Dezhi Qiu

Date of Award

January 2021

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Petroleum Engineering

First Advisor

Vamegh Rasouli

Abstract

During the last two decades, the oil and gas industry started production from unconventional reservoirs, thanks to the rapid development of hydraulic fracturing technology. Fractures such as joints, faults, veins, and bedding planes are ubiquitous in unconventional formations such as laminated reservoirs. These discontinuities always form complex networks affecting the hydrological and mechanical behavior of subsurface rocks. Ideally, hydraulic fractures are expected to communicate these fracture networks to form a continuous path for fluid flow. However, the interaction mechanism between hydraulic fracture and natural fractures may result in different propagation paths to form various fracture geometries and stimulated reservoir volume (SRV). In order to optimize the fracturing treatment and predict the SRV in fractured reservoirs, it is necessary to investigate the fracture propagation pattern from the simple interaction modes between hydraulic fracture and natural fractures to complicated single and multi-stage fracture propagation in laminated reservoir perspectives. This research is divided into three sections. In the first section, a novel model was proposed based on a lattice-based simulator, XSite, to predict interaction modes between hydraulic fracture and natural fractures considering the effect of formation mechanical properties, stress state, and fluid injection parameters. To build this predictive model, a number of fracturing simulations were executed to provide pressure time and interaction modes data. The conception interaction pressurization rate index (IPRI) obtained from pressure time data was proposed as an indicator to characterize the interaction modes. Several lab experiments were used to verify the accuracy of the predictive model. In the second section, a more common fracture model was built to study the hydraulic fracture propagation in the laminated reservoir, which contains the natural interfaces and caprock layers, both significantly affecting the hydraulic fracture geometry. The results indicated that injection rate and caprock Young’s modulus prone to the fracture propagation in the horizontal direction or along the interfaces, thus stress anisotropy and interfaces and caprocks tensile strength favor to the fracture propagation in the vertical direction as a tensile fracture. In the third section of this research, a representative multi-stage model was developed to study the influence of formation properties and injection parameters on fracture evolution in the laminated reservoir. Tension and shear stimulated area were proposed to quantify the fracture propagation modes and directions in formation. A statistical method was used to build the predictive model to evaluate the formation stimulation potential based on considering contribution of all influential parameters. A series of artificially generated in possible range influencing factors verified the accuracy of the proposed model. These three sections progressively investigate the propagation of hydraulic fracture in laminated reservoirs and develop a model for evaluating the reservoir's stimulation potential, which provides a guide for fracturing field operations.

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