Present-day overpressure in southern Tunisia: Characterization, possible causes and implications for drilling operations. (December 2021)

• Record Type: Journal Article
• Authors: Akrout, Dhaou; Ahmadi, Riadh; Mercier, Eric; Montacer, Mabrouk
• Is Part Of: Journal of African earth sciences. Volume 184(2021)
• Publication Date: 2021-12
• Subjects: Pore pressure -- Tectonic stress -- Overpressure -- Gypsum beef -- Drilling operation -- Southern Tunisia; Earth sciences -- Africa -- Periodicals; Earth sciences -- Middle East -- Periodicals; Geology -- Africa -- Periodicals; Geology -- Middle East -- Periodicals; Sciences de la terre -- Afrique -- Périodiques; Sciences de la terre -- Moyen-Orient -- Périodiques; Géologie -- Afrique -- Périodiques; Géologie -- Moyen-Orient -- Périodiques; Earth sciences; Geology; Africa; Middle East; Periodicals; Electronic journals; 556.05
• DOI: 10.1016/j.jafrearsci.2021.104356
• Languages: English
• ISSNs: 1464-343X

Abstract

Abstract: Formation pore pressure in sedimentary basins is known to vary with depth. These variations are caused by one or more sedimentary, tectonic or diagenetic mechanisms. In Mesozoic basins of southern Tunisia, a detailed study has been carried out in order to characterize the regional pore pressure profile. The results show an over-pressure interval ranging from upper Triassic to lower Jurassic salts series. The study of possible overpressure mechanisms allows us to conclude that the present-day overpressure can be explained by the active compressional tectonics that is affecting the North African margin. Nevertheless, other past overpressures have been interpreted from this study and have been attributed to different mechanisms. One of the most important paleo-overpressure mechanisms was gypsum dehydration. This diagenetic reaction has led to pore pressure approaching lithostatic pressure, demonstrated by hydraulic fractures and beef veins observed in fields. In this study, we established a method based on a depth chart diagram enabling the identification of the likely mechanism involved in reservoir overpressure build-up and/or the prediction of a potential mechanism. This result could be important in the analysis of unexplored basins to predict the anticipated pressure profile and thereby reduce the risk of encountering unexpected overpressured zones and related drilling hazards. This method could be applied to other sedimentary basins with standard geological backgrounds. Highlights: Pore pressure profile in southern Tunisian basins. High overpressure magnitude in Triassic-Jurassic interval. Gypsum beef joints as evidence of paleo-overpressure. Modelling overpressure and paleo-overpressure origins. Gypsum dehydration and horizontal compaction mechanism.