Deep geological repositories are a feasible and reliable way to dispose of spent nuclear fuel, and the mechanical and thermal properties of the host rock are key factors in their long-term safety. The mechanical properties of rock, including uniaxial compressive strength, tension strength and elastic modulus are thermally-dependent - for example, the uniaxial compressive strength of rock will decrease with increasing temperature, as a result of thermally-induced cracks between mineral particles. However, thermally-induced cracks and the micro-mechanisms of rock damage are difficult to observe by experiments. We therefore used uniaxial compressive strength test and Brazilian disk PFC models with heterogeneous thermal expansion properties to reveal the micro-mechanisms of rock damage induced by thermal heating.
Based on the mineral compositions of granite, heterogeneous models contained four particle types with different thermal expansion properties (quartz, potassium feldspar, plagioclase, and biotite). A series of heating simulations (temperature increment: ΔT = 80 – 300 °C) showed that thermally-induced cracks occurred when the temperature increment exceeded 250 °C, and that the main crack type was tension crack. In homogeneous PFC models no thermally-induced cracking occurred even at ∆T = 300 °C. In simulations of thermal-mechanical coupling, the heterogeneous PFC models have the advantage of revealing differences in radius expansion of various mineral particles with increasing temperature, resulting in the additional and uneven distribution of contact force, stress concentration between different particles and bond breaking, and it lead to decreases in uniaxial compressive strength, elastic modulus and initial crack stress.
In the construction and operation of deep geological repositories of nuclear waste, the physical and mechanical properties of host rock are influenced by excavations and decay heat induced by the installation of nuclear waste canisters. This may result in a variety of changes in rock porosity and seepage conditions in the rock mass, the formation of excavation damage zones and the occurrence of thermally-induced rock damage, etc. Thermally-induced damage results from heterogeneous thermal properties in rock - for example, the thermal expansion coefficient of quartz (24.3 × 10−6 /°C) is three times that of biotite (8.0 × 10–6 /°C), leading to the differential expansion of mineral volume and macro-mechanical properties of rock with increasing temperature. In order to understand and interpret the influences of thermally-induced damage on the mechanical behavior of rock, homogeneous and heterogeneous bonded particle models were adopted to simulate a uniaxial compressive test (UCS) and Brazilian indirect tensile test in this study.
Guo, Hu (China University of Petroleum-Beijing) | Dong, Jiayu (No. 3 Oil Production Plant of Daqing Oilfield Company, Petro China) | Wang, Zhengbo (Research Institute of Petroleum Exploration & Development, Petro China) | Liu, Huifeng (Tarim Oil Company, Petro China) | Ma, Ruicheng (China University of Petroleum-Beijing) | Kong, Debing (China University of Petroleum-Beijing) | Wang, Fuyong (China University of Petroleum-Beijing) | Xin, Xiankang (China University of Petroleum-Beijing) | Li, Yiqiang (China University of Petroleum-Beijing) | She, Haicheng (Xi'an University of Technology)
This paper provides field scale EOR survey in China which is in line with biennial worldwide EOR survey published by Oil& Gas Journal (OGJ). The EOR progress in China is not available due to language difference and other reasons in OGJ EOR survey. From 2018, EOR survey in China will be published biennially. The first part of this survey mainly focuses on basic information. Chemical flooding, unconventional heavy oil, green recovery and natural gas recovery progress in China will be surveyed and discussed in detail in the other four parts elsewhere. The EOR projects including field tests and field applications in China are summarized in the same pattern as OGJ to the largest extent for better readership outside China. Most data is collected from published journal papers and reports. Different from other countries, there are only four major oil companies in China: CNPC, SINOPEC, CNOOC and Yanchang Oil. The 28 branch companies of these four companies are both operator and owners. Oil and gas production from CNOOC is all offshore. CNPC is the largest oil company in China and its oil production in 2016 accounts for 54% oil production in China. EOR survey in China includes chemical flooding (polymer, SP and ASP flooding, gas flooding (CO2, nitrogen and air), thermal production, MEOR, and foam flooding. EOR production in China in 2016 accounts for 18% total oil production, while chemical EOR accounts for 10 %. Up to present, there has been more than 34 ASP flooding projects in China, most in Daqing. The total ASP oil production in 2016 is 407 million tons. More than 30 SP flooding projects have been carried out, with incremental oil recovery factor of 7%-18% OOIP. More than 170 polymer flooding projects have been carried out. Polymer flooding has been used widely in Daqing, Shengli, Xinjiang, Liaohe, He'nan and Bohai. The incremental oil recovery from polymer flooding and ASP flooding is 7%-15% and 18%-30% OOIP respectively. Gas flooding in China is not as successful as chemical EOR. Polymer flooding production in the largest offshore oilfield in CNOOC accounts for 25% total oil production in 2016. While EOR production in China accounts for 15%-18% in recent years, however, the world EOR oil production only accounts for about 3.3% total oil production. EOR is greatly affected by oil price, as indicated from 26 years EOR content change in America. It is the first time that detailed EOR survey in China in line with worldwide EOR survey in OGJ is given. The EOR survey in China provides valuable and helpful information for engineers and researchers in oil and gas industry.
The probabilistic neural network (PNN) is functional in recognizing complex patterns without doing any pretraining of source data. However, for some data clusters, independence and colinearity characteristics of the variables in learning samples can seriously distort the window lengths of their probability density distributions, then leading to the incorrect or totally wrong calculated probability values and final recognition results. In view of such drawbacks, an improved PNN that incorporates two techniques of mean impact value (MIV) and correlation analysis is proposed in order to perfect the original PNN’s calculation mechanism by removing those interference and colinear variables from the source data. The data used to validate the method are from two wells in the Iara oilfield. Recognition accuracies of the improved network in four experiments are, 74.05%, 71.7%, 83.02% and 88.24%, respectively, each of which is the highest accuracy. The validation results demonstrate that the new network has the capability of recognizing complex carbonate lithofacies and the results are reliable enough to serve as the reference data for other geological efforts, such as analyzing sedimentary process and building a sequence framework.
In geological resarch, lithofacies identification is generally viewed as an important basic step because the results can provide remarkable revelations to other geological areas of study, such as analyzing sedimentary cycles, establishing sequence frameworks and constructing sedimentation models. For a particular well, in order to continuously obtain its lithofacies information, collecting rich source data in terms of lithology, electrical and petrophysical properties at each depth is essential, thus almost all the relevant identification methods are realized by processing logs (Baldwin et al., 1990; Carrasquilla et al., 2008). Crossplots are a classic tool used to predict lithofacies. The crossplot axes represent two well-log types that have significance in lithofacies classification, such as natural gamma ray (GR) and acoustic log (AC) logs, in the case of distinguishing sand and shale. With the advantage of crossplots, the lithofacies of noncored intervals can be predicted in accordance with the identification principles discovered from the data analysis of cored intervals (Busch et al., 1987; Dubois et al., 2007; Gifford and Agah, 2010; Grana et al., 2012). Nonetheless, crossplots methods require that each lithofacies has distinct characteristics on all the analyzed logs, which could not be recognized when dealing with complex lithofacies identification. As such, two other methods, statistics and neural networks, are rapidly being developed in place of the crossplot method (Tang and White, 2008; Insua et al., 2015).
The slopes in open pit mines are typically excavated to the steepest feasible angle to maximize profits. However, there is a greater risk of slope failure associated with steeper slopes. An open pit slope represents a complex multivariate rock engineering system. Interactions between the factors affecting slope stability in open pit mines are therefore more complex and often difficult to define, impeding the use of conventional methods. To address the problem, the primary role of rock mass structure, in-situ stress, water flow, and construction have been extended into 18 key parameters. The stability status of slopes and importance of these parameters are investigated by means of computational intelligence tools such as artificial neural networks. An optimized back-propagation network is trained with an extensive database of 141 worldwide case histories of open pit mines. The inputs refer to the values of extended parameters, which include 18 parameters relating to open pit slope stability. The output is an estimated potential for instability. To minimize subjectivity, the method of partitioning the connection weights is applied in order to rate the significance of the parameters involved. The problem of slope stability is therefore modelled as a function approximation. A new open pit mine slope stability index is thus proposed to assess the potential status regime from a holistic point of view. These values are validated by computing the predicted values against the observed status of stability. The reliability of the predictive capability is computed as the mean squared error, and further validated through a receiver operating characteristic curve. Together with a mean squared error of 0.0001, and receiver operating characteristic curve of 98%, the application illustrates that the prediction of slope stability through artificial neural networks produces fast convergence giving reliable predictions, and thus constitutes a useful tool at the preliminary feasibility stage of study.
Warming hydrates releases enough methane to sustain a flame. Oil was first discovered in northeast India in 1889 in the town of Digboi, Assam. However, India remains a vastly unexplored territory with only a small percentage of its 26 sedimentary basins (2.14 million km2/1.21 million sq mi) under active exploration or development. Since their discovery in 1974, the massive Mumbai High fields constitute the majority of the domestic hydrocarbon production. To meet growing energy needs (and offset declining production and drilling inventory), the government of India launched a strategic public-private initiative to spur the development of indigenous hydrocarbon resources with the New Exploration and Licensing Policy (NELP).
Zhenghe, Yan (CNOOC) | Xiaofei, Gao (CNOOC) | Yong, Yang (CNOOC) | Zhihua, Rao (CNOOC) | Donghong, Luo (CNOOC) | Azwar, Olivia (Schlumberger) | Chao, Wang (Schlumberger) | Halomoan, Parlindungan Monris (Schlumberger) | Bisain, Amarjit Singh (Schlumberger)
After more than 20 years of intensive production in XiJiang oil field, a sand group that consists of multiple reservoirs with a thin oil column of less than 4 m and with strong bottom water drive has been revisited. Some assessments were made previously, including drilling horizontal wells with average recovery factor or only 2.3%. In early 2013, new horizontal well drilling was initiated to reassess these reservoirs with a different approach. The objectives were to optimize the standoff between the lateral and the oil/water contact, which is very critical to well performance, by placing the lateral as close as possible to the reservoir top and to evenly regulate the downhole flow across the draining lateral. The program was successful in reassessing the development reservoirs in the mature oil field that had previously been considered to be uneconomic through a reentry horizontal well drilling program and the implementation of the best practices in operations. The operational practices included the precise landing and lateral placement of horizontal wells and the use of inflow control devices (ICD) for completion. Logging-while-drilling (LWD) bed-boundary mapping, with the ability to map multiple key boundaries, including fluid contact for precise well placement, was integrated with multifunction formation evaluation LWD, which provides real-time formation evaluation to optimize the ICD design for completion.
Zhan, Shang-Shu (National Taipei University of Technology) | Teng, Zeng-Rax (National Taipei University of Technology) | Lin, Jing-Han (National Taipei University of Technology) | Wang, Tai-Tien (National Taipei University of Technology) | Huang, Tsan-Hwei (National Taiwan University)
Aperture characteristics of fracture sets highly affects hydraulic properties of fractured rocks. Determination of fracture aperture and hydraulic conductivity is one of major issues for hydrogeological investigation on fractured rock aquifers. Exampling of a well site in central Taiwan with transmissivity of fracture set stochastically determined through a series of in-situ hydrogeological tests, this study carries out laboratory joint tests using the in-situ drilled rock core to further determine the joint roughness coefficient (JRC) of fracture plane. The aperture of various fracture plane is determined by emirical formula, and thus adopted to evaluate the hydraulic conductivity of the plane. The results show that the aperture of fracture with high dip angle resembles that of fracture with moderate dip angle under the overburden stress in study area. The aperture of farcture plane is dominated by JRC, which is a measured-size dependent variable. Finally, this study integrates test results obtained from laboratory and in-situ tests with testing scales to determine the equivalent mechanical aperture and hydraulic conductivity of fracture sets. The hydrogeological characteristics of the studied area is also addressed.
Electrochemical stabilization is a promising technique to improve the engineering properties of weak soils by injecting chemical cementation agent(s) into the soil matrix during the electrokinetic process. The predominant mechanism of electrochemical stabilization is the combination of electroosmosis and electromigration, the movement of water and ions, respectively in the soil by applying a direct current (DC). In the meantime cementation is induced by electrochemical reactions. The technique has been implemented successfully in geotechnical engineering, including the increase of the shear strength and improvement of other geotechnical properties of weak soils. This paper presents an overview of the electrokinetic theory and state-of-theart review of studies on electrochemical treatment of offshore and onshore soils. The review serves as a guidance for future research and applications of electrochemical stabilization of natural soils and other geomaterials.
Surface features such as ground ruptures and folding along this segment are consistent with reverse/left-lateral fault dipping 30 to the east. The ground ruptures deviate from the trend of the Chelungpu fault at the northern end in the east/west Fongyuan-Tongshih section where rupture occurred in a 3-km-wide zone consisting of six segments of north and south dipping reverse faults. Although there are many studies on the Chelungpu fault from the morphology or earthquake geology point of views, the geomechanics study of the active fault or the fault system in central Taiwan is still limited. The objective of this study is to numerically simulate the stress field transition of the fault system in central Taiwan from 1935 to 1999. Such that we can understand the mechanics of the active fault systems, including the Figure 1. The fault system in central Taiwan and the surface rupture induced by 1999 Chi-Chi earthquake.
Andersen, Niels (National Space Institute – DTU Space & Polar DTU) | Bekker, Pieter (University of Dundee and Steptoe & Johnson LLP) | Bishopp, David (Galp Energia) | Nassif, Toufic (Sonde Resources Corporation) | Nordentoft-Lauridsen, Sune (National Space Institute & Polar DTU) | van de Poll, Robert (Fugro N.V.)
This paper provides an overview of the history of global maritime boundary issues, mechanisms to resolve boundary disputes, and the economic potential that can be unlocked by coastal States through the exploitation of hydrocarbons trapped in areas currently unavailable for exploration and production operations.
Vast hydrocarbon reserves are tied up in areas, either underlying waters greater than 200 nm offshore or disputed by coastal States. In the former case technology in the form of deepwater drilling has made testing the potential feasible, whilst in the latter case many of the 311 or so areas in dispute are able to be tested and developed using conventional techniques.
Anything that appears to show a sovereign entity ceding control of land or sea to another country inevitably takes on a high profile in the countries concerned, which in the worst case can lead to armed conflict. It is a credit to those States that subscribe to the principles of the United Nations Charter and the United Nations Convention on the Law of the Sea ("UNCLOS") that they have reached agreement on how the economic potential trapped in disputed areas may be divided or shared.
High-profile, high-stakes disputes relating to offshore oil and gas deposits underscore the importance of the modern law of the sea, and international law generally, to the peaceful settlement of boundary disputes affecting the energy industry. Yet boundary disputes form an overlooked area of investment risk management in the energy sector.
This paper will introduce the technical and legal principles behind the solutions reached by States and will highlight some of the areas with the greatest hydrocarbon potential that have yet to be exploited as well as the areas of risk that require mitigation before investors will advance risk capital.