Modelling Case-Based Reasoning in Situation-Aware Disaster Management

Situation-aware disaster management (SADIM) is a continuous decision-making and action taking process. This process requires prior knowledge of the ongoing environment and context. SADIM comprises two major processes: situation awareness (SA) - a cognitive process that assesses current situations and anticipate future situations in the environment; and, disaster management (DM) which is a decision-making process preventing, preparing, responding, and recovering for and from a disaster. One of the decision-making technologies used in current SADIM is case-based reasoning (CBR) CBR is used for the disaster management element only. Situation awareness process in current SADIM is carried out using domain rules, statistical reasoning and other methods. This paper therefore presents a method of using CBR to carry out both situation assessment and disaster management decision-making processes in SADIM, building on previous work focusing in SA alone. Using CBR for both processes provides the capability of using past experiences to understand the state of the environment and also solve specific disaster problems. The paper evaluates the method through implementation in disaster prevention in the petroleum drilling domain for early kick detection to prevent a blowout disaster. The results show a clear improvement in similarity assessment and problem solving prediction to prevent blowout

Gas-condensate flow modelling for shale reservoirs.

Condensate banking is the most challenging engineering problem in the development of gas-condensate reservoirs where the condensate accumulation can dramatically reduce the gas permeability resulting in impairment of wells productivity. An accurate assessment of condensate banking effect is important to predict well productivity and to diagnose well performance. Traditionally, Darcy law, combined with relative permeability models, has been used for modelling condensate banking effect in conventional reservoirs. This approach is also widely adopted in reservoir engineering commercial tools. However, for shale gas-condensate reservoirs, the gas flow deviates from Darcy flow to Knudsen flow due to the very small pore size in shale matrix (3-300 nm), compared to conventional reservoirs (10-200 'm). This gas flow is highly dependent on pore size distribution and reservoir pressure. In this paper, the effect of condensate saturation on Knudsen flow in shale matrix kerogen is investigated using a 3D pore network with a random pore size distribution. The Knudsen flow is incorporated at the pore level and gas permeability is evaluated for the whole network. In addition, the pore distribution effect in terms of log-normal mean and standard deviation is investigated. The concept of relative permeability in Darcy flow is extended to Knudsen flow by defining a new parameter called relative correction factor to evaluate the effect of condensate banking on Knudsen flow. This parameter can be employed directly in reservoir engineering tools. Simulation results showed that the relative correction factor is not only dependent on condensate saturation but also on pressure. This is due to the impact of pressure on the contribution of pore size ranges into the gas flow. In addition, results showed the effect of the pore size distribution where the standard deviation controls mainly the behaviour of Knudsen flow under condensate saturation. Disregarding this effect can lead to an overestimation of Knudsen flow contribution in well production under condensate banking effec

Experimental investigation of the displacement flow mechanism and oil recovery in primary polymer flood operations.

Polymer flooding is a mature chemical enhanced oil recovery method employed in oilfields at pilot testing and field scales. Although results from these applications empirically demonstrate the higher displacement efficiency of polymer flooding over waterflooding operations, the fact remains that not all the oil will be recovered. Thus, continued research attention is needed to further understand the displacement flow mechanism of the immiscible process and the rock–fluid interaction propagated by the multiphase flow during polymer flooding operations. In this study, displacement sequence experiments were conducted to investigate the viscosifying effect of polymer solutions on oil recovery in sandpack systems. The history matching technique was employed to estimate relative permeability, fractional flow and saturation profile through the implementation of a Corey-type function. Experimental results showed that in the case of the motor oil being the displaced fluid, the XG 2500 ppm polymer achieved a 47.0% increase in oil recovery compared with the waterflood case, while the XG 1000 ppm polymer achieved a 38.6% increase in oil recovery compared with the waterflood case. Testing with the motor oil being the displaced fluid, the viscosity ratio was 136 for the waterflood case, 18 for the polymer flood case with XG 1000 ppm polymer and 9 for the polymer flood case with XG 2500 ppm polymer. Findings also revealed that for the waterflood cases, the porous media exhibited oil-wet characteristics, while the polymer flood cases demonstrated water-wet characteristics. This paper provides theoretical support for the application of polymer to improve oil recovery by providing insights into the mechanism behind oil displacement

Numerical Modelling of the Effect of Wettability, Interfacial Tension and Temperature on Oil Recovery at Pore-Scale level

A numerical investigation into the effect of wettability and temperature on oil recovery with a hot water injection at different temperatures is reported in this paper. The computational domain is a two-dimensional porous medium (reservoir) maintained at a fixed temperature with pore spaces of varying sizes and interconnected pore-throats. ANSYS-Fluent VOF (volume of fluid) model was used to simulate the two-phase transport through the reservoir with hot water injections at varying temperatures (20, 40 and 60 °C) and wettability contact angles of 45°, 90° and 150°. In addition, an investigation was conducted on the effect of combined interfacial tension and matrix wettability on oil recovery process at low and high interfacial tension of 0.025 N/m and 0.045 N/m respectively for the three different wettability contact angles. The results showed that, the displacement behaviour of water and oil-wet system is affected significantly by the contact angle with a profound effect on the oil recovery factor. In the water-wet case (with the water wetting the matrix wall and the oil phase surrounded by water), relatively more oil is displaced from the domain thereby improving the oil recovery factor. The water-wetter system resulted in about 35–45% oil recovery than the oil-wet system, with the unrecovered oil mainly adhering to the wall region of the pore bodies for oil-wet system. For the intermediate wet case, initial fluid distribution is seen to have a more significant effect on the displacement behaviour than the contact angles. In conclusion, by altering the wettability from oil-wet to water-wet condition, the oil recovery rate is improved. The results from this study are consistent with the experimental and numerical studies in literature and it will further enhance the understanding of the phenomenon that is critical to the mechanism of recovery such as surfactant and polymer flooding process

Casing structural integrity and failure modes in a range of well types: a review.

This paper focus on factors attributing to casing failure, their failure mechanism and the resulting failure mode. The casing is a critical component in a well and the main mechanical structural barrier element that provide conduits and avenue for oil and gas production over the well lifecycle and beyond. The casings are normally subjected to material degradation, varying local loads, induced stresses during stimulation, natural fractures, slip and shear during their installation and operation leading to different kinds of casing failure modes. The review paper also covers recent developments in casing integrity assessment techniques and their respective limitations. The taxonomy of the major causes and cases of casing failure in different well types is covered. In addition, an overview of casing trend utilisation and failure mix by grades is provided. The trend of casing utilisation in different wells examined show deep-water and shale gas horizontal wells employing higher tensile grades (P110 & Q125) due to their characteristics. Additionally, this review presents casing failure mixed by grades, with P110 recording the highest failure cases owing to its stiffness, high application in injection wells, shale gas, deep-water and high temperature and high temperature (HPHT) wells with high failure probability. A summary of existing tools used for the assessment of well integrity issues and their respective limitations is provided and conclusions drawn

Stress effects on flow partitioning in fractured reservoirs: equivalent porous media versus poro-elasticity coupled modeling.

In this paper the effects of overburden stress on fracture-matrix flow partitioning were numerically analyzed using two different numerical approaches; the analysis was validated using a fractured Clashach core flood laboratory experimental data. In the first numerical approach, the fracture aperture variation under different overburden stresses, measured using a back calculation method based on the treatment of the fracture as an equivalent porous medium, was adopted in a coupled Darcy law, Brinkman flow and Navier-Stokes fluid flow formulation. In the second numerical approach, poro-elasticity was applied in order to accurately account for fracture aperture change under overburden stress loading. The resulting displacements were coupled to the same fluid flow equations used in the first approach through a moving mesh technique. This was further coupled with stress dependent permeability within the matrix. Flow partitioning from the two numerical approaches were compared to the experimental data. This comparison highlighted the inefficiency of treating fractures as equivalent porous medium. Moreover the cross-flow between the fracture and the matrix was monitored in both modeling approaches and a critical stress beyond which the matrix can no longer feed the fracture was identified. This critical stress can be very important in designing production scenarios for highly-stressed fractured reservoirs

Multicriteria material selection for casing pipe in shale gas wells application.

The conventional method of casing selection is based on availability and/or order placement to manufacturers based on certain design specifications to meet the anticipated downhole conditions. This traditional approach is very much dependent on experience as well as constructing oil and gas wells at minimum budget. However, this material selection approach is very limited in meeting the requirement of shale gas wells. This study utilises the material performance indices and ANSYS Granta database to examine three different casing pipe buckling scenarios including the buckling with corrosion potentials and buckling with impact and long-term service temperature conditions. Consequently, numerical evaluations of the response of the selected casing materials established the stress, deformations, and safety factor for the first scenario (shale gas well with buckling tendencies). The significance of this new method is added advantage in terms of integrating materials' physicochemical, thermal and mechanical properties and the casing functional performance to establish ideal selection within the design space or requirements. Results obtained in this study shows that there are optional materials that outperform the most common casing grades (P110 &Q125) utilised in shale gas development in terms of both safety and cost. This study established a procedure between cost, safety, performance indices and materials' physical and mechanical properties for a typical well design scenario. This procedure will assist the design engineer justify the selection of a particular material(s) safely and technically for a given shale well casing application in future. In all the 10 materials investigated, even though the P110 (API casing grade) meets the buckling design scenario and widely used in shale gas well development, there are many alternative viable material candidate options that outperform P110 Grade with the best material candidate studied in this work being BS 145

User interface design for situation-aware decision support systems.

Information recall about general situations incurs memory and cognitive loads on operators. Recognition of information for specific situations identified with users context and the state of the world is helpful to operators in performing tasks in complex environments. The emergence of ubiquitous, ambient, and pervasive technologies is increasingly providing methods to help operators to perform their tasks in smart and intelligent ways. Existing user interface design does not solve the problem of drawing together the information required for situation-aware decision support systems in a way that minimises cognitive load. This paper discusses a framework for user interface design of situation-aware systems that exploit inputs from users and the environment to provide information tailored to the users tasks in specific situations. The user interface can reconfigure automatically in order to adapt to the current situation. The adaptation of the user interface to the current situation and the presentation of a reusable sequence of tasks in the situation reduces memory loads on operators. Hierarchical Task Analysis (HTA) is used to describe tasks for various types of situations. HTA is supplemented with scenarios to stimulate design ideas and requirements analysis is used to represent interrelationships between tasks

Rheological behaviour of single-phase non-Newtonian polymer solution in complex pore geometry: a simulation approach.

One of the most important criteria for evaluating chemical enhanced oil recovery (EOR) processes that use polymers is its rheological behaviour which in turn account for other physical effects of adsorption and resistance factors during polymer-rock interactions. However, complete knowledge of behaviour of polymer solution in porous media has not yet been fully gained. A computational fluid dynamics simulations implemented in COMSOL Multiphysics is used to simulate 1-D single-phase, non-elastic xanthan gum flow in geometries approximating formation pore throats. Simulation results show the degree of solution viscosity degradation at different inlet pressures and shear rates at varying pore constriction diameters. Results also show that numerical techniques can predict the performances of polymer solution applications in actual field operational conditions

Case-based situation awareness.

Situation-aware case-based decision support (SACBDS) systems comprise two distinct parts: situation awareness (SA) and case-based reasoning (CBR). The SA part keeps a finite history of the time space information of the domain and uses rules to interpret cues from the environment with respect to an individual user's context, and then anticipates future situations by performing statistical inference over historical data. The CBR part is the part that seeks to accomplish a particular task with knowledge of the environment from the SA component. This paper discusses the fusion of the CBR model and the SA model into a case-based situation awareness (CBSA) model for situation awareness based on experience rather than rule, similarity assessment and problem solving prediction. The CBSA system perceives the users' context and the environment and uses them to understand the current situation by retrieving similar past situations. Every past situation has a history. The future of a new situation (case) is predicted through knowledge of the history of a similar past situation. The paper evaluates the concept in the flow assurance control domain to predict the formation of hydrate in sub-sea oil and gas pipelines. The results provided the CBSA system with greater number of accurate predictions than the SACBDS system