As the demand for natural gas is increasing, the exploration and appraisal activities for unconventional gas resources is expanding and becoming significant to fulfill the global demand. These Unconventional resources are known to have complex geochemistry and rock physics. Understanding the complex nature of unconventional rocks is challenging and requires comprehensive integration with an advanced reservoir characterization approach. In this study, a comprehensive integrated rock characterization workflow was designed to understand the challenges and uncertainties associated with the Diyab Formation unconventional rocks. More than 800 ft of unconventional cores were analyzed to characterize the Jurassic carbonate succession of Jubaila, Hanifa and Tuwaiq Mountain Formations through an integrated workflow. The workflow includes core and OH logs based initial rock classification through machine learning known as "Heterogeneous Rock Analysis" (HRA). Based on HRA, the samples selection for Unconventional and advanced Geomechanical core analysis was applied, followed by core data interpretation, core to logs integration and refining reservoir quality. Unconventional and advanced core analysis in this workflow include but not limited to following types, liquid TRA, TOC, HAWK, Vitrinite Reflectance (VR), Core-NMR T2, MICP, 2D/3D SEM, Dean Stark, XRD/XRF, Geomechanics (Brazil Tensile Strength, Unconfined Compression (UCS), Single (TXC) and Multi Stage Triaxial (MTXC), Multi-Stress Compression (MSC), Biot coefficient test), etc. Core analysis results were interpreted and integrated with the logs to better understand and characterize the unconventional reservoir qualities. Sample selection was performed using all available data, to capture the variations in petrophysics as well as geomechanics and geochemistry, particularly organic matter content, and mineralogy within each identified petrophysical rock class. Core logs, plug analysis, and wireline data have been integrated and generally showed excellent agreement within the range of associated uncertainties, which can be attributed to rock tightness and resolution variations. Geochemistry (TOC, HAWK & VR) shows high concentration of kerogen, initially of type IIS but presently with low HI in which maturity reflects the dry gas window and possible condensate. Porosity ranges from 2.7% to 8% with a maximum reading reported from MICP data. The 2D & 3D SEM images provided some key findings, associated with different porosities either connected, isolated and/or organic matter porosity systems in given samples. These complex porosities systems cannot be captured by only conventional methods. The organic type of porosity is important as it provides further support to matrix porosity connectivity. Integrating this knowledge with logs, geochemistry, petrophysics and mineralogy helped to refine the initial characterized rock properties. In addition, the geomechanical understanding took the integration step further to identify potential zones for fracking and testing based on the classified stress regime.

The development of unconventional target in the Shilaif formation is in line with the Unconventional objective towards adding to ADNOC reserves. For future optimization of development plans, it is of utmost importance to understand and test and therefore prove the productivity of the future Unconventional Horizontal Oil wells. The Shilaif formation was deposited in a deeper water intrashelf basin with thicknesses varying from 600 to 800 ft from deep basin to slope respectively. The formation is subdivided into 3 main composite sequences each with separate source and clean tight carbonates. The well under consideration (Well A-V for the vertical pilot and Well A-H for the horizontal wellbore) was drilled on purpose in a deep synclinal area to access the best possible oil generation and maturity in these shale Oil plays. Due to the stacked nature of these thick high-quality reservoirs, a pilot well is drilled to perform reservoir characterization and test hydrocarbon type and potential from each bench. Fracturing and testing are performed in each reservoir layer for the primary purpose to evaluate and collect key fracturing and reservoir parameter required to calibrate petrophysical and geomechanical model, landing target optimization and ultimately for the design of the development plan of this stacked play. Frac height, reservoir fluid composition and deliverability, pore pressure are among key data collected. The landing point selected based on the comprehensive unconventional core analysis integrated with petrophysical and geomechanical outcomes using post vertical frac and test results. Well A-H was drilled as a sidetrack from the pilot hole Well A-V. This lateral section was logged with LWD Triple Combo while Resistivity Image was acquired on WL. Based on the logging data the well stayed in the target Layer / formation, cutting analysis data for XRD and TOC was integrated with the petrophysical results in A-H well. Production test results from subject were among the highest rate seen during exploration and appraisal of this unconventional oil plays and compete with the current commercial top tier analog unconventional oil plays. Achieving those results in such early exploration phases is huge milestone for ADNOC unconventional exploration journey in UAE and sign of promising future development.

Economical hydrocarbons production from unconventional resources is intrinsically related to stimulation effectiveness and capacity of the created hydraulic fractures to drain the target resource in an efficient manner, this is certainly without overlooking the significance of other resource geological, petrophysical, geomechanical, and other rock quality aspects. Considering the unique characteristics of each unconventional resource and the varying rock qualities and geological features, each resource should be considered separately when attempting to define the most optimum stimulation design approach that yields the best well productivity results and best EUR's, this means that a stimulation design approach that was successful in a specific play might not yield the same success if applied in a different play. In general, the overall stimulation effectiveness in unconventional horizontal multi-stage completions requires a good understanding of the geological, petrophysical, and geomechanical characteristics of the asset in hand as well as an understanding of the natural fracture's distribution, rock heterogeneity, and other aspects, eventually integrating those understandings to design an effective stimulation approach that similarly considers cost and operational efficiency parameters. Efficiency of the stimulation treatments requires an optimal placement of perforation clusters, with reasonable spacing that allows for creating the target fracture geometry/complex fracture network while considering fracture interferences, and other geometry controlling aspects. One of the most important considerations when designing a fracture treatment is fracture conductivity which is the ability of fractures to convey produced fluids into the wellbore (fracture permeability multiplied by fracture width (md-ft). In general, fracture conductivity along the created fracture network as well as in the near-wellbore area defines how effective is the fracture in delivering hydrocarbons into the wellbore, the target fracture conductivity values however vary with respect to formation rock permeability ranges and nature of produced fluids. This paper presents a comparative study of fracturing design and operational execution approaches for two exploration wells drilled in the oil-bearing Shilaif unconventional formation in the UAE, both wells are drilled targeting the same rock sequence and both possess very similar rock qualities. The paper covers aspects studied to analyze the suboptimal performance of the first well and the adjustments made to the fracturing design and fracture conductivity improvement of the second well, and how it entirely changed the productivity profiles and significantly improved the EUR for the target resource, which in turn had made this asset much more attractive for future full development plans.

The paper outlines the technical and operational journey experienced in completing this appraisal program, from wellbore preparation to the production. The paper will describe how the intervention tools and practices varied between the two wells drilled in same target and 500 ft a part. Also, the paper going to address the maximize operational efficiency, reduce emissions and availability of local resources. In addition to the modification and customization of available technologies and tools to address the UAE unconventional formations. Multistage well completions have been developed in the last two decades. Much of this advancement can be attributed to the unconventional shale Oil and Gas plays technology revolution, in which numerous transformational tools, techniques, and concepts have led to the efficient development of ultralow- permeability resources on a massive scale. However, careful consideration must be taken because these techniques cannot be used in areas outside in early in life fields, where reservoir rock properties and stress regimes are considerably different. Therefore, if not properly designed this can compromise the effectiveness of the hydraulic fracture treatment and impair project success which, impact energy self- sufficiency followed by strategy for the country. Diyab Reservoir is an organic-rich limestone unconventional play and our focusing area is located in Al Dhafra region, 250 km west of Abu Dhabi. The target formations comprise of extremely high stress rock in addition to the high-pressure and high temperature (HPHT). The appraisal strategy included two horizontal wells PAD that completed simultaneously (zipper) with massive multistage hydraulic fracture treatments using the perf and plug technique. Wells were long term flow tested through an early production facility to reduce emission while collecting key information to reduce the associated uncertainties and design a robust field development plan. The obstacles that have been faced and are still ongoing with this campaign is highlighting the importance of several critical factors. These including multidisciplinary integration and planning, wellbore construction impacts, contractor performance and tool reliability. This paper is providing a summary of case histories and operational results for the first horizontal wells intervention techniques used in UAE high-pressure and high-temperature (HPHT) reservoirs. This represents a very important contribution and key factors to UAE Gas self-sufficiency and Energy transition strategy plan.

The Diyab Formation is an organic-rich carbonate rock with low permeabilities and is one of the first unconventional targets to emerge in the Middle East. Vertical and horizontal exploration wells were drilled during the past years with proven productivity in the United Arab Emirates (UAE). Coupled geomechanical and reservoir characterizations of the Diyab formation are crucial for the successfulness of Stimulated Rock Volume (SRV) Creation and hydraulic fracturing operations which can have a direct impact on production performance. The objective of this study was to perform a full characterization of the Diyab formation based on extensive datasets that include logs and cores. The outcome of this integrated characterization work is used to assess the behavior of the Diyab formation across the concession block. First, we present the geology and general context of the studied area. Next, we detail the current understanding of the structural lineaments and natural fractures across the block. Then, based on full characterization work originating from data acquired on exploration and appraisal wells, we show how the results of geomechanical characterization together with the analysis of reservoirs quality/geological data allow us to suggest a vertical sub-division for Diyab formation. We explain further how the reservoir/geology, geomechanical parameters and natural fractures change laterally between wells. Reservoir characterization work concluded that there are some lateral variabilities in Diyab formation such as the change in the thickness/mineralogy of the carbonate bench and thickness of the porous wackestone. Some lateral variations in geomechanical/SRV parameters are observed within the block, resulted mainly from change in natural fractures density and properties of the carbonate bench and porous wackestone. This work is the first result of the integration of the current available data and the knowledge on Diyab formation, which could potentially evolve with the acquisition of new data and analyses. The combination of a full geomechanical characterization with a reservoir quality and structural geology study allows to propose a detailed reservoir and geomechanical sub-division for the Diyab formation. This approach will aid to better understand the lateral variability of facies, reservoir quality and geomechanical properties within the block which are crucial for successful development of this unconventional play.