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Pressure- and rate-transient model for interfering horizontal wells
Makhatova, Meruyert
Makhatova, Meruyert
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2024
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Abstract
Multiple fractured horizontal wells (MFHW) are extensively used to enhance hydrocarbon production from ultra-tight unconventional reservoirs by increasing surface area for fluid flow. Hydraulic fracturing creates or rejuvenates the existing network of fractures surrounding the hydraulic fractures and horizontal well and forms a stimulates reservoir volume (SRV) around the well. The combination of the wellbore features, hydraulic fractures, and stimulated and unstimulated reservoir properties complicates fluid dynamics in unconventional reservoirs. In multi-well systems, fluid flow becomes more intricate due to inter-well interference.
Multi-well systems are essential to maximize reservoir drainage. Oil and gas operators often drill multiple wells from a single pad, resulting in close well spacing, or place infill wells, which can disrupt production in both parent and child wells due to spatial and temporal factors, as well as interwell communication between stacked formations. These development decisions, complicated by interwell connectivity, raise practical concerns of optimum well spacing and stimulation strategies.
To address these challenges by covering numerous options of well placement and stimulation and uncertainties increased by the complex reservoir features, there is a need for efficient models capable of providing quick and robust evaluations of reservoir performance. The objective of this dissertation is to develop a multi-well analytical model that accurately represents the complex interactions in systems with interfering MFHWs in both single- and multi-layered unconventional reservoirs. This model is designed for pressure- and rate-transient analysis (PTA/RTA), crucial for determining reservoir properties and predicting well performance. Unlike traditional PTA/RTA diagnostics that assume standalone wells, this model accounts for spatial and temporal variability of interfering wells.
We consider a reservoir sector including a group of horizontal wells. The sector is divided into blocks for a boundary-element approach, which is simplified by incorporating the trilinear flow assumption. The transient flow problem for each block is solved analytically in Laplace domain and coupled with the neighboring blocks through pressure and flux continuity on their mutual boundaries to obtain the wellbore-pressure solutions.
Analytical solutions developed for multi-well systems, both in single and multiple layers, have been verified against existing analytical models and numerical simulations. Pressure and rate responses generated by the models are analyzed to decipher flow regimes, evaluate reservoir and completion characteristics, discuss well and reservoir performances, history-match production and pressure histories, and predict future performances under complex well interference. Field applications demonstrate the use of these models in well pad development and parent-child well configurations. Sensitivity analyses examine the impact of well spacing and stimulation scenarios. These outputs are instrumental in performance prediction and guiding decision-making processes for infill drilling and stimulation strategies.
The model proposed in this dissertation is a proxy model proposed for specific applications of pressure- and rate-transient analysis (PTA and RTA), evaluation of completion and well-placement options, and provide initial guidance for more detailed numerical simulations. Although there have been some attempts in the literature to build analytical or semi-analytical multi-well models in unconventional reservoirs, the assumptions used in their development limit their utility to reservoirs with uniform properties, require fine gridding and small time-steps, or contradict with the moving boundary problem created by the unsynchronized start and stop of production with different rate and pressure schedules. The model proposed in this dissertation is more general, comprehensive, and robust than the existing models.
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