Neftegaz.RU #3-17 ENG

OFS
inhibitor injection. Mutual solvents
(WAW85202 (Baker Petrolite),
ВР-1 (Experimental plant
NefteHim and others) or nonionic
or cation-active surfactant water
solutions are used as liquid mud.
Injection is performed with
maximum flow rate of injected
mutual solvent without hydraulic
fracture in the following sequence:
• cementing unit AC-32 (CA-320),
[АЦ-32 (ЦА-320)], is connected
to the well tube side for injection
of the solution;
• when casing valve is opened,
the required volume of liquid
mud is injected by means of acid
pumping unit. When casing valve
is opened, there will occur only
the borehole cleanout without
affecting the formation;
• delivery of the main volume of
inhibitor is performed by injection
of the inhibitor (lacking volume
after the mutual solvent injection
for displacement of well-killing
fluid from the tubing), it is injected
when casing valve is opened in
order to fill the remaining voidage
of the tubing. Then the injection
is stopped, the valve is closed
and the remaining solution pills in
required volume are injected into
the formation. The 10% inhibitor
solution is used (depending on
the predicted protective effect).
The injection is carried out using
the same unit with maximum flow
rate without hydraulic fracture;
• delivery of the overflush fluid
volume is carried out in order to
push the inhibitor deeper into
the formation. For displacement
of inhibitor solution it is
recommended to use 2% KCl
solution, when injecting water
solution of inhibitor and degassed
oil, when injecting organic
inhibitor solution. The injection
is carried out, when the casing
valve is closed, with maximum
flow rate without hydraulic
fracture.
• response – the well is shut in
for 12 – 24 hours, all works are
suspended in order for corrosion
inhibitor to be adsorbed on the
reservoir formation;
• technological tubing is pulled out
and underground equipment is
lowered;
• well is put into run, then it is put
into operation.
Required quantity of mutual solvent
is calculated by the following
equitation:
where – volume of mutual
solvent for formation washing, m 3 ,
– penetrated-formation
thickness, m.
When the bottom-hole formation
zone is used as a natural dosing
unit, then the empirical rule of "onethird"
is working (same as when
applying salt inhibitors) [2]. This
rule is as follows: the third part of
corrosion inhibitor injected in the
formation is irrevocably adsorbed
on the deposit rock (during the first
few treatments); the third part of
corrosion inhibitor injected in the
formation is subtracted during the
first few days (from 3 to 15) after
start of well performance; and only
the remaining third part of corrosion
inhibitor injected in the formation is
being subtracted for long period of
time.
Therefore, calculation of corrosion
inhibitor weight for injection in
the bottom-hole formation zone
is carried out using the following
formula:
where – concentration of this
corrosion inhibitor in produced fluid
that provide the required protective
effect in the system or corrosion
coupon, mg/l (approximately
g/t); – fluid mass flow rate,
m 3 /d (approximately t/d); –
estimated time of corrosion inhibitor
subtraction from the formation, d;
1,000 – factor for conversion of
grams into kilograms; 3 – coefficient
of "one-third" rule.
Overflush fluid volume , m 3 , is
calculated by the following formula:
where – effective formation
porosity, unit fraction; – internal
radius of ingress of burned inhibitor
solution in the formation, m. It is
taken as 1.5 – 2.0 m and is specified
based on the results of observation
over the duration of reagent
subtraction; – formation
thickness, m; – tubing volume,
m 3 ; – volume of production casing
from pump suction or tubing intake
to bottom perforations, m 3 ; = 3,14.
If well-killing fluid volume is 130 m 3 ,
then overflush fluid volume will be
0,2 · 3,14 · 1,5 2 · 500 + 130= 840 m 3 ; in
this case the well protection time will
be not less than 365 days.
When installing the block-pills, the
squeezing process is carried out till
their installation by squeezing the
reagent through the tubular annulus.
Technology of intermittent
dosing of inhibitor into the
casing annulus
Technology of well treatment using
the method of intermittent injection
of corrosion inhibitor solution into
the casing annulus is simpler
compared to the technology of
inhibitor solution injection into
the bottom-hole formation zone
described above. Partly therefore,
the method of inhibitor injection
into the casing annulus is more
common. Corrosion inhibitor is
delivered to casing annulus in form
of 10% solution in oil or water.
The advantage of this technology
compared to the technology of
inhibitor solution injection into the
bottom-hole formation zone is that
batch treatments can be carried out
during well operation, and not only
when the wells are being serviced.
The disadvantage of this technology
is the necessity of more frequent
(in average 1 time per 30 days)
treatments [3].
The technology of intermittent
dosing of inhibitor into the casing
annulus solves the following main
problems:
• protection of well underground
equipment against corrosion with
time between repairs of more than
60 – 150 days.
• protection of working level casing
column against corrosion;
• corrosion inhibitor saving (due to
the absence of required adsorption
on the deposit rock).
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