Formation testing challenges in a high-temperature 6.5-in exploration
After drilling a high-temperature exploration well offshore Mexico into
a tight, deep carbonate reservoir, the operator needed high-quality formation
pressure measurements and sample collection for downhole fluid analysis (DFA).
This information was of critical importance for understanding the reservoir
fluid composition and identifying potential compartments.
The main concern was the large water influx that had occurred during
the drilling phase and required control through managed pressure drilling. Was
the water indicative of problems in well construction or was the well dry?
Representative pressures and sampling with zero sump fluid
To efficiently resolve these questions, Schlumberger deployed the MDT
Forte-HT formation tester with a dual-packer module and the 5-in Saturn 3D
radial probe. This combination provided operational reliability at high
temperatures and the flexibility to effectively isolate the test intervals for
addressing the challenging co-occurrence of lowpermeability matrix and open
fractures that were revealed by openhole logging images.
The Saturn probe acquires formation fluid with four self-sealing
elliptical probes that have the industry’s largest inlet flow area in
this hole size, totaling more than 59 in². Even in tight and challenging
formations, flow is quickly established and maintained from the entire
circumference of the wellbore instead of funneling fluid from the reservoir to
a singleprobe access point, thereby optimizing DFA, sampling, and transient
testing applications. This design also eliminates any sump volume, minimizing
storage volume effects and accelerating fluid cleanup.
The InSitu Fluid Analyzer real-time downhole fluid analysis system was
included in the formation testing toolstring to conduct DFA, ensure sample
quality, and definitively characterize the fluids at reservoir conditions.
Identification of reserves and completion guidance
The water influx during the drilling phase was causing the operator to
consider abandoning the well as water filled. Despite this poor prognosis, the
formation testing program proceeded, with the MDT Forte-HT tester, 5-in Saturn
3D radial probe, and InSitu Fluid Analyzer system efficiently returning
representative pressure and fluid composition data as the basis for a new
perspective on the reservoir potential. Formation fluid samples were also