Semester

Summer

Date of Graduation

2021

Document Type

Dissertation

Degree Type

PhD

College

Statler College of Engineering and Mineral Resources

Department

Petroleum and Natural Gas Engineering

Committee Chair

Kashy Aminian

Committee Co-Chair

Samuel Ameri

Committee Member

Ilkin Bilgesu

Committee Member

Tim Carr

Committee Member

Zamirian Mehrdad

Abstract

Shale gas development has become a crucial part of the global oil and gas industry in recent years, especially in North America. Even though the application of horizontal drilling and hydraulic fracturing techniques have successfully unlocked considerable reserves of natural gas in shale-gas reservoirs, production rates from unconventional reservoirs decline more rapidly than conventional reservoirs. This is because production from a reservoir results in an increase in net stress due to a reduction in the pore pressure, while overburden pressure remains constant. This leads to the reduction in permeability of both the matrix and the fissures, as well as the conductivity of the hydraulic fractures. Furthermore, the propagation of a fracture cause stress change in the vicinity of the fracture, commonly known as stress shadow. Stress shadow influences the properties of the subsequent hydraulic fracture stages and results in less-than-optimal production.

The objective of this study was to investigate the impact of the net stress changes and the stress shadow on gas production from a horizontal well with multiple hydraulic fractures completed in Marcellus Shale. In addition, the impacts of stage (cluster) spacing, treatment size, treatment sequencing, and the formation mechanical properties on the gas recovery are investigated. The available information from a Marcellus Shale horizontal well including well logs data, diagnostic fracture injection test (DFIT), and fracture stimulation treatment data were analyzed to determine the formation mechanical properties, minimum horizontal stress, instantaneous shut-in pressure (ISIP), process zone stress (PZS), and leak-off mechanism. The results of the analysis were utilized as the inputs for a commercial hydraulic fracturing software to predict the hydraulic fracture properties influenced by stress shadowing.

A reservoir model for a horizontal well with multi-stage hydraulic fractures in Marcellus Shale was developed using the published Marcellus Shale properties. The results of the published laboratory studies on Marcellus shale core plugs provided the foundation for evaluating the geomechanical factors which quantify the impact of net stress on the permeability of the matrix and fissure as well as the fracture conductivity. The geomechanical factors as well as the predicted hydraulic fracture properties, were then incorporated in the reservoir model. A commercial reservoir simulation software was then utilized to predict the production performance of the developed Marcellus Shale horizontal well model. The results were then compared to the production history of the horizontal well for evaluation and verification. Finally, The model was finally used to perform a number of parametric studies.

The inclusion of geomechanical factors and stress shadow provided an accurate prediction of the gas production from the horizontal well under study. Geomechanical factors have a significant impact on gas production from Marcellus Shale, particularly at the early stage of the production (2-5 years). The fissure permeability geomechanical factor has the most impact on the production. Additionally, the propped fracture conductivity geomechanical factor is influenced by the fracture half-length and initial fracture conductivity. The impact of propped hydraulic fracture conductivity geomechanical factor is more prominent in the formations with low Young’s modulus. The stress shadowing has a negative effect on gas production. The stress shadowing effects were found to be dependent on fracture spacing. This research finds that stress shadowing effects can be reduced by increasing the distance between the neighboring fracture stages. Furthermore, the predicted fracture grows vertically upward in Marcellus Shale if the stress shadowing effects are ignored. Moreover, the stress shadowing impact on the gas production increases as the volume of the injected fluid and the sand amount per stage are increased. The impact of the stress shadowing appears to be lower for simultaneous fracturing as compared to sequential fracturing. This research finds that the hydraulic fracture properties and gas recovery from Marcellus shale improve as Poisson’s ratio decreases. However, the production enhancement due to the lower Poisson’s ratio can be obscured by stress shadowing when the stage spacing is close. Additionally, this research finds that the gas recovery is influenced significantly by the fracture half-length and less significantly by non-uniform fracture-length.

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