Wells – Processes – Producing the well
Reexamination Certificate
2001-06-14
2003-10-07
Bagnell, David (Department: 3672)
Wells
Processes
Producing the well
C166S325000, C166S328000, C166S332800
Reexamination Certificate
active
06629566
ABSTRACT:
FIELD OF INVENTION
This invention relates to an improved method and apparatus for the removal of water from the well-bore of gas wells so as to reduce the hydro static head associated with the produced water and to thus unload the well and permit more efficient production of gas.
BACKGROUND OF THE INVENTION
Numerous gas wells in Alberta, Canada, and throughout the world, produce a minimum of natural gas because of problems associated with water produced with the gas, which accumulates at bottom-hole, and by virtue of its weight provides a hydrostatic back pressure which partially or entirely defeats the ability of formation gas pressure to move well gas to the surface for collection.
There are a number of methods in use to remove water from the well-bore of a producing gas well when the column height of water in the bore produces a hydrostatic pressure greater than the pressure of the gas from formation sufficient to impair production.
The gas in those situations has typically been produced out of a smaller diameter tubing string inserted into the well because the smaller cross-section of the tubing produces higher velocities of gas flow at formation pressures which it is hoped will carry the water out of the well-bore during production and thus “unload” the well.
As a reference, the article “A Practical Approach to Removing Gas Well Liquids” written by E. J. Hutlas and W. R. Granberry (published August 1972 in
Journal of Petroleum Technology
) discusses the history of methods of removing unwanted accumulations of liquids from gas wells. The article states that the best methods for removing liquid from producing gas wells are pumping units, (for shallow fields having very low pressure), liquid diverters, intermitters and gas lifts (for deeper higher-pressure fields), and inserted tubing strings for wells where severe formation damage could result from stopping operations (e.g. well shock).
U.S. Pat. No. 4,265,312 to Thein, METHOD FOR DEVELOPING WATER WELLS, issued May 5, 1981, pertains to a method of developing a water well, but is instructive in that it deals with the introduction of a gas-lift water pump into a well-bore, the pump's action being provided by introduction from surface of high-pressure gas (air, in that case) in an inner tube deployed such that its bottom end is above the bottom end of an outer tube in which the inner tube is centered, and the bottom of both of which tubes are deployed submersed in the well-bore's accumulated water. The pressured gas escapes from the bottom of the inner tube and is collected and exits the well-bore, rising up through the annulus between the pressurized tubing and the second, outer tube, taking with it entrained water from the wellbore (within which the tubes were deployed).
In the Thein patent, the purpose was to provide a gas-lift pumping means with some agitation at the well-bore's bottom end to remove settled solids and improve water flow within a water well. The apparatus is a good example of a form of gas-lift pump (concentrically deployed tubing strings, providing pressurized gas from surface to the inner tube, permitting gas and entrained liquids to exit using the annulus between inner and outer tube as a discharge path).
There are two related prior art downhole pump systems, U.S. Pat. Nos. 3,894,583 and 3,894,814 to Morgan, both issued Jul. 15, 1975, titled ARTIFICIAL LIFT FOR OIL WELLS, which describe a two-chamber down-hole pump apparatus to be removably inserted into an oil well's casing to pump oil from an oil well where production pressure is insufficient to provide lift to surface.
Morgan's '583 patent describes an apparatus and system where the well's casing is isolated by a packing from the production zone and from the pump at bottom-hole to provide a storage tank for compressed air, an accumulator below the packing to collect oil from formation via a check valve which is vented to surface, said vent line being periodically pressurized by connecting tubing and valves to the casing's stored pressurized air to force the collected oil from the accumulator up a secondary tubing string to surface. A piston, pig or swab is deployed below the oil in the production tubing string. The vent/pressure tubing is deployed adjacent/concentrically to said production tubing. Crossover conduits between production tubing/venting tubing are used to switch annulus mid-bore. An electric switch/ball float is deployed in the lower well-bore to sense the accumulator's state (full or not), and to energize an air pump top-hole and electrically switched valves to pressurize the vent tubing.
Morgan's '814 patent describes and claims the same system and apparatus, absent the use of the upper casing as a pressure tank and requiring an electrically actuated 3-way valve and down-hole sensor.
Morgan's '583 patent also describes an embodiment where the accumulator means is formed by a chamber comprised of the well's casing below the packer isolating the upper casing's compressed air storage area from production, and also below a second packer below the perforations in the casing to formation, with a check valve from the thereby isolated production zone of the casing into the accumulator chamber below said second packer, said production and vent tubing extending in a sealed way through both packers and into the accumulator zone.
In U.S. Pat. No. 3,797,968 to Elfarr, issued Mar. 19, 1974 APPARATUS FOR FLOWING LIQUID FROM A WELL, describes a downhole siphon pump apparatus for producing oil from an oil well where formation pressure is insufficient to move oil from bottom-hole to surface, powered by compressed gas from surface. The Elfarr system is comprised of two concentrically deployed tubing stings inserted within the well's casing. The inner tubing string for its length to near bottom carries compressed gas from surface. The annulus between the two tubing strings carries oil from the bottom-hole pump to surface. Near the bottom, the conduits cross-over via cross-over passages in a fitting. At various heights in the production annulus, check valves are deployed to permit upward-only flow of oil. At bottom, a check valve permits oil from the formation in the casing to enter the outer conduit and accumulate in the tubing string's outer annulus. A check valve in the bottom of the inner tubing string, below cross-over and above the lower check valve is deployed permitting oil to flow upward only into the production passageway for pumping. The inner tubing at surface can be pressurized, causing the pressure differential across the check valves at bottom to (a) close communication between the two tubing strings and the casing; and (b) open communication between inner and outer conduits, permitting and causing the accumulated captured oil to flow upward toward the surface. The formation is thus not exposed to higher than bottom-hole ambient pressure. The check valves in the outer production annulus and the system can be cleared by removal of the inner tubing string, which is for most of its length (from surface to cross-over) used only to carry pressurized gas from the surface.
There is thus formed a pump with two chambers deployed up-hole, formed of concentric-tubing strings, cross-over fittings, and check valves, with the removable inner string sitting on nipples and seats on the inner surface of the outer tubing string, for pumping oil from wells using introduced pressurized gas from surface. The pump was designed to move oil to surface in an oil well to enhance production, but it is complex, small-diameter, and requires specialty fittings, seats and nipples, and it has a large number of complex and special-purpose valves. It would interfere significantly with free gas-flow, and while it operates on pressure differentials (a siphon-like function), it is for the specific purpose of pumping oil to surface.
U.S. Pat. No. 4,509,599 to Chenoweth et al, GAS WELL LIQUID REMOVAL SYSTEM AND PROCESS, issued Apr. 9, 1985, describes a system and apparatus for dewatering a gas w
Bagnell David
Bomar T. Shane
Northern Pressure Systems Inc.
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