Modeling In-situ tectonic stress state and maximum horizontal stress azimuth in the Central Algerian Sahara – A geomechanical study from El Agreb, El Gassi and Hassi Messaoud fields

• Published in: Journal of natural gas science and engineering 2021-04, Vol.88, p.103831, Article 103831
• Main Authors: Baouche, Rafik, Sen, Souvik, Chaouchi, Rabah, Ganguli, Shib Sankar
• Format: Article
• Language: English
• Subjects: Breakouts; Image logs; In-situ stresses; Maximum horizontal stress; Saharan Algeria; Stress orientation
• ISSN: 1875-5100
• DOI: 10.1016/j.jngse.2021.103831

Central Algerian Sahara hosts many prolific hydrocarbon accumulations in the Paleozoic successions. In this work a contemporary stress field of the Saharan platform has been evaluated using the dataset from recently drilled wells in El Agreb, El Gassi and Hassi Messaoud fields. A pore fluid pressure gradient of 0.56 PSI/feet is interpreted from the in-situ measurements in the Paleozoic reservoir units. Vertical stress (Sv) modeled from the bulk-density data indicates an average of 1.02 PSI/feet gradient. Rock elastic property-based approach is employed to model the magnitudes of minimum (Shmin) and maximum horizontal stress (SHmax) components, which were calibrated with leak off test/minifrac and breakout widths, respectively. Paleozoic stress profiles reveal Shmin/Sv range of 0.74–0.84, while SHmax/Sv varies between 1.1 and 1.33. Subsurface stress distribution indicates that the present-day stress field in the Saharan platform is principally strike-slip faulting (SHmax > Sv > Shmin). A cumulative 1490 m of B-D quality wellbore breakouts, inferred from the acoustic image logs, suggest a NW-SE/WNW-ESE SHmax orientation, which is parallel to the absolute African plate motion and Africa-Eurasia plate convergence direction, implying ridge push force to be the dominant contributor to the tectonic stress field. Mean SHmax orientation shows slightly anticlockwise rotation (126°N to 144°N) from south (El Agreb) to north (Hassi Messaoud field). Inferences are discussed regarding the fault slip potential and hydrocarbon reservoir development. •This work interprets the pore pressure and in-situ stress magnitudes of the Central Algerian Sahara.•B-D quality wellbore breakouts from acoustic image logs suggest NW-SE/WNW-ESE SHmax orientation.•Regional SHMax is parallel to the absolute African plate motion and Africa-Eurasia plate convergence direction.•The present-day stress field is principally strike-slip faulting (SHmax > Sv > Shmin).