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Pei, Yanli (The University of Texas at Austin) | Yu, Wei (The University of Texas at Austin / Sim Tech LLC) | Sepehrnoori, Kamy (The University of Texas at Austin) | Gong, Yiwen (Sim Tech LLC / The Ohio State University) | Xie, Hongbin (Sim Tech LLC) | Wu, Kan (Texas A&M University)
The extensive depletion of the development target has triggered the demand for infill drilling in the upside target of multilayer unconventional reservoirs. To optimize the hydraulic fracturing design of newly drilled wells, we need to investigate the stress changes in the upside target induced by parent-well production. In this work, an integrated parent-child workflow is presented to model the spatial-temporal stress evolution and propose the optimal development strategy for the upside target using a data set from the Permian Basin. The stress dependence of matrix permeability and fracture conductivity is determined based on available experimental data and incorporated in our reservoir simulation with the aid of an embedded discrete fracture model (EDFM). With calibrated reservoir properties from history matching of an actual well in the development target (i.e., 3rd BS Sand), we run the finite element method (FEM) based geomechanics simulator to predict the 3D spatial-temporal evolution of the local principal stresses. A displacement discontinuity method (DDM) hydraulic fracture model is then applied to simulate the multi-cluster fracture propagation in the upside target (i.e., L2BSSh) with the updated heterogeneous stress field. Numerical results indicate that stress field redistribution associated with parent-well production not only occurs within the development target but also vertically propagates to the upside target. A smaller parent-child horizontal offset induces a severer deviation of child-fractures towards the parent wellbore, resulting in more substantial well interference and less desirable oil and gas production. The parent-child fracture overlapping ratio in our study is in 0.6 ~ 0.8 for the 400 ft horizontal offset and 0.2 ~ 0.5 for the 600 ft horizontal offset. Varying the parent-child vertical offset gives the same trend as we change the horizontal offset. But with a delayed infill time, placing child-well in different layers causes more significant variation in the ultimate recovery. Moreover, infill operations at an earlier time are less affected by parent-well depletion because of the more homogeneous stress state. The candidate locations to implement infill-wells are suggested in the end for different infill timing by co-simulation of the parent-child production. With the reservoir-geomechanics-fracture model, this work provides a general workflow to optimize the child-well completion in multilayer unconventional reservoirs. The conclusions drawn from this study are of guiding significance to the subsequent development in the Permian Basin.
Stephenson, Ben (Shell Canada Energy) | Galan, Earl (Shell Canada Energy) | Fay, Mathew (Shell Canada Energy) | Savitski, Alexei (Shell International Exploration & Production Inc.) | Bai, Taixu (SEPCO)
Abstract The evidence for large-scale structural features (lineaments/faults) affecting a hydraulic stimulation is much more compelling than for small-scale features (natural fractures). Large-scale features are weaker and have similar dimensions to a typical hydraulic fracture. But is it beneficial to stimulate these features and what are the potential consequences? An analysis of structural features from the Marcellus and Duvernay formations has been undertaken, with static characterization (seismic, image logs and outcrops), dynamic characterization (fracture diagnostics and well performance) and geomechanical modeling; ultimately to understand whether, in the presence of structural features, any field development decisions might get impacted. Maps of structural features supported by seismic attributes are commonly challenged as to what they physically represent. Outcrop analogues demonstrate how strain is distributed in intrinsically layered media, such as shale. Therefore a shale may preferentially fold above a fault. Folding may result in strain partitioning, with bedding-parallel slip (shear) limiting the vertical extent and opening (dilation) of discrete fracture planes. Lineaments in Marcellus folds are either broad zones of axial kink-band deformation associated with higher bedding dips, or planar zones comprising reactivated natural fractures forming an inherited en echelon fabric. Lineaments in the Duvernay are zones of distributed deformation commonly associated with a subtle flexure above faults. A novel interpretation method of microseismic events in time reveals how lineaments are involved during a hydraulic fracture treatment driven by changes in net pressure. Hydraulic half-length is limited when fracs intersect a lineament at a high angle. This was confirmed by geomechanical modelling showing that lineament dilation prevents the opposite branch of the bi-wing frac from propagating. Diagnostics from plays with lineaments oriented close to maximum horizontal stress indicate that the length-scale of hydraulic communication is increased, because tensile reactivation is facilitated. Tracer data have been used to calibrate the conductive length-scale of these features in the sub-surface and also confirm that external fluids may be brought into the well-bore from underlying formations. Whether a lineament helps well productivity depends partly whether it is ‘contained’ or ‘uncontained’ within the over-pressured formation. In the uncontained case, stimulation efficiency and enhanced risk of external fluids needs careful monitoring. In the contained case, stimulation of a lineament may enhance productivity of a stand-alone well, but conversely this same lineament may exacerbate the Parent-Child impact once adjacent wells are drilled. A potential mitigation measure may be to modify the proppant or stimulation design to screen-out these high conductivity (or leak-off) pathways, rather than trying to stimulate them, thereby enhancing near-wellbore complexity. Paradoxically, the best way to handle large-scale structural lineaments may be to stimulate them in order to shut them off.
Temizel, Cenk (Halliburton) | Energy, Aera (Halliburton) | Betancourt, Dayanara (Halliburton) | Aktas, Sinem (Turkish Petroleum) | Susuz, Onur (Turkish Petroleum) | Zhu, Ying (University of Southern California) | Suhag, Anuj (University of Southern California) | Ranjith, Rahul (University of Southern California) | Wang, Aaron (Halliburton)
Abstract Hydraulic fracturing is a very robust tool in terms of not only increasing production in tight reservoirs but also accelerating production from reservoirs with higher permeability and porosity. The success of a hydraulic fracturing treatment is highly correlated with control of the created fracture geometry. Control of fracture growth and geometry is challenging in formations where the boundary lithologies are not highly stressed compared to the pay zone, allowing out-of-zone migration of fractures. As several factors influence the growth and geometry of fractures, including the reservoir, wellbore, and fluid/proppant parameters, it requires a good understanding of reservoir parameters, including stress distribution along with appropriate use of corresponding wellbore components and fluid/proppant for successful and efficient results. Our objective is to outline the main differences between different fracture models along with the key parameters and their significance in fracture performance. Fracture treatment designs involve selecting fracturing fluids, additives, proppant materials, injection rate, pump schedule, and fracture dimensions. Although hydraulic fracturing has become more important due to development of unconventional resources in tight formations, the use of fracture models before implementation of the treatment is limited, leading to undesired fractures either with limited growth or propagation out of zone. Literature lacks a study that combines the evaluation of different fracture models in an optimization process where economics is taken into account with an objective function maximizing the net present value (NPV), providing detailed information on the financial side of this technical phenomenon, too. In this study, different numerical fracture models are used to design the fractures in a tight oil reservoir, the performance of designed fractures are analyzed to measure the success of different numerical models applied in design along with an overview of critical operational parameters together with the significance of parameters, including size, number, and location, phasing angle of perforations, fluid and proppant type, rock strength, porosity, and permeability on fracture design optimization‥ In our paper, a comprehensive literature review of previous studies on tight oil reservoirs and hydraulic fracturing provides a thorough theoretical comparison of fracture models used in oil industry along with the analysis of significance of each factor throughout the process of hydraulic fracturing tight oil reservoirs. An objective function that maximizes NPV is used in this study investigating the phenomenon not only from the physical but also the economical aspects of fracturing that is still an expensive but an effective way of production enhancement technique when applied wisely.