In this paper, we present for the first time, a classification system for naturally-occurring gas hydrate deposits existing in the permafrost and marine environment. This classification is relatively simple but highlights the salient features of a gas hydrate deposit which are important for their exploration and production such as location, porosity system, gas origin and migration path. We then show how this classification can be used to describe eight well-studied gas hydrate deposits in permafrost and marine environment. Potential implications of this classification are also discussed.
Prabhakar, Abhinav (National University of Singapore) | Lee, Namkon (Korea Institute of Civil Engineering and Building Technology) | Ong, Khim Chye Gary (National University of Singapore) | Zhang, Minhong (National University of Singapore) | Moon, Juhyuk (Seoul National University) | Cheng, Arthur (National University of Singapore) | Kong, Kian Hau (National University of Singapore)
This study aims to design and evaluate a well cement slurry as an alternative to the standard API ‘G’ slurry for utilization in plugging and abandonment (P&A) of oil and gas wells. OWC slurries are formulated with Portland API ‘G’ cement as the base material, along with calcium sulfoaluminate (CSA) cement, gypsum and chemical additives. The slurries are experimentally tested using API standard procedures to determine gel transition time and right-angle-set (RAS) tendency at a temperature of 50 °C and pressures up to 34.5 MPa (5000 psi). The hydration characteristics of CSA cement can be utilized to control the gel development behaviour of a well cement slurry in order to minimize fluid or gas migration. Formation of ettringite greatly influences early age gelation. The potential to enhance gel strength development of an OWC slurry with CSA cement is presented whereby the gel transition time decreases with higher dosages of CSA cement. Thickening time studies to investigate the RAS tendency of the designed cement slurries are presented.
This paper describes the interaction between hydraulic fractures and the multi-porosity system of matrix porosity and natural fracture porosity in shale reservoirs. During the process of hydraulic fracturing, a complex fracture network consisting of primary and secondary hydraulic fractures as well as natural fractures is created. It is postulated that only shale porosities connected with this network will contribute to hydrocarbon production. Furthermore, we propose a way to maximise well productivity by injecting microsized proppants that are less than 150 μm (100 mesh) into the natural fractures and secondary hydraulic fractures to prevent them from closing and thereby increasing the stimulated reservoir volume. The size of the micro-sized proppant should be designed to be between one-seventh and one-third the aperture size of the natural fractures. In addition, various materials for micro-sized proppants are proposed and discussed. Of these, hollow glass microsphere shows more promise because of its light density and track record of being used as an additive material in the oilfield. Although limited laboratory experiments and field tests have shown encouraging results of using micro-sized proppants to enhance the productivity of Barnett shale, more research is warranted to optimize the use of these micro-sized proppants in production enhancement in various shale formations.
Zhang, X. Y. (American Bureau of Shipping) | Yong, F. (National University of Singapore) | Li, Y. P. (Hohai University) | Yi, J. T. (Chongqing University) | Lee, F. H. (National University of Singapore) | Chen, X. (Beijing Jiaotong University) | Wang, S. Q. (American Bureau of Shipping)
The quest for reliable and cost-effective solution of installing piles in deepwater led to the development of dynamically installed piles that embed themselves into the seabed through free-fall. Several variations of dynamically installed piles have been devised and successfully entered into service at deepwater offshore sites. The most notable one is the torpedo pile patented by Petrobras.
To facilitate the design and installation of the dynamically installed piles, ABS has developed Guidance Notes to provide geotechnical design and structural assessment methods. This paper presents an overview of the guidance and details of the technical development that forms the basis of the recommended methods.
In support of the development of the guidance, finite element analyses and centrifuge tests were conducted to study pile/soil interaction and to verify and further improve the prediction methods for pile pullout capacity. The pile inclination after installation, which has a significant effect on the pile pullout capacity and is of significant concern to the offshore industry, was thoroughly studied. Since the dynamic installation process results in lower short-term pullout capacity of the pile, it is recommended that the piles be installed for a sufficiently long period to allow the development of the pullout capacity. A prediction of the pile capacity restoration over time was developed based on the results of a series of centrifuge tests. A framework on the normalized vertical and horizontal component is proposed to predict the pile pullout capacities subjected to different loading angles.
Introduction Of the three permafrost regions, our calculations show Mohe Basin has the thickest hydrate stability (1300 m). This is followed by Qinghai-Tibet Plateau (1200 m) and Qilian Mountain (800 m).
The behavior of monopile subject to repeated lateral loads in normally consolidated clay is investigated using centrifuge modeling technique. A strain-softening model of clay is characterized by T-bar cyclic tests. A comparison between the results with the strain-softening model and the test results on monopiles under displacement-controlled repeated loading reveals that the accumulation of plastic strain leads to a reduction in the soil undrained shear strength and lateral stiffness. Further tests are conducted under load control. By interpreting the gradual changes in the progressive pile deflection with the strain-softening model, the mechanism for the lateral stiffness degradation of monopiles subject to repeated lateral loads is discussed.
This paper identifies several best practices for improving employee competency and productivity. They include aligning reward and promotion practices with company core values, promoting those who are already leading and have the capacity to perform at the next level, and using both internal and external benchmarking to help employees to set stretch goals for competency training and improving productivity.
Shale reservoirs contain predominantly micro and mesopores (<50 nm), within which gas is stored as free or adsorbed gas. Due to the ultra-small pore size, multiple transport mechanisms coexist in shale reservoirs, including gas slippage, Knudsen diffusion of free gas and surface diffusion of adsorbed gas. In this work, we propose a new transport model, valid for all ranges of Knudsen number, which combines all transport mechanisms with different weighting coefficients. To quantify the effects of influence factors, we introduce the compressibility factor for real gas effect and effective pore radius for gas adsorption and stress dependence. The model is proven to be more accurate than existing models since the deviation of the analytical solution of our model (3%) from published molecular simulation data is lower than that of existing models (10~20%). Based on this model, we compare (1) the contribution of each transport mechanism to gas transport in pores of different radii, (2) shale permeability measured in laboratory and at reservoir conditions, and (3) permeability of nanopores and natural fractures. It is found that gas transport is dominated by gas slippage and surface diffusion when the pore radius is over 10 nm and below 5 nm, respectively. Knudsen diffusion only becomes significant when the pore radius is between 2 and 25 nm and pore pressure is below 1000 psi. Furthermore, laboratory measurements usually over-estimate shale permeability. We also propose a promising enhanced gas recovery method, which is to open and prop up closed natural fractures using micro size proppants.
Fang, Gang (National University of Singapore) | Li, Yunyue Elita (National University of Singapore) | Du, Yue (National University of Singapore) | Ma, Joseph Ho Yin (National University of Singapore) | Yu, Diming (Cambridge Sensing Pte. Ltd.)
Continuous near-surface seismic monitoring is a crucial tool for surveillance of the surface changes due to natural and manmade events. However the cost of the conventional continuous seismic monitoring methods limit its widespread applications. Surface distributed acoustic sensing (DAS), as a recent developed seismic surveillance technology, provides a low-cost, non-intrusive and high-resolution method for continuous nearsurface monitoring. We use the quarry blasts data recorded by the "Stanford DAS Array" to evaluate the feasibility of the surface DAS array to monitor the manmade near-surface changes. We apply data processing and seismic interferometry analysis to this data and extract the near-surface velocity information around a basement construction site. Our results show good temporal and spatial correspondence between the velocity changes and the basement constructions, supporting the feasibility for monitoring despite strong construction noise.
Presentation Date: Thursday, October 18, 2018
Start Time: 8:30:00 AM
Location: 204A (Anaheim Convention Center)
Presentation Type: Oral
Du, Yue (National University of Singapore) | Li, Yunyue Elita (National University of Singapore) | Yang, Jizhong (National University of Singapore) | Cheng, Arthur (National University of Singapore) | Fang, Xinding (Southern University of Science and Technology)
VSP has advantages to detect and monitor the objects around the borehole due to its geometry. Multicomponent VSP can add rich information about the elastic properties of the subsurface near wellbore. However, the elastic wave imaging has been challenging due to the complexities in wave physics. The uncertainties in near surface structure will also affect the image accuracy. In this abstract we utilize the elastic image conditions with scalar wave equations for VSP reverse-time migration (RTM) to image the complex structures. We also provide an alternative way of using the source-free convertedwave (SFCW) RTM imaging for VSP to avoid the complex overburden structures. With multiple numerical examples, the PP, PS and SFCW images demonstrate the ability to image the complex sediment layers around the wellbore. Using both PP and PS image can provide a good interpretation for the complex subsurface but they rely on a relatively correct velocity model. The SFCW image is target oriented and is robust for the complex overburden velocity issue, while it has a lack of illumination for the areas further away from the borehole.
Presentation Date: Wednesday, October 17, 2018
Start Time: 8:30:00 AM
Location: 212A (Anaheim Convention Center)
Presentation Type: Oral