Velikanov, Ivan (Schlumberger) | Isaev, Vadim (Schlumberger) | Bannikov, Denis (Schlumberger) | Tikhonov, Alexey (Schlumberger) | Semin, Leonid (Schlumberger) | Belyakova, Ludmila (Schlumberger) | Kuznetsov, Dmitry (Schlumberger)
We demonstrate the advantages of a new hydraulic fracturing simulator comprising a fine-scale fracture hydrodynamics and in-situ kinetics model. In contrast to existing commercial modeling tools, it has a sufficient resolution and other functionality for adequate representation of modern stimulation technologies: pulsing injection of proppant, mixtures of multiple fracturing materials (fluids, proppants, fibers, etc.), materials degradation, etc. This simulator accounts for the influence of materials distribution on fracture propagation and calculates fracture conductivity distribution. We coupled it with a production simulation model and established a complete framework for hydraulic fracturing treatment design. In addition to the selection of the pumping schedule, this model can be used to define specifications for novel hydraulic fracturing materials. This is a step change tool for wellbore stimulation and production forecast.
Multi-stage fracturing in horizontal well is the core technology for commercial exploitation of shale gas reservoir, in which the cluster spacing plays an important role to impact the fracturing performance—undersized cluster spacing might make the stimulated reservoir volume (SRV), activated by different hydraulic fractures, excessively overlap with each other, while oversized cluster spacing might leave unstimulated regions between neighboring hydraulic fractures; in either case the fracturing would be inefficient. However, most current cluster spacing design methods are imperfect without a reliable SRV estimation model. This paper established a numerical model to estimate the SRV by simulating four key processes during multi-stage fracturing—hydraulic fractures propagation, formation stress changing, reservoir pressure lifting, and natural fractures failure. Then, based on this SRV model, an optimization method for cluster spacing was proposed and applied in Fuling shale gas field in Southwest China. We analyzed the influence of geological conditions and fracturing parameters on the optimal cluster spacing, and drew the reference charts for cluster spacing design in Fuling gas field. This research developed an effective cluster spacing optimization method, reduced the uncertainty in cluster spacing design, and provided some new insights on the optimal design of multi-stage fracturing in horizontal shale gas well.
Aggarwal, Ankit (Norwegian University of Science and Technology) | Chella, Mayilvahanan Alagan (Norwegian University of Science and Technology) | Bihs, Hans (Norwegian University of Science and Technology) | Pákzodi, Csaba (SINTEF Ocean) | Berthelsen, Petter Andreas (SINTEF Ocean) | Arntsen, Øivind A. (Norwegian University of Science and Technology)
Offshore structures are exposed to irregular sea states consisting of breaking and nonbreaking waves. They perpetually experience extreme wave loads after installation in the open ocean. Thus, the study of steep waves is an important factor in the design of offshore structures. In the present study, a numerical investigation is performed to study steep irregular waves in deep water. The irregular waves are generated using the Torsethaugen spectrum, which is a double-peaked spectrum defined for a locally fully developed sea and which takes both the sea and swell waves into account. Thus, the generated waves can be very steep. The numerical investigation of such steep waves is quite challenging because of their high wave steepness and wave–wave interaction. The present investigation is performed using the open-source computational fluid dynamics (CFD) model. The wave generation and propagation of steep irregular waves in the numerical model are validated by comparing the numerical wave spectrum with the experimental input wave spectrum. The numerical results are in good agreement with experimental results. The changes in the spectral wave density during the wave propagation are studied. Further, the double-hinged flap wavemaker is also tested and validated by comparing the numerical and experimental free-surface elevations over time. The time and the frequency domain analysis is also performed to investigate the changes in the free-surface horizontal velocity. Complex flow features during the wave propagation are well captured by the CFD model.
Offshore wind turbines are exposed to extreme irregular sea states. Extreme waves exert extreme hydrodynamic loads on substructures. Thus, the study of such irregular waves is very important in the design of offshore wind turbines. Several experimental and field investigations have been performed in the past to study extreme waves. Such spectra exhibit two peaks, because of the presence of swell and wind waves. Ochi and Hubble (1976) carried out a statistical analysis of 800 measured wave spectra in the North Atlantic Ocean. They derived a six-parameter double-peaked spectrum that is composed of two parts: the first primarily includes the low-frequency wave components and the second contains the high-frequency wave components. Each part of the wave spectrum is represented by three parameters. The six-parameter spectrum represents almost all stages of the sea conditions associated with a storm. Guedes Soares and Nolasco (1992) analyzed wave data from the North Atlantic and the North Sea and proposed a four-parameter double-peaked spectrum. This double-peaked spectrum was formulated by superimposing individual spectral components of the JONSWAP-type single-peaked spectrum.
Multiwell-completion techniques, such as sequential fracturing, zipper fracturing, and simultaneous fracturing, have been proposed to improve fracture complexity and connectivity. Critical geomechanics behind the multiwell-fracturing techniques include pore-pressure propagation, cooling stress, tip-induced shear stress, and reversal of stress anisotropy. To optimize multiwell-fracturing treatments, we numerically investigated fracture growth from the perspective of thermo/hydromechanical (THM) coupling. The coupled geomechanics and fluid-heat-flow model is derived from a mixed finite-element (FE) and finite-volume (FV) method, which is capable of simulating multifracture growth in heterogeneous reservoirs. In this study, both hydraulic-fracture (HF) propagation and natural-fracture (NF) reactivation in opening or shearing patterns were taken into account. Particularly, an elastoplastic fracture constitutive model was adopted to predict permanent enhancement of fracture aperture. The effects of perforation-cluster spacing, well spacing, and the fracturing sequence of multiwell completion upon fracture complexity were studied, where the total hydraulically fractured area was treated as the primary indicator of HF effectiveness. By numerical parametric studies, we determined four findings. First, there is an optimal cluster spacing for maximizing the total fracture area for a stage with a given length. Cluster spacing mainly affects stress distribution during HF, which subsequently affects the path of newly created fracture propagation and crossing behaviors (i.e., crossing, arresting, or offsetting). Second, suitable well spacing should be chosen carefully to avoid the hydraulic interconnection between the tip-to-tip stages, as well as to make use of tip-induced shear stresses. Third, the fracturing sequence for multiwell completion is of critical importance. Among three multiwell-completion schemes (i.e., sequential, zipper, and simultaneous fracturing), the zipper-fracturing technique achieves the best fracturing effectiveness for this case study. Fourth, the effect of stress perturbation on NFs can be quite different, depending on the position relative to the created stimulated reservoir volume (SRV). The coupled model significantly improves our understanding of multiwell-fracturing treatments and then provides us with a means to optimize the multiwell completion, enhancing fracture complexity to effectively improve productivity.
This paper describes three applications of a fully integrated hydraulic fracturing, reservoir, and wellbore simulator. The simulator describes hydraulic fracturing, shut-in, and production in a single continuous simulation. It describes multiphase effects (using either the black oil model or a compositional fluid model), thermal effects, transport of tracers and/or non-Newtonian fluid additives, stress shadowing from fracture propagation, and poroelastic stress effects from depletion, and uses a detailed proppant transport algorithm. It uses constitutive relations that smoothly transition from equations for flow through an open crack to equations for flow through a closed crack (with or without proppant). In the first example, we build a simulation model of Staged Field Experiment #3, a well-known historical dataset. Our result is compared with other published simulations and is matched to 15 years of production data. The simulation shows how the transport and settling of proppant in the fracture during injection and shut-in are impacted by processes such as clustered and hindered settling. Gel crosslinking and breaking are described with first-order reaction rate constants. In the second example, we perform a sensitivity analysis on cluster spacing in a generic slickwater fracturing treatment in a horizontal well. The simulations show complex interactions between stress shadowing, fracture propagation, proppant transport, and multiphase flow. The sensitivity analysis indicates that minimizing near-wellbore pressure drop is critical for improving production. Closer cluster spacing decreases near-wellbore pressure drop by providing more conduits for flow. In the third example, we simulate a vertically stacked parent/child scenario. Depletion of the overlying parent well leads to upward propagation from the child well and direct frac hits. The frac hits remobilize proppant as water sweeps into the parent well fractures, displacing gas. In the
Hamza, Farrukh (Halliburton) | Sheibani, Farrokh (Massachusetts Institute of Technology) | Hadibeik, Hamid (Halliburton) | Azari, Mehdi (Halliburton) | Esawi, Mohamed (Halliburton) | Ramakrishna, Sandeep (Halliburton)
Hydraulic fracturing is now considered to be a standard completions process used to improve oil and gas recovery in unconventional reservoirs. Injection/fall-off pressure from a micro-fracturing test contains important geomechanical information, including the inference of the minimum horizontal stress, natural fracture permeability, and in-situ pore pressure. The determination of in-situ stress is crucial for designing, modeling, and evaluating hydraulic fractures. This paper presents a field example of a micro-fracturing job to determine minimum horizontal stress and characterize natural fractures in terms of permeability.
The analysis of micro-fracturing data consists of two parts: pre-closure analysis and after-closure analysis. The pre-closure analysis involved the analysis of early pressure fall-off data to determine the fracture closure stress of a particular formation at a specific depth. The tests were performed by injecting a small volume of fluid into a small, confined, and isolated zone at low rates to create a small fracture. The closure stress was determined from the analysis of the pressure decline after shut-in. To estimate natural fracture permeability, a series of numerical fully coupled hydro-mechanical simulations of hydraulic fracture propagation was conducted in a naturally fractured reservoir by varying the natural fracture initial permeabilities.
The pressure decline after shut-in of the formation tester pump was analyzed using G-function and square-root-time methods. The point at which the G-function derivative began to deviate downward from the linear trend was identified as the point at which the fracture closes. The cycle of injection and fall-off was repeated four times. After the first cycle, in each subsequent cycle, the fracture pressure was reduced by approximately 20 psi. Based on these four cycles and petrophysical data, a customized model was developed, and poro-mechanical simulations were performed to characterize natural fractures in the formation. The simulation results explain the variation of micro-fracturing pressure history, during the four injection cycles. A comparison of the pressure history from the micro-fracture tests with the injection pressure obtained from the numerical simulation suggested that the formation included relatively impermeable natural fractures.
The characterization of natural fractures during micro-fracturing provides additional information not captured by a traditional G-function or square-root-time analysis. Multiple cycles of injection and pressure fall-off provide a qualitative assessment of in-situ pore pressure and a consistent minimum in-situ stress. Understanding the fracture pressure and natural fractures in the formation is a key component of successful reservoir completion and development. However, challenges exist in the measurement of these reservoir properties with conventional methods of diagnostic fracture injection testing (DFIT™). This new analysis method represents a step forward in terms of overcoming such challenges.
The propagation of foam in an oil reservoir depends on the creation and stability of the foam in the reservoir, specifically the creation and stability of foam films, or lamellae. As the foam propagates far from in injection well, superficial velocity and pressure gradient decrease with distance from the well. Experimental (
In our experiments, nitrogen foam is generated in a core of Bentheimer sandstone. The foamgeneration experiments consist of measuring the critical velocity for foam generation as a function of gas fractional flow at three surfactant concentrations well above the critical micelle concentration. Experimental results show that critical velocity decreases with increasing liquid fraction, as shown by previous foam generation studies (
Mukherjee, Soujatya (Wintershall Holding GmbH) | Garrido, Gerardo Incera (Wintershall Holding GmbH) | Prasad, Dhruva (Wintershall Holding GmbH) | Behr, Aron (Wintershall Holding GmbH) | Reimann, Sabrina (Wintershall Holding GmbH) | Ernst, Burkhard (Wintershall Holding GmbH)
Schizophyllan is a new biopolymer developed by Wintershall for its applicability particularly in high temperature and high salinity assets. Previous work on Schizophyllan (
Polymer filterability tests involving high pressure gradients are generally not representative of polymer transport deep inside the reservoir. Thus, a few standard coreflood tests were performed in-house for obtaining a better understanding on polymer injectivity and propagation in porous media. Since, corefloods are relatively expensive and time consuming, a new set-up comprising of a small core holder (1cm length) was assembled in Wintershall's laboratory. In comparison to normal corefloods, this assembly allowed a quicker assessment of polymer propagation using a narrower pore size distribution. Additionally, specialized corefloods were conducted at varying ranges of temperature (55 to 92 °C), salinity (up to > 200 g/L), permeability (94 to 5200mD), etc. to characterize polymer parameters such as retention, RF (resistance factor), RRF (residual resistance factor) and IPV (inaccessible pore volume).
Corefloods using consolidated outcrop (Gildehaus Sandstone) and reservoir cores usually showed good injectivity and propagation of Schizophyllan at permeabilities greater than 200 mD. In comparison, reduced injectivity was seen through synthetic cores of similar permeability but narrower pore size distribution (sintered Quartz). Based on these results, pore size limits for propagation of Schizophyllan can be estimated. Static adsorption values measured on both outcrop and reservoir sand reported values in the range of 560μg/g and 680μg/g, respectively. Dynamic retention values with and without residual oil saturation ranged from 9 to 21 μg/g for outcrop cores, depending on various polymer concentrations. For reservoir cores, dynamic retention values varied between 20 to 50 μg/g, which can be attributed to the poor handling of oxidized cores, mineralogical variation and core scale heterogeneity. The corresponding RRF values for reservoir cores ranged from 1.4 to 3.8 respectively, for different IPV values. Further analysis showed that calculated IPV values are very sensitive and have considerable uncertainty based on its method of interpretation. For the coreflood experiments conducted at higher temperatures (greater than 90°C), no loss of Schizophyllan solution viscosity was observed, confirming the good thermal stability of the biopolymer.
This paper focuses on quantifying the limits of related Schizophyllan parameters such as polymer retention, RF, RRF and IPV. It also elaborates on the qualification of Schizophyllan for porous media using a novel core plug set-up with regards to polymer injectivity and propagation. Considering sandstone reservoirs, such data have not been previously reported in the literature for biopolymer Schizophyllan.
Li, Yanchao (Chuanqing Drilling Engineering Company Downhole Service Company, CNPC) | Yin, Congbin (Chuanqing Drilling Engineering Company Downhole Service Company, CNPC) | Qian, Bin (Chuanqing Drilling Engineering Company Downhole Service Company, CNPC)
In the past five years, shale gas development had made great progress in Longmaxi shale of Southwestern China. Different from the North American shale, the Chinese shale reservoir has the characteristics of deep and multi-stage tectonic movement, which presents a huge technical challenge for economic development. Especially, great horizontal stress difference resulted it was difficult to create complex fracture network during hydraulic fracturing. So it is vitally important to provide a workflow of geo-engineering integrated fracturing design for Chinese shale economic development.
In this paper, a workflow of geo-engineering integrated fracturing design is proposed to optimize fracturing parameters, which is based on geology modeling and formation quality evaluation. This workflow contains stress and natural fracture prediction and modeling, perforation sweet spot optimization, stimulated fracture network and productivity prediction, treatment parameters optimization, and fracturing design evaluation. In order to improve the use of convenient and complex data processing of fracturing engineers, the simulation system of shale stimulation (CQ-4S) is developed which is based on this workflow.
The applications of workflow and system during more than thirty shale gas wells in Southwestern China illustrated that the workflow and system could effective optimize design of shale stimulation, which contains some advice of perforation sweet spot, cluster spacing, treatment volume of fluid and proppant. The predicted fracture network had good agreement with microseismic data, and predict well performance also had good agreement with real-measured results. According to fracturing analysis and evaluation of more than thirty cases with this workflow and system, we also recognized that there were 13 geoengineering parameters which determined fracturing effectiveness of Chinese shale gas.
The results of this paper provide some guidelines for shale gas stimulation design and evaluation in Southwestern China, which is also can provide reference for other emerging shale gas development.
Big data technology is applied to analyze massive micro-seismic data set, which incorporates previously over-looked data set. This, in turn, will give redundant fracture modelling in stages and exact fracture propagation map in real time. Micro-seismic is pivotal to the success of Hydraulic Fracturing activity. However, with the advent of advanced geophones, the massive dataset requires a different analytical point of view, currently absent in conventional database processing and algorithms. HADOOP equips with the necessary tools for better and advanced real-time processing and analysis.
Various Algorithms are developed to show comprehensive fracture operation analysis. Previous job failures are used to predict future anomalies, hence enhancing success ratio. The holistic dataset for the reservoir (Exploration, Drilling, and Production) are considered to synchronize the reservoir information. For example, drilling data (ROP, drillability, WOB etc.) is analyzed to predict the type of formation (like Brittle or Ductile), poroelastic constant, elasticity etc. Comprehensive analysis of fracture propagation would consider all the parameters associated not just conventional ones.
The dataset is stored in Hadoop and called upon whenever needed. The massive amount of dataset is not being processed in conventional databases but can be integrated using Hadoop. The analytical results provided from Hadoop stands out from conventional formulae based software. The visualization of results keeps the minimum scope of error contradicting with the currently used ones. In current ones, many data trends and parameters are left out which are not used in formulae. Those patterns are visually shown and incorporated into the analysis, causing better mapping of fractures. Not only just complementing current analysis, Big Data provides the scope of comprehensive analysis from start to end. When 3D seismic appeared, it was a radical change. It not only showed 2D maps were of low resolution, rather those were rendered misleading. The Hadoop analytics is providing a unique perspective, leaving some mismatches, which are needed and to be seriously considered for future planning.
The resulting model does not use conventional formulae, hence not limited to consider the real-time data. Rather field data (associated with noise) is analyzed using algorithms, generating trends from noises and deviations. The conventional software misses massive relevant data, which apparently cannot be incorporated into formulae. That inability is being met with Big Data analytics. Conventional database management is unable to handle so much data, which are being taken care off by Hadoop platform.