Prediction and control of hydraulic fracture trajectory in enhanced geothermal system

ABSTRACT

A new fully coupled numerical model is presented to analyze artificial fracture morphology and artificial fracture propagation during synchronous fracturing. The interaction mechanism between natural and artificial fractures is also considered in this new model. The new numerical solution, based on the boundary element method (BEM) and the finite difference method, is used to solve the problem of coupled rock deformation, fluid interference, stress interference, interface slipping, and opening and to investigate the effect of natural fractures and interference between fractures on fracture morphology during synchronous fracturing. An analysis of factors of influence showed that synchronous fracturing can be used to control the fracture trajectory and construct an effective enhanced geothermal system (EGS). Artificial fractures of two adjacent wells attract each other during synchronous fracturing, and eventually, the two fractures become connected, and the two wells become connected. The choice of well location also has an important influence on the successful establishment of an EGS. To establish an effective EGS successfully, the fracture spacing should preferably be no more than 20 m, and the well spacing should preferably be greater than 400 m. An EGS is easier to construct in a hot dry rock reservoir with a high natural fracture density and small natural fracture angles (preferably less than 30º).

KEYWORDS:

• Enhanced geothermal system
• hydraulic fracturing
• fracture trajectory
• synchronous fracturing
• numerical simulation

Highlights

• Prediction and control methods for artificial fracture trajectories in EGS are proposed.

• A new simultaneous fracturing model considered the effects of natural fractures is established.

• The energy release rate is considered when multiple fractures are simultaneously propagation.

• Fracture spacing should be as small as possible when developing EGS.

• EGS is easier to construct in reservoirs with high natural fracture density and small natural fracture angles.

Additional information

Funding

This work was financially supported by the National Science and Technology Major Project of China (2017ZX05049-006-007).

Notes on contributors

Xiaogang Li

Xiaogang Li is a professor from Southwest Petroleum University with a research interest in theory and technology of unconventional reservoir stimulation. He is a member of Society of Petroleum Engineers (SPE). He holds a PhD from Southwest Petroleum University.

Yuting He

Yuting He is a PhD student from Southwest Petroleum University with a research interest in mechanism of hydraulic fracturing and rock mechanics. He is a member of Society of Petroleum Engineers (SPE).

Zhaozhong Yang

Zhaozhong Yang is a professor from Southwest Petroleum University with a research interest in theory and technology of unconventional reservoir stimulation. He is an academic and technical leader in Sichuan Province. He holds a PhD from Southwest Petroleum University.

Rui Song

Rui Song is a petroleum engineer, graduated from Southwest Petroleum University with a master's degree in offshore oil and gas engineering in 2015, mainly engaged in offshore drilling and completion technology and management.