Tony Martin – DLOnline 21 May - Questions/Answers
Prashant Agarwal
In Case History-5, after Re-Fracking, how long did the
Production sustained? Please share if you have any data.
The case history is documented in SPE 101026. The postrefrac production quoted in the presentation is over the
following periods:Well A – 8 months
Well B – 8 months
Well C – not supplied
Well D – not supplied
There is more information in the paper and I advise
anyone interested in refracturing to read it.
Michael Weber
What specifically make a well a good candidate for
refracture? Two things. First, if the previous treatment
was in any way sub-optimal, due to things like old
technology, size, poor execution or simply poor design
due to lack of formation information. Second, if we have
enough depletion to produce effective stress reorientation, so that the new fracture propagates in a
different direction (see SPE 25464, Ebel and Mack). Not
too much depletion, however, or the well won’t have
enough reserves to justify the expense of the refracturing.
Of course, ideally it’s nice to have both, which makes a
really good refracture candidate.
Abdel Doghmi
Thanks Tony, how does neutral density compare to
"traditional" proppant in terms of stress/conductivity”
can you elaborate on the common criteria for candidate
selection? Technology is developing all the time. Right
now they are stronger/more conductive than API “white”
frac sand, but not as good as the low density ceramics.
Possibly comparable to resin-coated frac sand.
Bo Gao
Muhammad Arsalan
What do you mean by mature fields? A field that has a
significant history of production and is currently, or will
shortly become, uneconomic without some kind of
redevelopment or secondary recovery
Surendra Bateja
Can we take up fracturing in old sick wells? Potentially
yes, but it really depends upon why they’re sick……..
we’re good, but we’re not miracle workers. We can
overcome most things, but if there is insufficient reserves
behind the casing, then the well is not just sick, it’s
terminal. Other big project killers include damaged casing
and excessive perforations, especially if the well has
insufficient economics to justify a workover
Abdel Doghmi
How is channel fracturing different from proppant partial
monoloyer? Channel fracturing – previously known as
“pillar” fracturing – relies on big clumps or pillars of
proppant to keep the fracture propped open around
unpropped flow channels. Partial monolayer replies on
dispersed proppant grains, with the flow being in between
the relatively widely dispersed individual proppant grains.
See SPE 90698, Brannon et al.
Alexander Tyler
When would foamed (N2 or CO2) propped fracturing
apply? Two cases. First, when the reservoir pressure is
very low – too low to successfully recover the treatment
fluid. The energy in the gaseous phase helps recover the
fluid and reduce wellbore hydrostatic head. Second, we
use gas to reduce the water/liquid content of the
fracturing fluid in water/liquid sensitive reservoirs.
Mariene Gutierrez
You mentioned that there is a well-established selection
criteria for candidate fields. Could you give references
where this is presented? See SPE 88604 for an example –
however, the selection criteria are not universal. They
need to be set for each individual field
Prashant Agarwal
Any comment on "Save the frac from being screenout" or
get more from Injectivity/mini frac data?
Taras Popadynets
What is your opinion about gas fracturing method? Good
method, great idea, but limited application unfortunately.
The logistics limit the size of treatment the effects are
very hard to model or predict.
Crystal Hart
How does refracturing compare to EOR for increase
production? How long is a piece of string? Every field is
different and there is no right or wrong solution and no
universal “magic bullets”. EOR might be best for one
field, whilst fracturing nest for another. You need to do
your engineering first.
Amir Khamsehnezhad
Hi Tony, my field of expertise is chemical engineering and
polymers. I am looking into the hydro fracking process to
see if there is any area of improvement for this process.
this is mainly because hydrofracking is being used for
Shale Gas extraction which means this process should be
optimised to its best. Good luck – I don’t want to
discourage you, but be aware that the major service
companies have spent hundreds of millions of dollars
doing exactly that for the last 5 decades. Plus there are
many academic institutions doing excellent research work
for just as long. So make sure you do your literature
searches first or you may spend a lot of time an effort
“discovering” something that is either already shown to
be ineffective, or is patented. And please, don’t us a “k”
and don’t call it “hydro fracking”. It’s hydraulic fracturing,
or fracturing.
Miguel Loya
Case Study 5: In regards to tight gas refracturing
candidates- Did you refrac using nitrogen or CO2 due to
depletion? No – see SPE 101026 for more details
Kristina Arutyunova
How does water conformance frac exactly work in gas
wells with some water influx? It reduces the relative
permeability to water – same as in oil wells.
Viet Le
Hi there, I am just wondering what is your take on the
different between acid treatment and skin frac for the
mature oil field? Generally an acid treatment is easier and
cheaper to perform, but you will get better results from a
skin bypass frac
Raymond Godderij
Question regarding Batch fracturing: What job size can
you pump with a set-up as shown on slide 25, what rates
can be achieved, and does pre mixing of the fluids cause
any issues with the quality of the fluid? In the region of
100 to 300 bbls of slurry, at rates of up to perhaps 8 or 10
bpm. Fluid quality is critical, as is agitation of the slurries
in the batch mixers (depending upon fluid and proppant
type)
Prashant Agarwal
Sick well is a well which is not mechanically able to
produce? I am pretty sure I did not use the term “sick” but
you’re the second question that has asked me this…….
Please refer to the previous answer.
Surendra Bateja
What is the preferred fracture azimuth for injection wells?
Perpendicular to the direction you want the injection
water to sweep through the reservoir.
Raymond Godderij
Question regarding partial monolayer: What type of
Brinell hardness is required to prevent proppant
embedment? Good one – for regular fracturing we say
that if the BH is below 5 or 6 kg/mm2 then embedment
could be a problem. For partial monolayer – where the
“load” is carried by fewer grains of proppant, it would
need to be significantly more than this, probably at least
twice.
Steve Wierenga
Have you experienced enhanced perforating techniques
(dynamic underbalanced, "Frac charge" or reactive)
where they allow easier breakdowns or better fraccing
operations? Mixed. This kind of thing is very formationand wellbore geometry-specific. However, in general the
deeper the penetration of the charge – unless you are
perfectly aligned with the fracture azimuth – the more
tortuosity you will experience. All we need to frac a well is
a hole or holes of sufficient flow area through the casing
and cement. Everything else is marketing.
Abdel Doghmi
You showed refrac giving rate close to initial frac - does
this means the first frac bypassed lots of gas? i.e. poor
initial frac? Probably – either due to the poor initial frac or
re-orientation of the second frac (See SPE 25464, Ebel
and Mack). But to get post-refrac rates like that they had
to be getting into relatively undepleted gas one way or
another.
Raymond Godderij
Question on neutral density proppant: What about the
compressive strength of neutral density proppant. IS it
comparable to "conventional proppant"? See previous
answer above
Brian Chacka
Can you discuss some of the better methods to maximize
refrac success in horizontal wells that were originally
stage frac'd such as diversion tools and techniques? You
discussed using workover, which we used in the Barnett
by cementing an entire wellbore, but are there any other
less expensive methods? – This is a Master’s thesis
question I am afraid. Technology is changing and (mostly)
improving all the time – and this is an area that is
receiving a lot of attention right now. Keep your ears and
eyes open…… Sorry I don’t have a quick snappy one-liner
answer for you Brian!
Muhammad Arsalan
After Secodary recovery can we use the HF?? Depends.
You need the reserves behind pipe no matter whether you
frac before or after EOR. If you do frac after EOR, be
careful you don’t produce a lot of your EOR material out
of the fractured well – in other words, candidate selection
is critical, as you don’t want to be too close to the “front”
of your EOR.
Jessica Iriarte
For the proppant partial monolayer: how is the proppant
hold in the fracture? Same way as any other frac – by the
closure force of the formation on the proppant.
Raymond Godderij
Question on water conformance fracturing: Is there any
statistics available on the success of water conformance
fracturing in gas reservoirs. Not that I am aware of. You
will need to go searching through the published literature
– and remember that people very rarely publish failures.
Prashant Agarwal
Can you tell about Slick water fracs and the kind of
formation it is mostly effective? Another Master’s thesis.
This is a big question, but in general…… Slick water is
low cost and good at producing fracture complexity and
more extensive fracture networks in shales. It is not good
at carrying proppant. Any well where you need to use
high density proppants, or any sand/proppant at more
than about 1.25 ppg in the slurry, you will need a viscous
fluid. You should also not use slick water in higher
permeability formations were you MUST NOT
OVERDISPLACE the treatment
AKSHAY JAGTAP
How does Porosity & Permeability of reservoir rocks
helps in hydraulic fracturing? The same way it does with
every other aspect of producing oil and gas. the higher
the permeability, the faster the well flows and the greater
the porosity, the more reserves you have. All fracturing
does is make it easier for the oil and gas (and water too, if
we are not careful) to get from the reservoir to the
wellbore.
Prashant Agarwal
Slick water fraccz in Very Tight Gas condensate field
What about them? Try to avoid retro-grade condensation
in the fracture – let it happen in the wellbore if possible.
Raymond Godderij
Question on case study 5: Any information on if the initial
frac design with respect to job volumes, proppant size &
volume compare to the refrac designs? Refer to SPE
101026
Muhammad Arsalan
Can we do HF in Lenticullar reservoirs? Yes, if you do
your engineering
Donald Nathan Meehan
Tony, Oneof the concerns I have is how much polymer is
left in the proppant filled created fracture. Since not all
fluid may be recovered and the concentration of broken
polymer in the recovered fluid is low I think we may
recover very little of that gel. How can we measure how
much of the injected polymer materials are recovered?
By taking samples of the flow back fluid and measuring
the polymer (or ploymer fragment) concentration – in a
similar fashion to how we assess the effectiveness and
longevity of scale inhibitor treatments. If you take a series
of samples and make a plot against time you cans ee how
much polymer has been produced back and how much is
still left in the formation. breaker that use insoluble or low
solubility systems are good for this situation, as they tend
to concentrate where the polymer concentrates – for the
same reason. Enzymes are good as well, as they keep
working until all the all polymer is broken, regardless of
their concentration.
Raymond Godderij
Question on costs: When comparing costs between
fracturing in Europe and US could you share how the
relative contribution of the costs vary for similar job sizes.
How much is the difference in costs attributable to
logistics, degree of equipment utilisation on equipment
rental costs and material costs. It depends…. European
fracturing is generally 2 or 3 times the cost per frac. Most
of this is down to equipment utilization (your CAPEX is
similar to the US but you are doing far fewer jobs), but
there is also no getting away from the fact that Europe is
a more expensive place. Everything from wages to fuel
costs more and you generally have to do more to
safeguard the local environment (“greener” fluid systems,
noise control, daylight operations only, etc.)
Frac Pup
How do we approach fracturing unproduced reserves
(higher pore-pressure) when we have high perm layers
that have been depleted? Didn’t I dodge this question
once already……? There’s no magic answer for this one, I
am afraid. These are simply very difficult formations to
fracture. I do have an idea, however, which I will be happy
to share with you some time when you are paying…..