Summary
This paper discusses the performance and productivity of fractured
horizontal wells in heterogeneous, tight-gas formations. Production
characteristics and flow regimes of unfractured and fractured horizontal wells
are documented. The results show that if hydraulic fracturing affects stress
distribution to create or rejuvenate natural fractures around the well, the
productivity of the system is significantly increased. Unless there is
significant contrast between the conductivities of the hydraulic and natural
fractures, hydraulic fractures may not significantly contribute to the
productivity. For extremely tight formations, the effective drainage area may
be limited to the naturally fractured region around the well and the hydraulic
fractures. It is also shown that very long transient flow periods govern the
productivity and economics of fractured horizontal wells in tight formations.
The results of this study are also applicable to oil production from fractured
shale.
Introduction
Economic gas and oil production from low permeability reservoirs has been a
challenge for the oil and gas industry. Because most of the high permeability
reservoirs have been exploited and many low permeability reservoirs remain
undeveloped, the latter have taken the industry attention recently. Particular
attention has been given to tight-gas reservoirs with permeability in the range
of micro-Darcies or below and to oil accumulation in fractured shale.
Hydraulically fractured horizontal wells are the proven technology to
produce oil and gas from tight formations. Hydraulic fractures reduce well
drawndown, increase the productivity of horizontal wells by increasing the
surface area in contact with formation, and provide high conductivity paths to
the wellbore. Depending on in-situ stress orientation, hydraulic fractures can
be parallel (longitudinal) or perpendicular (transverse) to horizontal well
axis. Project economics in tight formations, however, depends strongly on well
spacing and the number of hydraulic fractures required to drain the reservoir
efficiently. Field evidence indicates that the drainage areas of fractured
horizontal wells in tight formations may be limited to a rectangular region
confining the horizontal well and the transverse hydraulic fractures. Also,
there has been evidence that hydraulic fracturing in tight formations changes
stresses in fracture drainage area, which could create or rejuvenate natural
fractures in the near-vicinity of the horizontal well. This fracture network,
which may be characterized as a dual-porosity system, may contribute
significantly to improve productivity of the fractured horizontal well.
Much work has been done (Soliman et al. 1990; Larsen and Hegre 1994; Temeng
and Horne 1995; Raghavan et al. 1997; Wan and Aziz 1999; Al-Kobaisi et al.
2006) to investigate pressure-transient analysis and short- and long-term
productivity of horizontal wells with single or multiple hydraulic fractures.
The effect of a dual-porosity zone surrounding hydraulic fractures, however,
has not been considered in the previous studies. The main objective of this
study is to investigate the combined effects of a dual-porosity region and
hydraulic fractures on the productivity of horizontal wells.
The results presented in this work are based on a semianalytical model
developed by Medeiros et al. (2006). The model was derived from the Green's
function formulation of the solution for the diffusivity equation (Gringarten
and Ramey, 1974, Ozkan and Raghavan, 1991a, 1991b) and has the capability to
incorporate local heterogeneities. In this work, we use the semianalytical
model to incorporate induced finite-conductivity fractures (transverse and
longitudinal) along the horizontal well and naturally fractured zones around
the hydraulically fractured horizontal well by using the dual-porosity
idealization. We use the example data sets given in Tables 1 through 3 to
consider different cases of horizontal wells with and without induced and
natural fractures.
© 2008. Society of Petroleum Engineers
View full textPDF
(
2,467 KB
)
History
- Original manuscript received:
20 February 2007
- Meeting paper published:
16 April 2007
- Revised manuscript received:
21 February 2008
- Manuscript approved:
26 February 2008
- Version of record:
25 October 2008
View Cart
