T R Walsgrove, M Daneshzadeh
Amoco (UK) Exploration Company
J P Dusang
Schlumberger Exploration & Reservoir Services (UK)
ABSTRACT
Advancements in logging and MWD technology now allow for the acquisition of all basic formation evaluation measurements while drilling ‘high risk” or difficult wells. This application can result in significant cost savings to operators, but only if geologists, petrophysicists and reservoir engineers are willing to accept Measurement While Drilling (MWD) data in lieu of traditional wireline (WL) measurements.
On a typical development well 22/17-T12 in the Arbroath Field of the North Sea, considerable difficulty was encountered while attempting to log with conventional and drillpipe-conveyed logging methods. Finally, after many unsuccessful attempts over a period of one week, MWD equipment was inserted into the bottom-hole assembly (EHA) and acquired all basic formation evaluation data in one “wash down” trip through the primary target interval.
In order to demonstrate the similarity of traditional wireline data, with data acquired using MWD technology, an equivalent suite of both measurements was obtained on the subsequent well 22/17-Tl3. The corresponding data sets were then compared for differences. A computer processed interpretation (CPI) was also generated for each data set and the results compared to assess the impact on reservoir calculations.
A cost analysis was performed on the possible savings which could be realised by utilising MWD preferentially to wireline in “high risk” or highly deviated wells. As these situations normally require considerable rig time, either because of borehole problems or drillpipe-conveyed logging services, the primary savings centred about increasing rig efficiency.
The result of the data comparison between WI and MWD indicated the primary differences are related to general depth control and vertical resolution of the analogous measurements. CPI comparison showed insignificant differences between final reservoir calculations from the two data sets. The foremost benefit of MWD was in the rig time.