FRIKKEN, HARM, Nederlandse Aardolie Maatschappij, Assen, Netherlands

ABSTRACT: Subhorizontal Drilling, L13 Block Central Offshore Netherlands: Remedial Action for Underperforming Rotliegende Gas Fields

The first development well in the L13-FE gas field showed a rapid production decline resulting from a marked pressure depletion. Material balance data indicated less than 10% of the expected volumetric reserves to be connected. This poor connectivity is thought to be due to compartmentalization by minor strike-slip faults, as confirmed by lineations on seismic attribute maps. Fault-related diagenesis and a limited number of scattered, stratigraphically isolated prolific layers, diminishing the vertical permeability, can also contribute to the disappointing well performance.

The well was sidetracked subhorizontally with the aim to connect a larger number of the scattered prolific sands, different fault compartments and possible open fracture systems. The reservoir section was drilled with graded rock salt mud in order to minimize formation impairment.

During drilling of the 500 m long, 5 7/8 in. subhorizontal section, numerous problems were encountered due to mechanical failures and the heterogeneous nature of the reservoir. Slim-hole equipment failures also necessitated a second sidetrack.

A significant amount of prolific sand was encountered and the presence of subseismic faults was recognized from log correlations. The well is producing 1.3 x 10{6}cu m/d, which is above expectation considering that only 60% of the well could be completed. Nederlandse Aardolie Maatschappij's first attempt to challenge such geologically complex, labyrinth-type reservoirs by subhorizontal drilling therefore can be considered successful.

AAPG Search and Discovery Article #90990©1993 AAPG International Conference and Exhibition, The Hague, Netherlands, October 17-20, 1993.