Wells – Processes – Parallel string or multiple completion well
Reexamination Certificate
2001-03-07
2004-03-30
Dang, Hoang (Department: 3672)
Wells
Processes
Parallel string or multiple completion well
C166S050000, C166S117600, C175S061000, C175S080000, C175S081000
Reexamination Certificate
active
06712144
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to a method for drilling and, more particularly, the present invention relates to an improved method for drilling one or more lateral wells.
BACKGROUND ART
My previous U.S. Patent Application cited hereinabove discloses how to provide a reliably sealed junction with a lateral well wherein one preferred embodiment utilizes an under-reamed section of borehole. In some cases, it may be desirable to limit the diameter of the under-reamed section for reasons discussed hereinafter. The present application describes how a smaller diameter under-reamed section can be used and still provide, if desired, a lateral wellbore having a diameter substantially the same as the primary well.
Drilling multilateral or horizontal wells from an initial wellbore has become an increasingly popular method for enhancing production and recovery of oil and gas from wellbores. In many cases, the use of multilateral wells has dramatically increased the profitability of oil and gas wells as compared to that of conventional wells. As a result of an increased return on investment, the drilling of multilateral wells has become and is projected to further develop into an important aspect of well enhancement. Moreover, the drilling of multilateral wells has significantly increased the efficiency of oil and gas recovery operations. Multilateral well techniques have been found to be especially effective in areas where the pay-zone or oil/gas deposit may be thin or hard to reach with standard downhole drilling operations.
One primary advantage for drilling multilateral wells involves cost reductions obtained by utilizing a previously drilled wellbore. In drilling multilateral wells, a driller can dramatically reduce the cost of drilling a new well by beginning the new drilling operations at a convenient kickoff depth in a previously existing well. Therefore, many of the modern methods that have been developed for drilling lateral wells make use of an existing wellbore to eliminate the additional cost of drilling the wellbore from the surface.
The technique of drilling multilateral wells has typically consisted of laterally drilling from a previously drilled borehole, sometimes referred to as the primary borehole. It should be noted that the previously drilled borehole is typically cased and cemented, but methods exist in the art for open hole operations, i.e., wellbores or wellbore sections which are not cased or cemented.
However, prior art methods of drilling lateral boreholes suffer from a common significant problem of providing a good seal at the junction between the primary wellbore and the lateral wellbore and/or reliably maintaining this sealed junction over time. If there is a poor seal at this junction, then leakage may occur between the primary borehole and one or more of the lateral boreholes. Leakage at the junction may prevent the possibility of good zone isolation. Zone isolation is an important aspect in the success of many oil and gas recovery operations and may also be required by governmental regulations either now or in the future. Thus, the lack of a reliable seal at this junction is a significant potential problem for multilateral well operations.
My prior application, as identified hereinbefore, discloses in one embodiment use of an under-reamed section of primary borehole which may have a diameter larger than three times the diameter of the primary borehole. However, under-reaming may be problematic in some cases, especially as the size diameter of the under-reamed section increases. For instance, greater torque on the hole opening string is required for larger diameter under-reaming. The larger torque required may lead to more mechanical failures. As well, larger amounts of earth have to be removed from the borehole. Another problem relates to subsequent operations. Depending on the well program, wellbore strings inserted after the under-reaming or hole opening, especially in deviated wells, may tend to be more difficult to guide past the under-reamed section. Thus, the larger the diameter of under-reaming or hole opening, the more likely it is that problems may arise due to the under-reaming or hole opening. Thus, the present invention teaches a drilling method using a reduced diameter under-reamer or hole opener.
A common example of the prior art drilling methods is embodied in U.S. Pat. No. 5,458,209 to Hayes et al. (the '209 patent). The '209 patent discloses a method and system for drilling a lateral well with respect to a primary well which is cased. The method discloses positioning a guide means defined as comprising three main parts; a lower end, a central part with an angled ramp and an upper end, and drilling out the casing along the guide at a preselected location. This method may be used to effectively drill multilateral wells, but does not insure a sealed junction.
Accordingly, it would be desirable to somehow provide a method and/or device for drilling one or more lateral wells and establishing a sealed junction between the lateral well and the primary wellbore.
U.S. Pat. No. 5,564,503 to Longbottom et al (the '503 patent) discloses a method of drilling a lateral well encompassing the steps of setting a diverter within a wellbore, boring through the sidewall of the wellbore at a desired location, lining the lateral well, and cementing the periphery of the junction around the lateral well to obtain a pressure bearing seal around the wellbore. One difficulty encountered when cementing using conventional techniques is that of ensuring a homogeneous flow of cement at the periphery of the junction because of the presence of tubulars and the limited space between the tubulars and the formation about the junction. Another common difficulty is ensuring a uniform fill of the cement about the junction without leaving spaces or voids because of the irregular shape of the interstices about the junction. Accordingly, this method does not necessarily provide a homogeneous cement bond around a lateral well. Another difficulty encountered with the method disclosed in the '503 patent is the practical impossibility of the using the method to warranty the seal of the junction with the passage of time. Moreover, the amount of cement that actually provides a seal is limited to the cement that actually fills the interstices around the junction between the casing and the formation. Accordingly, pockets filled with mud may prevent the flow of cement into those pockets and therefore could result in structural weakness of the junction. As well, the dirt and debris from the formation can easily mix with and contaminate the cement as it fills the interstices so that the cement is less effective for sealing purposes.
U.S. Patent No. 5,795,924 to Chatterji et al. (the '924 patent), U.S. Pat. No. 5,820,670 to Chatterji et al. (the '670 patent) and 6,006,835 to Onan et al (the '835 patent), which are hereby incorporated herein by reference, disclose use of more elastic materials such as epoxy resin materials or a cement slushy that may be used to provide resilient cement compositions. The cement compositions have improved mechanical properties including elasticity and ductility and may, for instance, be basically comprised of cementitious material, an aqueous rubber latex and a latex stabilizer. Unfortunately, these cements do not necessarily overcome the problems discussed earlier related to pockets, difficult to reach interstices around the junction, and contamination or mixture of such materials by downhole chemicals which may include a wide variety of contaminants. Merely pumping such cements at higher pressures or velocities will not necessarily result in displacing existing fluids or reaching all pockets around the junction. Moreover, high pump pressures and flow velocities may actually increase contamination or mixture problems.
As well, prior art methods for drilling multilateral wells have often required that the lateral well be of a smaller diameter than the primary wellbore. This reduction in size can severe
Dang Hoang
Frank's International, Inc.
The Matthews Firm
LandOfFree
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