)Sr/(86)Sr, δ(18)O, δ(2)H) of surface waters (n = 29) in areas impacted by oil and gas wastewater spills in the Bakken region of North Dakota. We establish geochemical and isotopic tracers that can identify Bakken brine spills in the environment. In addition to elevated concentrations of dissolved salts (Na, Cl, Br), spill waters also consisted of elevated concentrations of other contaminants (Se, V, Pb, NH4) compared to background waters, and soil and sediment in spill sites had elevated total radium activities ((228)Ra + (226)Ra) relative to background, indicating accumulation of Ra in impacted soil and sediment. We observed that inorganic contamination associated with brine spills in North Dakota is remarkably persistent, with elevated levels of contaminants observed in spills sites up to 4 years following the spill events.

A study on the future of unconventional oil development under different oil price scenarios: A system dynamics approach

Fluctuations in the oil global market has been a critical topic for the world economy so that analyzing and forecasting the conventional oil production rate has been examined by many researchers thoroughly. However, the dynamics of the market has not been studied systematically with regard to the new emerging competitors, namely unconventional oil. In this paper, the future trend of conventional and unconventional oil production and capacity expansion rates are analyzed using system dynamics approach. To do so, a supply-side modeling approach is utilized while main effective loops are modeled mathematically as follows: technological learning and progress, long and short-term profitability of oil capacity expansion and production, and oil proved reserve limitations. The proposed model is used to analyze conventional and unconventional oil production shares, up to 2025, under different oil price scenarios. The results show that conventional oil production rate ranges from 79.995 to 87.044MB/day, which is 75–80 percent of total oil production rate, while unconventional oil production rate ranges from 19.615 to 28.584MB/day. Simulation results reveal that unconventional oil can gain a considerable market share in the short run, although conventional oil will remain as the major source for the market in the long run.

Tight Cardium Multistage-Fractured Horizontal-Oil-Well-Performance Study Focusing on the Effectiveness of Various Fracture-Fluid Systems

Summary In recent years, the tight Cardium sandstones of west central Alberta have observed significant new development with the application of multistage-fractured horizontal wells (MFHWs). This case study reviews the completion costs, economics, and production performance of 148 horizontal oil wells completed in the Pembina field halo areas (west and east), central Pembina, Willesden Green, and Garrington fields. Production analysis was performed on all wells using the Duong decline-curve-analysis technique. This technique has been used successfully on tight multistage-fractured wells in other areas, and has proved successful at predicting long-term well performance and recoveries. Wells were chosen for comparison that were in the same geological and pressure regions, had a minimum of 2 years of production information, and were stimulated with various fracture-fluid systems. In one of the analyzed areas, a definite trend was identified; it was found that wells drilled in a certain orientation performed better than wells drilled with other orientations. Completions and hydraulic-fracturing costs were gathered from public sources in order to understand the cost differences between areas and types of fracture-fluid systems. Using decline curves and cost information, full-cycle economics were run on the ’average’ well for each area in order to determine the net present value (NPV) of each area. This case study shows there is value in optimizing fracture designs through look-back studies, and there is a need to focus on more-effective fracture-treatment designs in unconventional oil development. The overall results of the study showed: (1) the choice of fracture-fluid system is a key component in optimizing economics in the Cardium halo areas; and (2) the optimum fluid system varies in different areas of the Cardium.

The Prospect of Deepwater Heavy Oil Production Using CO2-EOR

The prospect of unconventional oil development has long been coming to offset the rapid decline of conventional crude. And looking ahead, the worry is already turning away from the onshore exploitation to the challenging offshore environment, with the question being whether the emerging technology can overcome the challenges of deep-water heavy oil production. In economics terms, the immiscible process shows a negative return, a longer payback time, and a low net present value. With an increased revenue through increased production, there is a degree of strong, dynamic, and appealing prospect to any future heavy oil development using miscible process.

Case Study, Cost Benefit Analyses of Centralized Treatment versus Mobile Decentralized Treatment for Produced Water from an Unconventional Oil Development

Case Study, Cost Benefit Analyses of Centralized Treatment versus Mobile Decentralized Treatment for Produced Water from an Unconventional Oil Development

Comments: Supply Growth

Editor's column The growth in US oil production led by the rise in unconventional supply is well under way, and similar growth in other regions could pave the way for great increases in global supply. A new global field-by-field study of oil investment suggests that world oil production capacity could grow to more than 110 million BOPD by 2020, an increase of 20% from today. Analysis of oil exploration and development projects around the world indicates that more than 49 million BOPD in additional production capacity could be gained by 2020. Taking into account risk factors and depletion rates, net additional production capacity is likely to increase by more than 17 million BOPD by 2020, the most capacity growth since the 1980s. The figures come from a report released in June by the Belfer Center for Science and International Affairs at Harvard Kennedy School titled Oil: The Next Revolution. It was authored by Leonardo Maugeri, former ENI senior executive vice president of strategies and development. Leading the way in this new surge of production, in order, are Iraq, the US, Cana-da, Brazil, and Venezuela. And much of the production is unconventional—shale/tight oil in the US, pre-salt in Brazil, oil sands in Canada, and extra-heavy oil in Venezuela. The study predicts that four current major producing areas will show declines during the period: Norway, the UK, Iran, and Mexico. Other conclusions of the study include: The US will continue to see great gains in output from unconventional resources, thanks to “the technological revolution brought about by the combined use of horizontal drilling and hydraulic fracturing.” The states of North Dakota and Texas will see the largest growth in supply. These technologies used in shale also will be used to reopen and recover oil from conventional, established fields. “The United States could increase oil production by 3.5 million BOPD … making it the second largest oil producer in the world after Saudi Arabia.” Oil prices could collapse when these large volumes of oil hit the market, contradicting conventional wisdom that global supply will struggle to keep up with world demand. The report concludes that oil production capacity is growing so rapidly that it might outpace consumption. “The oil market will remain highly volatile until 2015 and prone to extreme movements in opposite directions. After 2015, however, most of the oil projects analyzed in the report will advance significantly.” Shifts in the supply/demand balance will affect geopolitics. The US could be producing 65% of its oil consumption needs domestically, becoming less dependent on Middle East countries. And while the US shale boom likely will not be easily replicated elsewhere, development of known and unknown unconventional resources globally “could be surprising,” says the report. The increase in unconventional oil development will lead to heightened environmental protection and regulation challenges. “Industry needs to develop technological solutions to minimize water use, minimize and report chemical use, and carefully monitor production sites,” says the report. “If such a collective effort by industry does not materialize, government may respond with more onerous regulation in the near future that could impact US shale oil production.”