Successful Isolation of a Loss Circulation Zone of a Short Radius Horizontal in a Highly Fractured Environment

Abstract

This paper addresses the successful isolation of a loss circulation zone of a short radius horizontal completion utilizing the cement retainer technique in a highly fractured environment. The process was applied to a well in a highly fractured carbonate reservoir undergoing pressure maintenance by water injection. Fracture orientation in the area is running mainly NE/SW. While drilling the horizontal section, complete lost circulation was encountered in the middle of the planned lateral section, most probably through a fracture. Circulation could not be regained by pumping LCM pills or placing cement plugs. The horizontal section had to be plugged and a new horizontal lateral was drilled in a different direction. A drillable squeeze packer was used to hold a good kick-off cement column above the loss circulation zone. Prior to the workover, the well was producing 3.3 MBOD at 47% water cut. The initial post workover test showed 3.0 MBOD restricted (choked) water-free production. Introduction The main objective of applying the horizontal drilling technology is to realize a greater economic benefit through increased well productivity by enlarging the area of contact with the reservoir rock at reduced pressure drawdown. Horizontal wells can offer significant economic as well as recovery benefits when properly applied. Increasing the production rate reduces the operating cost and thus increases the rate of return. In addition, horizontal drilling reduces the number of wells needed to deplete an area. Another benefit of horizontal completions is the diminished risk of water coning due to the lower drawdown in the wellbore. It also improves the areal and the vertical sweep efficiencies. On the characterization side, the horizontal technology improves the information gathering process. Horizontal drilling have proven that formations are more heterogeneous in the lateral direction than indicated by the vertical wells. Failures in horizontal drilling are mostly attributed to inadequate reservoir characterization and poor site selection due to lack of petrophysical data. Planning for a horizontal well includes a thorough review of, but not limited to, reservoir performance, reservoir geology, fracture presence and orientation, permeability anisotropy, well pressure transient testing and well logging. Most of this data are available since horizontal applications are development rather than exploration. Fractured reservoirs are mostly targeted for horizontal drilling. However, as in this case, the fracture systems presented the challenge. Background Horizontal drilling technology was first introduced in the Arab-D reservoir in Ghawar Field in 1994. Initially, the main objective was to deplete thin oil column areas while minimizing water production. The area the well was drilled in is highly swept. There are wells producing at 72% water cut or higher. The average water cut in the area is about 45%. Several workover techniques were tried to control water production, from through-tubing bridge plug isolation to polymer treatment. When successful, these techniques reduced water production only temporarily. In the field, produced water is treated and injected back in the reservoir through water disposal wells. It is imparative that a better way is needed to control water production to cut cost and injection volume when neccessary. Horizontal drilling is one choice.

Risk Planning and Mitigation in Oil Well Fields

“…The complete prevention of lost circulation is impossible because some formations, such as inherently fractured, vugular, cavernous, unconsolidated (high-permeability zones) or depleted low-pressure formations (usually sands), are not avoidable if we want to reach the target zone (Al Ubaidan et al, 2000;Algu et al, 2007;Bell et al 1987;Davidson et al, 2000;Ferras et al, 2002). The problem of lost circulation was considerably magnified when operators began drilling deeper and/or depleted formations (Sanders et al, 2003;Suyan et al, 2009).…”