First, I would like to express my profound gratitude to my academic supervisor Dr. Sepehrnoori for the continuous guidance and support during these two years of graduate school. I am truly grateful for his interest and willingness to guide me since the very first day of my graduate studies. I would also like to express sincere gratefulness to Dr. Wei Yu for his dedication, expertise advises, and insistent valuable guidance. I will always appreciate how he shared part of his extensive expertise in unconventional reservoirs, and reservoir modeling with me. Also, I would like to thank Erich Kerr and his company for supplying the field data that made this research possible. I gained great practice and understanding through their suggestions for my research work. Their invaluable support received weekly through my entire career will always be appreciated. There are not enough words to express how convinced I am that this would not have been possible without the support of my family. I thank my father Mario and my mother María for covering part of my tuition, and also my sister Carla Adriana for their continuous encouragement to pursue my dreams. I would like to thank Carolina for her caring love and support. I am indebted to my parents, my sister and my girlfriend who never stopped encouraging during both the good and the not so good times. I would also like to thank Reza, Sutthaporn, Fabio, Jorge, and Esmail for their collaboration and assertive comments for my work and my research. Finally, a very special acknowledgment is extended to the Fulbright Commission of Ecuador, the Department of State of the United States, and the Cockrell School of Engineering for being the sponsoring entities which provided me the scholarships to fund and make this accomplishment possible.

As the pressure drops below dew point in an unconventional gas-condensate reservoir, the liquid drops out of gas phase and forms an oil phase in matrix and fracture. The volume of oil phase formed in the matrix mostly stays below the residual oil saturation, i.e., the oil will be trapped in matrix permanently if enhanced oil recovery techniques are not applied. The huff-n-puff process has been performed and shown the potential of improving the recovery from tight oil reservoirs. The objective of the study was to investigate the feasibility of huff-n-puff EOR in a gas condensate reservoir in Eagle Ford. The studied section of the field contains 13 horizontal producers. The wells have been producing for 4 to 8 years and the oil production rate of each well declined below 10 barrels per day. Compositional reservoir simulation was used to predict the performance of enhanced oil recovery. A sector model was built for the area selected as the prospective candidate for gas injection. The embedded discrete fracture model (EDFM) was used for modeling the fractures. A Peng-Robinson equation-of-state model was prepared based on the early produced samples from the wells. The only available gas for injection was the produced gas from the surrounding producers. A thorough phase behavior analysis was conducted to understand the miscibility of the injected gas and the in-situ fluid. The field production data was used to history match the sector model. The field data of the initial huff-n-puff cycles were incorporated into the history match to fine tune the model. The robust sector model was employed to forecast the performance of gas huff-n-puff in 4 infill wells for 5 years of EOR operation.

In this study, the non-intrusive embedded discrete fracture model (EDFM) in combination with the Oda method are employed to characterize natural fracture networks fast and accurately, by identifying the dominant water flow paths through spatial connectivity analysis. The purpose of this study is to present a successful field case application in which a novel workflow integrates field data, discrete fracture network (DFN), and production analysis with spatial fracture connectivity analysis to characterize dominant flow paths for water intrusion in a field-scale numerical simulation. Initially, the water intrusion of single-well sector models was history matched. Then, resulting parameters of the single-well models were incorporated into the full field model, and the pressure and water breakthrough of all the producing wells were matched. Finally, forecast results were evaluated. Consequently, one of the findings is that wellbore connectivity to the fracture network has a considerable effect on characterizing the water intrusion in fractured gas reservoirs. Additionally, dominant water flow paths within the fracture network, easily modeled by EDFM as effective fracture zones, aid in understanding and predicting the water intrusion phenomena. Therefore, fracture clustering as shortest paths from the water contacts to the wellbore endorses the results of the numerical simulation. Finally, matching the breakthrough time depends on merging responses from multiple dominant water flow paths within the distributions of the fracture network. The conclusions of this investigation are crucial to field modeling and the decision-making process of well operation by anticipating water intrusion behavior through probable flow paths within the fracture networks.

Duvernay shale is a world class shale deposit with a total resource of 440 billion barrels oil equivalent in the Western Canada Sedimentary Basin (WCSB). The volatile oil recovery factors achieved from primary production are much lower than those from the gas-condensate window, typically 5–10% of original oil in place (OOIP). The previous study has indicated that huff-n-puff gas injection is one of the most promising enhanced oil recovery (EOR) methods in shale oil reservoirs. In this paper, we built a comprehensive numerical compositional model in combination with the embedded discrete fracture model (EDFM) method to evaluate geological and engineering controls on gas huff-n-puff in Duvernay shale volatile oil reservoirs. Multiple scenarios of compositional simulations of huff-n-puff gas injection for the proposed twelve parameters have been conducted and effects of reservoir, completion and depletion development parameters on huff-n-puff are evaluated. We concluded that fracture conductivity, natural fracture density, period of primary depletion, and natural fracture permeability are the most sensitive parameters for incremental oil recovery from gas huff-n-puff. Low fracture conductivity and a short period of primary depletion could significantly increase the gas usage ratio and result in poor economical efficiency of the gas huff-n-puff process. Sensitivity analysis indicates that due to the increase of the matrix-surface area during gas huff-n-puff process, natural fractures associated with hydraulic fractures are the key controlling factors for gas huff-n-puff in Duvernay shale oil reservoirs. The range for the oil recovery increase over the primary recovery for one gas huff-n-puff cycle (nearly 2300 days of production) in Duvernay shale volatile oil reservoir is between 0.23 and 0.87%. Finally, we proposed screening criteria for gas huff-n-puff potential areas in volatile oil reservoirs from Duvernay shale. This study is highly meaningful and can give valuable reference to practical works conducting the huff-n-puff gas injection in both Duvernay and other shale oil reservoirs.

With the increased exploration and development of unconventional reservoirs, the complicated production mechanisms of unconventional wells have gradually become a hot topic among the oil and gas industry. Due to the ultra-low permeability and porosity, the fluid phase behavior in shale reservoirs significantly differs from the conventional fluid phase behavior, increasing the production forecasting complexity. A substantial effort to better understand the mechanisms is the ability to characterize the unconventional well gas-oil ratio (GOR) behavior. The GOR always plays a critical indicator to help predict long-term oil/gas production trends and develop appropriate production strategies. In this paper, GOR behavior was discussed based on an unconventional parent-child horizontal well set in the Eagle Ford shale formation. Subsequently, fracture hit intensity can be determined through the producing GOR characterization. Afterward, the historical production data were well matched. The long-term GOR trends (20 years) were then predicted with the calibrated reservoir model. Based on the simulation results, an interpretation of the fracture hit impact on GOR behavior, and the well productivity was established. This study provides some key insights into GOR behaviors, especially for the parent-child well GOR trends with considering the impact of fracture hits. The Eagle Ford GOR is strongly influenced by the flowing bottomhole pressure. Meanwhile, the GOR trends of both parent and child wells are extremely sensitive to fracture hits, strong correlations between GOR and fracture hits are observed. Compared to the parent well, the flat GOR period of the child well is much shorter due to pressure depletion. The existence of a child well also reduces the rising speed of the parent well with a lower plateau. In addition, the long-term production prediction shows that fracture hits negatively influenced both well performances, where the child well has a more severe production loss than the parent well. Through the findings presented in this work, a better understanding of the unconventional well GOR behaviors can be obtained. The analysis approaches proposed in this paper provide valuable insights into GOR characterization and contribute to the production forecasting from unconventional plays. The results can help to improve the efficiency of reservoir management, field development, and economic valuation in future projects.

No abstract

Bedding-plane slip effects during hydraulic fracturing have recently gained interest in unconventional plays due to their influence in hydraulic fracture growth in vertical and horizontal directions. However, most of the current workflows cannot fully model field-scale sub-horizontal orientation of bedding planes because of complications with gridding techniques, or due to simplifications related to the use of 2D models. These challenges have motivated the assessment of 3D bedding plane interactions on well performance using the embedded discrete fracture model (EDFM) technology for field case scenarios. An efficient hydraulic fracture propagation model is used to model hydraulic fracture growth in the presence of bedding layers. The model captures shear slippage at the bedding layer interfaces and corrects the calculated stress intensity factor to account for height containment. A hydraulic fracture model, constrained by geomechanical information, is built in a corner point grid. Resulting hydraulic fracture geometries and identified bedding layer fractures are transferred to EDFM by using a 3D bedding plane generator, which places sub-horizontal polygons across the well trajectory, honoring its orientation and geometry. To locate the spatial position of bedding layers, geostatistical constrains, core analysis and petrophysical interpretations – including well image logs – can be taken into account. Lastly, a reservoir simulation model is built to evaluate the effects of bedding planes on well performance. 3D effects of bedding planes in a shale gas reservoir were captured in a field case scenario using numerical models. Higher contribution to production was observed in the results of this study. The main reasons are larger fracture lengths generated along the pay zone caused by bedding plane influence in the fracture propagation process and shear slippage along bedding plane fractures, which create a larger effective conductive surface area. When modeling bedding planes, computational efficiency is substantial due to the EDFM method, preserving spatial orientation and geometry of each bedding plane. Direct assessment of bedding plane properties is provided, which highlights the importance of capturing their interactions with hydraulic fracture growth and well performance. A seamless integration of bedding plane models can be achieved in an efficient workflow that provides key lessons for future fracture design and well spacing optimization.

Multi-stage hydraulic fracturing has recently gained strong interest in unconventional plays in the Middle East due to high natural gas production potential. However, prevalent characteristics of the area, including high-pressure / high-temperature (HPHT) conditions and presence of complex natural fracture networks, pose significant challenges to reservoir characterization. These challenges have motivated the development of an integrated workflow using microseismic data for the characterization of reservoir properties resulting from the interaction between natural and hydraulic fractures. This study proposes a reliable method for modeling hydraulic fractures from scarce microseismic data. Initially, a microseismic model—based on field records of microseismic data and natural fracture spatial characterization—was developed. Issues related to limited microseismic data availability were tackled through combination of a probabilistic algorithm, Gaussian Mixture Model, and a DFN model. Then, the resulting synthetic microseismic events enabled the generation of a hydraulic fracture model using the embedded discrete fracture model (EDFM) and an in-house microseismic spatial density algorithm that captured major hydraulic fracture growth tendencies. Next, the created hydraulic fracture geometries were validated against a physics-based hydraulic fracture propagation model. Lastly, a single-well sector model—based on a corner point grid that honored the original 3D discrete fracture network (DFN)—was history matched, confirming the successful application of the proposed methodology.