U.S. patent number 3,863,717 [Application Number 05/437,651] was granted by the patent office on 1975-02-04 for methods for forcing a liquid into a low pressure formation.
This patent grant is currently assigned to Compagnie des Services Dowell Schlumberger. Invention is credited to Robert Ernest Cooper.
United States Patent |
3,863,717 |
Cooper |
February 4, 1975 |
METHODS FOR FORCING A LIQUID INTO A LOW PRESSURE FORMATION
Abstract
A method for driving a well fluid column indicating a liquid
chemical agent into a low-natural pressure formation containing oil
and gas, through the use of a lightweight foam as the driving fluid
so that, after this driving, the low pressure within the formation
will be sufficient to force the foam out of the well thereby
allowing the oil and gas production of the well to resume
naturally. This method is applicable for the stimulation of wells
having a low-natural pressure formation.
Inventors: |
Cooper; Robert Ernest (London,
EN) |
Assignee: |
Compagnie des Services Dowell
Schlumberger (Paris, FR)
|
Family
ID: |
9113348 |
Appl.
No.: |
05/437,651 |
Filed: |
January 29, 1974 |
Foreign Application Priority Data
|
|
|
|
|
Jan 16, 1973 [FR] |
|
|
73.01379 |
|
Current U.S.
Class: |
166/279;
166/305.1; 166/310 |
Current CPC
Class: |
E21B
41/02 (20130101); E21B 21/16 (20130101); E21B
43/25 (20130101) |
Current International
Class: |
E21B
21/00 (20060101); E21B 21/16 (20060101); E21B
41/02 (20060101); E21B 43/25 (20060101); E21B
41/00 (20060101); E21b 043/25 () |
Field of
Search: |
;166/273,274,279,303,304,310,311,312,307,308,35R,309 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Novosad; Stephen J.
Assistant Examiner: Suckfield; George
Attorney, Agent or Firm: Roylance, Abrams, Berdo &
Kaul
Claims
We claim:
1. In a process for treating wells extending from the surface of
the earth to a reservoir formation from which oil having a gas in
solution therein is produced, the steps of:
injecting into the well a sufficient volume of a liquid chemical
agent adapted to stimulate said reservoir formation;
injecting a sufficient column of stable foam into the well under
sufficient pressure to drive the column of liquids then present
into the well back into the reservoir formation;
terminating pressure injection of said foam into said well when at
least a substantial portion of said column of liquids has been
forced back into said formation;
closing said well at the surface for a desired period of time;
and
opening the well and allowing said foam column and eventually the
remaining portion of said column of liquids to rise normally under
the influence of formation pressure, thereby ejecting said foam as
a column formed by a mixture of liquid chemical agent and of oil
and gas in solution rises within said well.
2. The process of claim 1, wherein the volume of foam that is
injected into the well is sufficient to force all of the liquids
within the well back into the formation without injection of any of
the foam into the formation.
3. The process of claim 1, wherein said well is maintained closed
for a sufficient period of time to enable the liquid chemical agent
forced into the reservoir formation to increase the formation
permeability by a convenient coefficient.
4. The process of claim 1, including the method steps of injecting
a quantity of gelatin into said well prior to said injection of
foam.
5. The process of claim 4 including the further step of injecting a
quantity of water into said well prior to said injection of
foam.
6. In a process for treating a well casing with a liquid chemical
agent, which casing extends from the surface of the earth to a
formation from which an oil/gas solution is produced, and wherein
the pressure of the formation is insufficient to raise a column of
degasified oil, the steps of:
injecting a quantity of gelatin into said well to prevent any
substantial mixing of the oil and gas solution with the chemical
agent;
injecting a desired quantity of said chemical agent into said
well;
injecting a second quantity of gelatin into said well to prevent
any substantial mixing of said chemical agent and a foam;
injecting a sufficient column of stable foam into the well under
sufficient pressure to drive the column of oil standing in said
well back into said formation, the hydrostatic pressure developed
at the level of the formation by the column of oil/gas solution,
gelatin, chemical agent and foam being less than the formation
pressure;
terminating pressure injection of said foam into said well when the
second quantity of gelatin has reached a convenient depth in the
well;
releasing the pressure at the well head of the well and allowing
the column of foam, chemical agent, gelating and oil gas solution
within said well to rise under the natural influence of formation
pressure.
Description
FIELD OF THE INVENTION
This invention relates generally to the production of oil and gas
from low-pressure oil and gas bearing earth formations and relates
more specifically to work-over operations on low-pressure oil and
gas wells. The invention is specifically directed to a new method
for injecting or driving well fluid back into low-pressure earth
formations as well as to derived methods concerning more
particularly the stimulation of wells which would have been
unproductive after a conventional stimulation operation because of
insufficient formation pressure.
BACKGROUND OF THE INVENTION
The injection of various fluids into oil and gas bearing formations
in order to improve the production of a well extending to the
formation is a stimulation method well-known to those skilled in
the art. When the formation pressure is higher than the hydrostatic
pressure generated by the driving fluid present in the well, there
is no problem in immediately restoring the production of the well
after releasing the pressure of the driving fluid, simply because
the higher formation pressure simply ejects the column of fluid
from the well and production of well fluid begins. That
conventional stimulation method is not applicable without killing
the well when the formation pressure is lower than the hydrostatic
pressure generated by the driving fluid present in the
bore-hole.
Likewise, when the formation pressure is relatively low and the
well flows only as a result of the presence of dissolved gas or gas
in bubbles in the oil, a problem arises whenever the production of
the well is stopped and the oil has time to degasify. In this case,
the gas gathers at the top of the well while the level of the
increasingly degasified oil drops gradually. If, at that moment,
the well is opened, the gas escapes and the well is unproductive
owing to insufficient formation pressure, that is to say, the
hydrostatic pressure of a degasified oil column having a height
lower than the depth of the well is then balancing or overbalancing
the formation pressure, depending upon the permeability of the
formation. The recompletion of wells which are unproductive owing
to insufficient formation pressure is so difficult and costly that,
in certain regions, it may be more desirable to continue production
and burn the produced oil and gas rather than cease production if
it is at all possible to do so.
One method for recompleting a well which is unproductive owing to
insufficient formation pressure consists of reinjecting the
degasified oil into the formations by means of a driving fluid
consisting of a neutral gas (natural gas or liquefied nitrogen)
injected under pressure into the well, the use of air being ruled
out because of the risk of explosion. This method has certain
drawbacks, in particular that of being costly and of requiring
relatively cumbersome liquid gas tanks. Moreover, owing to the very
low hydrostatic pressure generated by the gas, it requires
relatively high injection pressure with all the attendant safety
problems involved.
Accordingly, it is a primary object of the present application to
provide a novel method for stimulating and treating low-pressure
oil and gas producing wells wherein a light-weight compressible
medium is injected into the well under sufficient pressure to drive
the well fluid column standing in the well back into the formation
where it will regasify, thereby enabling production to begin
naturally as soon as the pressure on the well is released.
It is also an important object of the present invention to provide
a novel method of injecting a compressible light-weight medium into
a well wherein the compressible medium is generated through the use
of low-cost materials and through the use of low-cost injection
apparatus.
Another feature of the present invention is the provision of a
novel method for stimulating and treating low-pressure oil and gas
wells wherein stimulation operations may be accomplished readily
and simply without creating the hazards that are attendant other
methods of well stimulation.
It is also a feature of the present invention to provide a novel
method for stimulating and treating low-pressure oil and gas wells,
which method is of simple nature, is reliable in use and low in
cost.
Other and further objects, advantages and features of the present
invention will become apparent to one skilled in the art upon
consideration of the written specification, the attached claims and
the annexed drawings. The form of the invention, which will now be
described in detail, illustrates the general principles of the
invention, but it is to be understood that this detailed
description is not to be taken as limiting the scope of the present
invention.
SUMMARY OF THE INVENTION
The present invention provides a novel method for stimulating and
treating low-pressure oil and gas wells which may conveniently take
the form of injecting a light-weight driving fluid into such wells
under sufficient pressure to force at least a substantial portion
of a column of liquid formed by a mixture of a chemical agent and
crude oil standing in the well back into the formation and closing
the well at the surface where the column of light-weight fluid will
prevent production fluid from rising within the well. After the
well has been closed for a desirable period of time and resumption
of production is desired, the pressure at the well head will be
released and the formation pressure, being sufficient to raise the
column of light-weight fluid, will eject the light-weight fluid and
liquid chemical agent from the well and oil and gas will then be
produced in normal manner by the pressure of the formation. The
light-weight fluid may take the form of a foam fluid that is mixed
at the well site through the use of simple foam mixing apparatus.
Gelatin liquid separators may be utilized if desired to separate
the foam and/or the crude oil from any of the chemical agents.
BRIEF DESCRIPTION OF THE DRAWING
So that the manner in which the above recited features, advantages
and objects of the present invention, as well as others which
become apparent, are attained and can be understood in detail, more
particular description of the invention, briefly described above,
may be had by reference to the embodiment thereof which is
illustrated in the appended drawing, which drawing forms a part of
this specification.
It is to be noted however, that the appended drawing illustrates
only a typical embodiment of the invention and is, therefore not to
be considered as limiting of its scope, for the invention may admit
to other equally effective embodiments.
IN THE DRAWING:
The unigue FIGURE is a pictorial schematic representation of an oil
and gas well extending to an oil bearing earth formation and having
a tank of liquid chemical agent and a foam generating apparatus
both connected to the well head of the well and arranged for
injection of chemical agent and foam into the well.
DESCRIPTION OF THE PREFERRED EMBODIMENT
A compressible, low-density medium such as foam (emulsion of a gas
- air for example - in a high-surface tension liquid) has been used
as a circulation fluid either for the drilling of wells or for the
cleanout of well debris. It will be noted that in the case of an
air foam, there is no danger of explosion because the air is then
in the form of small bubbles trapped in liquid film which forms the
continuous phase of the emulsion. The use of foam as a circulation
fluid has been described in different publications and more
particularly in the U.S. Pat. Nos. 3,463,231 and 3,410,344.
Up to the present time, foam has not been proposed as a driving
fluid for the stimulation of wells in low-pressure earth
formations. The present invention relates precisely to the
conditions for the use of foam in such well stimulation
operations.
The equipment necessary for foam production is well known to the
prior art and is exemplified schematically in the FIGURE. It
consists primarily of two alternately employed tanks 10 and 12
containing a high-surface-tension liquid (sweet or salt water to
which is added a surfactant - 1 to 2 percent in general - or even
oil) in which tanks are immersed two conduits connected by a
change-over valve 14 at the inlet of a foam compressor or pump 16
which can, for examle, by means of a gearbox 17 and a motor 19,
generate two constant volume flow rates respectively V.sub.1 and
V.sub.2 dm.sup.3 /min, with a maximum output pressure of P.sub.l
kg/cm.sup.2. It also includes an air compressor 18 with a variable
delivery (for example from U.sub.1 to v.sub.2 m.sup.3 /min) also
having a maximum output pressure of P.sub.g kg/cm.sup.2. In the
case where the natural gas (or any other gas, and in particular
nitrogen) in liquid form or under pressure is available in the
well, the use of such a compressor is not necessary. In addition to
the pump and the compressor, foam generating equipment comprises a
mixing chamber 20 of elongated cylindrical form one end of which
has two inlet pipes 22 and 24 and the other end one outlet pipe 26.
This chamber is filled with slightly compressed stainless metal
chips intended to ensure the effective mixing of the liquid and of
the gas respectively delivered by the pump and the compressor to
the two inlet pipes so as to produce a good quality foam.
A given foam is characterized by its liquid mass concentration
.phi.. In other words, if water is injected into the mixing chamber
of a foam generator, to which is added a surfactant with a mass
flow of M kg/min and air with a mass flow of m kg/min, there is
obtained, at the output, a foam with a liquid mass concentration
.phi. = M/ (M+m). By way of example, for M = 200 kg/min and m = 26
kg/min (or a volume flow rate of 20 m.sup.3 /min at atmospheric
pressure), there is obtained a foam with a concentration .phi. =
0.885 and a mass flow rate D.sub.m = 226 kg/min. By varying the
relative mass flow rates of the surfactant-containing liquid and of
the gas, stable foams may be obtained (i.e., conserving their
physical properties for at least 10 hours or so) from a liquid mass
concentration .phi. of about 0.7 up to .phi. = 0.98 which, for air
and water, corresponds to volume ratios of 330 and 16 respectively
under ambient conditions.
When it is desired to treat a well as 27 with chemicals to
stimulate production or to accomplish any other desirable result
using foam as the driving fluid to force the chemicals to the
desired location within the well or formation, the following
procedure is used. After ceasing production of the well and shortly
thereafter (before degasifying of the oil) a suitable volume of the
treating chemicals may be injected from a tank 28, through a pump
30 and a pipe 32 into the well (a few cubic meters for example), so
that the same volume of oil is consequently reinjected into the
formation 33. Instead of continuing to pump chemicals, degasified
oil or water, all of which are fluids that, owing to their high
densities, may cause the well to become unproductive due to
insufficient formation pressure, foam is utilized as the injection
medium. The paratmeters of the foam to be injected (concentration
and amount of foam) are then determined according to the particular
characteristics of the well. When all the liquids (chemicals and
crude oil) initially contained in the well have been injected or
reinjected into the formations under the force of the foam, an
interval sufficient to allow the chemicals to act is then observed.
After this interval, the valve of the well is opened and the
natural recompletion conditions of the well are met, since the
formation pressure is then higher than the hydrostatic pressure
generated by the foam column.
Another utilisation of the method according to the invention is
also of value. It concerns the application of a corrosion
inhibiting or descaling product, depending on the case, to the
metallic casing of the well. Such inhibiting products are liquid
chemical compositions well known to the art. As the density of
these liquids is relatively high, in order to prevent them from
falling to the bottom of the well in the form of drips of varying
size, during a first phase, there may be introduced into the well,
by pumping, a separating plug made up of a certain amount of
gelatin which, owing to its very high viscosity, remains at the
surface of all liquids (whatever their density). During a second
phase, the volume of inhibiting product considered necessary in
accordance with the height of the well to be treated may be pumped
into the well. During a third phase, a second gelatin plug may be
introduced into the well by pumping.
These three phases typically take no longer than an hour or two,
i.e. a time sufficiently short so that the oil present in the well
does not have the time to degasify significantly. At the end of the
said third stage, pumping of foam may be begun. The liquid mass
concentration and the amount of the foam to be injected into the
well will be determined again from the particular characteristics
of the well. When the first gelatin plug has been lowered to the
convenient depth, under the action of the foam injected into the
well, it is sufficient to stop this injection and to open the head
valve in order for the well to begin producing immediately.
Owing to the process according to the invention the chemical
composition is regularly applied as a coating upon the casing wall.
Besides during the injection then the ejection of the foam into and
from the well, such a coating is not eroded because of the low
viscosity of said foam.
Another procedure would consist, preferably after having introduced
a gelatin plug into the well, of pouring into the well a sufficient
volume of water to generate a make-up hydrostatic pressure which
would proportionately relieve the injection pressure then required
from the foam generator, provided however that the final
hydrostatic pressure generated at the reservoir formation level is
lower than the formation pressure.
It is seen, therefore, that the present invention is one well
adapted to attain all of the objects and advantages hereinabove set
forth, together with other advantages which will become obvious and
inherent from a description of the apparatus itself. It will be
understood that certain combinations and subcombinations are of
utility and may be employed without reference to other features and
subcombinations. This is contemplated by and is within the scope of
the present invention.
As many possible embodiments may be made of this invention without
departing from the spirit and scope hereof, it is to be understood
that all matters hereinabove set forth or shown in the accompanying
drawings are to be interpreted as illustrative and not in any
limiting sense.
* * * * *