Unconventional reservoirs are developed by drilling long horizontal wells of up to 20,000 ft and produced using multistage hydraulic fracturing operations. The production profile of such wells has a steep decline at early life (3 to 12 months) during which the flow rates decrease with a diminishing bottom hole pressure and the flow starts oscillating at an increasing amplitude. After reaching the bubble point value, the gas starts releasing at the lateral section and slugs start to form and travel through the vertical section before reaching the wellhead. This flow instability affects the pressures with large variations, reaching several hundreds of psi at the sand face part. The pressure variations have an impact on the hydraulic fracture’s integrity and need to be considered for the safety operations envelop (SOE).In this study the effects of pressure variations have been studied by integrating the transient multiphase flow simulation results of a Bakken well into a reservoir and geomechanical model. Mid-life production performances were considered to capture the flow and pressure oscillation at their maximum rates. Using the reservoir model, the pressures, and saturations were calculated at different time steps. Also, the geomechanical model was built and calibrated using core data. The model was used to identify the potential for proppant dis-embedment. This was used to evaluate potential proppant dis-embedment which may lead to proppant settlement at the lower part of the fractures and closes the upper part, resulting in reduced productivity, and contributing to further production decline. The results of this study is used for an improved production management of unconventional plays and extended-reach wells.

The increasing popularity of unconventional wells has sparked a heightened interest in evaluating and predicting their production performance. With the use of extended reach well structures, these wells are able to generate and access larger reservoir volumes. Hence, it is crucial to understand how the well's lateral trajectory affects its transient production performance. The assessment of lateral trajectory undulating amplitude effect on the flow behavior is performed in the current study based on the experimental results obtained at the University of North Dakota, Undulated Two-Phase (UTP) Flow Loop, injecting air and water mixture through a variable undulating amplitude section followed by a vertical section. The experiments showed that the undulating amplitude increase induced lower translational velocity, frequency, and length, with a consistent slug acceleration through the system profile from the inlet to the vertical section and a decreasing frequency when the slugs travel through the vertical section. Measured data shows that an increase of the horizontal pressure losses and variability is expected with a higher undulation amplitude, translating the fact that larger instabilities are observed for higher amplitudes. The numerical simulation predicted lower translational velocity and frequency, higher slug’s lengths, and similar vertical pressure losses when compared to the experimental results.

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During the reservoir depletion and injection operations, the net effective stress is disrupted due to pore pressure changes. As a result, the reservoir properties, mainly porosity and permeability, are influenced by the change in the stress behavior in the reservoir rock. Understanding the porosity and permeability stress-dependent alteration is crucial since it directly impacts the reservoir storage capacity and the production/injection capabilities. Conventionally, lab experiments are conducted to understand the stress dependency of porosity and permeability magnitudes. Two methods are usually used: the unsteady-state method (Core Measurement System, CMS-300) and the steady-state method (Core Measurement System, CPMS). The challenges with these experiments reside in the fact that they are expensive and time-consuming and may cause the destruction of the core samples due to the applied stresses. This study aims to investigate the effect of stress variations on porosity and permeability changes. These properties were measured on a total of 2150 core data from the three members of the unconventional Bakken formation (upper, middle, and lower), applying 35 different Net Confining Stress (NCS) values, ranging from 400psi to 5800psi. A correlation was formulated between permeability and the NCS to illustrate the stress dependency relationships. The Grey Wolf Optimization algorithm (GWO) was used to tune the correlation for the Bakken formation. Machine Learning methods were also applied for the porosity and permeability stress dependency response prediction, which are as follows: Linear Regression (LR), Random Forest Regression (RF), XGBoost Regression (XGB), and Artificial Neural Network (ANN). The results demonstrate that the porosity and the permeability decrease with the increase of the NCS and vice versa. The permeability is highly sensitive to the NCS changes compared to the porosity. The developed correlations showed a good fit with the data extracted from the laboratory experiments of the pilot well. For the data-driven models, the coefficient of correlation R2-Score ranged from 91% to 93%. These models can be used to constrain the modeling work and reduce the uncertainties by introducing the effect of the net effective stress changes during reservoir depletion/injection on petrophysical properties.