Patent Application
20210355783
The disclosure relates generally to completion of wellbores, for example, for hydrocarbon production and more particularly to cementing of casings in wellbores.
When drilling a wellbore through subsurface formations to produce hydrocarbons, it is common practice to protect the wellbore with one or more casings. The first casing installed in a wellbore is called a conductor casing (or conductor pipe). The conductor casing typically prevents drilling fluids from circulating outside the wellbore and causing surface erosion. The conductor casing is usually no more than 20 to 50 feet long. The next casing installed after a conductor casing is a surface casing, which typically prevents hydrocarbons from encroaching into fresh water zones. Surface casing may also be used to anchor blowout preventers. Surface casing may extend several thousand feet into the subsurface. In some wells, intermediate casing may be installed in the wellbore after the surface casing. Intermediate casing may be used to protect against weak or abnormally pressured formations. The final casing installed in the wellbore is a production casing. Each of these casings extends from the surface to a depth in the wellbore and protects a certain section of the wellbore. Each casing is typically made of casing sections or joints that are screwed together to form a desired length of casing. Typically, the screwing together of the casing joints occurs as the casing is lowered into the wellbore. The first joint of a casing run into the well typically has a guide shoe, which is a short heavy cylindrical section filled with concrete and rounded at the bottom. The guide shoe prevents the casing from hitting rock ledges or washouts in the wellbore as the casing is lowered. The casing joints may also carry centralizers that assist in centering the casing in the wellbore.
Casings are typically bonded to the wellbore and other casings by cement. The process for cementing a casing in a wellbore typically includes pumping cement slurry down the interior of the casing and allowing the cement slurry to flow out of the bottom of the casing, around the guide shoe, and into an annulus outside of and surrounding the casing. The wellbore is then shut in to allow the cement slurry in the annulus to set or harden. Some wells require complete cementing of the casing, where the cement in the annulus extends from the bottom of the casing to the surface. In these cement jobs, cement slurry is pumped through the casing and into the annulus outside of the casing until cement return from the annulus is observed at the surface, indicating that the annulus has been filled with cement. However, there are instances where cement return is initially observed at the surface, followed by a drop in the column of cement in the annulus. This may occur if the bottom of the casing is set above a lost circulation zone (i.e., a formation zone that steals fluids from the wellbore) so that the cement slurry that should fill the annulus is sucked into the formation, which leaves the area above the lost circulation zone unprotected. In cases where the top of the cement is below the surface, a “top job” (i.e., filling the annulus with cement from the surface opening of the annulus) may be performed to bring the top of the cement to the surface. However, the top job will only be successful if the loss of cement from the annulus can be controlled.
A method of cementing a casing in a wellbore extending from an Earth's surface into a subsurface includes providing a tube having a bi-frustoconical shape defined by an upper tube part having an inverted frustoconical shape, a lower tube part having a frustoconical shape, and a waist intermediate between the upper tube part and the lower tube part. The method includes positioning the tube in an annulus formed between the casing and a wall of the wellbore from a surface opening of the annulus. The method includes urging the tube in a direction down the annulus and along the casing until the tube lands on a collar radially projecting from an outer surface of the casing into the annulus. The act of urging the tube in a direction down the annulus and along the casing may include loading an initial amount of a cement slurry into the upper tube part, wherein the tube moves down the annulus and along the casing under a weight of the cement slurry. The method may include loading an additional amount of the cement slurry into the annulus and on top of the initial amount of cement slurry until a top of the cement slurry is at a predetermined height within the annulus. Alternatively, the method may include loading an additional amount of the cement slurry into the annulus and on top of the initial amount of cement slurry until a top of the cement slurry is at or proximate the surface opening of the annulus. The method may include hardening the cement slurry to form a column of cement in a portion of the annulus above the upper tube part with the column of cement forming a seal between the wall of the wellbore and the outer surface of the casing. The method may include lowering the casing into the wellbore to form the annulus prior to positioning the tube in the annulus. The act of lowering the casing into the wellbore may include lowering the casing into a conductor section of the wellbore. The method may include installing a cement basket on the outer surface of the casing prior to lowering the casing into the wellbore. The cement basket may provide the collar on which the tube is landed.
A system for protecting a wellbore includes a casing disposed in the wellbore and separated from a wall of the wellbore by an annulus, a collar surrounding the casing and radially projecting from an outer surface of the casing into the annulus, and a cementing tool to be landed on the collar. The cementing tool includes a tube having a bi-frustoconical shape defined by an upper tube part having an inverted frustoconical shape, a lower tube part having a frustoconical shape, and a waist intermediate between the upper tube part and the lower part. The upper tube part and the lower tube part may be joined at the waist. The tube may have an asymmetric bi-frustoconical shape. The upper tube part may be sized to engage the casing and the wall of the wellbore when the cementing tool is landed on the collar. The inner diameter of the tube at the waist may be smaller than an outer diameter of the collar such that the lower tube part hangs off the collar when the cementing tool is landed on the collar. The system may include a cement basket retained on the casing with the cement basket providing the collar surrounding the casing. The casing may be disposed in a conductor section of the wellbore. The tube may be made of a metal or an alloy or an elastomeric material.
An apparatus to be landed on a collar surrounding a casing includes a tube having a bi-frustoconical shape defined by an upper tube part having an inverted frustoconical shape, a lower tube part having a frustoconical shape, and a waist intermediate between the upper tube part and the lower tube part. The tube engages an outer surface of the casing at the waist when landed on the collar. The tube may have an asymmetric bi-frustoconical shape.
The foregoing general description and the following detailed description are exemplary of the invention and are intended to provide an overview or framework for understanding the nature of the invention as it is claimed. The accompanying drawings are included to provide further understanding of the invention and are incorporated in and constitute a part of the specification. The drawings illustrate various embodiments of the invention and together with the description serve to explain the principles and operation of the invention.
The following is a description of the figures in the accompanying drawings. In the drawings, identical reference numbers identify similar elements or acts. The sizes and relative positions of elements in the drawings are not necessarily drawn to scale. For example, the shapes of various elements and angles are not necessarily drawn to scale, and some of these elements may be arbitrarily enlarged and positioned to improve drawing legibility. Further, the particular shapes of the elements as drawn are not necessarily intended to convey any information regarding the actual shape of the particular elements and have been solely selected for ease of recognition in the drawing.
In this detailed description, certain specific details are set forth in order to provide a thorough understanding of various disclosed embodiments and implementations. However, one skilled in the relevant art will recognize that embodiments and implementations may be practiced without one or more of these specific details, or with other methods, components, materials, and so forth. In other instances, well known features or processes associated with cementing jobs have not been shown or described in detail to avoid unnecessarily obscuring descriptions of the embodiments and implementations. For the sake of continuity, and in the interest of conciseness, same or similar reference characters may be used for same or similar objects in multiple figures.
The outer diameter of upper tube part 124 at top end 108 may be approximately the same as or slightly larger than the diameter of the section of the wellbore in which the casing is to be cemented. In general, a radial width w of upper tube part 124 may be selected such that when cementing tool 100 is disposed in an annulus between a casing and a wall of a wellbore (in
For illustrative purposes,
A method of cementing a casing to a wall of a wellbore may generally include pumping cement slurry through the casing into the wellbore, where the cement slurry should then rise up an annulus between the casing and the wellbore wall. If cement loss to a lost circulation zone is observed, the next action may be a cementing top job.
After upper tube part 124 is filled with cement slurry, additional cement slurry 256 can be loaded into the portion of annulus 220 above upper tube part 124, as shown in
Although specific embodiments, implementations, and examples have been described for illustrative purposes, various equivalent modifications can be made without departing from the spirit and scope of the disclosure, as will be recognized by those skilled in the relevant art. The teachings provided herein can be applied to other cementing scenarios besides the exemplary casing to wellbore cementing generally described above.
