ABSTRACT

A wide range of technologies and workflows is available to assist in optimising the horizontal drilling process in real time and provide thorough formation evaluation analysis while landing and steering the wells. Traditionally, advanced surface fluid logging (ASFL) has not been relied upon as one of these methods; however, developments in the real-time fluid analysis provided by this technology were utilised to achieve a better understanding of fluid distribution while supporting critical decisions landing the horizontal section of a production well.

Understanding the fluid complexity in a Danish North Sea chalk field was the main key in optimising the placement of the well. Initially, it was predicted that due to the migration of the gas cap, the fluids in the oil rim target would have undergone a significant compositional change from the virgin fluid. Placement of the well at the top of the expected oil column was critical to intercept as much of the oil as possible while mitigating against premature water/gas breakthrough and maintaining a minimum standoff from the gas-oil contact (GOC). To optimise this recovery, it was decided to integrate for the first time globally and in real time, ASFL with conventional logging while drilling (LWD) measurements. While building the inclination to the landing point of the well, a gradual variation in the composition from heavy to light oil was recorded. This is interpreted as an indicator of a moving GOC.

The ASFL technique provided accurate and immediate identification of subtle compositional changes in real time during the landing section and throughout the horizontal section. Oil was identified as the fluid in place at the point of landing, with six fluid facies identified throughout the reservoir section. The integration of petrophysical analysis from additional LWD tools with the ASFL service provided a better understanding of the fluid distribution in the reservoir while ensuring the wellbore did not exit into over- or underlaying formations.

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