Wells – Processes – Distinct – separate injection and producing wells
Reexamination Certificate
1999-02-15
2001-03-06
Bagnell, David (Department: 3672)
Wells
Processes
Distinct, separate injection and producing wells
C166S250150, C166S306000, C210S096100, C210S696000
Reexamination Certificate
active
06196314
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the production of hydrocarbons from subsurface formations and more particularly to a system and process for preventing plugging of formation fluid passageways caused by the accumulation of insoluble salts precipitates resulting from the interaction between precipitate precursor ions in injection water and resident cations in the subsurface formations.
2. Description of the Related Art
Hydrocarbons, such as oil and gas, are recovered from the earth's subsurface formations through production wellbores that penetrate hydrocarbon-bearing formations or reservoirs. Perforations are made from the production wellbore to the formation to facilitate flow of the hydrocarbons from the hydrocarbon-bearing formations to the production wellbores. Water is sometimes injected under pressure into injection zones formed in the subsurface formations to stimulate hydrocarbon production through the production wells in a field.
Water is injected by itself as a component of miscible or immiscible displacement fluids. Sea water (for offshore wells) and brine produced from the same or nearby formations (for onshore wells) are most commonly used as the water source. Such water usually contains large amounts (concentration) of precursor ions, such as divalent sulfate (SO
4
−
), which form insoluble salts when they come in contact with cations, such as Ba
++
, Sr
++
and C
++
, resident in the formations. The resulting salts (BaSO
4
, SrSO
4
and CaSO
4
) can be relatively insoluble at subsurface formation temperature and pressure. Consequently, such salts precipitate out of the solution. The precipitation of the insoluble salts accumulates and consequently plugs the subsurface fluid passageways. The plugging effects are most severe in passageways in the formation near the injection wells and at the perforations of the production wells. Solubility of the insoluble salts further decreases as the injection water is produced to the surface through the production wells, due to the reduction of the temperature and pressure as the fluids move to the surface through the production wells.
For the purpose of this invention, subsurface or formation fluid passageways includes pores in the formation matrix, fractures, voids, cavities, vugs, perforations and fluid passages through the wells, including cased and uncased wells, tubings and other fluid paths in the wells. The term precipitates means insoluble salts, crystals or scale. The term plugging as used herein means reduction in the porosity and/or permeability of fluid passageways. The term injection water as used herein means any fluid containing water that is injected into a subsurface formation to facilitate recovery of hydrocarbons from subsurface formations.
Mechanical methods, such as passing the untreated water through a nano-filtration membrane, have been used to remove substantial amounts of the precursor ions from the water at the surface before injecting it into the wellbore. Sea water typically contains between 2700 to 2800 ppm of divalent SO
4
−
. The nano-filtration membrane process usually reduces this concentration to between 50 and 150 ppm. Under many subsurface reservoir conditions, such a concentration of the precursor ions produces sufficient amounts of the insoluble salts to plug or seal the formation fluid passageways. Thus, the filtration of the injection water alone by nanofilters, in many cases, is not sufficient to prevent plugging of the subsurface formation passageways.
Chemicals or additives alone are often injected into the untreated water to inhibit the in-situ growth of crystals from insoluble salt precipitation. A variety of additives are injected into the injection water at the surface or directly into an injection well. Production wells are also often treated with back-flow of fresh brine containing additives to prevent plugging of the passageways. Use of chemicals alone can be cost-prohibitive, environmentally unfriendly, and not totally effective, especially when high concentrations of naturally-occurring cations are present in the subsurface formation.
The present invention provides a system and process which simultaneously utilize both a mechanical process and a chemical process to effectively control or prevent in-situ growth of crystals in the subsurface formation, thereby preventing the plugging of the formation fluid passageways.
SUMMARY OF THE INVENTION
The present invention provides a system and method for enhancing hydrocarbon production from a subsurface hydrocarbon-bearing formation (reservoir). The system includes a mechanical fluid treatment unit that substantially reduces the concentration of precursor ions from the injection water. The filtered water (also referred to herein as the “treated water”) is injected under pressure into a zone of an injection well (“injection zone”) to cause the hydrocarbons to flow toward a production well. A chemical control unit injects selected amounts of one or more additives into the treated water at the surface or into the injection zone or well to inhibit in-situ growth of crystals from insoluble salt precipitates formed due to the interaction of precursor ions present in the injected water and ions resident in the reservoir. The selected chemicals and their respective injection amounts are determined at least partially based on reservoir characteristics and the concentration of the precursor ions in the filtered water.
Injection well characteristics, reservoir characteristics and produced hydrocarbon characteristics are determined during the injection process. One or more of such characteristics are then utilized to determine the types of additives and their respective amounts that will continue to inhibit in-situ growth of crystals. These chemicals are then injected into the injection zone. Such adjustments to the chemical injection process are made on an ongoing basis to continuously prevent the accumulation of insoluble salt precipitates in the formation fluid passageways, thereby preventing plugging of such passageways during the injection process. Prediction models are utilized to determine the required chemicals, their respective amounts, and the timing of their injection into the injection wells.
Examples of the more important features of the invention have been summarized above rather broadly in order that the detailed description thereof that follows may be better understood, and in order that the contributions to the art may be appreciated. There are, of course, additional features of the invention that will be described hereinafter and which will form the subject of the claims appended hereto.
REFERENCES:
patent: 3620974 (1971-11-01), Stanford et al.
patent: 3704750 (1972-12-01), Miles et al.
patent: 3965003 (1976-06-01), Stanford et al.
patent: 4537684 (1985-08-01), Gallup et al.
patent: 4580627 (1986-04-01), Argabright et al.
patent: 4633949 (1987-01-01), Crowe
patent: 4723603 (1988-02-01), Plummer
patent: 4830766 (1989-05-01), Gallup et al.
patent: 5002126 (1991-03-01), Carlberg et al.
patent: 5073270 (1991-12-01), Gallup et al.
patent: 5263541 (1993-11-01), Barthorpe et al.
patent: 5346010 (1994-09-01), Adams et al.
patent: 5363915 (1994-11-01), Marquis et al.
patent: 5614476 (1997-03-01), Young
patent: 5622919 (1997-04-01), Brezinski et al.
patent: 6006832 (1999-12-01), Tubel et al.
patent: 2 335 688 (1999-09-01), None
Modern Petroleum A Basic Primer of the Industry, by B. Berger & K. Anderson, 3rd Ed., 1992, PennWell, 236-240.
Bagnell David
Baker Hughes Incorporated
Dawelbeit Kamal
Madan Mossman & Sriram P.C.
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