This paper will detail the coordination between multiple teams and across technical discipline groups to successfully drill a ϩ28000 feet (ft.) measured depth (MD) horizontal appraisal well in a high temperature, high hydrogen sulfide and carbon dioxide (H 2 S/CO 2 ) environment and acquire high quality measurement and logging while drilling (MWD/LWD) data.Strategic tripping practices were used to reduce the risk of temperature related MWD/LWD tool failures. Extensive fluid engineering work was conducted, to design a fit-for-purpose mud system to meet Al Hosn Gas's handling requirements. Effective surface gas removal techniques were used to preserve high quality drilling mud and insure communication with the MWD/LWD tools. Hole cleaning efficiency was determined and maintained by monitoring drilling trends against calibrated models. In addition, the bottom hole assembly (BHA) drive system was designed to maximize power at the bit.Specific drilling parameters allowed for a high rate of penetration (ROP) that effectively reduced exposure time of the down-hole tools to very high temperatures minimizing tool failures. Carefully planned fluid engineering provided constant stable mud properties, which allowed the removal of H 2 S/CO 2 , and insured adequate borehole cleaning and lubricity to alleviate torque and drag. This resulted in high quality borehole images. Lubricants to reduce torque to manageable levels were selected after exhaustive in-house testing. Similar fluid engineering practices were used to select H 2 S scavenger. An extension of the horizontal section beyond the directional plan was accomplished within operational limits set by Al Hosn Gas after all drilling risks were fully assessed.Acquisition of required high quality LWD data was successfully accomplished. LWD borehole images were available only in memory mode, however, azimuthal resistivity curves helped in making geosteering decisions in the absence of the real-time borehole image data. Despite the well being drilled in the pay zone for its entirety, a measurement after drilling (MAD) open-hole log was employed to acquire missing density data that was required after a tool failure. A full petrophysical analysis was completed using the recorded memory data. It was included in the reservoir geo-cellular model and helped to define reservoir properties with a high degree of confidence.Close collaboration and trust between all partners to continually challenge and redefine perceived technical and operational boundaries led to the successful drilling of Al Hosn Gas's longest well. All teams and personnel were aware of the challenges and developed solutions to acquire excellent MWD/ LWD data in one of Al Hosn Gas's most ambitious wells, to date.

In preparation for the hydraulic fracturing campaign, the Unconventional Resources Team at Abu Dhabi National Oil Company (ADNOC) has carried out stress measurements both in open-hole and cased-hole in a number of recently drilled wells. The current paper demonstrates the results of the stress measurements in open-hole in two wells drilled in two different geological settings. The main target chosen was the unconventional Shilaif formation. One well was located on top of an anticline and the other well penetrated the Shilaif formation in a syncline. High breakdown pressures were expected (especially in the syncline). In order to cope with the challenges expected during the stress testing in such environment, a wireline formation tester that included both single packer and dual packer was used to initiate breakdown and achieve measurement of fracture closure pressure. With the expected adverse rock properties, either natural fall-off or rebound technique was employed to obtain closure pressure. The single-packer module extended the differential pressure rating up to 12,000 psia in comparison to 4,500-psia rated dual packer. The single packer was used to initiate the fracture breakdown if dual packer was not considered sufficient. Formation pressures were measured at several depths with the dual-packer operations. The stress measurements were carried out not only in the Shilaif formation, but in the shale formations above (the Tuwayil formation) and below (the Mauddud formation) in order to check if the shales could be stress barriers for a large scale hydraulic fracture. The current paper explains the procedure followed during the stress measurements and shows an example of interpretation of the pressure data acquired with wireline formation tester comprising the single-packer and dual-packer systems. The stress measurements were used to calibrate results of the geomechanical modeling.

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.

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.

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.