FRIKKEN, HARM W., N.A.M. b.v. (Shell International), Assen, Netherlands

ABSTRACT: CBIL Logs: Vital for Evaluating Disappointing Well and Reservoir Performance, K15-Fg Field, Central Offshore Netherlands

The first two development wells in a gas field offshore Netherlands showed large variations in productivities, sharply declining rates and only 30% of the total field GIIP to be connected. This poor performance reflects stratigraphic and structural reservoir compartmentalisation.

A Circumferential Borehole Imaging Log (CBIL), run in the second development well, enabled a detailed stratigraphical analysis and identified otherwise undetected thin, frequently highly productive aeolian layers.

The CBIL also detected a small, sub-seismIc resolution reverse fault cutting the well, as well as anomalous structural dips around the well, which are probably the result of fault drag. Moreover the CBIL showed the presence of borehole break-outs and two families of shear fractures, confirmed by cores, indicating historical stress field rotation of up to 600. Disappointing production rates reflect the presence of near-wellbore, probably fault-related cemented shear fractures.

The CBIL data and lineations observed on seismic attribute maps contribute to a concept of dextral wrench tectonics across the field, with related synthetic and antithetic strike-slip faults, reverse faulting and folding. Such a configuration consisting of partly and fully sealing faults, confirmed by pressure behaviour, is the main cause for the poor gas connectivity.

The CBIL is a cost effective tool and its interpretation created scope for additional recovery by giving a better understanding of field architecture and well behaviour. This work enables optimization of the planning of locations and orientation of future development wells and design of hydraulic fraccing programs.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.