Wells – Processes – Placing fluid into the formation
Reexamination Certificate
1998-09-14
2001-01-16
Bagnell, David (Department: 3672)
Wells
Processes
Placing fluid into the formation
C166S300000, C166S304000
Reexamination Certificate
active
06173780
ABSTRACT:
This invention relates to oil field chemicals in particular oil field production chemicals and their use.
BACKGROUND OF THE INVENTION
Among oil field chemicals are scale inhibitors, which are used in production wells to stop scaling in the rock formation and/or in the production lines downhole and at the surface. Scaling not only causes a restriction in pore size in the rock formation matrix (also known as ‘formation damage’) and hence reduction in the rate of oil and/or gas production but also blockage of tubular and pipe equipment during surface processing. To overcome this, the production well is subjected to a so called “shut-in” treatment whereby an aqueous composition comprising a scale inhibitor is injected into the production well, usually under pressure, and “squeezed” into the formation and held there. In the squeeze procedure, scale inhibitor is injected several feet radially into the production well where it is retained by adsorption and/or formation of a sparingly soluble precipitate. The inhibitor slowly leaches into the produced water over a period of time and protects the well from scale deposition. The “shut-in” treatment needs to be done regularly e.g. one or more times a year at least if high production rates are to be maintained and constitutes the “down time” when no production takes place. Over the year there is a reduction in total production corresponding to the number of down times during the squeeze/shut-in operation, as well as reduced production as the scaling problem builds up. However, in some instances the scale inhibitor is poorly retained within the reservoir rock matrix and short squeeze lifetimes are experienced. The net result in these cases is frequent well interventions which impact on both well productivity and field profitability.
DESCRIPTION OF THE INVENTION
We have discovered means for and a method of increasing the effectiveness of production chemicals, in particular scale inhibitors, thereby decreasing the number of times squeezing/shut-in is needed and increasing the production rate. Moreover, we have discovered a formulation for this purpose which is stable to storage and transportation.
Accordingly, the present invention is a process for increasing the effectiveness of production chemicals by reducing the number of squeezing and shut-in operations needed to increase the production rate from an oil well, said process comprising injecting into an oil-bearing rock formation matrix a water-miscible formulation comprising:
(a) a water-miscible surfactant which is a glycol ether and
(b) at least one water-miscible oil field or gas field production chemical, said components of the formulation being introduced either as a pre-formed single homogeneous composition, or simultaneously in parallel or sequentially in either order into the rock formation characterised in that after introduction of (a) and (b) into the oil-bearing rock formation matrix, the well is shut-in for a period and, subsequently, the oil-bearing rock formation is over-flushed with an oil.
The glycol ether is suitably an alkyl substituted glycol ether in which the alkyl group may be straight or branched chain and suitably has 3-6 carbon atoms, preferably from 3-5 carbon atoms. The glycol ethers that may be used is suitably a mono alkyl ether of ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol or pentaethylene glycol and is preferably an alkyltriglycol ether and more preferably the alkyl group in the alkyltriglycol ether has 4 carbon atoms and is especially &eegr;-butyltriglycol ether (also known as triethylene glycol mono-&eegr;-butyl ether). More specifically these include inter alia one or more of
Ethylene glycol mono ethyl ether
Ethylene glycol mono-n-propyl ether
Ethylene glycol mono-iso-propyl ether
Ethylene glycol mono-n-butyl ether
Ethylene glycol mono-isobutyl ether
Ethylene glycol mono-2-butyl ether
Ethylene glycol mono-tert-butyl ether
Diethylene glycol mono-n-propyl ether
Diethylene glycol mono-iso-propyl ether
Diethylene glycol mono-n-butyl ether
Diethylene glycol mono-isobutyl ether
Diethylene glycol mono-2-butyl ether
Diethylene glycol mono-tert-butyl ether
Diethylene glycol mono-n-pentyl ether
Diethylene glycol mono-2-methylbutyl ether
Diethylene glycol mono-3-methylbutyl ether
Diethylene glycol mono-2-pentyl ether
Diethylene glycol mono-3-pentyl ether
Diethylene glycol mono-tert-pentyl ether
Triethylene glycol mono butyl ether (&eegr;-butyltriglycol ether)
Tetraethylene glycol mono butyl ether (&eegr;-butyltetraglycol ether) and
Pentaethylene glycol mono butyl ether (&eegr;-butylpentaglycol ether)
Where the formulation comprising (a) and (b) is injected into the rock formation as a pre-formed single composition, said formulation is suitably a homogeneous aqueous solution containing the two components in specific proportions so as to maintain the homogeneity of the formulation.
Thus, in the formulation comprising the two components in aqueous solution injected into the oil bearing rock before the over-flush with oil, (a) is suitably at least one surfactant comprising &eegr;-butyltriglycol ether in an amount of 1-30% w/w and (b) is preferably at least one oil field or gas field production chemical in an amount of 1-25% w/w.
The oil used for over-flush is suitably the oil produced by the well being treated but may comprise diesel or kerosine and is preferably the oil being produced by the well. The amount of oil used for over-flushing the production well is suitably such that it reaches and flushes a target zone which is up to about 6 meters (20 feet) from the well bore and is suitably in the range from about 4800 to 480000 liters (30 to 3000 bbls).
Following the oil over-flush, the well may be optionally subjected to an additional, final over-flush with an oleaginous or an aqueous stream. The oleaginous stream, where used, is suitably kerosine or diesel whereas the aqueous stream is suitably water which may be from fresh, tap, river, sea, produced or formation water, with a total salinity of eg 0-250 g/l such as 5-50 g/l and may have a pH of 0.5-9 and is preferably sea-water.
In another aspect, the present invention is a method of introducing a formulation comprising an oil field or gas field production chemical and a surfactant into a rock formation matrix comprising oil and/or gas, which process comprises (A) passing the formulation down a production well and thereby into before finally over-flushing said well with an oleaginous or aqueous stream.
The invention also provides for the process of the invention to increase the effectiveness of the oil field or gas field production chemical in a rock formation matrix, in particular by increasing the duration of retention of the chemical by the rock formation matrix.
The formulation comprising components (a) and (b) defined above may be a pre-formed homogeneous formulation. By the expression “homogeneous formulation” as used herein and throughout the specification is meant that the formulation is a single phase system. That is, each component is in itself homogeneous and is water-miscible when introduced sequentially or simultaneously into the rock formation matrix and is also homogeneous if introduced into the rock formation matrix as a pre-formed single composition.
It would be apparent that where the components (a) and (b) of the formulation are introduced simultaneously but separately, or, sequentially, it is not introduced as a pre-formed single composition and hence the concept of the formulation being homogeneous does not apply. In the sequential introduction of components (a) and (b), the injected glycol ether (a) may, in most instances, ‘move’ at a lower velocity than the scale inhibitor (b). In such a case, a double slug deployment system could be used. For instance, a slug of glycol ether (a) could be injected into the formation first, followed by a slug of scale inhibitor (b). The two could then be overflushed into the near wellbore in the usual way that scale squeeze treatments are performed. Optionally, a spacer of seawater can be placed between the two parts of the mai
Collins Ian Ralph
Stewart Nevin John
Bagnell David
BP Chemicals Limited
Dougherty Jennifer
Nixon & Vanderhye
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