This paper presents a field example of a short-radius horizontal drainhole which was completed by sidetracking an existing vertical well. The main reservoir characteristics are unconsolidated sand, high permeability and increasing production water cut due to strongly active bottom water. The horizontal drainhole was aimed at increasing the critical rate under which oil can be produced free of water. Since the reservoir has a high transmissibility (Kh/μ), a vertical well is enough for meeting the target rate as long as water cut is maintained at a low level.
Performance was compared between a vertical well and a horizontal drainhole using analytical methods before implementing the horizontal recompletion. As expected, the horizontal drainhole has successfully maintained a high oil production rate without any water cut for more than one year. The field data proved the effectiveness of the horizontal drainhole on water control. Although recompletion to a horizontal drainhole resulted in successful production performance, there still remains room for improvement in well completion techniques. The unconsolidated sand required the use of heavy weight mud and caused difficulties during drilling. Sand problems had to be tackled and required a detailed design for well completion. In this paper, the drilling procedures and problems are also briefly mentioned.