Wells – Processes – Cleaning or unloading well
Reexamination Certificate
1999-06-23
2001-06-26
Bagnell, David (Department: 3672)
Wells
Processes
Cleaning or unloading well
C166S222000
Reexamination Certificate
active
06250389
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method of oil or gas well stimulation.
BACKGROUND OF THE INVENTION
When an oil well is drilled, drilling fluids are pumped downhole. The drilling fluids serve several purposes. One purpose is to lubricate the drill bit. Another purpose is to carry cutting from away from the drill bit. Yet another purpose is to control pressure within the wellbore.
Papers have documented that these drilling fluids damage the formation by adversely effecting its relative permeability. At an annual technical meeting of the Petroleum Society of CIM in Calgary, May 9-12, 1993 one such paper, paper no. CIM 93-24, was presented entitled “Reductions in the Productivity of Oil and Gas Reservoirs due to Aqueous Phase Trapping”. This paper outlines mechanisms leading to aqueous phase trapping which are caused by the introduction of fluids into the well.
The recognition of this problem has lead to various methods being developed to stimulate oil or gas wells. These methods are used to stimulate a well prior to it being put into production or when production is falling below levels that make the recovery of the oil or gas commercially viable. The most common method of stimulating a well prior to it being put into production is acidizing a well through the use of a “stimulation fluid”. U.S. Pat. No. 5,152,907 which issued to Amoco Corporation in 1992 entitled “Solvent Systems for Use in Oil and Gas Wells” provides background relating to the composition of such stimulation fluids. It should be noted, however, that Paper no. CIM 93-24, lists among the fluids that cause formation damage through aqueous phase trapping, stimulation fluids (including spent acid).
There are various forms of venturi-style pumping apparatus that are presently used for cleaning sand from horizontal sections of unconsolidated reservoirs or pumping from vertical sections of said reservoirs. One example of such a pumping apparatus is U.S. Pat. No. 5,033,545 which issued to Sudol in 1991.
SUMMARY OF THE INVENTION
The present invention relates to a method of utilizing a venturi-style pumping apparatus in a new and unobvious manner to stimulate an oil or gas well.
According to the present invention there is provided a method of oil/gas well stimulation. Firstly, positioning a venturi-style pumping apparatus in a wellbore within a selected production zone of an oil/gas producing formation. The pumping apparatus is connected to a first conduit and a second conduit. Secondly, activating the pumping apparatus to induce a flushing of fluids and contaminants from the oil/gas producing formation into the wellbore. Thirdly, pumping power fluid that powers the pumping apparatus via the first conduit and directing a portion of the power fluid through at least one fluidizing nozzle to sufficiently fluidize contaminants to enable the contaminants to be removed from the wellbore along with pumped fluids by the pumping apparatus via the second conduit.
With the method, as described above, the flushing of drilling fluids and other contaminants from the formation is induced by the creation of a pressure differential. This method is more effective and prevents residual detrimental effects being sustained by the formation as a result of the use of stimulation fluids.
It is preferred that concentric tubing being provided. The power fluid is transported through an inner tube which serves as the first conduit. The pumped fluids are transported through an annulus formed between the inner tube and an outer tube which serves as the second conduit.
A major advantage of the method, as described above, is its ability to treat wellbores that have been completed with slotted tubular liners or perforated pipe. There are a number of variations of slotted liners and perforated pipe presently in use. These include slotted liners and perforated pipe that have been wrapped with a wire, screen, steel wool, and the like. One of the purposes of the slotted liners or perforated pipe is to limit the incursion of particulate contaminants into the wellbore. It is, of course, preferable to induce a flushing of the formation after the slotted liner or perforated pipe is in place so as to limit the incursion of particulate contaminants into the wellbore. Furthermore, once the slotted liners or perforated pipe has been in place for a period of time rust and mill scale develops. This rust and mill scale becomes one of the contaminants that restrict the production of the well. The method, as described above, provides a method of treating the well for rust and mill scale contamination at the same time as formation stimulations is occurring.
The power fluid is selected to be compatible with the formation. Depending upon the dominant fluid in the formation, the power fluid may be either water based or hydrocarbon based. Additives can be included in the power fluid to enhance fluidization of contaminants. Depending upon the nature of the contaminants, the dominant fluid in the formation and the nature of the formation, the additives may include surfactants, gas, or scaling agents. The power fluid may be heated where viscosity of liquids in the formation is of concern of where it may enhance stimulation.
In some cases the production zone has a considerable length. This is common with horizontal well completions. Where the production zone has such a length it is preferred that the additional step be taken of moving the pumping apparatus slowly along the wellbore in a traverse of the selected production zone.
The concentric tubing can pose a handling problem. It is, therefore, preferred that the concentric tubing be unwound from a coil as it is inserted into the wellbore. Similarly, the concentric tubing is wound back onto the coil as it is withdrawn.
The preferred method of fluidizing the contaminants is to place at least one fluidizing nozzle on the body of the pumping apparatus. With wells that have not been completed using slotted liners or perforated pipe, one can expect that some particulate matter is going to be drawn into the wellbore during treatment. In such cases, it is preferred that there be at least one forwardly directed fluidizing nozzle and at least one rearwardly directed fluidizing nozzle. The provisions of such nozzles ensure that the particulate contaminants are sufficiently fluidized to avoid having the pumping apparatus become stuck as it goes in and as it comes out of the wellbore. A valve is preferably provided for switching the fluidizing nozzles on and off. The valve may also have provision to allow switching between the at least one forwardly directed fluidizing nozzle and at least one rearwardly directed fluidizing nozzle.
It is preferred that the monitoring of certain parameters be included when practising the method. There are a number of further steps that can be included, depending upon the results that are desired. The further step of monitoring the flow rate of pumped fluids and determining the flow rate of fluids from the formation by subtracting from the flow rate of pumped fluids the flow rate of power fluid. The further step of sensing pressure in the wellbore while pumping. The further step of sensing temperature in the wellbore while pumping. The further step of monitoring the relative fractions of oil/water/gas/solids present in the pumped fluids. For example, if one key parameter is selected such as pressure; pressure sensing means can be placed into the wellbore along with the pumping apparatus. This enables an evaluation to be made of formation inflow capabilities. The pumping apparatus can then be operated at as low a pressure as the influx of fluids and contaminants during pumping will allow.
To enhance the stimulation effect or to address cases in which the incursion of particulate matter or the inflow of water from particular zones is a problem, it is preferred that a further step be taken of positioning sealing means, such as a packer, in the wellbore to hinder the movement of fluids and solids. This enables selected stimulation to be achieved, without drawing water from a water zone or
Bagnell David
Christensen O'Connor Johnson & Kindness PLLC
Dougherty Jennifer R.
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