Five representatives from the China University of Petroleum student chapter attended the monthly meeting for SPE-NCI in Beijing. The students were able to network with senior managers and technicians from oil and gas companies such as Schlumberger, Halliburton, Baker Hughes, Shell, ConocoPhillips, Anadarko, MIE, Roc Oil and Core Lab. The guest speaker was Yan Pan from Chevron. Yan graduated from Stanford University with an MS and PhD in Petroleum Engineering. After graduation she joined Chevron, engaging in well logging, reservoir simulation and the training program for engineers.
To assist in them maximizing the students' exposure to the industry, they organized a Schlumberger core lab visit; participated in the World Petroleum Conference in Paris; field trips to Mania Causeway and Udhailiyah; attended the Middle East Drilling Technology Conference in Bahrain; attended IPTC in Qatar; visited Texas A&M University in Qatar; as well as visited Weatherford Yard.
SPE Student Chapter Indian School of Mines recently held two guest lectures. A lecture on 12 August 2010 was lead by Mr. Vikas Kumar, a Testing Reservoir Engineer at Schlumberger. He is an esteemed alumnus of ISM Dhanbad working for one of the top-notch service providers. The topic for the guest lecture was "Practical Aspects of Wire line Formation Testing and Well Testing". His presentation proved to be highly beneficial for the students of petroleum engineering as it gave them an insight into the workings of various tools possessed by Schlumberger.
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.