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Abstract The natural gas in the Marcellus Shale is produced most efficiently through horizontal wells through multi-stage hydraulic fracturing stimulation treatment. Even though advances in technology have unlocked considerable reserves of hydrocarbon, the long-term production behavior of the horizontal well with multiple hydraulic fractures is not well understood. Therefore, it is essential to study and evaluate the impact of the different treatment parameters and formation properties on fracture properties and production performance. The objective of this study is to investigate the impact of the stress shadowing, stage sequencing, and the mechanical properties on gas production from multi-stage hydraulic fractured horizontal well completed in Marcellus Shale. A commercial hydraulic fracturing software was employed to predict the fracture properties for a multi-stage hydraulic fractured horizontal well in Marcellus Shale. The available information included gamma ray, density, resistivity, and sonic logs as well as the fracture treatment data. Minimum horizontal stress, instantaneous shut-in pressure (ISIP), process zone stress (PZS), and leak off mechanism were obtained from a Diagnostic Fracture Injection Test (DFIT). The predicted treating pressures by the model were matched to field data by adjusting the pipe friction and the number of perforations. The predicted hydraulic fracture properties were then incorporated in a reservoir model (simulator) to predict the gas production. The impact of stress shadowing, treatment size, fracturing sequencing, and formation mechanical properties on fractures properties (fracture half-length and conductivity) and gas production were then investigated. Stress shadowing was found to impact fracture properties especially, the fracture width. This in turn, resulted in lower gas recovery. The impact of the stress shadowing increases as the treatment size increases and stage spacing decreases. It must be noted that as the treatment size increases and the stage spacing decreases (more stages), the gas recovery will increase due to larger stimulated volume. At the same time, the stress shadowing would have more negative impact on the gas recovery. Additionally, the results indicated that the reduction in fracture width, and as a consequence the reduction in gas recovery, is more significant in sequential fracturing as compared to simultaneous fracturing.
Abstract It is very difficult to predict the hydraulic fracture properties in shale gas reservoirs, such as Marcellus shale, because of the complex nature of hydraulic fracture growth, lack of good quality reservoir information, and very low matrix permeability. Furthermore, Marcellus shale is more sensitive to stress changes caused by hydraulic fracture shadowing and the net stress increase with production. The inclusion of the stress shadowing and the geomechanical factors provide a more realistic approach to predict the production performance of the horizontal wells with multiple hydraulic fracture stages in Marcellus Shale. The objective of this study is to investigate the impact of the stress shadowing on the hydraulic fracture properties in Marcellus Shale horizontal wells and consequently the production performance. The natural gas in the Marcellus Shale is produced most effectively by horizontal wells with multiple hydraulic fracture stages. The propagating fracture causes a stress change, commonly known as a stress shadow, in the vicinity of the fracture. The stress shadowing effects may result in a decrease in the width and conductivity of the subsequent fracture stages. In this study, a commercially available software which accounts for the stress shadowing was utilized to predict the hydraulic fracture properties based on the available information from a Marcellus Shale horizontal well. The available information included gamma ray (GR), density (RHOB), resistivity, and sonic (DTC & DTS) logs as well as the fracture stimulation treatment data. Treating pressures were calibrated by modifying the frictional parameters such as pipe friction and tortuosity factors. The predicted hydraulic fracture properties with stress shadowing effects as well as the Marcellus Shale properties were then utilized as the inputs for a reservoir simulation model in order to predict the production performance. Laboratory measurements and published studies on Marcellus shale core plugs provided the foundation for evaluating the impact of net stress on the matrix and fissure permeabilities as well as the relation between fracture conductivity and the net stress. The geomechanical factors were then incorporated in the production simulation model. Finally, parametric studies were performed to investigate the impact of fracture spacing on stress shadowing. The hydraulic fracture properties for different spacing were then incorporated in the production simulator to investigate their impact on the gas production. The inclusion of the stress shadowing and the geomechanical factors provided a closer agreement between the simulated and actual production history for the well under study. The stress shadowing effects were found to increase with closer fracture spacing. The fracture half-length, fracture height and especially, fracture width stress were impacted by stress shadowing. Additionally, it was observed that the stress shadowing impact is more significant in Marcellus shale due to low in-situ stress contrast with the adjacent zones. Furthermore, the stress shadowing effects were found to have more impact on the production than the location of the fracture stages. Finally, the stress shadowing can reduce gas recovery by as much as 20%.
Abstract Unconventional resources play an important role in meeting the energy demand across the world. In the United States, the unconventional resource development especially shale gas is booming. In order to achieve commercial production from ultra-low permeability shale formations, it necessary to use horizontal wells with multiple hydraulic fracture stages. The properties of the hydraulic fractures and as a result the production performance of the horizontal well with multiple fractures are impacted by the stress conditions during the fracturing and the production. The objective of this study is to investigate the impact of the stress shadowing and geomechanical factors on the gas production from the horizontal wells with multiple hydraulic fractures completed in Marcellus Shale. The fracture treatment data and shale properties (Young's modulus, Poisson's ratio, and in-situ stresses) from a Marcellus Shale horizontal well were utilized in conjunction with a commercially available hydraulic fracturing software to estimate of the hydraulic fracture properties for different stages which are impacted by stress shadowing. Laboratory measurements as well as the published studies on Marcellus shale core plugs provided the foundation for establishing the geomechanical factors relative to the matrix permeability, fissure permeability, and the hydraulic fracture conductivity. The predicted hydraulic fracture properties for different stages as well as the geomechanical factors were incorporated in a reservoir simulation model to predict the production performance of the horizontal wells under study. The inclusion of the stress shadowing effects provided a close match between the simulated and actual production performance for the well under study. Furthermore, the inclusion of the geomechanical factors in the model improved the simulation results particularly in the early stages of the production. The results indicated the stress shadowing negatively impacted the production. The impact of the stress shadowing can be reduced by increasing the fracture spacing.
The natural gas from Marcellus Shale can be produced most efficiently through horizontal wells stimulated by multi-stage hydraulic fracturing. The objective of this study is to investigate the impact of the geomechanical factors and non-uniform formation properties on the gas recovery for the horizontal wells with multiple hydraulic fractures completed in Marcellus Shale.
Various information including core analysis, well log interpretations, completion records, stimulation design and field information, and production data from the Marcellus Shale wells in Morgantown, WV at the Marcellus Shale Energy and Environment Laboratory (MSEEL) were collected, compiled, and analyzed. The collected shale petrophysical properties included laboratory measurements that provided the impact of stress on core plug permeability and porosity. The petrophysical data were analyzed to estimate the fissure closure stress. The hydraulic fracture properties (half-length and conductivity) were estimated by analyzing the completion data with the aid of a commercial P3D fracture model. In addition, the information from the published studies on Marcellus Shale cores plugs were utilized to determine the impact of stress on the propped fracture conductivity and fissure permeability. The results of the data collection and analysis were utilized to generate a base reservoir model. Various gas storage mechanisms inherent in shales, i.e., free gas (matrix and fissure porosity), and adsorbed gas were incorporated in the model. Furthermore, the geomechanical effects for matrix permeability, fissure permeability, and hydraulic fracture conductivity were included in the model. A commercial reservoir simulator was then employed to predict the gas production for a horizontal well with multi-stage fracture stimulation using the base model. The production data from two horizontal wells (MIP-4H and MIP-6H), that were drilled in 2011 at the site, were utilized for comparison with the model predictions. The model was then also used to perform a number of parametric studies to investigate the impact of the geomechanical factors and non-uniform formation properties on hydraulic fractures and the gas recovery.
The matrix permeability geomechanical effect was determined by an innovative method using the core plug analysis results. The results of the modeling study revealed that the fracture stage contribution has a more significant impact on gas recovery than the fracture half-length. Furthermore, the predicted production by the model was significantly higher than the observed field production when the geomechanical effects were excluded from the model. The inclusion of the geomechanical factors, even though it reduced the differences between the predictions and field results to a large degree, was sufficient to obtain an agreement with field data. This lead to the conclusion that various fracture stages do not have the same contribution to the total production. Based on well trajectory, variation in instantaneous shut-in pressure ISIP along the horizontal length, shale lithofacies variation and natural fracture (fissure) in the reservoir, it is possible to estimate the contribution of different stages to the production for both wells MIP-4H and MIP-6H.
Unconventional reservoirs have high initial production rates followed by a steep decline as compared to conventional reservoirs. The increase in the net stress with the production results in matrix and fissure permeability reduction and hydraulic fracture compaction and conductivity impairment due to proppant embedment. At the same time, the pressure decline will result in gas slippage and matrix permeability enhancement. The impact of the net stress and pore pressure changes are often neglected when evaluating the production performance of the shale wells. The objectives of this study are to investigate the impacts of net stress changes (geomechanical) and pore pressure changes (gas slippage) on the gas production from horizontal wells with multiple hydraulic fractures completed in the Marcellus Shale. Laboratory measurements on Marcellus shale core plugs provided the foundation for evaluating the impact of pore pressure and net stress changes on the matrix permeability. Additionally, these laboratory measurements on Marcellus shale core plugs provided the fissure closure stress. The results of the published studies on Marcellus shale core plugs were also utilized to develop relationships for hydraulic fracture conductivity and the fissure permeability as a function of the net stress in the shale. Core, log, completion, stimulation, and production data from the wells located at the Marcellus Shale Energy and Environment Laboratory (MSEEL) were utilized to generate the formation and completion properties for the base model for a horizontal well completed in Marcellus Shale. The results of the laboratory measurements and published studies were then incorporated into the base model to account for the impact of the stress on the matrix, fissure, and hydraulic fracture permeability (conductivity), and consequently on the production performance.
The model was utilized to determine the effective properties of the hydraulic fractures by history matching the production data from two horizontal wells at MSEEL site. For the comparison purposes, the geomechanical effects were excluded from the model, individually and all combined, to history match the same production data from the horizontal wells. The results indicated that the geomechanical effects for fissure permeability have a significant impact on gas production as compared to geomechanical effect for matrix permeability and hydraulic fracture conductivity. The gas slippage was found to have an insignificant impact on the production. The base model was finally used to perform a number of parametric studies to investigate the impact of fracture half-length, initial fracture conductivity, and fracture stages spacing on the stress-dependent fissure permeability.