Patent Description:
When drilling oil and gas wells, under proper conditions during the drilling process, drilling fluids and drill cuttings are circulated away from the drill bit into the annulus around the drill stem and brought to the surface. Such drilling fluids are also important for providing hydrostatic pressure to prevent formation fluids from entering into the well bore, keeping the drill bit cool and clean during drilling, and suspending the drill cuttings while drilling is paused and when the drilling assembly is brought in and out of the hole. Because proper circulation is critical to the drilling process, any lost circulation is a significant problem that must be overcome for drilling to recommence.

Lost circulation is the partial or complete loss of drilling fluid or cement slurry to the formation during drilling or cementing operations or both. Lost circulation can be brought on by natural causes, such as naturally fractured formations or unconsolidated zones, or induced causes, such as when the hydrostatic fluid column pressure exceeds the fracture gradient of the formation and the formation pores break down enough to receive (rather than resist) the fluid. When lost circulation occurs, it typically results in the new expenditure of time and mud or cement, adding substantially to the overall cost of a well.

The consequences of lost circulation can be as little as the loss of a few dollars of drilling fluid, or as disastrous as a blowout and loss of life. If the amount of fluid in the well bore drops due to lost circulation (or any other reason), hydrostatic pressure is reduced, which can allow a gas or fluid which is under a higher pressure than the reduced hydrostatic pressure to flow into the well bore. Another consequence of lost circulation is dry drilling. Dry drilling occurs when fluid is completely lost from the well bore without actual drilling coming to a stop. The effects of dry drilling range from as minor as destroying a bit to as serious as major damage to the well bore requiring a new well to be drilled.

Dry drilling can also cause severe damage to the drill string, including snapping the pipe, and the drilling rig itself.

Lost circulation material (LCM) is the collective term for substances added to drilling fluids when drilling fluids are being lost to the formations downhole. Commonly used LCM types include fibrous (cedar bark, shredded cane stalks, mineral fiber and hair), flaky (mica flakes and pieces of plastic or cellophane sheeting) or granular (ground and sized limestone or marble, wood, nut hulls, Formica, corncobs and cotton hulls). The LCM, in combination with other fluids with increased viscosity, are used to fill fractures and heal the loss zone quickly.

As the LCM is delivered to the loss zone, accumulations and aggregations of the LCM can occur which may obstruct the necessary flow of fluids to the site. Therefore, it is desirable to prevent such obstructions by diffusing such aggregations or "clumps" as early and as quickly as possible. Given the nature of some types of LCM and their tendency to aggregate into such clumps, one solution is to cause such clumps to contact blades or cutters placed into the fluid path, but while not substantially decreasing the proper fluid flow during the healing process of the loss zone.

In addition to diffusion near the loss zone, there is also a need for diffusion of LCM clumps that form as the fluids are delivered through the drill pipe at the rig floor, as well as diffusion of LCM clumps which may form after leaving the mixing tank where the LCM is added to the drilling fluids. Furthermore, once drilling operations are concluded, the diffuser can also be deployed in various locations for LCM diffusion in completion and workover operations.

<CIT> discloses a drilling fluid filter that is placed within a tubular drill string, where the filter is a perforated receptacle for collecting debris in the drilling fluids. The filter is suspended within the drill string by a hanger comprising a mandrel with articulated struts and linkages.

The present invention provides a diffuser assembly as recited in claim <NUM>.

Further advantageous features are presented in the dependent claims.

For a further understanding of the nature, objects, and advantages of the present invention, reference should be had to the following detailed description, read in conjunction with the following drawings, wherein like reference numerals denote like elements.

Before the subject invention is further described, it is to be understood that the invention is not limited to the particular embodiments of the invention described below, as variations of the particular embodiments may be made and still fall within the scope of the appended claims. It is also to be understood that the terminology employed is for the purpose of describing particular embodiments, and is not intended to be limiting. Instead, the scope of the present invention will be established by the appended claims.

In this specification and the appended claims, the singular forms "a," "an," and "the" include plural reference unless the context clearly dictates otherwise. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this invention belongs. Unless otherwise specified herein, all materials of construction are preferably steel resistant to the corrosive effects common in oil and gas production environments. As used herein the term "conduit" shall mean any tubular member into which the diffuser <NUM> can be installed for the purpose of allowing LCM-containing fluid to flow through the conduit and be broken apart, or diffused, by the diffuser <NUM>. Non-limiting examples of conduits may be a carrier sub, drill pipe, stabilizer, or other tubular member such as shown in the figures.

Turning now to the figures, a preferred embodiment of the present invention is shown in <FIG> as a diffuser assembly <NUM> comprising a diffuser <NUM> adapted to reside within a conduit in the form of a carrier sub <NUM>, having an upper mounting member <NUM> mountable within the carrier sub <NUM> and having an fluid inlet port <NUM>, and a lower section having a diffuser screen <NUM>. As shown in more detail in <FIG> and <FIG>, a plurality of cutters <NUM> are removably attached to the diffuser screen <NUM>, wherein the cutters <NUM> are radially oriented relative to a central axis <NUM> of the diffuser screen <NUM>. The diffuser screen <NUM> is a cylinder having a plurality of diffuser slots <NUM> formed therein and a bottom cap <NUM> having a fluid port <NUM>.

In the embodiment shown in <FIG>, the diffuser assembly <NUM> further includes a plurality of centralizing members <NUM> adjacent to the diffuser screen <NUM>, wherein each of the centralizing members <NUM> extends between the mounting member <NUM> and the bottom cap <NUM>. The three centralizing members <NUM> serve to keep the diffuser screen <NUM> centered within the carrier sub <NUM>. It should be understood that the centralizing members <NUM> can take a wide range of structural forms which accomplish the purpose of centering the diffuser screen <NUM> within the carrier sub <NUM>.

As shown best in <FIG>, with the cylindrical diffuser screen <NUM> removed for clarity, each of the plurality of cutters <NUM> includes a cutting edge <NUM> and a mounting flange <NUM>, and wherein the mounting flange <NUM> is adapted to matably engage one of the plurality of diffuser slots <NUM> of the diffuser screen <NUM>. In a preferred embodiment, a first set <NUM> of cutters <NUM> is mounted at a first selected height H1 along the central axis <NUM> of the diffuser screen <NUM>, and a second set <NUM> of cutters <NUM> is mounted at a second selected height H2 along the central axis <NUM> of the diffuser screen <NUM>. In this embodiment shown in <FIG>, the cutters <NUM> are mounted to the diffuser screen <NUM> such that the cutting edges <NUM> are internal to the diffuser screen <NUM>. It should be understood that each individual cutter <NUM> may reside in any slot <NUM> to provide a varied and irregular pattern of cutters <NUM> on the diffuser screen <NUM>. However, it is believed that having organized sets of cutters <NUM> at selected heights may provide more consistent separation of LCM aggregations during the diffusion of the fluid through the diffuser assembly <NUM>.

As best shown in <FIG>, the diffuser assembly <NUM> further includes a bottom cutting device <NUM> extending from a post <NUM> affixed to the bottom cap <NUM> internal to the diffuser screen <NUM>, wherein the cutting device <NUM> includes a plurality of radially disposed cutting edges <NUM> similar to the cutters <NUM> positioned above the cutting device <NUM>. The cutting device <NUM> essentially serves as a third stage cutting step in addition to the first and second set <NUM>, <NUM> of cutters <NUM>, prior to the fluid <NUM> exiting the diffuser screen <NUM> through fluid port <NUM>.

In an operational configuration, fluid <NUM> flows through the carrier sub <NUM>, such as a stabilizer or other type of downhole sub, and into the inlet port <NUM> of the mounting member <NUM>. Any LCM aggregations or clumps in the fluid <NUM> pass against the cutting edges <NUM> of cutters <NUM>, and are separated into smaller portions to collect within the diffuser screen <NUM>, while the fluid <NUM> can exit the diffuser screen <NUM> through diffuser slots <NUM> and the fluid port <NUM>.

The preferred embodiment described above, as well as the alternate embodiments described below, are effective for diffusion of a wide range of fluids and materials, including oil and water based muds, barite drilling muds, cement, all drilling fluids, spotting acids for break-up of limestone formations, blended materials mixed in blending tanks, breakup of larger masses of carbide bombs, and any other "cake balls" mud clumps, LCM, cement, and the like that form in the string or from poor blending.

In an alternate embodiment shown in <FIG>, a similar diffuser assembly is configured to allow the flow of fluid <NUM> such that LCM aggregations are caused to contact cutters <NUM> positioned external to the diffuser screen <NUM>, and where LCM too large for the diffuser slots <NUM> is collected on the outside of the diffuser screen <NUM>. A mounting member <NUM> (similar to mounting member <NUM>) includes an inlet port <NUM> for entry of fluids <NUM>. The fluid <NUM> is then diverted by a cone-shaped diversion member <NUM> attached to a bridge <NUM> inside mounting member <NUM> and disposed between the fluid inlet port <NUM> of the mounting member <NUM> and the diffuser screen <NUM>.

As shown best in <FIG>, with the cylindrical diffuser screen <NUM> removed for clarity, each of the plurality of cutters <NUM> includes a cutting edge <NUM> and a mounting flange <NUM>, and wherein the mounting flange <NUM> is adapted to matably engage one of the plurality of diffuser slots <NUM> of the diffuser screen <NUM>. In this embodiment, three sets of cutters <NUM> are mounted at selected heights along the central axis <NUM> of the diffuser screen <NUM>, similar to the arrangement seen in <FIG>.

As shown in <FIG>, the diffuser assembly <NUM> further includes a lower diffuser element <NUM> attached below the diffuser screen <NUM>, wherein the lower diffuser element <NUM> is constructed from a slotted cylinder. A bottom cap <NUM> is attached to the bottom of lower diffuser element <NUM>, and which includes a fluid exit port <NUM>. A further embodiment is shown in <FIG> that is identical to the embodiment of <FIG>, except for the lower diffuser element <NUM>, which is constructed from vertical rods <NUM>.

As shown in <FIG>, the diffuser assembly <NUM> is deployed within another type of conduit in the form of a stabilizer <NUM>, which supports the bottom hole assembly (BHA) in the well bore in order to avoid unintentional sidetracking or vibrations, and ensures the quality of the hole being drilled.

As shown in <FIG>, the diffuser assembly <NUM> is deployed within a section of drill pipe <NUM> at the level of the rig floor <NUM>. Note that in <FIG>, the diffuser screen <NUM> includes a retrievable neck <NUM>, as is common in the art, that enables retrieval of the diffuser by conventional fishing tools. <FIG> includes an opening as shown in <FIG> and elsewhere herein. In this operation, the diffuser <NUM> is installed in the drill pipe <NUM> while drilling fluids containing LCM are pumped into the well bore during drilling. As the drill string moves deeper into the well bore and another section of drill pipe <NUM> is needed, the diffuser <NUM> is removed, and the next section of drill pipe <NUM> is threaded onto the drill string at the rig floor <NUM>. After the next section of drill pipe <NUM> is connected, the diffuser <NUM> is re-installed into the drill pipe <NUM>, after which the drilling and fluid flow can be restarted. Thus, any clumps of LCM that enter into the drill pipe <NUM> are diffused by the diffuser <NUM>.

As shown in <FIG>, the diffuser <NUM> deployed within a conduit <NUM> between a drilling fluid mixing tank <NUM> and a pump <NUM> located in proximity to the rig floor <NUM>. Tank <NUM> may be a fixed tank, or it may be a mobile tank located on a vehicle such as a truck or other vessel. The left side of <FIG> depicts the arrangement in a partial exploded view, while the right side of <FIG> depicts a fully assembled view with typical valves, hoses, and connectors to enable fluid flow from the mixing tank <NUM> to the rig floor <NUM>. Thus, any clumps of LCM that exist when the fluid leaves the mixing tank <NUM> can be diffused by the diffuser <NUM> prior to being pumped to the rig floor <NUM>.

Claim 1:
A diffuser assembly, comprising:
(a) a diffuser (<NUM>) adapted to reside within a conduit (<NUM>), having a upper mounting member (<NUM>) mountable within the conduit (<NUM>) and having a fluid inlet port (<NUM>), and a lower section having a diffuser screen (<NUM>);
(b) a plurality of cutters (<NUM>) below the fluid inlet port (<NUM>), wherein the cutters (<NUM>) are radially oriented relative to a central axis (<NUM>) of the diffuser (<NUM>); and
(c) a centralizing member (<NUM>) adjacent to the diffuser screen (<NUM>) and having a diameter greater than the diffuser screen (<NUM>); and
wherein the diffuser screen (<NUM>) is a cylinder having a plurality of diffuser slots (<NUM>) formed therein and a bottom cap (<NUM>) having a fluid port (<NUM>); and
wherein each of the plurality of cutters (<NUM>) extends substantially parallel to the central axis (<NUM>) and includes a diffusing edge (<NUM>).