Casing strings and related methods of deployment in horizontal wells

A casing string includes an uphole section, a downhole section, and a sealed chamber that is fluidically isolated from the uphole and downhole sections. The sealed chamber extends between the uphole and downhole sections. The casing string further includes a tube that is disposed within the sealed chamber and that fluidically connects the uphole and downhole sections to provide a fluid flow path that extends past the sealed chamber and through the casing string.

TECHNICAL FIELD

This disclosure relates to casing strings that permit mud circulation while being run in a horizontal section.

BACKGROUND

During deployment of a long casing string in deviated or horizontal well, the casing string may need to be floated in order to overcome a drag force that is exerted against the casing string by any mud present within the well and to ultimately locate the casing string at a target depth within the well. In some examples, an air chamber or relatively lightweight fluid may be used in a downhole section of the casing string in an attempt to provide buoyancy. However, in these cases, mud cannot be circulated through the casing string until the casing string reaches a bottomhole end of the well because of the presence of the air chamber. Furthermore, other challenges may be encountered while deploying the casing string to the bottomhole end of such a well. For example, the casing string may encounter a flow obstruction that must be cleared or encounter an excessive gel strength of mud in a surrounding annulus that may render a bottomhole end of the surrounding formation susceptible to fracture.

SUMMARY

This disclosure relates to casing strings that permit mud circulation while being run in a horizontal section. To this end, a casing string includes an air chamber that provides buoyancy to a downhole section of the casing string, as well as a fiberglass tubing that passes through the air chamber to provide a circulation flow path through the casing string.

In one aspect, a casing string includes an uphole section, a downhole section, and a sealed chamber that is fluidically isolated from the uphole and downhole sections. The sealed chamber extends between the uphole and downhole sections. The casing string further includes a tube that is disposed within the sealed chamber and that fluidically connects the uphole and downhole sections to provide a fluid flow path that extends past the sealed chamber and through the casing string.

Embodiments may provide one or more of the following features.

In some embodiments, the tube includes fiber glass.

In some embodiments, the casing string is configured to permit filling of the uphole and downhole sections with drilling mud.

In some embodiments, the sealed chamber includes a fluid that is less dense than drilling mud.

In some embodiments, the sealed chamber includes air.

In some embodiments, the uphole section includes multiple uphole casing joints and a chamber collar.

In some embodiments, the downhole section includes multiple downhole casing joints and a float collar.

In some embodiments, the tube extends between the chamber collar and the float collar.

In some embodiments, the tube includes a stinger, and the float collar is a stab-in float collar.

In some embodiments, the downhole section further includes a float shoe.

In another aspect, a method of deploying a casing string within a well includes flowing drilling mud into an uphole section of the casing string and flowing the drilling mud from the uphole section into a downhole section of the casing string past a sealed chamber that is fluidically isolated from the uphole and downhole sections and that extends between the uphole and downhole sections.

Embodiments may provide one or more of the following features.

In some embodiments, the method further includes flowing the drilling mud through a tube that is disposed within the sealed chamber and that fluidically connects the uphole and downhole sections.

In some embodiments, the method further includes flowing the drilling mud out of the casing string and circulating the drilling mud through an annulus disposed between the casing string and the well.

In some embodiments, the tube includes fiber glass.

In some embodiments, the method further includes installing the tube to the casing string to fluidically connect the uphole and downhole sections after forming the sealed chamber.

In some embodiments, the sealed chamber includes a fluid that is less dense than drilling mud.

In some embodiments, the sealed chamber includes air.

In some embodiments, the well includes a substantially horizontal section, and the method further includes floating the casing string within the horizontal section of the well.

In some embodiments, the uphole section includes multiple uphole casing joints and a chamber collar, and the downhole section includes multiple downhole casing joints and a float collar.

In some embodiments, the tube extends between the chamber collar and the float collar.

The details of one or more embodiments are set forth in the accompanying drawings and description. Other features, aspects, and advantages of the embodiments will become apparent from the description, drawings, and claims.

DETAILED DESCRIPTION

FIG.1illustrates an example casing string100that is designed to permit circulation of drilling mud103through the casing string100while the casing system100is run into a shallow horizontal well101. The casing string100includes a float shoe102at a downhole end, two casing joints104aarranged adjacent the float shoe102, a float collar106, multiple casing joints104b, a chamber collar108, an inner string110that extends from the chamber collar108to the float collar106within the air chamber120, a casing joint104c, a landing collar112, and multiple casing joints104dthat are sequentially arranged up to the surface. In some embodiments, the casing string100has a fully deployed length of about 1,600 meters (m) to about 8,500 m. In some examples, the length of the casing string100may vary depending on the directional trajectory and bottom hole targets.

The float shoe102is a leading joint with a rounded shape that facilitates running into the well101at a downhole end116of the casing string100. The float shoe102includes an internal check valve that permits fluid to flow out of the casing string100(for example, in a downhole direction105) and prevents fluid from flowing into the casing string100(for example, in an uphole direction107). The landing collar112includes internal components for landing cement plugs during a cementing operation and also allows fluid flow-through. The casing joints104(104a,104b,104c,104d) are substantially identical tubular sections (for example, cylindrical sections) that provide the majority of the length of the casing string100. The casing joints104are typically made of steel. In some embodiments, each casing joint104has an axial length of about 12.0 m to about 12.8 m and a wall thickness of about 1.8 centimeters (cm) to about 1.1 cm. In some embodiments, the casing joints104have an outer diameter (for example, defining an outer diameter of the casing string100) of about 17.7 cm to about 24.4 cm. In some examples, the diameter of the casing string100(for example, which will be floated) may depend on the directional trajectory and well casing design.

The casing joints104btogether define an air chamber120that is fluidically isolated from the remainder of the casing string100and from an annulus109that surrounds the casing string100. For example, the air chamber120is sealed at a downhole end by the float collar106and sealed at an uphole end by the chamber collar108. Therefore, the casing joints104d,104cand the landing collar112define a channel114into which drilling mud103can flow up until the location of the chamber collar108. Relative to the channel114(for example, which carries drilling mud103), the air chamber120provides a relatively reduced-weight section of the casing string100near the downhole end116that is not filled with drilling mud103. The reduced weight of the air chamber120provides buoyancy that facilitates advancement of the casing string100in the downhole direction105through drilling mud103in the well101.

The inner string110is a relatively narrow tube that passes through the air chamber120to complete a fluid path along which drilling mud103can flow from the channel114to a channel118provided by the casing joints104a. An uphole end122of the inner string110is fluidically coupled to the channel114at the chamber collar108. That is, the inner string110is hung at the chamber collar108. A downhole end124(for example, a stinger) of the inner string110is fluidically coupled to the channel118at the float collar106(for example, a stab-in collar). Thus, the inner string110allows drilling mud103to flow through the entire casing string100and circulate in the uphole direction107through the annulus109without the air chamber120being filled with drilling mud103. Therefore, the relatively reduced weight of the casing string100at the air chamber120is maintained, even while drilling mud103is able to circulate through the casing string100.

In some embodiments, the inner string110is made of fiber glass such that the inner string110is chemically resistant to drilling mud and other downhole fluids. In other embodiments, the inner string110may be made of any drillable material that may be drilled with a drilling bit. In some embodiments, the inner string110has a burst rating of about 3.5 megapascals (MPa) to about 24.1 MPa (for example, about 20 MPa). In some embodiments, the burst rating may be determined after the size of the inner string is selected according to operational conditions. In some embodiments, the inner string110has an outer diameter of about 7.3 cm to about 8.9 cm (for example, about 7.62 cm) such that the inner string110is about 2.7 times to 3.3 times smaller than the casing joints104in outer diameter. In some embodiments, the inner string110has a wall thickness of about 0.5 cm to about 0.8 cm. In some embodiments, the inner string110and the air chamber120have an axial length of about 305 m to about 3,000 m. The axial length may be determined via simulations that take into account a profile of the well101and a length of any horizontal sections of the well101.

In operation at a horizontal or highly deviated well101, the components of the casing string100are sequentially mated and run into the well101. For example, the float shoe102, the casing joints104a, the float collar106, the casing joints104b, and the chamber collar108are mated and advanced into the well101without any drilling mud103within the casing string100at this stage. With the air chamber120formed by the casing joints104b, the inner string110is deployed to the casing string100using a false rotary table at the surface and installed at the float collar106and the chamber collar108. Once the inner string110is installed, the casing joint104c, the landing collar112, and the remaining casing joints104dare sequentially mated to the casing string100as the casing string100is further advanced in the well101while drilling mud103is flowed into the casing string100. The series of casing joints104dwill extend to the surface such that the total number of casing joints104dis determined by an axial location of the bottom of the well101.

The inner string110diverts drilling mud103from the channel114to the channel118without compromising the sealed air chamber120to provide a complete circuit along which drilling mud103can flow through the casing string110. Therefore, drilling mud103can be circulated through the casing string100at any axial location while being run into the well101to clear (for example, wash down) a nearby obstruction in the well101without jeopardizing floatation of the casing string100(for example, by minimizing a hydraulic impact of the casing string100on the well100). Importantly, circulation of the drilling mud103can also break up (for example, condition) the drilling mud103and accordingly limit the gel strength of the drilling mud103within the annulus109. Circulating drilling mud103before the casing string100reaches the bottom-hole end of the well101advantageously prevents a scenario in which the gel strength of the drilling mud103at the bottom-hole end has increased to such a high level that the formation is vulnerable to fracture once circulation of the drilling mud103would finally commence for the first time at the bottom-hole end, as is the case for conventional casing strings that do not have a mechanism for circumventing an air chamber (for example, for circulating mud past or through an air chamber). Owing to the configuration of the inner string110within the air pocket120, the casing string100is especially equipped to be deployed in deviated or horizontal sections in wells with shallow true vertical depth (TVD).

Once the casing string100reaches the bottom-hole end and drilling mud103is further circulated through the casing string100to condition the surrounding drilling mud103, a cement operation is performed in which cement is pumped down into and through the casing string100to the annulus109, where the cement is allowed to harden. After the cement job is performed, a bottom hole assembly (BHA) is run into the casing string100to clean the various casing components of any leftover cement and to mill the fiber glass inner string100to ready the casing string100for a next section of the well101.

FIG.2is a flow chart illustrating an example method200of deploying a casing string (for example, the casing string100) within a well (for example, the well101). In some embodiments, the method200includes a step202for flowing drilling mud (for example, the drilling mud103) into an uphole section of the casing string. In some embodiments, the method200further includes a step204for flowing the drilling mud from the uphole section into a downhole section of the casing string past a sealed chamber (for example, the air chamber120) that is fluidically isolated from the uphole and downhole sections and that extends between the uphole and downhole sections.

While the casing string100has been described and illustrated with respect to certain dimensions, sizes, shapes, arrangements, materials, and methods200, in some embodiments, a casing string that is otherwise substantially similar in construction and function to the casing string100may include one or more different dimensions, sizes, shapes, arrangements, configurations, and materials or may be utilized according to different methods. For example, while the chamber120has been described as an air chamber, in some embodiments, the chamber120may be filled with a different fluid other than air, but that is also less dense than drilling mud103, such that the chamber120still provides a lightweight section relative to the remaining sections of the casing string100that are filled with drilling mud103. In some embodiments, the casing string100includes a different number of casing joints104than what are shown inFIG.1.

Accordingly, other embodiments are also within the scope of the following claims.