Shale gas formation exhibits some unusual reservoir characteristics: nano-darcy
matrix permeability, presence of natural fractures and gas storage on the matrix
surface that makes it unique in many ways. It’s difficult to design an optimum
fracture treatment for such formation and even more difficult is to describe
production behavior using a reservoir model. So far homogeneous, two wing
fracture, and natural fracture models have been used for this purpose without much
success. Micro seismic mapping technique is used to measure the fracture
propagation in real time. This measurement in naturally fractured shale formation
suggests a growth of fracture network instead of a traditional two wing fractures.
There is an industry wise consensus that fracture network plays an important role in
determining the well productivity of such formations. A well with high density of
fracture networks supposed to have better productivity.
Shale formations have also exhibited production pattern which is very
different from conventional or tight gas reservoir. Initial flow period is marked by
steep decline in production while the late time production exhibits a slow decline.
One of the arguments put for this behavior is linear flow from a bi-wing fractured
well at early time and contribution of adsorbed gas in production at late time. However, bi-wing fracture geometry is not supported by the micro-seismic
observation. A realistic model should include both the fracture network and adsorbed
gas property.
In this research we have proposed a new Power Law Permability model to
simulate fluid flow from hydraulically fractured Shale formation. This model was
first described by Valko & Fnu (2002) and used for analyzing acid treatment jobs.
The key idea of this model is to use a power law permeability function that varies
with the radial distance from well bore. Scaling exponent of this power law function
has been named power law index. The permeability function has also been termed as
secondary permeability.
This work introduces the method of Laplace solution to solve the problem of
transient and pseudo steady-state flow in a fracture network. Development and
validation of this method and its extension to predict the pressure (and production)
behaviour of fracture network were made using a novel technic. Pressure solution
was then combined with material balance through productivity index to make
production forecast.
Reservoir rock volume affected by the fracture stimulation treatment that
contributes in the production is called effective stimulated volume. This represents
the extent of fracture network in this case. Barnett shale formation is a naturally
fractured shale reservoir in Fort Worth basin. Several production wells from this
formation was analysed using Power Law Model and it was found that wells
productivity are highly dependent on stimulated volume. Apparently the wells flow
under pseudo steady state for most part of their producing life and the effect of
boundary on production is evident in as soon as one months of production. Due to short period of transient flow production from Barnett formations is expected to be
largely independent of the relative distribution of permeability and highly dependent
on the stimulated area and induced secondary permeability. However, an indirect
relationship between permeability distribution and production rate is observed. A
well with low power law index shows a better (more even) secondary permeability
distribution in spatial direction, larger stimulated volume and better production.
A comparative analysis between the new model and traditional fracture model
was made. It was found that both models can be used successfully for history
matching and production forecasting from hydraulically fractured shale gas
formation.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2359 |
| Date | 15 May 2009 |
| Creators | Kumar, Amrendra |
| Contributors | Valko, Peter,P |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Thesis, text |
| Format | electronic, application/pdf, born digital |
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