--> --> Impact of Geologic Description on Pore Pressure and Well Design: Shah Deniz, Offshore Caspian Sea

AAPG Annual Convention and Exhibition

Datapages, Inc.Print this page

Impact of Geologic Description on Pore Pressure and Well Design: Shah Deniz, Offshore Caspian Sea

Abstract

Shah Deniz is a giant, 30+ TCF gas condensate field containing multiple Pliocene reservoirs in multiple pressure regimes. The combination of the field's highly overpressured low net-to-gross intervals and pressure-regressed (and now depleted) reservoirs results in some of the most difficult drilling in the world. Due to the sheer extent of the field, covering nearly 150 km2, significant uncertainty still exists in multiple zones even after 6 appraisal wells and 20 development wells. The uncertainty encompasses not only pore pressure and fracture gradients, but also wellbore stability due to high maximum horizontal stresses. Geological models have informed recent updates to the Shah Deniz pore pressure profile from seabed to reservoir. Data from over 20 appraisal and development wells have been integrated into a new geological overburden model. The new holistic model results in an important update to a previous no drill zone, with impact on future exploration wells as well as a potential development manifold. In the reservoir section, the Shah Deniz team routinely performs open hole formation integrity tests (OHFIT) specifically to artificially strengthen, or stresscage, weak low pressure reservoirs in order to drill past high pressure zones to the primary producing reservoir. If fracturing occurs despite the well design, crossflow can occur from high pressured water sands into the gas reservoirs. Joint geological studies between reservoir management teams and new well delivery are required for a clear understanding of the crossflow risk and need for subsequent remediation. Lastly, geologically complex zones with a wide range of pore pressure uncertainty have the potential for influx and well control events. Geological description is crucial to define risk and design drilling parameters to mitigate risks from these zones.