Patent Publication Number: US-9410413-B2

Title: Well system with annular space around casing for a treatment operation

Description:
BACKGROUND 
     1. Field of the Disclosure 
     This disclosure relates generally to apparatus and methods for completing a wellbore for the production of hydrocarbons from subsurface formations, including fracturing selected formation zones in a wellbore, sand packing and flooding a formation with a fluid. 
     2. Background of the Art 
     Wellbores are drilled in subsurface formations for the production of hydrocarbons (oil and gas). Modern wells can extend to great well depths, often more than 1500 meters (about 15,000 ft.). Hydrocarbons are trapped in various traps in the subsurface formations at different depths. Such sections of the formation are referred to as reservoirs or hydrocarbon-bearing formations or zones. Some formations have high mobility, which is a measure of the ease of the hydrocarbons flow from the reservoir into a well drilled through the reservoir under natural downhole pressures. Some formations have low mobility and the hydrocarbons trapped therein are unable to move with ease from the reservoir into the well. Stimulation methods are typically employed to improve the mobility of the hydrocarbons through the reservoirs. One such method, referred to as fracturing (also referred to as “fracing” or “fracking”), is often utilized to create cracks in the reservoir to enable the fluid from the formation (formation fluid) to flow from the reservoir into the wellbore. To fracture multiple zones, an assembly containing an outer string with an inner string therein is run in or deployed in the wellbore. The outer string typically includes a screen placed proximate to the perforations. The inner string includes a crossover. To fracture a formation, a fluid is supplied under pressure from the inner string to the formation via the annular space between the screen and the casing through the perforations. Typically a certain minimum width of the annular space is required for the proper flow of the fluid through the perforations, which may be of the order of one half of an inch or more. The screen is left in the casing after fracturing for flow of reservoir fluid into the casing. The fracturing fluid typically contains a proppant, such as sand, which is corrosive to the screen. Also, it is desirable to reduce the width of the annular space so as to have as increased inside diameter of the casing for production of hydrocarbons from the reservoir. 
     The disclosure herein, in one aspect, provides an annular space outside of the casing for supplying treatment fluid to the formation, substantially bypassing the screen. 
     SUMMARY 
     In one aspect, an apparatus for use in a wellbore is disclosed that in one non-limiting embodiment includes A flow control device for use in a wellbore is disclosed that in one non-limiting embodiment may include a main flow passage and a weep hole, wherein the main flow passage closes when a fluid is supplied to a first end of the valve that exceeds a selected rate and opens when the fluid supplied is below the selected rate and wherein the weep hole continues to allow the fluid therethrough. 
     In another aspect a wellbore system is disclosed that, in one non-limiting embodiment, includes a casing in the wellbore, cement disposed between the wellbore and the casing, an annular space of a selected length in the cement between the casing and the wellbore, and perforations through the casing, cement and formation. In one aspect, the annular space is formed by dissolving a dissolvable material placed over an outside of the casing. 
     Examples of the more important features of a well treatment system and methods that have been summarized 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 that will be described hereinafter and which will form the subject of the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a detailed understanding of the apparatus and methods disclosed herein, reference should be made to the accompanying drawings and the detailed description thereof, wherein like elements are generally given same numerals and wherein: 
         FIG. 1  shows an exemplary wellbore lined with casing having a dissolvable material on an outside section of the casing, wherein the wellbore has been cemented and perforated, according to one non-limiting embodiment of the disclosure; 
         FIG. 2  shows the wellbore of  FIG. 1  after the dissolvable material has been removed to form an annular flow space or cavity in the cement along a length of the casing; and 
         FIG. 3  shows the wellbore of  FIG. 2 , with an assembly deployed proximate to the perforated section for performing a treatment operation, according to one non-limiting embodiment of the disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     In one aspect, a wellbore system is disclosed that provides an annular space (also referred to herein as a flow area or cavity) in the cement around a casing that may be utilized to supply a treatment fluid to perform a wellbore operation, including, but not limited to, fracturing (also referred to herein as fracing or fracking), and flooding a formation. The annular space enables to inject a treatment fluid into the formation without flowing such fluid over sand screens typically deployed proximate to the perforations inside the casing, which enables placing the screen closer to the inside of the casing, thereby providing increased inner diameter of the screens because the treatment fluid flow is directed to outside the casing. In one aspect, a dissolvable material of certain width or thickness may be placed or wrapped on the outer side of the casing along a section or selected length that be perforated. The casing with the dissolvable material is then deployed in the wellbore and the annular space between the casing and the wellbore cemented. Perforations are performed through the casing, dissolvable material, cement and the formation. A suitable fluid may then be supplied to perforations to dissolve the dissolvable material, which creates the annular space (cavity) around the casing. Typically, a screen is installed inside the casing to perform treatment operations, wherein the treatment fluid is supplied to the formation via the space between the screen and the perforated casing. The annular space enables installing the screen very close to the casing as such space is no longer utilized to supply the treatment fluid to the formation, which provides increased diameter for the installation of a production string in the wellbore for the production of fluid (including hydrocarbons) from the formation. 
       FIG. 1  is a line diagram of a section of a wellbore system  100  that is shown to include a wellbore  101  formed in formation  102  for performing a treatment operation therein, such as fracturing the formation (also referred to herein as fracing or fracking), gravel packing, flooding, etc. The wellbore  101  is lined with a casing  104 , which may be made by joining pipe sections  108  with connections  109 , known in the art. The casing  104  is lined on its outer side or outer diameter (OD) with a dissolvable material  110 , suitable for downhole use, along a selected length of the casing  104 . In one aspect, the material  110  may be dissolved by supplying a fluid, such as a fluid containing acid or another suitable material, or a hot aqueous solution or water. The dissolvable material  110  may be applied along the length of the casing that will be perforated. Once the casing  104  is placed in the wellbore  101 , the space  103  (annulus) between the wellbore  101  and the casing  104  is filled with cement  106 . After cementing, a length of the casing is perforated with perforations  120  that extend from the casing inside  104   a  into the formation  102  via the dissolvable material  110  and cement  106 . 
       FIG. 2  shows a process of dissolving the dissolvable material  110 . Prior to dissolving the material  110 , a lower packer  220  may be deployed to isolate the wellbore  101  below the perforations  120 . Another packer  222  may be placed above the perforations  120 . To dissolve material  110 , a suitable fluid  250  may be supplied through the packer  222  to the perforation  120 , causing the material  110  to dissolve. Dissolving the material  110  creates an annular space (or cavity)  230  between the casing  104  and the wellbore  101  along a selected length. In one aspect, the depth of the cavity (“d”) may be designed so that it provides sufficient radial space outside the casing  104  to inject a treatment fluid into the perforations  120  in the formation  102  to fracture the formation, as described below  FIG. 3 . In one aspect, the depth “d” may be about one half of an inch. 
       FIG. 3  shows the wellbore system of  FIG. 2  configured for performing a treatment operation via the annular space  230 , according to one embodiment of the disclosure. To perform a treatment operation an assembly  310  is deployed in the wellbore  102 , which may include an outer string  320  and an inner string  360  placed inside the outer string  320 . The outer string  320 , in one non-limiting embodiment, includes a sand screen  330  on a conveying member  312 , such as a tubing. The screen  330  may further include one or more flow devices, such as valves  332 , and a monitoring valve  334 . The outer string  320  also includes packer  314  above and below the screen  330  to isolate space  358  between the outer string  320  and the casing  104 . The inner string  360  includes a cross-over tool  374  that has a flow passage  375  from the inner string  360  to the outer string  320  and a relatively narrow passage  376  through the crossover tool  374  to provide fluid communication between space  374   a  below the crossover tool  374  and annulus  355  between the outer string  320  and the inner string  360 . The screen  330  also includes a flow passage (also referred to as frac port)  370  that provides a flow passage from inside the outer string  320  to the annular space  358  between the outer sting  320  and the casing  104 . A flow device or passage  380  is provided in the casing proximate to the flow passage  370  in the screen  330 . In this configuration, valves  332  are closed while the monitoring valve  334  is open. 
     To perform a treatment operation, valves  370  and  380  are opened. The packers  314  are deployed to isolate or seal space  358  between screen  330  and the casing  104 . A treatment fluid  350  is supplied under pressure to the inner string, which fluid is injected into the annular space  230  via passage  375 , valve  370  and valve  380 . Most of the fluid supplied flows from the inner string  360  into the annular space  230  via valves  370  and  380 , as shown by arrows  350   a . A relatively small amount of the treatment fluid  350  may flow through perforations in the casing  104  as the space  336  is relatively narrow compared to the annular space  230 . The fluid  350  creates fractures  390  in the formation  102  via perforations  120 . In one aspect, the treatment fluid  350  may include a proppant, such as sand. In such a case, the proppant packs or fills the fractures  390 , perforations  120  and space  336  between the screen  330  and casing  104 . Flow passage  334  provides a return path for the fluid  350  from the space  336  and from the formation  102  via sand screen  330 , as shown by arrow  350   b . Once the treatment operation is completed, valves  332  are opened and the inner string  360  is pulled out of the wellbore  101 . A production string (not shown), known in the art, is installed to enable fluid from the formation  102  to flow into the production string for retrieval of the formation fluid to the surface via screen  330  and valves  332 . 
     The foregoing disclosure is directed to the certain exemplary embodiments and methods. Various modifications will be apparent to those skilled in the art. It is intended that all such modifications within the scope of the appended claims be embraced by the foregoing disclosure. The words “comprising” and “comprises” as used in the claims are to be interpreted to mean “including but not limited to”. Also, the abstract is not to be used to limit the scope of the claims.