MXPA06006010A - A method and device for controlling drilling fluid pressure - Google Patents

Abstract

A method and device for controling drilling fluid pressure during subsea drilling, where drilling fluid is pumped down into a borehole (15) and then flows back to a drilling rig (1) via the lined and/or unlined sections of the borehole (15) and a liner (14), wherein the drilling fluid pressure is controlled by pumping drilling fluid out of the liner (14) at the seabed, and where the liner (14) annulus (30) above the drilling fluid is filled with a riser fluid having a density different from that of the drilling fluid.

Description

SI, SK, TR), OAPI (BF, Bl, CF, CG, CI, CM, GA, GN, GQ, For two-leitcr codes and other abbreviation. Referto the "Guid-GW, ML, MR, NE , SN, TD, TG). Ance Notes on Codes and Abbreviations "appearing at thebegbi- ning ofeach regular issue oflhe PCT Gazette Published: - with intemational search repon - befare the expiration of the time lanit for wnending the claims and to be republished in the eveni of receipt of amendmenis METHOD AND DEVICE TO CONTROL THE PRESSURE OF THE PERFORATION FLUID DESCRIPTIVE MEMORY This invention relates to a method for controlling the pressure of the drng fluid. More particularly, it relates to a method for controlling drng fluid pressure in an underground drng well, during the drng of wells from a fixed platform on the high seas. The invention also relates to a device for practicing the method. During drng operations, for example in oil production, the upper pressure of the drng fluid that is present in the borehole and up to the platform, may cause the liquid pressure found in the lower portion of the well of sounding becomes too high. Excessive pressures in the drng fluid can result in the drng fluid causing undesirable damage to the formation being drd, for example, through the drng fluid that enters the formation. The formation can also include special geological formations (salt deposits, etc.) that require the use of a special drng fluid to stabilize the formation.

According to the prior art it is difficult to reduce the specific gravity of the drng fluid to reduce the pressure to an acceptable level. In many cases it has been difficult to achieve a sufficient reduction in the specific gravity of the drng fluid, without causing an unacceptable degree of change in the physical properties of the drng fluid, such as viscosity. It is known to dissolve the drng fluid in a rising tube to reduce the pressure of the drng fluid, see US 6536540. When drng from floating installations, it is also known to reduce the pressure of the drng fluid in the well and the weight of the riser tube by pumping the drng fluid out of the riser tube to a level below the sea surface. The patents of E.U.A. 4063602 and 4291772 refer to drng vessels provided with a return pump for the drng fluid, wherein the drng fluid is pumped out of the riser tube immediately above the seabed. When using the prior art it is difficult to monitor the volumetric flow in the borehole, since the crown that is above the drng fluid in the liner, or alternatively the riser, is fd with gas, usually air. This gas-fd crown can be fd, or it can be emptied of the drng fluid without being easily observed.

The object of the invention is to remedy or reduce at least one of the disadvantages of the prior art. The objective is achieved according to the invention, with the features set forth in the following description and the appended claims. When drng from fixed platforms (drng devices), a driver is first driven into the seabed. When drng a borehole from a fixed drng device, the drng fluid is pumped through a drpipe to a drng tool. The drng fluid has several purposes, one of which is to transport the borehole cuts out of the borehole. The efficient transport of the drholes depends on the drng fluid being relatively viscous. The drng fluid flows back through the crown that lies between the wall of the borehole, the liner mentioned above and the drill pipe, and up to the drill rig, where the drilling fluid is treated and conditioned before being pumped back into the borehole. In many cases this results in a pressure head that is not recommended. By attaching a pump to the liner near the seabed as described above, the return drilling fluid can be pumped out of the crown and up to the drilling equipment. According to the invention, the annular volume above the drilling fluid is filled with a lifting fluid. Preferably, the density of the lifting fluid is smaller than that of the drilling fluid. The pressure of the drilling fluid in the seabed can be controlled from the drilling equipment by selecting an inlet pressure to the pump. The height Hi of the drilling fluid column above the seabed depends on the selected inlet pressure of the pump, the density of the drilling fluid and the density of the riser fluid, as well as the inlet pressure to the pump. equal to: P = ri, X Yb + H2 X Ys where: Yb = the density of the drilling fluid H2 = the height of the lifting fluid column Ys = the density of the lifting fluid Hi and H2 together make the length of the section of the ascending pipe that goes from the seabed to the deck of the drilling equipment. Filling the crown of the liner with a lifting fluid allows continuous control of the amount of fluid flow that flows in and out of the borehole. In this way it is relatively easy to detect, for example, the drilling fluid that flows into the drilling formation. It is also possible to maintain a substantially constant drilling fluid pressure in the seabed, also when the density of the drilling fluid changes.

Choosing another pump inlet pressure will immediately cause the Hi and H2 heights to change according to the new pressure. If desired, the outlet of the crown to the pump can be disposed at a level below the seabed, by coupling a first pump pipe to the crown, at a level below the seabed. To prevent the drilling fluid pressure from exceeding an acceptable level, for example, in the case of a pumping maneuver, the riser tube may be provided with a quick discharge valve. Such a quick release valve can be adjusted to open at a particular pressure for the outflow of drilling fluid into the sea. The following is a description of a non-limiting example of a preferred method and device that is illustrated in the accompanying drawings, in which: Figure 1 is a schematic view of a fixed drilling rig provided with one to return the fluid from perforation, the pump is coupled to a section of an ascending pipe near the seabed and the rising pipe section is filled with a fluid having a density different from the density of the drilling fluid; and Figure 2 is similar to Figure 1, but here the drilling fluid fills a larger part of the riser section. In the drawings the reference number 1 denotes a fixed drilling rig comprising a supporting structure 2, a cover 4 and a drilling tower 6. The supporting structure 2 is placed on the seabed 8 and is projected on top of the surface 10 of the sea. A riser section 12 of a liner 14 extends from the seabed 8 to the cover 4, while the liner 14 extends further into a borehole 15. The riser section 12 is provided with required valves for wellhead (not shown). A drill pipe 16 projects from the cover 4 and down through the liner 14. A first pump pipe 17 is coupled to the riser pipe section 12 near the seabed 8, through a valve 18 and the portion opposite end of the pump pipe 17 is coupled to a pump 20 which is located near the seabed 8. A second pump pipe 22 runs from the pump 20 to a collection tank 24 for the drilling fluid in the cover 4. A tank 26 for a riser fluid communicates with the riser section 12 through a connecting pipe 28 in the cover 4. The connecting pipe 28 has a volume meter (not shown). Preferably the density of the lifting fluid is lower than that of the drilling fluid. The power supply to the pump 20 is through a cable (not shown) from the drilling rig 1 and the pressure at the inlet of the pump 20, are selected from the drilling rig 1. The pump 20 can be powered optionally in hydraulic form by means of oil that circulates back to the drilling equipment by means of water that is thrown into the sea. The drilling fluid is pumped back through the drill pipe 16 in a manner known per se, returning to the cover 4 through the crown 30 between the liner 14 and the drill pipe 16. When the pump 20 turn on, the drilling fluid returns from the crown 30 through the pump 20 to the collection tank 24 which is on the cover 4. The lifting fluid passes from the tank 26 into the crown in the rising pipe section 12. The height H- of the drilling fluid column above the seabed 8 is adjusted according to the selected inlet pressure to the pump 20, as described in the general part of the description. The volume of the lifting fluid flowing in and out of the tank 26 is monitored, making it possible to make a revision, for example if the drilling fluid is disappearing in the well formation, or if gas or liquid flows from the formation and into the system . The invention makes it possible to use simple means to achieve a significant reduction in the drilling fluid pressure in the borehole 15. Figure 2 shows a situation in which a higher inlet pressure has been selected for the pump, and where the heights Hi and H2 of the fluid columns have changed in relation to the situation shown in figure 1.

Claims (5)

NOVELTY OF THE INVENTION CLAIMS

1. - A method for controlling the pressure of the drilling fluid during offshore drilling, where the drilling fluid is pumped into a borehole (15) and then flows back to a drilling rig (1) through the lined and / or unlined sections of the borehole (15) and a liner (14), wherein the drilling fluid pressure is controlled using a pump (20) to pump the drilling fluid out of the liner (14) near the seabed, and wherein the crown (30) of the liner (14) above the drilling fluid, is filled with a lifting fluid having a density that is lower than that of the drilling fluid, characterized in that the level of interface between the drilling fluid and the lifting fluid is regulated by adjusting the inlet pressure to the pump (20).

2. The method according to claim 1, further characterized in that the volume of the lifting fluid flowing in and out of the crown (30) is monitored.

3. The method according to claim 2, further characterized in that the volume of the drilling fluid and the lifting fluid flowing in and out of the crown (30) is compared to the volume of the drilling fluid that is introduced into the body. Well of sounding (15) through a drill pipe (16).

4. A device for controlling the pressure of the drilling fluid during drilling in the high seas, where the drilling fluid is pumped into a borehole (15) and then flows back to a drilling rig (1) through lined and / or uncoated sections of the borehole (15) and a liner (14), and wherein the drilling fluid pressure is controlled using a pump (20) to pump the drilling fluid out of the liner (14) near the seabed, and wherein the crown (30) of the liner (14) above the drilling fluid is filled with a riser fluid having a density that is lower than that of the drilling fluid, characterized in that it can be adjust the inlet pressure to the pump (20).

5. The device according to claim 4, further characterized in that the crown (30) communicates with a tank (26) in the drilling equipment (1) by means of a connection pipe (28), the pipeline Connection (28) is adjusted with volume measuring equipment.