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Self-compensated underbalanced bits

IP.com Disclosure Number: IPCOM000242030D
Publication Date: 2015-Jun-15
Document File: 4 page(s) / 541K

Publishing Venue

The IP.com Prior Art Database

Abstract

The underbalanced drilling (UBD) is to drill with lower mud pressure than the surrounding formation. It is much faster than conventional drilling due to less confinement on the wellbore bottom formation. It also avoids clogging reservoir pores with drilling mud or cuttings, thus reducing fluid loss and the time consuming clean-up of mud cake and giving better rate in well production. Due to the high benefits from both drilling and production, in operations, underbalanced drilling can increase the utilization of the reservoir up to multifold times.

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Self-compensated underbalanced bits

Abstract

The underbalanced drilling (UBD) is to drill with lower mud pressure than the surrounding formation. It is much faster than conventional drilling due to less confinement on the wellbore bottom formation. It also avoids clogging reservoir pores with drilling mud or cuttings, thus reducing fluid loss and the time consuming clean-up of mud cake and giving better rate in well production. Due to the high benefits from both drilling and production, in operations, underbalanced drilling can increase the utilization of the reservoir up to multifold times.

The difficulties with UBD are multifold. The first is the fluid pressure management. If not well controlled, the formation may blow out. The second is with the cleaning efficiency of the underbalance fluid pressure. Due to the low mud pressure, the cuttings, once generated, are not efficiently washed away as in a conventional drilling. A third is to consider any potential wall collapse due to the formation blowout. Strict limits on the lowest pressure needed to clean out the cuttings and prevent reservoir collapse must be posed. Due to these difficulties, UBD tends to be more complicated and more expensive.

One way to reduce the likelihood of formation blowout and thus reservoir collapse is to localize the underbalanced regions to the drill bit surroundings. US patent 2010/0147594 A1 employs a reverse nozzle design through which a portion of the drilling fluid is directed upwards as shown in Figure 1. The portion of the drilling fluid is diverted backwards directly through the reverse nozzles. Another portion is delivered through the nozzles near the bottom of the bit directing downwards, creating a region of relatively reduced pressure near the bit bottom, and thus localizing the underbalanced region to the formation under drilling. This design obtains a gain in the drilling efficiency through a sacrifice in the cleaning efficiency. The net result is unknown, as it may depend on the rock formation under drilling, the ROP, RPM, etc.

Figure 1. One embodiment of the reverse nozzle design

This invention provides a mechanism that can always achieve the UBD while automatically adjusting the level of the UBD as driven by the main characteristics of the current drilling requirement.

Enabling description

Figure 2 shows three states of our self-compensated flow design.

The shown section in Figure 1 (a) cut through junk slot 30. What makes the bit differ from the conventional design is the fluid chamber 120 and its associated flow diverting mechanism. One embodiment of a 3D chamber is illustrated in Figure 3. The flow chamber 120 can be screwed to the bit body 1 at connection 60 by the hexagon cut 180. The chamfer is drilled with several downward tilted holes 40 that are connected to the fluid chamber 110. The fluid passage 190-40-110 guides the fluid to the standard nozzles 100 facing downwards near the bottom of the bit. The fluid has an inlet pressure .  Once e...