16/1-11 A

General

Well 16/1-11 and the subsequent 16/1-11 A sidetrack was drilled to appraise the 16/1-9 discovery on the Gudrun Terrace just west of the Utsira High in the North Sea. The discovery well 16/1-9 was completed in April 2008 and revealed oil shows in the Middle Jurassic Vestland Group, but neither coring or logging was completed according to programme due to hole problems. In well 16/1-11, the Sleipner Formation proved to be hydrocarbon bearing with a gas cap of approximately 25 m thickness and a gas-oil contact interpreted at approximately 2407 m in the Skagerrak Formation. However, acquisition of pressure data and sampling in the water zone in the Skagerrak Formation proved to be difficult due to very low porosity and permeability. Thus, no reliable water gradient could be established from the RCI sampling programme.

The 16/1-11 A geological sidetrack was drilled down flank on the structure. The main objectives were to obtain pressure samples in order to delineate the oil/water contact and to obtain water samples from the Skagerrak Formation in order to establish reservoir properties. A sidetrack would also give useful facies and thickness variation input. Another objective was to acquire sidewall cores to pin down the expected hiatus on top of the Sleipner Formation.

Operations and results

Well 16/1-11 A was drilled with the semi-submersible installation Songa Delta. It was kicked off on 26 April 2010, with kick-off point at 1744 m in the parent well. It was drilled to TD at 2595 m (2528 m TVD), 94 m MD into the Late Triassic Skagerrak Formation. The well was drilled with Carbotech oil based mud from kick-off to TD.

The reservoir of the Sleipner Formation was penetrated at 2