For the development of Nahr Umr sandstone reservoir, in the lower part of this formation in Ratawi field, South Iraq, the standard architecture involves drilling highly deviated intermediate section and setting the 9 5/8' casing shoe within the middle of this formation. This interval corresponds to the Nahr Umr shale, which is known to be a problematic shale across the Middle East region. To define an optimal MW strategy, we conducted an extensive analysis of instability cases experienced by TotalEnergies and those reported in published literature. The various aspects of Nahr Umr shale have been addressed: in-situ stress orientation and stress regime, physical- mechanical properties, strength classification, anisotropy of the strength. We employed a multi-mechanisms failure model to predict the hole stability condition in terms of the minimum mud weight (MMW), including: shear failure, strength anisotropy, shale lamination, mud pressure filtration and creeping for this shale. Azimuthal effects, i.e well orientation, due to the anisotropy of horizontal stresses appear less significant than those of hole deviation angle because of strength anisotropy of the Nahr Umr shale. The strength anisotropy is estimated to have three times more impact than the hole azimuth. The cumulative effect of these failure mechanisms explains the persistent instability in both vertical and deviated wells, with well azimuth playing a relatively minor role. From a strict geomechanical point of view, drilling the high deviated well in NU shale requires a mud weight from 1.40 ~ 1.45 sg. This mud weight range should also be applied to wells with moderate deviation, i.e., between 30° and 60°, essentially due to the anisotropy of the NU shale. Success in drilling through the Nahr Umr shale requires not only appropriate MW but also effective mud sealing, compatible mud chemistry, and rigorous hole cleaning and back reaming practices.

To assess the risks related to induced seismicity due to operations in the subsurface, it is essential to employ appropriate simulation tools to assess the seismicity responses of faults. This paper presents a numerical workflow developed as part of the DynSEIS innovation project, which employs slip-weakening behavior through an advanced numerical framework. Initially, the approach was applied to 2D models, and the results were benchmarked against literature. A 3D realistic model was subsequently developed based on data from a real gas field and 3D numerical simulations were calibrated against field data and the seismogenic responses of the faults were assessed. Through these efforts, the use of an explicit solver in dynamic mode for calculating surface accelerations and velocities was demonstrated. Fault weakening laws with various descriptions for the fault (discrete, planes of weakness) were employed in different cases giving very consistent results compared to literature work. The capacity to quantify the surface response in terms of expected velocities and accelerations has been confirmed. The developed methodology demonstrates that using slip-weakening laws within relevant numerical schemes allows for better assessment of seismogenic fault slip, fault slip propagation, and the magnitude of energy released which is beneficial for better derisking of induced seismicity due to subsurface operations.

ABSTRACT: Solids production can occur in carbonate rocks even with high strength matrix, because of presence of natural fractures and vuggy or weak zones. Solid production is known to be a common factor in many oil and gas producing wells in carbonate reservoirs both at the early production period but also in later life of a reservoir under depleted conditions. There are many geomechanical material properties affecting the magnitude and behaviour of solids production. As part of the work done for a previous paper, a finite element model for an open-hole configuration was built to simulate a real case of solids production on a carbonate reservoir located in Abu Dhabi Offshore Field. This model was further enhanced to be extensively utilised for the scope of the current paper. Several simulations are conducted varying numerous geomechanical material properties of the model to assess the influence of each one of them on the magnitude and behaviour of the solids production. This assessment provides a comprehensive correlation between the variation of each geomechanical material property and the effect it has upon the amount and pattern of solids production. The assessment above and any possible future assessments of this type could guide the choice of completion and help the solid management decisions for the development of such carbonate reservoirs. 1. INTRODUCTION Solids production is a common industry dilemma in balancing efficient production volumes with damaging solids entering the well and top-side facilities. However, it should also be considered that solids production can occur in carbonate rocks, even with high strength matrix, due to the presence of natural fractures and vuggy or weak zones. A previous paper, (Pourpak et al., 2024) conducted a detailed postmortem analysis of solids produced from a fractured/vuggy carbonate reservoir from an Abu Dhabi offshore field. This analysis provided valuable insights regarding the mechanisms of solids production, and was supplemented with calibrated advanced finite element simulations. This paper further develops the modelling to explore the geomechanical parameters space of downhole and drilling conditions which may affect the volumes of solids produced. This aims to provide general guidance for operations in circumstances where data acquisition may be limited.

ABSTRACT: Solids production can happen in carbonate rocks even with high strength matrix, because of presence of natural fractures and vuggy or weak zones. Solids production is known to be a common factor in many oil and gas producing wells in carbonate reservoirs both at the early production period but also in later life of a reservoir under depleted conditions. In this paper, we present a real case study performed on a carbonate reservoir located in Abu Dhabi Offshore Field. The production of carbonate debris was observed in a 900m horizontal well completed as barefoot in Arab limestone formation which is a gas bearing reservoir on the area of study and is characterized by natural fractures and weak zones. Anomalous well head flowing pressure (WHFP) behavior and progressive reduce of gas rate were observed with choke fully open and the choke was found partially plugged by debris of centimetric size. The study goal was to investigate whether the solids production experienced was a result of the geomechanical behavior of the rock and fractures during production and to propose mitigations for future wells in terms of completion option and critical drawdown pressure (CDP). This solids production modeling study gave helpful insights regarding the mechanisms of solid production in open hole and cased/perforated wells for the studied carbonate formation. It could also guide the choice of completion and help the solid management decisions for the development of such carbonate reservoirs. 1. INTRODUCTION Solids production can happen from poorly consolidated carbonate rocks or even in high strength but naturally fractured vuggy carbonates including weak zones. The risk of solids production from carbonate rocks or mitigations of the risks have been discussed in recent literatures (Asadi et al, 2017, AL-Aamri et al, 2020, Ghazali et al, 2020). Solid production is a common factor in many wells in carbonates rocks (oil and gas) during production stages and especially in the later life of a reservoir under depletion conditions (Asadi et al, 2017). Clusters of cemented grains of the formation can be produced together with oil, gas, and water and these could have highly damaging effects on completion equipment, tubing, pipes, valves, and other facilities. Solids production is generally caused by mechanical failure of near wellbore formations due to effective stresses acting on borehole walls, and perforations under drawdown and well flowing conditions exceeding the mechanical strength of reservoir rocks (Asadi et al, 2017).

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.

The Diyab play is an emerging unconventional play in the Middle East. Up to date, reservoir characterization assessments have proved adequate productivity of the play in the United Arab Emirates (UAE). In this paper, an advanced simulation and modeling workflow is presented, which was applied on selected wells located on an appraisal area, by integrating geological, geomechanical, and hydraulic fracturing data. Results will be used to optimize future well landing points, well spacing and completion designs, allowing to enhance the Stimulated Rock Volume (SRV) and its consequent production. A 3D static model was built, by propagating across the appraisal area, all subsurface static properties from core-calibrated petrophysical and geomechanical logs which originate from vertical pilot wells. In addition, a Discrete Fracture Network (DFN) derived from numerous image logs was imported in the model. Afterwards, completion data from one multi-stage hydraulically fracked horizontal well was integrated into the sector model. Simulations of hydraulic fracturing were performed and the sector model was calibrated to the real hydraulic fracturing data. Different scenarios for the fracture height were tested considering uncertainties related to the fracture barriers. This has allowed for a better understanding of the fracture propagation and SRV creation in the reservoir at the main target. In the last step, production resulting from the SRV was simulated and calibrated to the field data. In the end, the calibrated parameters were applied to the newly drilled nearby horizontal wells in the same area, while they were hydraulically fractured with different completion designs and the simulated SRVs of the new wells were then compared with the one calculated on the previous well. Applying a fully-integrated geology, geomechanics, completion and production workflow has helped us to understand the impact of geology, natural fractures, rock mechanical properties and stress regimes in the SRV geometry for the unconventional Diyab play. This work also highlights the importance of data acquisition, reservoir characterization and of SRV simulation calibration processes. This fully integrated workflow will allow for an optimized completion strategy, well landing and spacing for the future horizontal wells. A fully multi-disciplinary simulation workflow was applied to the Diyab unconventional play in onshore UAE. This workflow illustrated the most important parameters impacting the SRV creation and production in the Diyab formation for he studied area. Multiple simulation scenarios and calibration runs showed how sensitive the SRV can be to different parameters and how well placement and fracture jobs can be possibly improved to enhance the SRV creation and ultimately the production performance.

This paper is devoted to study the elastic–plastic damage behavior of heterogeneous shale rocks. The representative microstructure of this kind of rocks is first studied in order to define the representative elementary volume for the implementation of homogenization procedure. Three relevant material scales are considered. Inter-particle pores are distributed at the nanoscopic scale. Fine grains of calcite and kerogen are immersed at the microscopic scale. Large grains of minerals are embedded at the mesoscopic scale. Effective elastic properties of shale rocks are first determined by using a three-step linear homogenization procedure. The plastic damage behavior is estimated by developing a three-step nonlinear homogenization method. The effective plastic behavior of porous clay matrix with nanoscopic pores is described by an analytical model. The effects of small and large grains of various mineral inclusions are investigated by using a two-step incremental model. The damage due to progressive debonding of mineral inclusions is taken into account. After the implementation of the proposed model, comparisons between numerical results and experimental data are presented.

Summary In this work, we concept-proved a core-to-log methodology that provides a fast calibration method for log-based elasticity. We measured rebound hardness in parallel to dynamic measurements of ultrasonic surface wave velocities (P and S) at the milimetric scale, then calibrated the results with discrete triaxial tests performed on plugs, representing all relevant lithological facies, and finally compared the results against log-based parameters. Our work shows that such integration helps at developing robust core-tolog elasticity relationships in the entire core length, eventually providing a proper foundation for better stiffness model prediction, at a fraction of the cost and time of traditional core acquisition programs. We have shown that calibrated high-resolution measurements at the core scale may be used to create accurate dynamic to static correlations, to identify and characterize potential barriers to fracture growth, and to characterize lithological facies for predicting their elastic properties at new wells when core data is not available.

Summary This project is aimed at simulation of the hydraulic fracturing process of naturally fractured tight/shale formation and optimization of SRV (Stimulated Rock Volume) and Production Performance using a data driven simulation approach taking into account operational costs and production benefits. A 3-dimensional geology model for a real unconventional formation was built in this study. Hydraulic fracturing simulation was conducted based on real hydraulic fracturing operations and the resulted model was then calibrated to the field data. Based on the calibrated model, a sensitivity study using a 3-well model (multi-well model) was performed to analyze the influence and importance of operational parameter variation such as well spacing, landing depth, stage design, slurry rate and slurry volume on hydrocarbon production. The resulted data driven models were combined with development/operational costs/benefits to optimize operational parameter taking into account the conflicting nature of EUR, NPV and ROI. The results of this study indicates that this data-driven optimization workflow is able to improve the decision-making process of hydraulic fracturing operations and shale/tight reservoirs development while including unit development costs and unit profitability.

Abstract The Upper Jurassic (Oxfordian to Late Kimmeridgian) Diyab Formation has served as the source rock for several world-class oil and gas fields in the Middle East. More recently it has become an emerging unconventional exploration target in United Arab Emirates (UAE), Saudi Arabia, Bahrain and its age-equivalent Najhma shale member in Kuwait. The Diyab is unique in comparison to other shale plays due to its significant carbonate mineralogy, low porosities, and high pore pressures. Average measured porosities in the Diyab are generally low and the highest porosity intervals are found to be directly linked to organic porosity created by thermal maturation. Despite low overall porosities, the high carbonate and very low clay content defines an extremely brittle target, conducive to hydraulic fracture stimulation. This coupled with a high-pressure gradient facilitates a new unconventional gas exploration target in the Middle East. However, these favorable reservoir conditions come along with some challenges, including complex geomechanical properties, a challenging stress regime and the uncertainty of whether the presence of natural fractures could enhance or hinder production after hydraulic fracture treatment. Only recently has the Diyab been studied in detail in the context of an unconventional reservoir. This paper presents an integrated approach allowing a multidisciplinary characterisation of this emerging unconventional carbonate reservoir in order to gain a better understanding on the plays’ productivity controls that will aid in designing and completing future wells, but already encouraging results have been observed to date.