During early 1991 West Australian Petroleum Pty. Limited acting as joint venture operator for Chevron Asiatic Limited, Texaco Oil Development Company, Shell Development (Australia) Pty. Limited, Ampol Exploration Limited and Western Mining Corporation Limited successfully drilled the first two medium radius wells in Australia.

The two wells G88B and Cowle No.2 were very different in many aspects.

The first well G88B achieved a 500m horizontal well bore at 615m true vertical depth (TVD) using build up rates to horizontal in excess of 10 degrees/30m(5.818E-03rad/m). The well was drilled onshore using a relatively small drilling rig with minimal additional equipment.

The Cowle No.2 well achieved a 1002m horizontal well bore at 1098mTVD using a build up rate of 9 degrees/30m(5.236E-03rad/m). This offshore well utilized a significantly higher capacity/capability drilling rig than that used on the G88B well.

Both wells were able to be horizontal within 240m of their surface locations representing a significant decrease in horizontal and vertical displacement required to build to horizontal.

Horizontal wells drilled within Australia had previously utilised long radius builds which require greater horizontal and vertical distances before reaching horizontal, longer well paths and generally longer drilling times1 .

The success of the first two medium radius build to horizontal wells in Australia confirms that horizontal sections can be accurately drilled with shorter horizontal displacements and vertical sections than previously thought possible. The practicality of drilling shallow horizontal wells onshore using available drilling rigs is also confirmed.

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