Significance of Fault Seal from Exploration to Field Development – Geomechanical Perspective

Abstract

In exploration prospects, it is important to quantitatively assess the seal. In traps where there is no limit to charge from migrating hydrocarbons, the column height will be determined by the weakest seal. It was found that hydrocarbon column height of 1200 feet would impose an additional 101.5 psi on the sealed fault plane (Yielding et al., 2002). However, uncertainty of fault seal breaching potential by stress built up is high, and hence makes it difficult for accurate prediction of hydrocarbon height without proper geomechanical assessment. In the case of field development, water or water alternating with gas (WAG) injection to maintain or improve production may cause irreversible damage to various fault seals where inevitable communication among different reservoir or horizons may occur. This article discusses the role of geomechanics, i.e. pore pressure and in-situ stresses and its impact on fault seal. Accurately mapping fault dip and dip azimuth from seismic interpretation are very key, as stress distribution across the fault is a function of dip of faults and dip azimuth relative to the stress orientation. Geomechanical analysis is performed to evaluate effective normal stress and shear stress on the fault plane. This analysis helps in understanding if the faults are critically stressed (tendency for shear slip) or not.

AAPG Datapages/Search and Discovery Article #90334©2018 AAPG Middle East Region, Second EAGE/AAPG Hydrocarbon Seals of the Middle East Workshop, Abu Dhabi, UAE, April 16-19, 2018