Long, Gongbo (Wuhan Institute of Technology) | Liu, Songxia (Texas A&M University) | Xu, Guanshui (University of California, Riverside and FrackOptima) | Wong, Sau-Wai (Shell International Exploration and Production) | Chen, Hanxin (Wuhan Institute of Technology) | Xiao, Boqi (Wuhan Institute of Technology)
Perforation pressure drop and its decrease caused by perforation erosion during a hydraulic-fracturing treatment are critical factors that need to be considered in treatment design, particularly when the limited-entry technique is implemented along multiple perforation clusters to ensure more-uniform fluid distribution. The simultaneous increases in the discharge coefficient Cd and perforation diameter D during perforation erosion require consideration of the temporal changes of these two variables to characterize the perforation-erosion behavior. In this paper, we present a perforation-erosion model dependent on abrasion mechanisms and the procedure to determine the specific erosion parameters that can be corroborated from laboratory data. Our modeling results demonstrate that it is inappropriate to assume an alternate increase in Cd and D, as considered in some conventional correlations. Once the erosion parameters are empirically inferred, we incorporate our model into a nonplanar hydraulic-fracturing simulator to determine appropriate perforation-number distributions at different clusters to ensure a successful limited-entry treatment that generates relatively even fluid distribution and uniform fractures.
The United States National Science Foundation has funded a sustainability-research network focused on natural-gas development in the Rocky Mountain region of the United States. The objective of this specific study is the assessment of the use of existing water wells to monitor the risk of contamination by the migration of fracturing fluids or hydrocarbons to freshwater aquifers. An additional objective of the study is to modify existing risk estimates using the spatial relationships between the existing water wells and producing oil wells. This will allow estimates of single-barrier failure and multiple-barrier failure, resulting in contamination projections for oil and gas wells in areas without surrounding water wells to detect migration, dependent on well-construction type.
Since 1970, the Wattenberg Field in Colorado has had a large number of oil and gas wells drilled. These wells are interspaced tightly with agricultural and urban development from the nearby Denver metropolitan area. This provides a setting with numerous water wells that have been drilled within this area of active petroleum development. Data from 17,948 wells drilled were collected and analyzed in Wattenberg Field, allowing wells to be classified by construction type and analyzed for barrier failure and source of aquifer contamination. The assessment confirms that although natural-gas migration occurring in poorly constructed wellbores is infrequent, it can happen, and the migration risk is determined by the well-construction standards. The assessment also confirms that there has been no occurrence of hydraulic-fracturing-fluid contamination of freshwater aquifers through wellbores. The assessment determines both the spatial proximity of oil and gas wells and surface-casing depth to water wells to then determine the utility of water wells to monitor migration in oil wells.
Propellants have been used in oil and gas wells to assist with perforating and creating near-wellbore stimulation. Propellants are electrically ignited in the wellbore at the perforated interval. Upon ignition, they rapidly create a large amount of gas, and the pressurization leads to breakdown of the formation. It has been postulated that the pressurization leads to creation of multiple fractures in the formation. This paper describes an experimental study with a new propellant and aims to understand the pattern of fracture creation with these propellants. The results are also compared with an older generation of propellant tested by Wieland et al. (2006).
A large-scale laboratory test was performed in a sandstone block (30×30×54 in.) with a 2-in.-diameter vertical centralized wellbore extending the full block height. The block was loaded in a polyaxial stress frame. A propellant cartridge was positioned in the center of the wellbore. Small holes were drilled in the rock to intersect the expected primary fracture and were instrumented with high-resolution pressure gauges to enable fracture-timing and -growth-rate analysis. Anisotropic stresses representative of field conditions were applied on the block, and the wellbore was pressurized before ignition.
The propellant ignition produced an initial peak pressure of 5,790 psi in 1.4 ms followed by an oscillatory pattern of pressure increase to a maximum pressure of 6,660 psi before decaying because of fracture growth and gas leakoff. The block was removed from the test frame and cut vertically and horizontally to examine the fracture pattern generated by the propellant. A dominant planar fracture was observed on either side of the wellbore, which propagated in the direction perpendicular to the minimum-horizontal-stress direction. It was verified that the propellant had a much-higher burn rate than the propellant tested by Wieland et al. (2006).
The large-scale block test provides critical insights and data that can serve as inputs to calibrate physics-based models for modeling propellant ignition and stimulation. The results help in understanding the benefits and limitations of using propellants for stimulation.
This paper documents the formation of natural fractures in the Horn River Group, a major Canadian shale gas play, and addresses relationships between natural-fracture development and rock-mechanical properties derived from cores and well logs. Most natural fractures in the Horn River Shale are narrow vertical fractures, sealed with carbonate minerals. In this study, the formation of observed fractures is primarily determined by a lithology type, mineral composition, and rock-mechanical properties at the timing of fracturing.
Brittleness is an important geomechanical property controlling the formation of fractures, because brittle shale is more easily fractured than ductile shale, and fractures in brittle shale tend to persist when the fracturing pressure is released. In this study, a hardness value measured by a commercial hardness tester is found to be a good proxy for the brittleness of shale layers. On the basis of a statistical analysis, the threshold values of both hardness and brittleness are estimated to predict the distribution of natural fractures, assuming that the mechanical properties of the host rock were relatively stable from at least the time at which fractures formed. Hardness values are shown to be more reliable than brittleness.
Chen, Chaohui (Shell International Exploration and Production Company) | Gao, Guohua (Shell Global Solutions US Incorporated) | Li, Ruijian (Shell Exploration and Production Company) | Cao, Richard (Shell Exploration and Production Company) | Chen, Tianhong (Shell Exploration and Production Company) | Vink, Jeroen C. (Shell Global Solutions International) | Gelderblom, Paul (Shell Global Solutions International)
Although it is possible to apply traditional optimization algorithms together with the randomized-maximum-likelihood (RML) method to generate multiple conditional realizations, the computation cost is high. This paper presents a novel method to enhance the global-search capability of the distributed-Gauss-Newton (DGN) optimization method and integrates it with the RML method to generate multiple realizations conditioned to production data synchronously.
RML generates samples from an approximate posterior by minimizing a large ensemble of perturbed objective functions in which the observed data and prior mean values of uncertain model parameters have been perturbed with Gaussian noise. Rather than performing these minimizations in isolation using large sets of simulations to evaluate the finite-difference approximations of the gradients used to optimize each perturbed realization, we use a concurrent implementation in which simulation results are shared among different minimization tasks whenever these results are helping to converge to the global minimum of a specific minimization task. To improve sharing of results, we relax the accuracy of the finite-difference approximations for the gradients with more widely spaced simulation results. To avoid trapping in local optima, a novel method to enhance the global-search capability of the DGN algorithm is developed and integrated seamlessly with the RML formulation. In this way, we can improve the quality of RML conditional realizations that sample the approximate posterior.
The proposed work flow is first validated with a toy problem and then applied to a real-field unconventional asset. Numerical results indicate that the new method is very efficient compared with traditional methods. Hundreds of data-conditioned realizations can be generated in parallel within 20 to 40 iterations. The computational cost (central-processing-unit usage) is reduced significantly compared with the traditional RML approach.
The real-field case studies involve a history-matching study to generate history-matched realizations with the proposed method and an uncertainty quantification of production forecasting using those conditioned models. All conditioned models generate production forecasts that are consistent with real-production data in both the history-matching period and the blind-test period. Therefore, the new approach can enhance the confidence level of the estimated-ultimate-recovery (EUR) assessment using production-forecasting results generated from all conditional realizations, resulting in significant business impact.
Surfactant-mediated enhanced-oil-recovery (EOR) techniques, such as surfactant/polymer (SP) flooding, have received increased attention because of their ability to reduce capillary forces at the pore-scale to ultralow values and mobilize trapped oil. Recently, there have been increased efforts in microemulsion-phase-behavior modeling capabilities by relying on the hydrophilic/lipophilic-difference (HLD) measure for surfactant-affinity quantification. One common assumption of most microemulsion-phase-behavior models is the assumption of pure excess phases, which states that the surfactant component is only present in the microemulsion phase. This assumption can lead to significant errors for some surfactant systems, especially when applied to chemical simulations in which discontinuities may arise.
The main novelty of this paper is to allow for surfactant partitioning into both the water and oil excess phases by use of a simple approach, and then relate relevant surfactant-partitioning coefficients (i.e., K-values) to HLD. Surfactant screening that is based on surfactant-structure parameters is also considered based on estimated K-values. Key dimensionless groups are identified as a function of activity coefficients, which allow for a simplified description of the surfactant-partition coefficients. These surfactant-partition coefficients are combined with the chemical-potentials (CP) equation-of-state (EoS) model to describe and predict the phase behavior when the excess phases are not pure. Further, the developed surfactant-partitioning model can be used in other microemulsion-phase-behavior models to allow for impure excess phases.
Efficient transport of sand or cuttings is very important in the oil and gas industry, and the fluid velocity in these processes should be sufficiently high to keep particles continuously moving along the pipe. This minimum fluid velocity below which particles deposit—defined as the critical velocity—depends on various factors, including flow regime, particle size, particle concentration, phase velocities, and fluid viscosity. The objective of this study is to investigate the effect of parameters such as particle size and liquid viscosity on solid/particle transport in horizontal pipelines by use of computational-fluid-dynamics (CFD) simulations and to validate the numerical-model predictions with experimental data. Also, a mechanistic model that is based on force balance is proposed to predict the critical velocity under various experimental conditions.
CFD simulations have been conducted with a commercially available software (ANSYS-FLUENT). An Eulerian model with a k-w shear-stress transport (SST) turbulence-closure model is used to simulate the fluid flow while particles are tracked as the Lagrangian phase. In these simulations, an eddy-interaction model is included to consider the effect of flow turbulence on particle tracking. The simulations are created for a 0.05-m pipe diameter with a 4-m length. The simulations are initialized at relatively high fluid velocity, which is gradually reduced until the particle velocity drops below the acceptable critical velocity.
The CFD simulation and proposed mechanistic model results are validated with experimental data from literature (Najmi 2015; Najmi et al. 2016) for two particle sizes and multiple liquid viscosities. The simulation and model results show that, depending on the flow regimes (laminar or turbulent) and particle size, the critical velocity demonstrates a similar trend with carrier liquid viscosity as that of the experimental data. However, both the CFD and developed models show poor performance for higher particle size (600 µm). Also, the CFD simulations, experimental data, and proposed-model results are compared with three models currently used in the industry, namely, the Oroskar and Turian (1980) model, the Salama (2000) model, and the Danielson (2007) model.
Research has been dedicated to the development of laboratory-scale simulation devices for studying mechanisms of gas migration. Cement-hydration analyzers (CHAs) are commercially available to assist industry in the design of gas-tight slurries. Although cement slurries under controlled conditions in the laboratory can be gas-tight, the in-situ performance of cement slurries is highly variable and difficult to predict. Therefore, a new approach has been designed to evaluate gas-migration potential under a range of representative borehole conditions. A laboratory-scale wellbore-simulation chamber (WSC) has been developed to replicate hydrostatic-pressure reduction in the cemented annulus and evaluate the potential for gas invasion under a range of borehole conditions. A discussion is presented on the development of the WSC that includes the details of the design and monitoring systems as well as the performance characteristics. Calibration-test results are examined to evaluate the performance of the WSC and the ability of the WSC to simulate in-situ wellbore conditions. Analysis of the results verifies the capability of the WSC in successfully recording the necessary parameters.
OSH professionals can find the following sentence in OSHA standards for general industry (29 CFR Part 1910.6), construction (29 CFR 1926.6), shipyard employment (29 CFR Part 1915.5) and marine terminals (29 CFR Part 1917.3): “The standards of agencies of the U.S. government, and organizations which are not agencies of the U.S. government which are incorporated by reference in this part, have the same force and effect as other standards in this part.” What does this mean?
The noted paragraphs are a list of the consensus standards written primarily by industry that OSHA has adopted as the law, officially called incorporation by reference (IBR). The OSH Act was signed into law Dec. 29, 1970, by President Richard Nixon. At Section 6(a), the OSH Act authorized the U.S. Secretary of Labor to adopt other federal standards and national consensus standards for a period of 2 years without having to go through the official rulemaking process.
Congress decided that since national consensus standards were written by highly knowledgeable, experienced professionals and had gone through a comprehensive review process, adopting these standards would simplify standards promulgation and provide immediate protection for America’s workforce.
This new agency (OSHA) chose to adopt several hundred of these other standards, and those adopted standards are incorporated into the law by means of a specific OSHA standard referring to that adopted standard.
Emery, Robert J. (University of Texas Health Science Center at Houston and School of Public Health) | Patlovich, Scott J. (University of Texas Health Science Center at Houston and School of Public Health) | Jannace, Kalyn C. (University of Texas Health Science Center at Houston and School of Public Health)
A variety of safety and health risks exist on college and university campuses based on the types of teaching and research activities conducted. OSH programs are typically implemented to help identify and control these risks to keep students, faculty, staff and visitors safe. A significant challenge for decision makers at these institutions is how to determine appropriate staffing and resourcing levels for such programs. A further challenge to staffing is ensuring that the job description and duties accurately represent those activities that truly fall under the purview of the position.
Existing methods of measuring efforts often include some level of intense observation or surveillance, which staff may consider to be intrusive and cumbersome (Sewell, Barker & Nyberg, 2012). As a result, the Hawthorne Effect, described in other time and motion studies, may alter the way a staff member conducts his/her routine activities leading to an observed effect further from the normal (Fernald, Coombs, DeAlleaume, et al., 2012). Brown, Emery, Delclos, et al.’s (2015), recently developed predictive models provide the ability to estimate staffing and resourcing needs in academic settings using institutional drivers such as total net assignable square footage, but the models do not account for staff productivity.
In this pilot study the authors utilized the ecological momentary assessment (EMA) research technique to record the work activities being undertaken by OSH personnel during a typical 8-hour work day in an effort to augment the Brown, et al., models by addressing worker productivity. Practicing OSH professionals were evaluated 1 day per week over a 5-week period (for a total of 5 work days, all weekdays) to determine the type of work conducted during the normal 8-hour work shift.