American Oil and Gas Reporter - July 2015 - 54

vertical;
* Flowback of proppants from near
the wellbore in transverse fracs; and
* Poor contact with pay through losing or wasting proppant out of zone, or
poor transport in the first place.
Vincent says cross-linked fluids can
lead to occlusion of narrow propped fractures. Gel residue or durable gel filter cakes
may completely block narrow fractures.
Perforation design also can be the culprit
in production decline, Vincent goes on. He
says there may be poor alignment with pay
zones or too many perforations to allow
sufficient diversion. As a result, a high percentage of the lateral may have no associated fractures.
Yet another engineering mechanism
for failure is insufficient conductivity for
high-velocity hydrocarbon flow, Vincent
suggests. He says this results from convergence near the wellbore, especially in
liquids-rich formations. The mechanisms
cited normally can be identified and addressed solely by an engineering group.

Geology And Responsibility

stood to diagnose potential problems in the
original fracture stimulation, remedy
them, and avoid them in the refracturing
process. "When engineers design refracs
without involving the G&G team, remediating these issues typically is less than
optimal," he remarks.
The final category of suspected damage mechanisms includes a variety of operational or strategic items that often
cannot be attributed to a specific technical "owner." Vincent says these problems
can be more difficult to address because
they cross boundaries of responsibility and
expertise. Examples include:
* Laterals landed at undesirable
depths, or with undulating or undesirable
architectures;
* Unrecovered water in portions of the
fracture below wellbore elevation;
* Complex fracture geometries that require stronger or more conductive proppant in the turns and pinch points;
* A "factory approach" to completions;
* Aggressive drawdown; and

Sometimes the best explanation for the
collapse of propped fractures can be addressed by geology experts, Vincent offers.
He says some common problems include:
* Proppant embedment, spalling of the
frac face, and rock creep;
* Fluid sensitivity leading to softened
formation and clay swelling, which exacerbates embedment and spalling;
* A misplaced lateral that does not
land in strata that will accommodate the
commonly overflushed completions;
* Precipitation of salt, asphaltenes,
barium sulfate and calcium carbonate
scales, or migration of formation fines;
* Corrosion, bio-slime, hydrogen sulfide, and carbon dioxide damage;
* Chemical diagenesis of proppant;
* Slippage of frac faces; and
* Pore pressure depletion, subsidence,
and compaction that offsets or truncates
thin proppant ribbons.
Vincent says the reservoir and surrounding formations must be well under-

FIGURE 4
Incremental Oil Production after Refrac and Tri-Frac
(Conventional Oil Well)
4,000
Original Frac

3,500

Phase I Refrac

BFPD from same perfs

3,000

Phase III Trifac

2,500
2,000
Incremental
Oil exceeds
1,000,000
barrels

1,500
1,000

Incremental
Oil exceeds
650,000
barrels

500

Months
54 THE AMERICAN OIL & GAS REPORTER

4
20

2
19

0
18

8
16

6
15

4
14

2
13

0
12

8
10

96

84

72

60

48

36

24

12

0

0
American Oil and Gas Reporter - July 2015

Table of Contents for the Digital Edition of American Oil and Gas Reporter - July 2015
