Bedding-plane slip effects during hydraulic fracturing have recently gained interest in unconventional plays due to their influence in hydraulic fracture growth in vertical and horizontal directions. However, most of the current workflows cannot fully model field-scale sub-horizontal orientation of bedding planes because of complications with gridding techniques, or due to simplifications related to the use of 2D models. These challenges have motivated the assessment of 3D bedding plane interactions on well performance using the embedded discrete fracture model (EDFM) technology for field case scenarios. An efficient hydraulic fracture propagation model is used to model hydraulic fracture growth in the presence of bedding layers. The model captures shear slippage at the bedding layer interfaces and corrects the calculated stress intensity factor to account for height containment. A hydraulic fracture model, constrained by geomechanical information, is built in a corner point grid. Resulting hydraulic fracture geometries and identified bedding layer fractures are transferred to EDFM by using a 3D bedding plane generator, which places sub-horizontal polygons across the well trajectory, honoring its orientation and geometry. To locate the spatial position of bedding layers, geostatistical constrains, core analysis and petrophysical interpretations – including well image logs – can be taken into account. Lastly, a reservoir simulation model is built to evaluate the effects of bedding planes on well performance. 3D effects of bedding planes in a shale gas reservoir were captured in a field case scenario using numerical models. Higher contribution to production was observed in the results of this study. The main reasons are larger fracture lengths generated along the pay zone caused by bedding plane influence in the fracture propagation process and shear slippage along bedding plane fractures, which create a larger effective conductive surface area. When modeling bedding planes, computational efficiency is substantial due to the EDFM method, preserving spatial orientation and geometry of each bedding plane. Direct assessment of bedding plane properties is provided, which highlights the importance of capturing their interactions with hydraulic fracture growth and well performance. A seamless integration of bedding plane models can be achieved in an efficient workflow that provides key lessons for future fracture design and well spacing optimization.
Multi-stage hydraulic fracturing has recently gained strong interest in unconventional plays in the Middle East due to high natural gas production potential. However, prevalent characteristics of the area, including high-pressure / high-temperature (HPHT) conditions and presence of complex natural fracture networks, pose significant challenges to reservoir characterization. These challenges have motivated the development of an integrated workflow using microseismic data for the characterization of reservoir properties resulting from the interaction between natural and hydraulic fractures. This study proposes a reliable method for modeling hydraulic fractures from scarce microseismic data. Initially, a microseismic model—based on field records of microseismic data and natural fracture spatial characterization—was developed. Issues related to limited microseismic data availability were tackled through combination of a probabilistic algorithm, Gaussian Mixture Model, and a DFN model. Then, the resulting synthetic microseismic events enabled the generation of a hydraulic fracture model using the embedded discrete fracture model (EDFM) and an in-house microseismic spatial density algorithm that captured major hydraulic fracture growth tendencies. Next, the created hydraulic fracture geometries were validated against a physics-based hydraulic fracture propagation model. Lastly, a single-well sector model—based on a corner point grid that honored the original 3D discrete fracture network (DFN)—was history matched, confirming the successful application of the proposed methodology.
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.
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