System for Lagtime Measurement During Drilling

This invention relates to measurements made relative to circulating drill fluid during the drilling of a well; and more particularly, it relates to a system for lagtime measurements concerning the returning drilling fluid.

During the drilling of a well, it is most important to collect samples of formations being penetrated by a drill bit rotated at the bottom of an extended length of drill string. Samples of formation cuttings are relatively easily taken from the outflowing drilling fluid usually at a shale shaker that separates solids from the drilling fluid.

One problem in taking these samples is in correlating a particular "rock" sample to the depth at which the formation resides that produced the sample. Obviously, there is a certain lagtime time required for the cuttings sample to travel upwardly in the well from the drill bit to the earth's surface. The "mud logger" usually has the responsibility to solve the correlation problem and collect proper samples. However, he is generally not a part of the drilling crew, and therefore, he is tolerated on the derrick floor only if no interference is made with the drilling operations.

In the past, the mug logger has tried to solve the lagtime problem by using a "carbide bomb." The bomb is simply a paper sack or other container that encloses a few ounces (e.g., 4 oz) of calcium carbide. Immediately prior to the derrick crew assemblying the next joint of drill pipe into the string, the mud logger makes a quarter back dash to the turntable where the drill pipe is held by "slips" with the open box connection yet overflowing by drilling fluid, i.e., mud. He pushes the bomb down into the mud and it hopefully stays in the box connection until the joint is threaded together. Unfortunately, the next pipe section is held by the hook from the traveling block with the pin connection only a few inches above the box connection. This pipe section may weigh a ton or more and it is swaying and bobbing directly above the box connection. The mud logger must be fast and careful even when being rushed by the driller, otherwise lowering the drill joint to thread the pin and box connectors could mangle exposed fingers etc. Naturally, the several derrick men on the drilling rig must be avoided in machinery cluttered 20 by 20 foot space by the mud loggers fast entry, fast bomb stuffing and faster exit from the turn table area. Many times the bomb is flushed from the box connection by backflowing drilling fluid. As a result of this event, or premature release of acetylene gas, the mud logger in a cloud of acetylene gas becomes a persona non-grata to the rig crew.

Assuming the pin and box connection is assembled with the bomb in place, the resumed downflow of drilling fluid pushes the bomb down the drill string. At this point, the water components of the drilling mud enter the bomb and convert the calcium carbide to acetylene gas. Continued circulation of the drilling fluid moves the acetylene gas through the drill bit and then the gas returns in the well annulus to the earth's surface. The acetylene gas can be readily detected at the shale shaker by conventional instruments, such as gas, explosion or hydrocarbon detectors.

The mud logger calculates the lagtime it takes cuttings to travel from the drill bit to the shale shaker by subtracting from the total time of acetylene gas travel (bomb insertion to shale shaker) the time the bomb travels from the box connection at the turn table to the drill bit (a function of drilling fluid flow rate and volumetric capacity of the drill pipe). Thus, if the lagtime is "x" minutes, the rock samples from a given formation appear at the shale shaker this "x" minutes later in time. Therefore, the mud logger can correlate a rock sample to a certain formation.

As the well becomes deeper, the lagtime determination becomes increasingly more important and also increases in magnitude. Another use of the lagtime measurement by the bomb technique relates to checking the functioning of gas detection equipment, to determine borehole uniformity, presence of formation washout conditions and identify pressure indicators. In a deep well, e.g., 15,000 feet, the drilling operation is very expensive and critical to control for safe and effective drilling results. A correct lagtime determination becomes critical and is the foundation of the penultimate decision-a production well or cement and abandonment.

The present invention is a system, including a drop device, method of use and manufactured article so that the mud logger can easily and safely place the "carbide bomb" into the pin connection of the hanging pipe joint and secure it in place without risking his safety or premature release of the acetylene gas.

In accordance with this invention, there is provided a system for making determinations (i.e., lagtime) in a drilling fluid at dynamic circulating conditions during the drilling of a well with a fluid circulating bit on a drill pipe having pin and box connections. A drop container is provided of sheet material having a guide end, non-porous sides and an enclosing floor. The container encloses an indicator material which reacts with drilling fluid to produce a readily detectable gas (e.g., acetylene).

Preferably, the container is water proof paper formed into a right cone with a disc sealing the bottom or floor. An elastic elongated resilient member is secured at the floor and includes a loop adapted to be slipped over the threaded end of the hanging pipe joint. The user grasps the resilient member and slips the loop over the end of the hanging pipe while inserting the guide end upwardly into the threaded end (usually the pin connection). Releasing the manual tension on the resilient member secures the container in place on the pipe. Assembly of the pin and box connection severs the resilient member and circulation of drilling fluid moves the container towards the drill bit. The container preferably is made of sheet material that is fragmented and dispersed by the drilling fluid flow or passage through the drill bit, or both conditions.

A drop device made of a right cone of water proof paper sealed by a paper disc and containing calcium carbide provides good results in determining lagtime in circulating drilling fluid in a well.

FIG. 1 is a perspective, partially sectional, showing the drop device positioned in a pin connection of drill string according to the present invention;

FIG. 2 is a perspective with the drop device inverted to illustrate its construction, and

FIG. 3 is an expanded element view illustrating the several components of the drop device.

In these drawings, the several embodiments have common elements of construction in the drop device. In regard to the several figures, like elements carry like numerals to simplify description of the present system.

Referring to FIG. 1, there is shown the drop device used in the system of this invention in a conventional rotary drilling operation. The drop device 11 is shown immediately after installation within a pin connection 12 carried at the lower end of a pipe 13 that may be suspended from the hook of the traveling block on a drilling rig.

The pipe 13 is positioned above but spaced a few inches from the pipe 16 in the turn table forming part of the drill string in the well used with a down hole drilling bit which penetrates the subterranean formations. The pipe 13 is now lowered to interengage the box connection 14 on the pipe 16. Rotation of the pipe 13 treads the pin and box connections together. At this time, downward circulation of drilling fluid in the drill string is resumed with the drilling operation. The drilling fluid travels the flow passage 18 and lastly exits the bit and returns with cuttings in the well annulus to the earth's surface where it is treated in shale shakers desander, desilters and other mud processing machinery. Samples of cuttings are readily secured at the first shaker.

Usually, there is a back flow of drilling fluid, as indicated by arrows 17, from the box connection 14. Also, water and small amounts of drilling fluid may dribble from the pin connection 12 as shown by arrows 19. If the prior art carbide bomb were stuffed onto the box connection 14, the mud backflow or downflow 19 could either dislodge it or prematurely convert it into explosive acetylene gas.

The drop device 11 is arranged to avoid these problems with the prior art carbide bomb and provide a complete safe installation in both method and structure for the mud logger, and reduce any interference to the drilling crew. All of these unique results are obtained while providing for an accurate determination of lagtime in the well.

As seen in FIGS. 2 and 3, the drop device 11 is formed integrally in a container 20 with a guide end 21, non-porous sides 22 and a base or floor 23, and a resilient member or bond 24.

Preferably, the drop device 11 is constructed into the form of a right cone with the floor 23 being a disc that is secured as by adhesives to the tapered sides 22.

The container 20 can be constructed of suitable thin sheet material such as paper. The sheet material is treated in manufacture or later so that it fragments and disperses during traveling through the drill string and out of the drill bit. Although the container should be constructed of any suitable sheet material, good results are obtained using several different paper sheet materials.

For example, the container 20 has an outer cone member 26 that prevents permeation of drilling fluid. A waxed paper construction of the cone member 26 gives excellent results with water based drilling fluids. An inner cone member 27 is positioned and secured within the cone member 26. The member 27 can be of a suitable sheet material, such as thin paper that does not have to be waterproofed.

The cone member 27 is end closed by interleafing a plurality of flaps 28. The flaps 28 may leave exposed some of the indicator material 29 that fills the container 20. The flaps 28 are sealed and secured by the disc 31 which may also be untreated or unwaxed paper and to the cone 26.

Any indicator material 29 (liquid or solid) can be used that goes into a gas state upon direct contact and reaction with a component of the drilling fluid. Usually, the indicating material 29 will include calcium carbide that reacts with water in drilling fluids to produce the readily detected acetylene gas.

The container 20 is handled and positioned in the pin connection 12 by using the band 24 in a manner to prevent placing the users hands between pin and box connection where digit severence and other injury can occur so suddenly and disastorously. For this purpose the band 24 is formed from an elongated elastic strip such as natural or synthetic rubber. Preferably, the band 24 is molded in one piece but it can be formed of several pieces integrally joined by adhesives or other mechanical arrangements.

The band 24 has an enclosed loop 32 that is adapted to be stretched about the pin connection 12 and released to securely grip the exterior of the pipe 13. Where the pin connection 12 is of the external upset type, the loop 32 should be secured above the shoulders 33.

The band 24 has strap parts 34 and 36 extending from the loop 32. The strap parts 34 and 36 are preferably of equal lengths and part of a continuous strip which include strap part 37 that is secured between the disc 31 and the cone members 26 and 27.

The band 24 has a thickness and width as an elastic member of insignificant structure so that it doesn't interfere in properly threading together of the pin and box connections. Threading these connections together severs strap parts 34 and 36 releasing the container 20 within the passageway 18.

The drop device 11 may have varied amounts of the indicating material 29 but good results have been obtained using between 4 and 8 ounces of calcium carbide.

The installation of the drop device 11 is safe and easy even to a fast moving mud logger on a crowded drilling floor. When the driller has picked up the pipe 13 (e.g. ninety feet in length) and holds the pin connection 12 a few inches above the box connection 14, the drop device 11 is held by the strap parts 34 and 36 with hands spread apart to clear the threaded connection. At the same time, the loop 32 is spread open sufficiently to pass over the pin connection onto the pipe 13. Now, the container 20 is inserted upwardly into the passageway 18 with the guide end 21 entering first into the pin connection 12. The loop 32 is released to secure the container 20 in the pin connection with the floor 23 being flush with the lower end of the pipe 13.

If any water or drilling fluid 19 flows onto the container 20, the waterproof cone 26 protects the indicator material from premature conversion into the gas state.

Upon threaded assembly of the pin and box connections, the container 20 is free to move with the drilling fluid in passageway 18.

Circulation of drilling fluid through the passage 18 usually will open the container 20 and convert the indicator material 29 into the gas state. However, the gas remains much like a bubble and travels committantly with the drilling fluid. In any event, passage of any remaining container through the drill bit produces total conversion of the indicator material 29 into the gas state by exposure thereof to the activating components of the drilling fluid.

The time when circulation is resumed is noted as is the time the gas appears at the shale shaker in the outflowing drilling fluid from the well. The time required for the drop device 11 (or its products) to travel downhole in the passage 18 to the drill bit is calculated by dividing the volumetric capacity of the drill string by the volumetric inflow of the drilling fluid. The difference between the total time in passage of the drop device and its gas produce is reduced by the downhole travel time to give accurately the lagtime in drilling fluid circulating in the well annulus from the drill bit to the shale shakers. As a result, the mud logger can determine exactly the correlation between a formation at a certain depth to cuttings from that formation arriving at the shale shaker. Other conditions associated with the circulating drilling fluid can also be determined by the use of the drop device 11.

In water based or containing muds, the indicator material will usually be calcium carbide and the resulting gas is acetylene. However, metallic sodium pellets can be used which produce readily detectable hydrogen gas, and many oil based muds have sufficient alcoholic hydroxyl compounds to release the hydrogen gas. Other gas forming materials, such as the effervescent sodium citrate which produces carbon dioxide upon reaction with water, can also be used. Generally, for any given drilling fluid, a suitable indicator material and construction of the container 20 can be employed following the present description.

From the foregoing, it will be apparent that the system of this invention has provided a unique drop device, a method of use, and an article of manufacture especially suited for the method to determine lagtime and in other cases where a detectable gas is desired. It will be appreciated that certain changes and alterations can be made in this system without departing from the spirit of this invention. These changes are contemplated by and are within the scope of the appended claims which define the invention. Additionally, th present description is intended to be taken as an illustration of this invention.