Outcrop Analogues to Fractured Reservoirs, UAE

Fractures were not the focus of reservoir studies in Abu Dhabi for the last decades, although its importance in enhancing production, as the general understanding considering fractures are not contributing to production. The fractured carbonate outcrops provide useful analogue observations, data and concepts to support subsurface hydrocarbon reservoir characterization from well and seismic data. The fracture orientation, size, porosity, length, spacing, crosscutting relationships, fracture density versus lithology and bed thickness and connectivity are difficult to measure directly from subsurface well and core data. The understanding of fracture formation and distribution and their effects on fluid flow has been greatly improved by the use of outcrop analogue data through the current work. This paper address the fracture geometry, kinematics and mechanical properties based on outcrops matching Abu Dhabi subsurface reservoir analogues. Integrating outcrop data with fracture orientation and fracture density from core and borehole image data, and seismic capturing fractures characteristics. The outcrop analogues constrain the uncertainty and developing new concepts in characterizing the interplay of rock matrix and fracture networks relevant to fluid flow and hydrocarbon recovery. Analysing the fractures with fracture lengths, aperture, spacing per each interval and relate them to the tectonic event are extracted strictly in the reservoir section. The results showing developed highly dipping shear fractures with short length, small spacing and bimodal aperture distribution that related to fracture orientation. Fracture porosity is dependent on size and controlled by lithology, bed thickness, paleostress and rock composition. Understanding fractures and their behaviour will optimize production greatly and they create exploration targets in otherwise tight reservoir zones, including under-explored sections.

A Vertical Joint Spacing Calculation Method for UDEC Modeling of Large-Scale Strata and Its Influence on Mining-Induced Surface Subsidence

While universal discrete element code (UDEC) is widely used for understanding the mechanism of large-scale strata movement and the effects of mining subsidence on the environment, the fundamental knowledge of how to set vertical joint spacing (VJS) in UDEC is still not fully understood. To address the knowledge gap, we first present a novel VJS calculation method, then conduct UDEC experiments, and finally compare the predictions of UDEC models with field subsidence observation. The results suggest the following: (1) when compared to the conventional VJS setting (1× to 3× bed thickness), the maximum surface subsidence (MSS) prediction via UDEC models based on our proposed VJS setting method is closer to field observation; (2) a smaller but varying VJS setting can also have the effect of a larger VJS setting; and (3) with the increase in VJS, MSS first drops, then rises, and reaches the minimum when VJS is set at approximately 7× bed thickness. This paper provides an explanation of the VJS setting in UDEC and establishes a bridge between the KS theory and VJS, which is helpful for the sustainable development of such an UDEC modeling strategy and for a better understanding of the influences of mining subsidence on the environment in mining-affected areas.

Use of spectral decomposition technique for mapping geologic features of ‘Reigh’ field, Onshore Niger Delta

Spectral Decomposition Technique based on Short-Window Discrete Fourier Transform (SWDFT) was applied to threedimensional (3D) seismic data obtained from ‘Reigh’ field, onshore Niger Delta with a view to enhancing stratigraphic interpretation for geological features which are beyond seismic resolution. Two sands units from the study area were studied to produce spectrally decomposedsurfaces. The result of the study revealed thin bed layer at the centre of the field on sand unit ‘A’. Sand-filled meandering channel wasdetected and highlighted in the northern part of sand unit ‘B’ based on Red-Green-Blue frequency modulation of spectral decomposition. The study has enhanced geologic understanding of the field by improving thin bed resolution, highlighting geologic features and displaying bed thickness variation of studied sand units in the study area. Keywords: geologic features, Niger Delta, seismic data, spectral decomposition

Deep anterior lamellar keratoplasty for corneal penetrating wounds

Purpose: To report our surgical experience of deep anterior lamellar keratoplasty (DALK) performed in eyes with scarring resulting from a corneal penetrating wound without tissue loss. Methods: Case series of three eyes of three patients that underwent DALK for poor vision due to a scar resulting from a previous corneal penetrating wound. Surgery was performed at least 1 year after the initial injury. Manual dissection technique was used in all cases. Preoperative and postoperative best correct visual acuity (BCVA), postoperative residual bed thickness, and postoperative endothelial cell count (ECC) were evaluated. Results: Preoperative BCVA ranged from 1.3 to 1.0 LogMAR. Two eyes were pseudophakic and one eye had a traumatic cataract. Manual DALK was successfully accomplished in all three cases. The mean residual recipient bed thickness was 103 µm (range 68–130 µm). The mean endothelial cell loss at the 6th month of follow-up was 6% (range 3%–11%) with a further 1% decrease at 4 years. One of the patients underwent cataract surgery and limbal relaxing incisions 1 year after DALK having a total endothelial cell loss of 4.8% at 2 years of follow-up. BCVA at 2 years of follow-up was 0.1 LogMAR (range 0.22–0.0 LogMAR). No episode of rejection was recorded, and all grafts remained clear at last follow-up (5 years, range 4–6 years). Conclusions: Manual DALK should be considered in cases of corneal scars in optical zone resulting from penetrating wound.

CFD Analysis of Turbulent Flow of Power-Law Fluid in a Partially Blocked Eccentric Annulus

This study focuses on analyzing the turbulent flow of drilling fluid in inclined wells using the Computational Fluid Dynamics (CFD) technique. The analysis is performed considering an annulus with a fixed eccentricity of 90% and varying fluid properties, diameter ratio, and bed thickness to examine velocity profile, pressure loss, and overall wall and average bed shear stresses. CFD simulation results are compared with existing data for validation. The pressure loss predicted with CFD agrees with the data. After verification, predictions are used to establish a correlation that can be applied to compute bed shear stress. The established correlation mostly displays a discrepancy of up to 10% when compared with simulation data. The correlation can be used to optimize hole cleaning and manage downhole pressure.

Post-LASIK keratectasia in the context of a thicker than intended flap detected by anterior segment optical coherence tomography

The corneal flap created in LASIK is responsible for most of its advantages in comparison with surface ablation. However, lamellar dissection of the corneal layers in LASIK can also result in serious complications such as corneal ectasia. A 23-year-old man underwent LASIK for correction of −4.75 −2.00@15 in the right eye and −4.50 −2.00@160 in the left eye with a preoperative thinnest corneal thickness of 518 µm/right eye and 513 µm/left eye in 2009. An intended flap thickness and ablation depth in both eyes were 160 µm and 94 µm, respectively, and subsequently, residual stromal bed thickness was 264 µm/right eye and 259 µm/left eye. Several years after surgery, he was referred for the decreased vision. His corrected-distance visual acuity was 0.50 in both eyes. A scissoring reflex was found in retinoscopy. Orbscan imaging was compatible with keratoconus. Anterior segment optical coherence tomography was performed to measure the LASIK flap. It was much thicker (200 µm) than intended (160 µm), and therefore, the residual stromal bed thickness was much thinner. In summary, keratectasia may develop in cases where thicker than expected flaps result in excessive thinning of the residual stromal bed. The obtained results from this case emphasize and remind the importance of intraoperative measurement of flap thickness and using femtosecond and new criteria for patient selection to avoid post-LASIK keratectasia.