Integrated Approach for the Quantification of Best Reservoir Quality (kerogen Vs Bitumen) and Production of Unconventional Oil Play - A Case Study From Onshore Abu Dhabi - UAE
Authors: Ibe Eziulo , Jha Bhawesh , Uluyuz Sila , Kerrouche Nawal , Panchakarla Anjana , Kulkarni Aditee , Van Laer Pierre , Al Marzooqi Hassan , Alharthi Amena , Baig Muhammad , Al Hashmi Abdulla , Brooks Trevor 
Published: October 2022

Several challenges are associated with reservoir characterization of organic-rich, unconventional plays, most significantly with estimating producible hydrocarbons and identifying potential zones to land horizontal wells and subsequent stimulation. This paper illustrates integrated approach towards successful characterization of the Cretaceous carbonate major source rock-a lateral seal Shilaif formation in the recently developing area of syncline shape field in Onshore UAE.

The Shilaif formation that was deposited under intra-shelf basinal conditions, contains sediments of argillaceous limestone, mostly fine-grained packstones and shaly lime mudstone-wackestones with subordinate calcareous shales in the lower part. Presence of bitumen and low permeability indicate the requirement to stimulate the wells effectively. Quantification of bitumen and light hydrocarbon through integration of advanced and conventional log data with core data and mud logs plays a critical role in the evaluation and development of these organic-rich reservoirs.

Extensive data acquisition was planned with a wireline suite that included resistivity/density/neutron/spectral gamma ray; acoustic logs; resistivity image; nuclear magnetic resonance (NMR); advanced elemental spectroscopy; and dielectric technologies to characterize the hydrocarbon potential of organic-rich Shilaif unconventional play.

NMR and Spectroscopy were used to refine lithology and porosity, which reduces the associated uncertinity in the evaluation of total organic carbon (TOC) and volumes. The advanced elemental spectroscopy data provided the mineralogy, the amount of carbon in the rock, and consequently the associated organic carbon within the Shilaif formation. The NMR technology provided lithology-independent total porosity and moveable versus non-moveable fluids quantification when integrated with density/neutron. NMR technology in this present case study was used to identify and differentiate the organic matter and hydrocarbon presence within the Shilaif formation. The water filled porosity and textural parameter from dielectric inversion results helped in more accurate water saturation estimation in the tight formation.

Acoustic data results and high-resolution resistivity image logs were used to evaluate the geomechanical properties. In addition, Resistivity image data provided detailed knowledge of geological features, faults and natural fracture networks within the study zone to enable optimization of development scenario based on the reservoir properties.

The data integration work illustrated in the paper is a key for unconventional reservoir characterization that enabled identification of the potential zone/zones of interests for horizontal wells and the successful development of the organic rich rocks of the Shilaif formation.