Methods for increasing production from a wellbore

#1. Field of the Invention

#The present invention relates to methods for increasing the productivity of an existing well. More particularly, the invention relates to methods for under-reaming a wellbore. More particularly still, the invention relates to methods for under-reaming a wellbore in an underbalanced condition to reduce wellbore damage.

#2. Description of the Related Art

#So that the manner in which the above recited features and advantages of the present invention are attained and can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings.

#It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.

#FIG. 1 is a cross-sectional view of a wellbore having a layer of skin damage on the surface thereof.

#FIG. 1 is a cross-sectional view of a wellbore 100 having a layer of skin 110 on the surface thereof. As illustrated, a horizontal portion of wellbore 100 is uncased adjacent a formation 115 and is lined with casing 105 at the upper end. The uncased portion is commonly known in the industry as a “barefoot” well. It should be noted that this invention is not limited to use with uncased horizontal wells but can also be used with cased and vertical wellbores. The layer of skin 110 is created throughout the diameter of the wellbore 100 in the initial overbalanced drilling operation of the wellbore 100. The skin 110 clogs the wellbore 100, thereby restricting the flow into the wellbore 100 of formation fluid 120 as illustrated by arrow 122. Because the skin 110 restricts the flow of formation fluid 120, the skin 110 is said to have a positive skin factor.

#FIG. 2 is a cross-sectional view of the wellbore 100 illustrating an under-reamer 125 positioned at a predetermined location near the formation 115. As illustrated, the under-reamer 125 and a motor 130 are disposed at the lower end of coiled tubing 135. The under-reamer 125 is a mechanical downhole tool that is used to enlarge a wellbore 100 past its original drilled diameter. Typically, the under-reamer 125 includes blades that are biased closed during run-in for ease of insertion into the wellbore 110. The blades may subsequently be activated by fluid pressure to extend outward and into contact with the wellbore walls. Under-reamers by various manufacturers and types may be used with the present invention. One example of a suitable under-reamer is the Weatherford “Godzilla” under-reamer that includes blades disposed on a front portion and a rear portion.

#In the preferred embodiment, the under-reamer 125 and motor 130 disposed on coil tubing 135 are run into the wellbore 100 to a predetermined location. While the under-reamer 125 is illustrated on coil tubing, it should be noted that under-reamer 125 may also be run into the wellbore 100 using a snubbing unit, jointed pipe using a conventional drilling rig, a hydraulic work over unit or any other device for lowering the under-reamer 125. The predetermined location is a calculated point near the formation 115. If more than one formation exists in the wellbore, each formation will be individually treated, starting with the formation closest to the surface of the wellbore. In this manner, a selected region within the wellbore 100 may be under-reamed without effecting other portions of the wellbore 100.