Abstract Stratigraphic trapping mechanism plays a critical role for hydrocarbon entrapment within the Middle-Late Cretaceous reservoirs in the Al-Khafji area. 3D seismic data are acquired aiming at to delineate the stratigraphic and possible strati-structural traps and their associated reservoir setting. Seismic attribute analysis of 350 sq. km. of 3D seismic data of Al-Khafji oil field shows number of sinuous (channel-like) events in the north and north-east of the main Khafji Structure in Tayarat Formation of Late Cretaceous age. The present study utilizes twenty two well data in the crestal part of the Khafji structure to generate a semi-regional facies log, which is turn up-scaled using seismic attribute map. As the area is not covered by any well or other form of data a variogram analysis followed by sequential indicator simulation method was used to derive a facies model between Tayarat and Bahra Formation of Lower Cretaceous age. A volume extraction method was used to extract channel events and integrate into the modeling process to visualize and track channels.
Present study infers a possible definition of facies inside sinuous events and their exploration potential. Porosity estimation using seismic attributes as well as borehole data provides most likely reservoir properties exist in shallow Tayarat Formation. The depth converted and extracted sinuous bodies along with possible porosity profile not only provide a rapid inside into the geology but also indicate further exploration potential particularly in the north-eastern part of the main Al-Khafji field.
Introduction During Cretaceous times, the eastern part of the Arabian plate was covered by extensive carbonate platforms, which are the reservoir rock for the major hydrocarbon fields in the Arabian Gulf. Aggradations of carbonates in extensive shallow-water areas have been dominant, where many fields are prolific producers. Previous studies in the Arabian Gulf (Al-Fares et al.1998) critically investigate the Cretaceous platform edge consisting of well defined progradational features associated with structural highs. These platforms seem to consist of complex internal geometries, which have been identified from the seismic signatures of high resolution seismic data. The Al-Khafji oil field is located in the offshore part of Neutral zone between The Kingdom of Saudi Arabia and the State of Kuwait in the Arabian Gulf as shown in Figure 1. The field has been producing since 1958 mostly from Lower to middle Cretaceous carbonate sequences. The upper Cretaceous sequence has not been well explored, although it produces oil west of the Al-Khafji area, onshore in the SUG and Wafra main fields. 3D seismic survey was acquired in the Al-Khafji, where a number of wells have been correlated and calibrated with the Tayarat Formation.
In the exploration area to the north and northeast of the Al-Khafji field, sinuous shaped channel features may be interpreted as possible strati-structural traps at the top of Tayarat Formation. Good porosity is reported at the top of this formation from many wells. Furthermore, an unconformity at the top of the Cretaceous sequence may have facilitated lateral and or intra-formational migration of hydrocarbon into the Tayarat Formation reservoir units. An attempt has been made to explore this petroleum system using the newly acquired 3D seismic, well log motifs and seismic modeling of porosity attributes.
Problem Definition Structural and Strati-structural trapping mechanisms play critical roles for hydrocarbon entrapment within Upper Cretaceous reservoirs in the Al-Khafji area. The newly acquired 3D seismic data were aimed at delineating the stratigraphic and strati-structural traps and their associated reservoir settings. Predicting the porosity in any hydrocarbon reservoir is essential and it is one of the critical reservoir properties that assist in determining the reservoir potential of the top Tayarat Formation. The sparse wells in the area provide insufficient data to accurately predict the lateral variations in porosity, but results can be vastly improved by integrating the well data with the high density coverage provided from the 3D seismic data.