Increase formation pressure understanding in Arctic environment
An operator was developing the central and eastern parts of a field
located offshore the Kara Sea in the Yamal-Nenets district of northwest
Siberia, Russia, and decided to drill extended-reach wells from land. Often,
produced layers are penetrated in the buildup section of the wells. In this
well, however, the layer in the buildup section had an unknown level of
depletion, introducing risk to the operation.
The drilling environment included several potential challenges, such as
wellbore instability, mud losses, packoff, and differential sticking. The main
risk in obtaining stationary pressure measurements was the possibility of
differential sticking in the target layer, which could have had very low
formation pressure caused by dramatic depletion.
Acquire and analyze formation pressure while drilling
After considering the challenging environment and narrow mud-weight
window determined by pore pressure and fracture gradient studies, Schlumberger
recommended running the StethoScope formation pressure-while-drilling service.
Because this was the first time that this service was used in continental
Russia, expert collaboration and extensive preparation were required to secure
the success of the operation.
The StethoScope service enables acquiring accurate, real-time pressure
and mobility measurements while drilling the well. In addition to classic
pressure data applications like determining reservoir potential and
hydrodynamic connectivity, the real-time StethoScope service allows calibrating
the wellbore stability model, optimizing drilling fluid weight and casing
depth, and enhancing well placement based on pressure and mobility values.
Optimized decisions with real-time pressure and mobility data
The Schlumberger team performed 21 pretests and used the results to
calibrate the existing geomechanical model that influenced the operational
recommendations for subsequent drilling programs.
Using the StethoScope service, the operator successfully acquired
pressure and mobility profiles across the target layer. The acquired data was
transmitted to and interpreted in a processing center that allowed controlling
test quality and adjusting the program in real time.
Actual formation pressure numbers confirmed that the layer’s
depletion was 70 psi higher than expected. The team also used the pressure
measurements to construct the formation fluid gradient, which suggested high
connectivity inside the layer. Because of good planning and flawless execution,
Schlumberger delivered high-quality data that enabled the operator to optimize
its field development plan.
