Downhole Surge Tools

SUMMARY OF THE INVENTION

The invention has as its objective to provide the means whereby an oil or gas well can be completed efficiently, utilizing the natural reservoir energy to bring the well in, while simultaneously expelling damaging fluids and solids that may have invaded the pay zone during drilling, cementing and perforating operations. Use of the tools allows for the well to be perforated for maximum reservoir penetration, in acid, removing the guns, attaching the apparatus to the production tubing, then floating the production tubing into the well dry. A retrievable production packer is run above the surge tool assembly and the well completed. A recoverable bar is then dropped down the tubing to knock out a unique surge plug from a unique steel nipple. The bar and plug fall away, leaving the tubing fully open, with no internal restrictions. A split second after impact, the hydrostatic pressure below the packer is relieved, which in turn releases the potential reservoir energy. The natural reservoir pressure is thus applied across each casing perforation to expel perforating damage, acid, cement and drilling fluid invasion. A dynamic flow then occurs up the dry tubing.

The knock-out plug surging method is essentially fail-safe, both with regard to successfully running the tubing dry, and being able to expel the plug. The surge plug and nipple can be pressure tested before use. Hydrostatic testing of the tubing can be accomplished while completing the well. The surge tools cannot open prematurely, while being lowered into a well. Surging, or opening the tools can be accomplished only by knocking out the plug with an appropriately weighted object applied from above, or by pumping fluid down the tubing at a nominal pressure. After the plug is ejected by impact of the bar, both bar and plug fall safely below the production apertures of a catcher sub and remain therein. Where the catcher sub is not utilized, the bar falls into the well casing. The unique construction of the plug prevents the high velocity flow stream of the surge from jamming the plug back into the nipple.

Adoption of this apparatus is desirable, but not limited to, wells having fluid sensitive formations. Other benefits from the use of the surge tools include: reduced completion time and expense; increased assurance of zone isolation from proximal water and lower breakdown pressures when subsequently stimulating. Lower stimulation pressures reduce the risk of hydraulic fracturing out of zone. The surge tools are also adaptable to clean-up of existing wells and to more successful casing recoveries in abandonment procedures. The apparatus is not generally suited to wells known to have low permeability or low pressure in the pay zone.

The best of the known prior art is represented by the patents to Bramlett, U.S. Pat. No. 3,095,040; to Courtney, U.S. Pat. No. 3,003,565; and to Bielstein, U.S. Pat. No. 2,776,015, as well as to Vann, U.S. Pat. No. 3,812,911. See also New Backsurging Cleans Even Old Perforations by Emmett F. Briezer - WORLD OIL, June 1978.

Bramlett's apparatus requires a breakable relief plug positioned above a bevelled, full diameter sealing plug. In Bramlett, the bevelled plug is secured in place by hydrostatic pressure applied across the full cross-sectional area of the plug, necessitating the use of the breakable plug to relieve the high sealing pressure due to the hydrostatic effect. In contrast, the surge plug of this invention is secured in place by hydrostatic sealing pressure acting across the significantly smaller cross-sectional area of the inner diameter of the nipple, thus eliminating the need for initial pressure relief. As a result of the smaller hydrostatic effect, and the uniqueness of the present plug and nipple construction, the pressure is relieved simultaneously with the plug's being ejected by the weighted bar. This occurs as a result of the water flowing upward along the plug, through the courses and relief groove therein, and into the large nipple bore. The Bramlett invention, in further contrast, was developed for preparing a well for through tubing perforating, whereas the device of the present invention is adapted to wells which have already been perforated by guns which shoot deeper into the rock, resulting in better well completions. The present invention is thus adapted for applications where perforation at high differential pressure is desirable. Additionally, in operation under the present method, one may employ the catcher sub, a feature not described or considered in the Bramlett concept. It is further considered impossible for use on Bramlett's tool as described in U.S. Pat. No. 3,095,040.

In the drawings:

FIG. 1 is a view of invention in side elevation showing the disposition of the assembly in the bottom of a well.

FIG. 2 is an enlarged side elevation of the nipple, the attached nipple being in vertical section.

FIG. 3 is a view in perspective of the surge plug.

FIG. 4 is a vertical sectional view of the entire nipple-plug-catcher sub assembly taken along the lines 4--4 of FIG. 1.

Referring to the drawings, the basic elements comprising the assembly include the surge plug 100 and its associated nipple 150, together with the optionally useable catcher sub 200. Although the plug may be formed of a mild steel, it is preferably fabricated from high strength aluminum, owing to desirable solubility in acids. The plug is circular in horizontal cross-section, having a rounded impact surface 110 beneath which are plural annular grooves 112 for seating O-rings 114. As indicated, the diameter of the plug at the top is slightly less than the inside diameter of the central portion of the nipple 150, the O-rings providing a secure hydrostatic seal between the plug and the nipple while the tools are being positioned in casing 190. It is desirable to have two in-line O-ring seals so that the plug will be balanced, irrespective of distortional hydrostatic forces applied by back surging pressures. Immediately beneath the O-ring grooves is the relief groove 116. This has connection with the courses 122, four of which are disposed at quadrant positions of the plug. The courses terminate at 124 adjacent the abutment or shelf 126. As mentioned, the plug has a smaller upper diameter, commencing with the bottom of the rounded impact surface 110, this diameter extending one-third the overall length of the plug. The lower two-thirds of the plug are, as shown, of greater diameter. The courses 122 are cut along the length of this lower two-thirds of the plug from the flat, circular bottom thereof upward, connecting with the relief groove 116 which is cut around the plug's smaller circumference. Bores 128 are drilled axially upwardly into the plug from the flat bottom to a horizontal center line of the relief groove 116. These bores 128 are preferably five in number, four being disposed at positions which are oriented at 45.degree., relative to the location of the courses 122 and one being disposed axially at the center of the plug.

Nipple 150 is provided with a long interior top portion 152 which is tapered outwardly, the nipple having a threaded outer portion which is adapted to engage the coupling 160. As shown, the long tapered nipple bore 152 is adapted to guide a conventional drop bar, not shown, to the dome of the plug. Adjacent the lower end of the nipple 150 is an abutment or shoulder 154 for continuously seating the corresponding shelf 126 of the plug thereon; to fix its upward position as shown in FIG. 2. Also at the bottom of the nipple 150 is a thread 156 which corresponds to the connected coupling 212 of an optionally usable catcher sub 200.

As the plug and nipple assembly are lowered below the existing surface of the liquid in the well casing 190, hydrostatic forces will act upward through the courses 122 of the plug inside the lower nipple bore and up to the lowest O-ring sealer 114, the magnitude of the hydrostatic forces naturally increasing with the depth of submergence of the tool. These upward forces are applied to the smaller horizontal cross-sectional area of the nipple tending to literally pull or lift the plug upward against the restricting shoulder 154 of the nipple bore, the O-ring seals 114 preventing well fluids from entering the tubing 180 prematurely. See FIG. 1.

As earlier indicated, the catcher sub 200 and its attachment to the plug-nipple assembly is optional; for example, where it may be desirable to pull the tubing 180 after surging. As best shown in FIG. 4, the catcher sub 200 is adapted to attachment to the lower end of the surge nipple 150 by means of the coupling 212, said coupling engaging the corresponding threaded portion 156 of the nipple. The catcher sub is provided with production apertures 210 and a hydraulic pressure relief port 220 at the bottom. If, as in operating shallow wells, the catcher sub may not be desirable, the drop may be recovered, if its removal is necessary, by wire line and appropriate fishing tool. In such instances, and because of the construction material and design, the plug is readily drillable or destructible in time by acid or other corrosive well fluids. Such is the utility of the bores 128, reference FIG. 3. In the operation of deeper wells, wherein a given surge may result in a high velocity fluid flow, the plug is so constructed that as the drop bar falls below the plug, reentry and jamming of the nipple by the plug, due to the flow stream will not occur. Where the catcher sub is utilized in such wells, the drop bar shoves the lightweight, asymmetrical plug past the production apertures 210 of the catcher sub 200 to a final state of rest in the sub. As the tubing 180 is removed from the well, the bar and plug 100 are thereby recovered and all tools are reusable.

The downhole surge tool assembly herein may include connecting the catcher sub to the nipple as indicated in FIG. 4, after the plug has been inserted therein. In operation, these interconnected and coactive tools are then lowered into a well such as may have been perforated as at 191, in acid, by a deeply penetrating gun. Above the surge tool assembly comprising the elements 100, 150 and 200, the production packer 170, other production tools and production tubing 180 are interconnected, all while hydrostatic testing is being undertaken, if testing is desirable. The tubing 180 is floated into the well dry, the packer is set above the casing perforations 191 and the well is then completed. The tubing outlet may then be connected to a secure flow line before surging the well. Completion surging is accomplished by dropping a bar of appropriate size and weight such that it will fall through the tubing and strike the plug 100 with a force which is sufficient to eject the plug. The conventional retrievable bar, not shown, must have an adequate weight which, upon striking the plug, develops sufficient kinetic energy to overcome the work necessary to expel the plug from the nipple. Where the use of a drop bar becomes undesirable, the plug may be ejected by pumping a suitable volume of fluid down the tubing at a pressure which is sufficient to balance the hydrostatic head at the plug and to overcome the friction of the O-ring seals. When the plug has been ejected, the tubing is fully opened, having a diameter which is no smaller than an appropriately sized API seating nipple.