Abstract

For more than 30 years of exploration in Tunisia, the Upper Cretaceous Campanian - Maastrichtien Abiod formation carbonates were not considered as a potential reservoir. This view was held in spite of the numerous hydrocarbon shows observed in several wells. With the discovery of oil in Maamoura followed by Sidi El Kilani (SLK) and Zinnia, the Abiod formation carbonates have become the focus of further exploration interest in northern and central Tunisia.

The attraction of this play is enhanced by the presence of fractures and an excellent overlaying seal provided by the formation shales. The Tunisian Sidi El Kilani Field was discovered by Kuwait Foreign Petroleum Exploration Company (KUFPEC) in 1989 with the successful drilling and completion of SLK-1 well, which tested 3,360 bopd from fractured limestones of the Campanian-Mastrichtian Abiod formation. Production commenced from several SLK wells in 1993 and cumulative production had passed 45 mmbo by the end of January 2005.

3D seismic survey along with several boreholes studies were conducted to better understand and characterize the fractured reservoir behavior within the hydrocarbon system. In late 2004 KUFPEC decided to run 3D visualization reservoir modeling for understanding the geological, geophysical and petrophysical data that is available to estimate the remaining reserves.

The main result gained from this study is indicated by the new reserve calculation and adding 2 million barrel of oil as a new recoverable attic reserve from SLK field to KUFPEC reserves.

Introduction

Sidi El Kilani oil field, which is, located 190km SSE of Tunis (Fig.1) was discovered by KUFPEC (TUNISIA) Ltd. In April 1989. Since then four wells have been drilled where two of them failed to prove any hydrocarbon accumulation, while the other two wells have been completed as oil producers. Field production started from early 1993 with an average rate of 5000 STBD. The production from three wells at a rate of 15000 STBD started in late 1993. Oil is contained mainly in fractures of the upper Abiod carbonates and is most likely sourced from the Turonian - Upper Cenomanian Bahloul Formation with yields from Middle Eocene time.

The Sidi El Kilani field is located in North-Central Tunisia within the Pelagian Platform, which forms the foreland area of the Atlas Thrust Belt. The region is part of the North Africa Craton, which has been subjected to several major tectonic events from Paleozoic to late Tertiary times. These include continental collision and uplift in Late Paleozoic (Hercynian), followed by relative movements between African and European plates in the Mesozoic leading to Jurassic rifting (neo-Tethys) and eventually plate convergence with subduction, and subsidence during Tertiary. The Tethyan extension from Mid Jurassic onwards caused fault block rotation, which locally resulted in facies and thickness variations particularly of Cretaceous carbonates in North-Central Tunisia. The dominant fault trends associated with this tectonic phase are NW-SE and NE-SW.

During Late Cretaceous compressive stresses resulted in thrusting which created asymmetric folds trending NE-SW. These movements were repeated in Eocene and Upper Eocene to Oligocene times associated with the Alpine/Atlassic tectonic events and the closure of the western Tethys Ocean. The SLK structure is N-S oriented elongate faulted anticline that formed in a transgression tectonic regime. A major wrench fault displaying left lateral movement (sinistral), indicating NNW principle stress field, cross cuts the field. Sidi El Kilani structure is a north to south-elongated anticline with four-way dip closure at the top of the Abiod reservoir (Fig. 2). The principal period of structural growth is dated late Eocene to early Miocene. A strong angular unconformity marks with movement. The uplift was probably due to halokenesis associated with a predominant extensional stress regime. This resulted in a large number of normal faults with NE-SW trend on the flanks and over the crest of Sidi El Kilani structure. These faults are dated to post Oligocene A major Wrench fault transects the structure along a NW - SE trend and separates the field into two main lobes. This fault is deep-seated, steep and has a significant left lateral strike- slip component. Its latest movement took place during the Plio-Pleistocene period (Ben Brahim, 1993).

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