Summary
An injection-well model is presented and used to history match a field
injector's bottomhole pressures (BHPs) and injection profile (injection rate
into each layer), taking into account plugging of formation caused by suspended
solids in the injection water, poro- and thermoelastic stresses, injector
shut-ins/restarts, and changes in both the injection rates and the average
reservoir pressure. Fracture lengths and injection profile are estimated for a
field injector as a case study. The injection-well fracture model is very
similar to the Perkins and Gonzalez (1985) model except that it has integrated
a more comprehensive and experimentally tested internal filtration model
(Rajagopalan and Tien 1976; Pang and Sharma 1997; Gadde and Sharma 2001; Suri
2000; Wennberg and Sharma 1997) for calculating permeability reduction. It has
also added a pressure-transient model that makes the earlier reservoir flow
models more accurate.
The solids deposition is modeled using a filtration model (Rajagopalan and
Tien 1976). The fluid flow in the reservoir is modeled using three approximated
composite zones with uniform saturations and average mobilities, and the
pressure for the fractured wellbore is calculated with the help of Gringarten's
infinite-conductivity solution. The induced-fracture lengths are calculated on
the basis of the Perkins and Gonzalez fracture-propagation model (1985) that
accounts for the thermal and poroelastic stresses. The model is developed into
a semianalytical numerical simulator that can predict and history match an
injector's daily BHP, fracture lengths, and injection profile. Future estimates
of pump pressures, BHP, injectivity, skin, front locations, fracture lengths,
and injection profile can be obtained from this model. Both short-term pressure
transients and long-term pseudosteady pressures observed over several years of
injection can be history matched to capture effects that are important at both
short and long time scales.
Finally a field-case injection-well study is presented in which BHP and
injectivity are history matched over a period of 3 years. We show that the
model can be used to estimate the minimum horizontal stresses in the layers if
they are not known, which was the case. Estimates of fracture lengths, fraction
of flow, permeability reduction, and skin and front locations are also
obtained. There is significant uncertainty in the results because of
uncertainty in the model inputs and in the completeness of the physics of the
model of fracturing itself. Both the solids deposition and the opening/closing
of the injection-induced fractures had to be accounted for to obtain the
history match. The layer/sand stresses and the water quality are the most
important parameters that determine the well's injectivity, fracture growth,
and injection profile. Microseismic surveys are needed to delineate the
fractures in injection wells.
© 2011. Society of Petroleum Engineers
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History
- Original manuscript received:
30 March 2010
- Meeting paper published:
28 May 2010
- Revised manuscript received:
14 April 2011
- Manuscript approved:
2 May 2011
- Published online:
12 August 2011
- Version of record:
15 August 2011
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