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Glover, Paul W. J. (University of Leeds) | Lorinczi, Piroska (University of Leeds) | Al-Zainaldin, Saud (University of Leeds) | Al-Ramadhan, Hassan (University of Leeds) | Sinan, Saddam (University of Leeds) | Daniel, George (University of Leeds)
New reservoirs are increasingly more heterogeneous and more anisotropic. Unfortunately, conventional reservoir modelling has a resolution of only about 50 m, which means it cannot be used to model heterogeneous and anisotropic reservoirs effectively when such reservoirs exhibit significant inter-well variability at scales less than 50 m. This paper describes a new fractal approach to the modelling and simulation of heterogeneous and anisotropic reservoirs. This approach includes data at all scales such that it can represent the heterogeneity of the reservoir correctly at each scale.
Three-dimensional Advanced Fractal Reservoir Models (AFRMs) can be generated easily with the appropriate code. This paper will show: (i) how 3D AFRMs can be generated and normalised to represent key petrophysical parameters, (ii) how these models can be used to calculate permeability, synthetic poro-perm cross-plots, water saturation maps and relative permeability curves, (iii) the effect of altering controlled heterogeneity and anisotropy of generic models on fluid production parameters, and (iv) how AFRMs which have been conditioned to represent real reservoirs provide a much better simulated production parameters than the current best technology.
Results of generic modelling and simulation with AFRMs show how total hydrocarbon production, hydrocarbon production rate, water cut and the time to water breakthrough all depend strongly both on heterogeneity and anisotropy. The results also show that in heterogeneous reservoirs, the best production data is obtained from placing both injectors and producers in the most permeable areas of the reservoir – a result which is at variance with common practice. Modelling with different degrees and directions of anisotropy shows how critical hydrocarbon production data depends on the direction of the anisotropy, and how that changes over the lifetime of the reservoir.
We have developed a method of fractal interpolation to condition AFRMs to real reservoirs across a wide scale range. Comparison of the hydrocarbon production characteristics of such an approach to a conventional krigging shows a remarkable improvement in the modelling of hydrocarbon production when AFRMs are used; with AFRMs in moderate and high heterogeneity reservoirs returning values always within 5% of the reference case, while the conventional approach often resulted in systematic underestimations of production rate by over 70%.
Carbon capture and storage (CCS) is regarded as one of the main alternatives for the reduction of anthropologic CO2 emissions. In the CCS process, CO2 from power plants and from other large CO2 point sources are captured and transported at dense (liquid or supercritical) conditions after which it is injected into storage sites. Accurately predicting internal corrosion rates in high-pressure CO2 environments is critical to the design and operation of pipelines used for CCS systems. In water-containing dense phase CO2 environments, corrosion rate increases in conjunction with humidity, typically reaching a critical humidity, beyond which corrosion rates become particularly high. The presence of impurities in the CO2 stream influence the solubility of water and hence the humidity and corrosivity of the CO2 stream. If the CO2 stream is under saturated and below a particular humidity level, then there can be significant cost saving on CCS projects, as this enables carbon steel pipelines to be used with confidence.
The purpose of this work is to develop models to calculate corrosion rates of CO2 systems with under-saturated water conditions in presence and absence of impurities. These models depend on the solubility of water in the CO2 rich phase at saturated conditions. A modified Peng-Robinson equation of state (EoS), E-PPR78 (Jaubert and Mutelet (2004)), available in literature is modified to match water solubility in the CO2 phase for CO2 systems in the presence and absence of impurities at both supercritical conditions and on both sides of the two phase-region.
The corrosion performance of 3Cr-N80 and N80 steels in simulated oil field formation water with CO2 partial pressure of 0.23 MPa at 80°C was investigated using weight loss measurement and surface characterization techniques. The results showed that 3Cr-N80 steel exhibited better localized corrosion resistance, while N80 steel experienced severe pitting attack under the testing conditions. The corrosion rate of 3Cr-N80 steel decreased sharply at early stage of exposure, followed by decreasing with time, and finally reached a relatively stable value. The formation of corrosion products on 3Cr-N80 steel was rich in Cr content and Cr content was about 8 times higher than that of in the substrate, resulting in high corrosion resistance and providing better protection to the steel. FeCO3 and Cr(OH)3 co-deposited films have a critical effect on the CO2 corrosion resistance of 3Cr-N80 steel. Corrosion products formed on N80 steel surface was composed of Ca(Mg,Fe)(CO3)2 where Fe2+ was replaced by Ca2+ and Mg2+ ions.
Carbon steels have been widely used in oil and gas field based on their excellent mechanical properties and low cost.1 However, carbon steel is susceptible to corrosion in sweet condition due to the presence of CO2 is able to react with water and forming corrosive carbonic acid, result in the failure of casing and pipeline.2, 3 In recent years, because of the increasing in market demand, modern oil exploitation and transportation have shifted to harsher and high temperature and high pressure (HTHP) environments.
Materials with better corrosion resistance than carbon steel is need to be developed in order to use in harsh environments.4, 5 The capabilities of low Cr steels to improve the corrosion resistance of carbon steels and enlarge their application regime.1 Many researchers have studied the corrosion rate,1, 6-8 surface film growth process1,9-11 and corrosion mechanisms 12-15 of low-Cr steel in CO2 environment. It was found that adding 3 wt. % Cr to conventional carbon steel could increase the CO2 corrosion resistance of the material by 2.5-40 times and the cost increased would be less than 50%.16
Sui, Pengfei (China University of Petroleum) | Sun, Chong (University of Alberta) | Hua, Yong (University of Leeds) | Sun, Jianbo (China University of Petroleum) | Wang, Yong (China University of Petroleum)
The influence of flow rate on corrosion behavior of X65 carbon steel in water-saturated supercritical CO2 phase containing 1000 ppmv H2S impurity was studied at 35 °C and 8 MPa from 0 m/s to 1.5 m/s. Weight loss tests showed that the general corrosion rate reached maximum at the flow rate of 1 m/s and then decreased with flow rate to 1.5 m/s. Turtle pattern corrosion morphology was observed on the sample surface when the flow rate exceeded 1 m/s. The corrosion product mainly consisted of FeCO3 and FeS, and the average size of spherical corrosion product changed with flow rate. Besides, the percentage composition of FeS presented the same change trend as the average size of spherical corrosion product. In supercritical CO2 phase, wall shear stress was not big enough to cause mechanical damage on corrosion film but can affect the formation process and the characteristics of the corrosion film of X65 carbon steel.
Carbon capture and storage (CCS) has been regarded as one of effective way to reduce CO2 emission, which is mainly caused by the burning of fossil energy or the exploration of oil and gas field.1, 2 CCS process is consisted by three main steps: capturing CO2 from gas source, transporting CO2, and storing it for long-term isolation from air.3, 4
Among different transporting methods, pipelines transportation is a safe, reliable and cost-effective way for large quantity and long-distance transportation of CO2, in which the captured CO2 is typically compressed into a supercritical state or liquid state to avoid two-phase flow regime.5, 6 It is believed that dry CO2 is non-corrosive. However, the captured CO2 gas from different industrial sources such as coal-fired plants, cement production or refineries, inevitably contains various impurities. The presence of impurities such as H2O, O2, SO2, and H2S, may pose a great risk to the security and stability of pipeline.7-10 In recent years, corrosion problem of CO2 transport pipelines has aroused wide public concern. Many researchers have studied the effect of different impurities or the temperature and pressure on corrosion behavior of carbon steels, which is summarized in Table 1.11-23 Compared with different results in Table 1, most studies were carried out under a static state,14-17, 19-21 while few studies were in dynamic conditions.11-13,18,22-23 These corrosion tests may be not in accordance with the actual transport situation. Though, enough attention has been paid on different factors that may lead to internal corrosion of CO2 transport pipelines, some influential parameters still need to be further investigated.
The re-passivation kinetics and composition of the passive film of CoCrMo alloys in simulated body fluids have been investigated, with key emphasis being to assess the effect that proteins have on these features. The kinetics were analyzed using potentiostatic polarization, applying a second order exponential decay to the current transients obtained, which consists of two phases: coverage and thickening. Repassivation occurred quickest in a phosphate environment with presence of bovine serum albumin (BSA) hindering the process as it inhibits access of the oxidant. By using X-ray photoelectron spectroscopy (XPS) the composition of the re-passivated layer was studied. As expected, the film is mainly composed of chromium (III) oxide with small amounts of cobalt (II) oxide and molybdenum oxides (IV-VI). When exposed to BSA the percentage of molybdenum in the passive film decreases. This is shown to be due to the protein having a high affinity for the element causing it to be lost to solution when the metal was exposed to corrosion.
Throughout the last century, orthopedic surgery has helped to improve the quality of life for millions of people around the world by restoring mobility and reliving pain . Prosthetic joint replacement is one of the most successful and common treatments for people suffering from arthritis/rheumatism, due to great advancements in joint replacement technology over recent years in terms of investment, research and clinical trials . For the majority of patients this occurs on the weight-bearing joints which are the knee and hip. According to statistics approximately 400,000 hip replacements are performed annually in the USA, with operations being carried out on people under 60 rising dramatically in the last decade alone .
Since the 1990’s metal-on-metal (MoM) hip joints saw a drastic increase in use as the much used metal-on-polymer (MoP) was proven to generate polyethylene wear particles which cause osteolysis i.e. destruction of bone tissue [1,3,4]. CoCrMo hip implants were chosen due to possessing excellent corrosion resistance and a postulated higher longevity which bodes well for the greater need of younger people requiring an implant . Some MoM devices have lasted up to 25 years in-vivo with a wear rate even lower than that in a MoP device . These have become extremely contentious in recent years due to clinical problems arising due to adverse effects, release of debris and metal ions from the device have meant that instances of CoCrMo for hip implantation has dropped to almost zero . The metal ions that are released can enter the bloodstream where they are absorbed by erythrocytes allowing them to enter cells, remain in localized tissues or be transported throughout the body which can lead to genotoxicity and immunological effects .
The porosity and permeability of binary mixtures of spherical grains were modelled theoretically and studied empirically against such variables as grain-size, grain-size ratio, grain volume fraction and grain packing. The results confirmed that binary mixing of different-sized grains always results in a porosity loss. The degree of porosity loss was found to be a function of the grain-size ratio. Consequently, the mixture with the highest grain-size ratio of 3 dropped to the lowest minimum porosity of 0.3116 while the mixture with the minimum grain-size ratio of 1.5 experienced the highest minimum porosity of 0.3716. The observed porosities could not be described by some of the existing porosity models including the ideal and fractional packing models due to the assumptions of ideal packing and no-mixing respectively underlying these models. Thus, a corrected fine packing (or replacement) model wasdeveloped during this research to incorporate the grain-size ratio effect on porosity. Together with the interstitiation model, the corrected replacement model gave the best fit to the observed porosities. The mixtures’ permeabilities could not be modelled by the grain-size/porosity-dependent permeability models because these models tend to mimic the trend of the representative porosity used. The weighted geometric/harmonic mean permeability models (weighted by volume fraction) described the observed permeabilities best.
Presentation Date: Monday, October 15, 2018
Start Time: 1:50:00 PM
Location: 202A (Anaheim Convention Center)
Presentation Type: Oral
ABSTRACT: The majority of open-pit mineral workings are established in hydrogeological environments in which unsaturated drainage or saturated groundwater flow occurs predominantly via discrete fracture networks. Stress relaxation resulting from open-pit mineral extraction can lead to a change in host rock fracture network configuration and fracture hydraulic properties, with the potential to change local hydrogeological characteristics and groundwater flow regimes. Research being undertaken at the University of Leeds is applying a DFN approach to investigate the hydrogeological significance of such effects in relation to methodologies for impact assessment at mineral sites. The paper presents a summary of the research approach and preliminary results. A discrete finite element approach to geomechanical modelling has been undertaken with simulation of DFN evolution in response to lithostatic unloading for a range of pre-existing discontinuity configurations, lithological types and variations in in-situ stress regimes. Preliminary modelling results have provided improved understanding of the vertical and lateral extent of potential DFN response for a range of excavation profiles. Research results will be used to define conditions under which open-pit mineral extraction could lead to hydrogeologically significant change in fracture flow drainage characteristics at a scale relevant to hydrogeological impact assessment for new and existing mineral workings.
ABSTRACT: Rock fractures have a crucial role in geomechanics affecting rock behavior. Seismic waveforms carry information about the medium through which it has propagated. Extracting information from waveforms can lead to conclusions about the heterogeneity and anisotropy of the medium and an estimation of density and mechanical stiffness of fractures. The stress field in a fractured medium is also important as it controls the closure of the fracture and hence the fracture stiffness. Using seismic waveforms, we can make indirect conclusions about the stress state of the medium. Models and experiments in a medium with discrete parallel fractures have led to confidence that the models can accurately reproduce wave interaction with fractures. But what about waveforms for waves propagating through a more complex fracture network? In this work we use a DFN tool to create a fracture network and pass seismic waves through the medium recording velocity waveforms. From this we reach conclusions on how the fracture networks are affecting the seismic waveforms with implications for real-world problems. We extend this work to include the local stress field which alters fracture stiffness along fractures establishing how these changes affect seismic waveforms compared to the initial uniform stress model.
ABSTRACT: The growing global population is leading to reduced space and a need for more resources. This is causing engineered structures to be designed within rock masses at greater depths, and subjected to significant thermo-mechanical loading. Numerous hydro-thermo-mechanical in-situ experiments, including block tests and heated plate load tests have demonstrated the effects of temperature on discontinuity mechanics at a large scale. In this study we propose two methodologies for the multi-stage testing of discontinuity shear strength at incremental temperatures under triaxial conditions. The two methodologies result in different thermomechanical behavior of the specimens. If deformation of the specimen is constrained during heating, no change in residual shear strength of the discontinuity is seen, however, if the specimen is unloaded and free to deform under thermal loading, it displays reduced shear strength upon reloading. This preliminary data has potential implications for the design of engineered structures in these elevated thermo-mechanical environments.
Advancements in engineering capability have led to structures being designed within rock masses at greater depths, where they are expected to withstand not just greater stresses, but also elevated temperatures. The thermal loading of a rock mass can occur due to the geothermal gradient in the cases of deep tunneling, mining and geothermal heat production, or due to the heat generation from high-level radioactive waste in a geological disposal facility.
Rock masses are heterogeneous and discontinuous. Under applied stresses, the mechanical behavior and strength of a rock mass is commonly controlled by the behavior and strength of the discontinuities (Hoek, 1983). Discontinuities vary widely in terms of their origin (joints, bedding, foliation, faults, shear zones etc.) and associated physical characteristics. Characterizing their mechanical properties under different conditions is therefore paramount to understanding the behavior of a rock mass under these conditions. Numerous hydrothermo-mechanical in-situ experiments, including block tests and heated plate load tests have explored the effects of temperature on discontinuity mechanics at a large scale and shown modifications in the mechanical behavior of discontinuities at these elevated conditions (Cramer and Kim, 1986; Hardin et al., 1981; Zimmerman et al., 1985). However there have been no small scale studies to understand the mechanics of individual discontinuities under these loading conditions.
Glover, Paul W. J. (University of Leeds) | Lorinczi, Piroska (University of Leeds) | Al-Zainaldin, Saud (University of Leeds) | Al-Ramadan, Hassan (University of Leeds) | Daniel, George (University of Leeds) | Sinan, Saddam (University of Leeds)
The hydrocarbon industry is currently transitioning from a world where hydrocarbon reservoirs were large and homogeneous to one where reservoirs are often small, heterogeneous, anisotropic, as well as having other challenges. Heterogeneous and anisotropic reservoirs are extremely difficult to model and simulate. The reason lies in our lack of knowledge of the inter-well volume where much of the variability of the reservoir occurs. Conventional approaches use interpolation between wells that is influenced by 3D seismic information. As the resolution of that seismic information is about 50 m, no information can be included in the reservoir model below that scale.
In this paper we describe the creation and validation of advanced fractal reservoir models (AFRMs) which use fractal mathematics to represent heterogeneous and anisotropic variation in reservoirs at all scales from the scale of the model cell to that of the whole reservoir. These deterministic models take into consideration variability in the reservoir at all scales.
Generic modelling of AFRMs shows how reservoir heterogeneity can reduce hydrocarbon and water production by as much as 69%, an effect that would not be seen if conventional reservoir modelling had been carried out. Furthermore, anisotropy has an additional effect on both oil and water cumulative production and production rate as well as the time to water breakthrough and water cut. The effect of anisotropy has been shown by generic modelling of AFRMs to be significant in early and middle production and becomes less important in late production. Generic modelling has also confirmed that placement of wells (both injectors and producers) in high permeability rock provides the best production in heterogeneous reservoirs.
Recent work has allowed AFRMs to be conditioned to real reservoirs, making their application of wider use. In this paper we compare the performance of conditioned AFRMs to more conventional reservoir models by comparing them against a reference ideal reservoir. This shows that the conventional approach performs well for homogeneous reservoirs but breaks down badly for heterogeneous reservoirs, while the conditioned AFRMs accurately portray the reservoir from fluid production point of view irrespective of its heterogeneity.