Coiled Tubing Drilling of Horizontal Sidetrack in House Mountain Field, Alberta
Authors: Milligan M. , Andreychuk M. , Lunan B. 
Published: December 2007

Abstract
The first horizontal section of an oil well was successfully drilled directionally using 2-3/8-in., 0.188-in. wall coiled tubing (CT) in House Mountain Field, Alberta. The objective was to drill underbalanced a 37/8-in. diameter by 300 m long horizontal sidetrack from an existing -vertical well. The well (12-33-69-09 WSM) was re-entered using a conventional drilling rig and the window milled and the build section drilled to an inclination of 90 degs. CT was used to directionally drill the horizontal section underbalanced with nitrified water. The zone was the Devonian Slave Point limestone which is primarily a reef edge (shoal) structure.
A case history of the horizontal sidetrack using directional coiled tubing drilling (CTD) is summarized. CTD provided a cost effective alternative to drilling a horizontal sidetrack without the use of a conventional rig. Smaller location layout. shorter trip times, ability to drill underbalanced Competitive rate of penetrations (ROP), and the ability to maintain weight on bit were all achieved. ROPs while drilling underbalanced with nitrified water increased by up to a factor of three.

Introduction
The accelerating growth of underbalanced drilling in western Canada has led to the expansion of CTD. During the last three years, global applications of CTD have exponentially increased from three in 1992 to about 150 in 1994. A large percentage of wells drilled with CT have been horizontals. In western Canada, over the past few years, several horizontal wells have been attempted to be directionally drilled with CT without success until completion of the 12-33-69-09 WSM sidetrack in January 1995.
The CTD project consisted of re-entering an existing 4-1/2-in. cased wellbore with a conventional drilling rig, and milling a window at 2010 m. A bottom trip whipstock was set on a bridge plug at 2012 m and oriented to an azimuth of 70 degs. After completion of the window, the rig continued to drill the build section. The build section was landed at 2210 m with a maximum dogleg severity of 25.3 degs./30 m. The rig completed the openhole by spotting a viscous (HEC) pill in the build. The rig then tripped out of the hole and a wireline set retrievable bridge plug (RBP) was set at 1000 m. After the rig moved off location, CT and production equipment were rigged up to pull the RBP and directionally drill the horizontal section (3-7/8-in. hole by 300 m in length) in the underbalanced mode.

Reservoir Background
The House Mountain field, located in north central Alberta, has been producing from three cycles of reef growth of the Middle Devonian Slave Point formation for over 30 years. The field is located about 250 km northwest of Edmonton near the town of Swan Hills. It was discovered in 1963, and unitization and pattern waterflood began in 1965. API 42 gravity oil is produced from the Middle Devonian Slave Point part of the Beaverhill Lake Group. at depths from 2200 m to 2590 m.
The Slave Point formation is comprised of a stromatoporoid rich reefal and shoal complex built on a tabular stromatopoid platform. The reservoir is limestone with porosity (10 %) and permeability (10 mD) related to original depositional fabrics and patterns. The reservoir has no gas cap or underlying acquifer. Original oil in place is estimated at 60 E03 m3 with current recovery of 19 E06 m (32%)and a target recovery efficiency of 38%. The field produces about 800 m3/d oil from 146 wells, 20 of which are horizontal. Horizontals produce 25 % of the oil. Fifty waterflood injectors currently support the producers.

Horizontal Wells Background
The first five horizontal wells in House Mountain were drilled in 1993 and were sidetrack re-entries out of existing vertical producers (beam pump) equipped with 5-1/2-in. casing.
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