Abstract

The first horizontal wells in the Prudhoe Bay Unit were drilled in the central gravity drainage area to increase standoff between the wellbore and the gas cap for improved recovery and increased production rates. Subsequent applications of horizontal wells have included producers in the peripheral area or the field and adjacent waterflood regions, drainholes and gas injections. Innovative and cost effective horizontal drilling and completion techniques were developed. Horizontal wells have been drilled at angles up to 98 degrees and for lengths exceeding 2100'. There are currently twenty seven horizontal wells, including two gas injectors, in the Prudhoe Bay Unit with significant opportunity for further development utilizing horizontal well technology.

The performance or the Prudhoe Bay Unit horizontal wells have been evaluated after 1–5 years of production to determine the incremental benefits for future justification of the additional costs associated with drilling and completing horizontal wells in comparison to conventional completions.

This paper describes the overall performance of horizontal wells in the Western Operating Area of the Prudhoe Bay Unit including surveillance and wellwork achievements, drilling and completion technology developed and the reservoir modeling and analytical efforts to date. The current and future strategies of horizontal well applications are also addressed.

References and illustrations at end of paper.

Introduction

Production from the majority of wells in the Prudhoe Bay Unit (PBU) is governed by a large expanding gas cap. As gas approaches the productive intervals, coning necessitates production well rate restrictions to control rate sensitive GOR's due to facility gas handling constraints. Horizontal wells, which are referred to as non-conventional wells (NCW's), were initially drilled to provide additional stand-off from the gas cap and greater oil rates and recoveries than the conventional well (CW) offsets.1 The peripheral areas of the PBU receive limited direct pressure support from the gas cap and some sections are being waterflooded in a pressure maintenance program. The peripheral area outside or the waterfloods was the next target for NCW application where thin light all column's (LOC's) require increased well bore exposure for high productivity. NCW's were then drilled as peripheral waterflood producers in boundary patterns. Current development has targeted the low productivity zones at the base of the up structure reservoir. These zones an characterized by poor reservoir quality and reduced formation thickness.

In addition, the use of NCW's for gas injection in a peripheral extension of the field, the Eileen West End (EWE), maximized injectivity for a minimum number of gas injectors. The conversion of existing vertical well bores into NCW's using drainhole technology has also been applied.

NCW's will continue to be applied for development of the up structure base zones and peripheral areas of the PBU. Future potential application of NCW's include additional waterflood development as injectors and/or producers and drainhole completions to produce the thin oil lenses left behind by gas encroachment as the field continues to mature.

There are currently twenty-seven NCW's (Figure 1) in the PBU including two gas injectors.

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