Abstract
Complex fracture networks are easily developed along the horizontal wellbore during hydraulic fracturing. The water phase increases the seepage resistance of oil in natural fractured reservoir. The flow regimes become more intricate due to the complex fractures and the occurrence of two-phase flow. Therefore, a semi-analytical two-phase flow model is developed based on the assumption of orthogonal fracture networks to describe the complicate flow regimes. The natural micro-fractures are treated as a dual-porosity system and the hydraulic fracture with complex fracture networks are characterized explicitly by discretizing the fracture networks into multiple fracture segments. The model is solved according to Laplace transformation and Duhamel superposition principle. Results show that seven possible flow regimes are described according to the typical curves. The major difference between the vertical fractures and the fracture networks along the horizontal wellbore is the fluid “feed flow” behavior from the secondary fracture to the main fracture. A natural fracture pseudo-radial flow stage is added in the proposed model comparing with the conventional dual-porosity model. The water content has a major effect on the fluid total mobility and flow capacity in dual-porosity system and complex fracture networks. With the increase of the main fracture number, the interference of the fractures increases and the linear flow characteristics in the fracture become more obvious. The secondary fracture number has major influence on the fluid feed capacity from the secondary fracture to the main fracture. The elastic storativity ratio mainly influences the fracture flow period and inter-porosity flow period in the dual-porosity system. The inter-porosity flow coefficient corresponds to the inter-porosity flow period of the pressure curves. This work is significantly important for the hydraulic fracture characterization and performance prediction of the fractured horizontal well with complex fracture networks in natural fractured reservoirs.
Highlights
Hydraulic fracturing is an important stimulation technique to increase the productivity of horizontal wells
Due to the large quantity of micro-fractures developed in natural fractured tight oil reservoir, complex fracture systems are generated along the horizontal wellbore after hydraulic fracturing treatments
As seen from the figure, the water content in complex fracture networks has a major influence on the fluid feed flow period from the secondary fracture into the main fractures
Summary
Hydraulic fracturing is an important stimulation technique to increase the productivity of horizontal wells. Based on the material balance theory, Yang et al (2016) and Chen et al (2018) proposed semi-analytical method to analyze the two-phase flow preformation of the horizontal well with complex fracture networks. We developed a semi-analytical method to analyze the oil/water two-phase flow pressure behavior in natural fractured tight oil reservoirs. The proposed model considered the twophase flow both in the fracture networks and dual-porosity system in fractured reservoir, which is more accurate to describe the flow and pressure behavior for the fractured horizontal well with complex fracture networks. As seen from the figure, the water content in complex fracture networks has a major influence on the fluid feed flow period from the secondary fracture into the main fractures. The larger the water content in the complex fracture system, the deeper the dip on the pressure curves become and the lower the curve is offset
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