Various topics in unconventional reservoir simulation

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Zhao, Yajie

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With the recent progress in technologies such as hydraulic fracturing and horizontal drilling, unconventional resource development has exploded in recent years. Nevertheless, significant challenges remain for shale reservoirs because of the extensive number of uncertainties. Without proper characterization processes, extracting economic values from these projects will be difficult, and optimizations for future plans will also be challenging. Therefore, efficient models in production mechanism, management and optimization have gradually become hot topics among the petroleum industry. This study aims to address various crucial challenges during the production process of shale reservoirs, including unconventional well gas oil ratio (GOR) characterization, choke management, and well spacing optimization. Due to the ultra-low permeability and porosity, the fluid phase behavior in shale reservoirs significantly differs from the conventional fluid behavior and increases the production forecasting complexity. A substantial effort to better understand the mechanism is to characterize the unconventional well GOR, which always plays as a critical indicator to help predict long-term oil/gas production trends and develop appropriate production strategies. In this research, GOR behavior was first evaluated by a set of comprehensive sensitivity studies in a tight oil well model, which helped to investigate the key drivers that can impact the GOR response in unconventional resources. Then, a parent-child well-set case in Eagle Ford was presented. Through detailed characterization of the producing GOR, an improved understanding of the parent-child well behavior and the fracture hit impact can be obtained. In order to improve the efficiency of field operation, seeking for proper operation plan has been the focusing topic among the oil and gas industry. Choke management strategy selection is one of the essential measures to regulate fluid flow and control downstream system pressure, which could significantly impact the well production rate and estimated ultimate recovery (EUR). In this study, we utilized the non-intrusive embedded discrete fracture model (EDFM) method to handle complicated fracture designs and predicted the long-term EUR from conservative to aggressive choke strategy. Meanwhile, a series of sensitivity studies were presented to evaluate the impacts of various factors on shale gas production, including fracture permeability modulus, fracture closure level, and natural fractures network. The model becomes a valuable stencil to design fracture closure and complex fracture networks, which is a significant improvement for a more reliable choke management model in unconventional area. Another crucial part for well performance improvement is well spacing optimization. Consistent estimates of well spacing help reduce the impact of complex uncertainties from unconventional reservoirs, thereby improving the EUR and enhancing economic growth. We demonstrated a case study on well spacing optimization in a shale gas reservoir located in the Sichuan Basin in China. By using the advanced EDFM technology, complex natural fractures can be effectively captured and simulated. In this study, five different well spacing scenarios ranging from 300 m to 500 m were simulated individually to find the optimum well spacing that maximizes the economic revenue. As the practicability and the convenience showed in this workflow, it becomes feasible to be utilized in any other shale gas well.


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