A Geochemical Technique for Formation Evaluation and Oil Water Contact OWC Identification in a Mature Tight Carbonate Reservoir Field in Abu Dhabi, UAE

Abstract

Abstract Direct hydrocarbon measurement on extracts of core and cuttings and SARA (Saturate, Aromatic, Resin and Asphaltene) compositional analysis integrated with mud log and petrophysical data provide a high confidence reservoir saturation assessment and oil-water-contact (OWC) identification where testing and perforation decisions can be timely and cost effectively achieved. A suite of forty eight (48) core plug and cuttings samples from seven (7) wells were analyzed. SARA composition were determined on extracted samples to assess hydrocarbon saturation and OWC through the reservoir of interest. Log and core data comparison with a vertical well, drilled nearby previously, may help to provide hydrocarbon saturation assessment of the section drilled in the horizontal section. However, despite detailed core studies on the vertical well drilled nearby, encountering surprises in the horizontal section due to the complexity of geology is not un-common. In order to circumvent these surprises, here we propose a cost optimized quasi real time formation evaluation and OWC identification using analytical and interpretive protocol that has proved extremely helpful in X reservoir in an oil field in Abu Dhabi. Data and interpretive protocol adopted in this study, although applied to an appraisal scenario, has equally good application potential for development drilling for the selection of an optimal perforation interval. The novel integrated approach presented here utilizing mud log, extract yield normalized to rock weight and SARA composition, though present and utilized independently for decades in the industry, has been adopted concurrently to assess hydrocarbon saturation and OWC identification. Coupled with conventional open hole logs, mud log and extracts geochemical data on core and cuttings samples provide a robust perforation or completion interval selection. Such perforation interval selection or isolation of high water zone in a horizontal well scenario is particularly very critical in thin and tight reservoirs where improper well completion may severely impact reservoir performance and project's economics.