Patent Application
20130043030
1. Field of the Invention
The present invention relates to processes and systems for fracturing a subterranean environs after significant movement of tubulars in a well bore have occurred, and more particularly, to processes and systems for fracturing a subterranean environs wherein a fracturing fluid is used to set packers adjacent an opening in tubing positioned in a subterranean well bore and to fracture a subterranean formation.
2. Description of Related Art
In the production of fluid from a subterranean well, a well bore may be drilled in a generally vertical, deviated or horizontal orientation so as to penetrate one or more subterranean formations. The well is typically equipped by positioning casing which may be made up of tubular joints into the well bore and securing the casing therein by any suitable means, such as cement positioned between the casing and the walls of the well bore. Thereafter, the well may be completed in a typical manner by conveying a perforating gun or other means of penetrating casing to a position that is adjacent the subterranean formation of interest and detonating explosive charges so as to perforate both the casing and the subterranean formation. In this manner, fluid communication may be established between the subterranean formation and the interior of the casing to permit the flow of fluid from the subterranean formation into the well. Production tubing that is equipped with a packer for sealing the annulus between the casing and the production tubing may be run into the well. Care must be taken in lowering the production tubing through the fluid that is present in the well. If the velocity of formation fluid passing the production packer as the production tubing is lowered into the well is too great, the occurrence of severe suction effects or swabbing may cause deformation of the packer resulting in premature setting thereof. Accordingly, care is taken to either lower the production tubing within the well at a low enough rate to ensure against premature setting due to swabbing or to employ a packer that is designed with means, for example internal flow paths and/or mechanical locking mechanisms, that allow it to be lowered at higher speeds. Once positioned in the well, the elastomeric sealing element of the packer can be mechanically or hydraulically expanded into sealing engagement with the casing. Fluid produced from the subterranean formation into the casing can be produced to the surface via the production tubing.
Alternatively, a well may be completed as an “open hole”, meaning that intermediate casing is installed and secured within the well bore by conventional means, such as cement, but terminates above the subterranean formation of interest. Typically, a tubular liner may be positioned within the well bore along the subterranean formation of interest and may be anchored to the intermediate casing near the end of the liner proximate to the well head. As positioned within the well, cement is not employed in the annulus between the tubular liner and the well bore. The well may be subsequently equipped with production tubing or casing and conventional, associated equipment so as to produce fluid from the subterranean formation of interest to the surface. As with a fully cased well, the lower casing or tubular liner may be equipped with one or more packers on the exterior thereof. This well system may also be used to inject fluid into the well to assist in production of fluid therefrom or to inject fluid into the subterranean formation to assist in extracting fluid therefrom.
Further, it is often desirable to stimulate the subterranean formation of interest to enhance production of fluids, such as hydrocarbons, therefrom by pumping fluid under pressure into the well and the surrounding subterranean formation of interest to induce hydraulic fracturing thereof. Thereafter, fluid may be produced from the subterranean formation of interest, into the well bore and through the production tubing and/or casing string to the surface of the earth. Where it is desired to stimulate or fracture the subterranean formation of interest at multiple, spaced apart locations along a well bore penetrating the formation, i.e. along an open hole, isolation means, such as packers, may be actuated in the open hole to isolate each particular location at which injection is to occur from the remaining locations. Thereafter fluid may be pumped under pressure from the surface into the well and the subterranean formation adjacent each isolated location so as to hydraulically fracture the same. The subterranean formation may be hydraulically fractured simultaneously or sequentially. Conventional systems and associated methodology that are used to stimulate subterranean formation in this manner include swellable packer systems with sliding sleeves, hydraulically set packer systems, ball drop systems, and perforate and plug systems.
In conventional open hole operations, many if not all of the isolation packers deployed on a tubular liner may be set substantially concurrently. For example, an isolation packer may include an elastomer which swells upon contact with liquid, such as formation liquid, drilling liquid or other liquids injected into the well. As these packers are set prior to injection of fracturing fluid through the production casing or tubing, the subsequent injection of fracturing fluid at relatively high rates and pressures balloons the tubular liner outwardly thereby causing the same to contract in length. Further, the injection of fracturing fluid from the well head at generally ambient temperatures, e.g. 60° F. to 70° F., and at relatively high rates does not allow sufficient time for the fracturing fluid to warm up to bottom hole temperatures, e.g. 250° F. Thus, the relative cool fracturing fluid causes the tubular liner to contract in length even more. Such contraction, which can amount up to 10 feet or more in length, often may damage the packers that were previously set thereby causing the packers to fail, i.e. leak, thereby allowing fluid communication around the packer in the annulus between the tubular liner and walls of the open hole. Also, the relatively high pressure at which the fracturing fluid is injected often causes the set packers to fail. Previous methods employed to mitigate the effects of such tubing movement, such as the use of expansion joints in the tubular liner, are expensive and have not proved to be reliable. Accordingly, a need exists for processes for stimulating intervals of a subterranean environs at spaced apart locations which minimizes failure and damage to packers used to isolate intervals that may occur due to tubing movement.
To achieve the foregoing and other objects, and in accordance with the purposes of the present invention, as embodied and broadly described herein, one characterization of the present invention may comprise a process wherein a first volume of fracturing fluid is pumped through at least a portion of tubing positioned in a subterranean well bore at a velocity sufficient to deform at least one packer that is carried on the tubing into sealing engagement with the well bore. Thereafter, the first volume of fracturing fluid is pumped at a pressure sufficient to fracture a subterranean environs.
Another characterization of the present invention may be a process for pumping a stimulation fluid through a liner positioned in an open hole of a subterranean well, wherein each packer that is positioned on the exterior of the liner is not set until substantially all movement of the liner due to a change in temperature and pressure has occurred.
A further characterization of the present invention may be a process for pumping a first volume of fracturing fluid within an annulus formed between a subterranean well bore and a tubular positioned within the subterranean well bore at a velocity sufficient to deform at least one first packer into sealing engagement with the well bore. Thereafter, at least a portion of the first volume of fracturing fluid may be pumped into the subterranean environs in proximity to the at least one first packer at a pressure sufficient to fracture the subterranean environs.
A still further characterization of the present invention may be a process for actuating at least one packer into sealing engagement with a subterranean well bore adjacent a first opened port in a tubular positioned in the subterranean well bore. The tubular has a plurality of closed ports and packers adjacent to each of the plurality of closed ports which are not actuated
The accompanying drawings, which are incorporated in and form a part of the specification, illustrate the embodiments of the present invention and, together with the description, serve to explain the principles of the invention.
In the drawings:
The processes and systems of the present invention may be practiced and deployed in a subterranean well 10 which may be formed by any suitable means, such as by a rotary or percussive drill string, as will be evident to a skilled artisan. The subterranean well 10 extends from the surface of the earth 13, including a sea bed or water platform or vessel, and penetrates one or more subterranean environs 18 of interest. As used throughout this description, the term “environs” refers to one or more areas, zones, horizons and/or formations that may contain hydrocarbons. The well may have any suitable subterranean configuration, such as generally vertical, generally deviated, generally horizontal, or combinations thereof, as will be evident to a skilled artisan. Once the well is formed, it may be completed by cementing a string of tubulars, i.e. a casing string, in the well and establishing fluid communication between the well and the subterranean environs of interest by forming perforations through the casing and into the environs. Such perforations may be formed by any suitable means, such as by conventional perforating guns. Thereafter, production tubing may be positioned within the well and the annulus between the production tubing and casing (or well bore in the case of an open hole completion) may be sealed, typically by means of a plurality of packer assemblies as hereinafter described. Fluids, such as oil, gas and/or water, may then be produced from the subterranean environs of interest into the well via the perforations in the casing and to the surface via production tubing for transportation and/or processing. Where the well has a generally horizontal configuration through the subterranean environs of interest, the well may be provided with intermediate casing which may be secured within the well by any suitable means, for example cement, as will be evident to a skilled artisan. The intermediate casing may extend from the surface of the earth to a point near the subterranean environs of interest so as to provide an open hole completion through a substantial portion of the subterranean environs of interest that are penetrated by well. Another tubular, such as a tubular liner, may also be positioned within the well and may be sized to extend through the intermediate casing and into the open hole of the well within the subterranean environs of interest. Such tubular liner may be uncemented through the subterranean environs of interest and anchored near one end thereof to the intermediate casing in any manner as will be evident to a skilled artisan.
In accordance with a broad embodiment of the present invention as illustrated in
A set of packers 22A-N, 23A-N are positioned on the tubular liner 16 adjacent to each of the tools 20A-N as close as practical to the selective opening in each tool. As the number of packers 22, 23 will vary depending upon the exact application and the total number of tools 20 that are positioned within a well, the total number of packer sets that are positioned in a well and capable of being selectively opened and closed is designated by the letter “N”. The packers 22A-N, 23A-N of each set are designed to be subject to deformation or swabbing at a given pressure which can be generated by fluid flow across the packing element exceeding a predetermined velocity. Any suitable packer which can be deformed by application of sufficient fluid pressure and flow rate to the exterior thereof may be employed in the processes of the present invention as will be evident to a skilled artisan, for example conventional cup seal packers. The set of packers distal from the surface of the earth may only consist of the packer 22A since the toe or end of the well 10 may serve to direct fracturing fluid into the subterranean environs 18 adjacent tool 20A in lieu of packer 23A.
In operation, the sliding sleeve in tool 20A may be opened by any suitable means, such as by a ball dropped in intermediate casing 14 and tubular liner 16, and a suitable fracturing fluid can be pumped from the surface 13 through intermediate casing 14 and into tubular liner 16 by any suitable means as will be evident to a skilled artisan. As illustrated by arrows 40 in
The following example demonstrates the practice and utility of the present invention, but is not to be construed as limiting the scope thereof.
A well is drilled with intermediate casing set and cemented to 10,000 feet and at this depth the wellbore deviation is nearly 90 degrees, horizontal with 7″ OD intermediate casing. The well is subsequently drilled to 18,000 feet measured depth by further horizontal drilling. A 4.5″ OD liner is run from 18,000 feet and hung off in the 7″ casing with a liner packer at 9,700 feet. As hung off the casing, this liner is positioned within the open hole and has integral sliding sleeves and packers attached to the exterior thereof. Fracturing fluids are pumped into the lowermost zone (only a single cup packer to keep fluid from moving upward above the sleeve). As this pumping continues at high pressure and with cold fluid, liner contraction occurs and the lowermost interval is fracture stimulated. A ball is dropped and the second frac sleeve is opened. Very little additional liner contraction occurs because of continual operations at substantially the same pressure rate and the same temperature of the fracturing fluids being pumped. As soon as flow at high rate exits the second port, the packers either side of the second port actuate and create a pressure barrier to keep fracturing fluids contained along a short section of the horizontal wellbore. As pressures increase, the formation fractures and fluids are injected into the formation for wellbore stimulation.
Thus, it can be readily appreciated that the processes and systems of the present invention may be employed to set packers associated with a tool that can be selectively opened and closed by use of the same fluid that is used to fracture the subterranean environs adjacent an open tool. The packers 22, 23 of the present invention can be further designed so that when deformed the packers seal the annulus 17 against flow only in one axial direction when it is desired to permit flow from an interval of unfractured subterranean environs into production tubing 16 or these packers can be designed to seal flow in both axial directions when it is desired to isolate an interval of unfractured subterranean environs from production tubing 16.
As packers used in accordance with the processes and systems of the present invention are set by the application of fracturing fluid just prior to fracturing, it will be readily appreciated that the majority of tubing movement, i.e. tubing contraction, caused by the relatively cool temperature of the high injection rate fracturing fluid occurs prior to packers being set, and thus, the problems associated with setting packers well in advance of the injection of fracturing fluid, i.e. failure due to tubing movement, are inhibited. Further, although the processes and systems of the present invention have been illustrated in
While the foregoing preferred embodiments of the invention have been described and shown, it is understood that the alternatives and modifications, such as those suggested and others, may be made thereto and fall within the scope of the invention.
