CONCLUSIONS and RECOMMENDATIONS
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1. Because of the neglected Friction Loss
Effects, the presented equations obtained from Joshi (Reference 21) could be much over estimating the horizontal/multilateral well productivity along its
wellbore length.
2. For idenntifying the Horizontal/Multilateral
"Optimum Length", a relationship between the well
connection-productivity index (NOT the total connection-production rate) and
the wellbore length should be used. The total connection-production rate at the
wellbore-end masks the drop in the incremental connection-productivity due to
higher drawdown.
3. The simuulator's calculation of the Well
Productivity Index (WPI keyword) should not be used for a horizontal well, as
the assumption of a steady radial flow regime perpendicular to the wellbore
exists out to the drainage radius. For a horizontal well, this flow regime will
rapidly be disrupted by the top and bottom boundaries of the formation, and the
ultimate flow regime may be linear or pseudo-radial depending on the geometry
of the well and its drainage region.
4. In a 2x11 km area of homogeneous
fully-communicated clean sandstone reservoir, regardless the economical value
of accelerating oil recovery, a Single-horizontal hole is recommended for the
purpose of development.
5. Assumingg the possible minimum Kv>/Kh ratio in the Upper Ness Formation of the Don-NE
Field, a maximum of 1,500 feet is recommended for a Single-horizontal hole.
More than 90% of well productivity is achieved at this length.
6. The highher the Kh>*hn value the lower will be the productivity gain of a
single horizontal over a vertical well, and so the drilled wellbore length
shall be extended longer. For example, in the PIPER Group of the Scott Field, a
Single-horizontal hole shall be extended to 2,200 feet.
7. Completion size of less than 5" is NOT
recommended for any type of multilateral well. The impact of wellbore diameter
on the vertical flow (lifting) curves should be studied as an extension for
this project work.
8. In a resservoir with dip equal to or higher
than 30°, the best multilateral configuration (in terms of productivity gain
over a Single-horizontal hole), in the BRENT Sequence, was found to be a
Dual-lateral well with 50° apart.
9. In the NNess Formation of the Don-NE Field
and in the PIPER Group of the Scott Field, minimum of 50° apart angle and maximum of 1,800 feet branch length
are recommended for a Dual-lateral well. The model neglects the expected improved
permeability between the well branches at the well heel.
10. In bothh BRENT and PIPER sequences, a 150
feet minimum distance between its branches are recommended for a Quad-lateral
well with an optimum wellbore length per branch of 2,500-3,000 feet.
11. Due to the high interference existing
between its branches, a Tri-stacked well is NOT recommended in the BRENT Group
of the Don-NE Field. The case is different in the PIPER Group, where the
Shale-Member between the bottom of Piper Sandstone and the top of Sgiath
Sandstone works as a permeability barrier to vertical flow, and that adds a
significant value to the Tri-stacked well (113 feet apart) productivity.
12. A Dual--stacked well with less than 150 feet
apart is NOT recommended in the Ness Formation of the Don-NE Field.
13. Completting a Multi-stacked well in
highly-different-pressure-regime reservoir layers is NOT recommended. A 1,000
psi initial reservoir pressure difference causes a reduction of 25%-50% in the
well productivity.
14. The minnimum apart distance/angle, for all
types of multilateral wells could be less in a highly dipping reservoir (e.g.,
salt domes) due to the observed less interference between the lateral-branches.
15. A heterrogeneous model, with a defined trend
of quality improvement, recommends drilling the well lateral-branches in the
direction of increasing permeability.
16. Adding a lateral branch, to a
Single-horizontal well, in the direction of increasing permeability vertically
is more gainful than adding more than one branch laterally in a direction of
lower permeability.
17. The folllowing Topics need to be
investigated in further studies as an extension for this project work:
- Impact of different
oil characteristics, heavy oil and condensate, on a multilateral well productivity.
- Impact of multi-phase
flow.
- Impact of different
trend-heterogeneity patterns of reservoir characteristics.
- Impact of random
heterogeneity of reservoir characteristics.
- Impact of random
changes of formation dip angle ( q ), "zigzag" wellbore
path.
- Impact of different
lifting curves (Vertical Flow Performance).
- Identification of the
Optimum Length per each lateral-branch, of a multilateral well, beyond which
the productivity of one branch will drop due to the production contribution
from the others.
- Detailed economic
evaluation of the net revenue (productivity gain) versus drilling and
completion costs (multilateral wellbore length). Can the economic optimum
length of a multilateral wellbore be SHORTER than the estimated technical
optimum length?