An Experimental Investigation of Fracture Propagation During Water Injection
Roberto Suárez-Rivera, Jørn Stenebråten, TerraTek
Inc., Phani B. Gadde and Mukul M. Sharma, SPE, The University of Texas
at Austin
This paper was prepared for presentation at the SPE International Symposium and Exhibition on Formation Damage Control held in Lafayette, Louisiana, 20–21 February 2002.
Copyright 2002, Society of Petroleum Engineers Inc..
Abstract
Water injection for pressure maintenance, waterflooding or disposal of
produced water has become an important issue in the management of produced
fluids. However, suspended particles in the injected water cause formation
damage and can lead to fracture initiation due to an increase in injection
pressure. Injectivity decline in injection or disposal wells can have
a large impact on the economic feasibility of water disposal operations.
Fracture propagation could potentially result in undesirable environmental
and reservoir engineering consequences.
The paper presents results of a study conducted to understand the mechanisms
of injectivity decline and fracture propagation during water injection.
Large-scale injection tests were conducted under simulated in-situ stress
and pore pressure conditions, using rock blocks 27”x27”x32”,
representative of a consolidated reservoir rock and laboratory-made produced-water.
Results indicate that the rate of fracture growth is strongly dependent
on the type and concentration of particles in the injected fluid. The
shape, size and compressibility of the injected particles play an important
role. Our results clearly demonstrate that the injectivity remains almost
constant once a fracture is initiated. The injected particles are filtered
largely near the tip of the fracture where the leakoff is the highest.
The depth of penetration of the particles into the matrix appears to
be small. Analyses using optical microscopy observations on thin sections
show that the filter cake is not a continuous film but rather a region
(from 3 to 10 grains deep) where the connected flow paths have been effectively
blocked by solid particle deposition. Results from these experiments
provide a basis for developing analytical and numerical modeling tools
for injectivity decline and fracture propagation in fractured injectors.
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