Stylolites and porosity controls in the thamama-b reservior (part of the Lower Cretaceous Kharaib Formation) of Sahil Field, Abu Dhabi, U.A.E

Abstract

Stylolitization is a widespread diagenetic feature in Lower Cretaceous limestone reservoirs of the United Arab Emirates. The origin of stylolites and the controls on stylolitization are still debated, and the interaction between stylolitization and diagenetic fluid flow and porosity modifications is complex. This study interpreatate these topics by a petrographic and geochemical study of stylolitization in the Thamama B zone. The results provided quatitative documentation of the relationship among stylolite amplitude, stylolite spacing, and clay content of the host rock. These correlations suggest that higher clay content correlates with smaller stylolite amplitude and higher abundance of stylolites. Two generations of stylolites are identified in the Thamama B zone. Early stylolites (before oil accumulation) occur in the top and basal interval (top 3.7m and basal 5.2m respectively) of the Thamama B zone, while late stylolites (post-oil) are mainly located in the center main part of the B zone. Because the top interval has high bulk-rock alumina content than the certer interval (too few data collected for basal interval), it is concluded that clay minerals have facilitated early formation of stylolites. Negative correlation is observed between porosity and stylolite amplitude, which supports the hypothesis that stylolitic dissolution provided cement that was precipitated in the pores of the surrounding rock. Negative correlation between porosity and distance to nearest stylolites further suggests that most of the carbonate ions released by dissolution along the stylolites were precipitated before diffusional transport over a distance of roughly 7 ft (5.2m). Diagenetic kaolin, dolomite, calcite, and small amounts of pyrite and sphalerite occur along and in the vicinity of the stylolites, which suggest the influx of hydrocarbon and iron-zinc rich fluid along the stylolite during the late stage of burial diagenes

Date of Award	2015
Original language	American English
Supervisor	Stephen Ehrenberg (Supervisor)