Many hydraulically fractured shale gas horizontal wells in the Barnett shale have been
observed to exhibit transient linear behavior. This transient linear behavior is
characterized by a one-half slope on a log-log plot of rate against time. This transient
linear flow regime is believed to be caused by transient drainage of low permeability
matrix blocks into adjoining fractures. This transient flow regime is the only flow regime
available for analysis in many wells.
The hydraulically fractured shale gas reservoir system was described in this work
by a linear dual porosity model. This consisted of a bounded rectangular reservoir with
slab matrix blocks draining into adjoining fractures and subsequently to a horizontal well
in the centre. The horizontal well fully penetrates the rectangular reservoir. Convergence
skin is incorporated into the linear model to account for the presence of the horizontal
wellbore.
Five flow regions were identified with this model. Region 1 is due to transient
flow only in the fractures. Region 2 is bilinear flow and occurs when the matrix drainage
begins simultaneously with the transient flow in the fractures. Region 3 is the response for a homogeneous reservoir. Region 4 is dominated by transient matrix drainage and is
the transient flow regime of interest. Region 5 is the boundary dominated transient
response. New working equations were developed and presented for analysis of Regions
1 to 4. No equation was presented for Region 5 as it requires a combination of material
balance and productivity index equations beyond the scope of this work.
It is concluded that the transient linear region observed in field data occurs in
Region 4 – drainage of the matrix. A procedure is presented for analysis. The only
parameter that can be determined with available data is the matrix drainage area, Acm.
It was also demonstrated in this work that the effect of skin under constant rate
and constant bottomhole pressure conditions is not similar for a linear reservoir. The
constant rate case is the usual parallel lines with an offset but the constant bottomhole
pressure shows a gradual diminishing effect of skin. A new analytical equation was
presented to describe the constant bottomhole pressure effect of skin in a linear
reservoir.
It was also demonstrated that different shape factor formulations (Warren and
Root, Zimmerman and Kazemi) result in similar Region 4 transient linear response
provided that the appropriate f(s) modifications consistent with lAc calculations are
conducted. It was also demonstrated that different matrix geometry exhibit the same
Region 4 transient linear response when the area-volume ratios are similar.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2009-05-316 |
| Date | 2009 May 1900 |
| Creators | Bello, Rasheed O. |
| Source Sets | Texas A and M University |
| Language | English |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | application/pdf |
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