1.1 Abstract:- Structural timing in relation to hydrocarbon charge timing has a significant impact on hydrocarbon prospectivity for Khuff and pre-Khuff reservoirs in Abu Dhabi. Maturation of Silurian source rocks began more than 150 million years ago and continues on until today in some parts of Abu Dhabi. A mix of structural growth histories is also observed with some very old structures pre-dating source rock maturation and other very young structures related both to emplacement of the Semail Ophiolites and Zagros uplift. Some of these young structures are located in areas where charge had already finished before the structure formed. Comparing the growth history of each individual structure to the Silurian source rock maturation history at each structure location can explain much of the observed Paleozoic gas distribution that has been observed by exploration drilling. This study investigates the impact of growth timing on the presence of hydrocarbons. It is believed that the use of this analysis substantially increases the confidence in assessing prospect risk ahead of drilling. In this paper, we reflect on our efforts to undertake comprehensive investigations of the geology of the region. This discussion will cover the methodology which is used to perform the analyses of the growth history. Measuring the growth from seismic sections and from depth contour maps were the two basic methodologies applied. The interpreted growth histories are compared to the tectonic history of the basin. Basin modeling to understand the timing of source maturation was a separate study, but the results of that work will be shown and the growth history will be compared to the charge history. Examples from Abu Dhabi fields are provided in this study to illustrate our concepts. 1.2 Introduction:- An intensive joint exploration study has been conducted by Abu Dhabi National Oil Company (ADNOC) and ExxonMobil (XOM) in order to understand the mechanism of hydrocarbon system in the Paleozoic section. During the study, both onshore and offshore areas have been investigated and evaluated. The study classified some key elements that would control important factors to review and rank exploration opportunities in Abu Dhabi. As in any general exploration study seismic data should be good enough to produce reliable maps hence each available seismic data set was utilized to help in this study. The well data was also integrated into the project, which allowed seismic horizon to be tied to their actual depths. Several technologies were employed and many data sets were evaluated to achieve the study objectives. The major work highlighted and discussed here is the structural timing which led to emphasizing new insights for the Paleozoic hydrocarbon system that helped in classifying areas of highest exploration interest.

Producing hydrocarbon directly from the early mature source rock is becoming a subject of interest for Abu Dhabi National Oil Company (ADNOC) in recent years. The maturation modeling done in ADNOC for the Cenomanian Shilaif formation indicated the presence of early mature kitchens in the offshore and southern onshore synclines.Another maturation modeling showed that the Oxfordian Diyab Formation is also prospective mainly in the northwestern offshore area of Abu Dhabi.Several conventional stimulation attempts were made in order to produce hydrocarbon from these source rock intervals encouraged by strong hydrocarbon shows while drilling and high hydrocarbon saturation from interpreted logs. Unfortunately, no successful results were obtained during all previous trials.A volumetric calculation showed that the estimated volume of the hydrocarbon available in these new areas is significant and once a successful production method is implemented, an economical hydrocarbon recovery can be obtained.In 2011, ADNOC drilled one well in the onshore area of Abu Dhabi. A secondary objective of the well was to test productivity of Diyab source rock and for the first time in Abu Dhabi a new approach was planned and implemented to produce these source rock intervals.Due to logistical issues, the original testing design was not excuted, and a re-designed program was performed with the available equipments on site to prove the concept of producing hydrocarbon from such formations.Promising results of gas and condensate were obtained and assuming much better results if the well is drilled in the optimum potential location in the most northwestern onshore area of Abu Dhabi.In this paper, we will explain both the geological aspects of the potential Diyab source rocks in Abu Dhabi and the planned program, difficulties, executions and results of the new approached stimulation.

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