Horizontal wells have been used to increase reservoir recovery, especially in unconventional reservoirs, and hydraulic fracturing has been applied to further extend the contact with the reservoir to increase the efficiency of development. In the past, many models, analytical or numerical, were developed to describe the flow behavior in horizontal wells with fractures. Source solution is one of the analytical/semi-analytical approaches. To solve fractured well problems, source methods were advanced from point sources to volumetric source, and pressure change inside fractures was considered in the volumetric source method. This study aims at developing a method that can predict horizontal well performance and the model can also be applied to horizontal wells with multiple fractures in complex natural fracture networks. The method solves the problem by superposing a series of slab sources under transient or pseudosteady-state flow conditions. The principle of the method comprises the calculation of semi-analytical response of a rectilinear reservoir with closed outer boundaries. A statistically assigned fracture network is used in the study to represent natural fractures based on the spacing between fractures and fracture geometry. The multiple dominating hydraulic fractures are then added to the natural fracture system to build the physical model of the problem. Each of the hydraulic fractures is connected to the horizontal wellbore, and the natural fractures are connected to the hydraulic fractures through the network description. Each fracture, natural or hydraulically induced, is treated as a series of slab sources. The analytical solution of superposed slab sources provides the base of the approach, and the overall flow from each fracture and the effect between the fractures are modeled by applying superposition principle to all of the fractures. It is assumed that hydraulic fractures are the main fractures that connect with the wellbore and the natural fractures are branching fractures which only connect with the main fractures. The fluid inside of the branch fractures flows into the main fractures, and the fluid of the main fracture from both the reservoir and the branch fractures flows to the wellbore. Predicting well performance in a complex fracture network system is extremely challenged. The statistical nature of natural fracture networks changes the flow characteristic from that of a single linear fracture. Simply using the single fracture model for individual fracture, and then adding the flow from each fracture for the network could introduce significant error. This study provides a semi-analytical approach to estimate well performance in a complex fracture network system.

<p>Biomaterials used for stabilization of compressed vertebraes due to osteoporosis, have mainly been based on resin materials, like PMMA (polymethyl methacrylate), but have recently expanded to consist of injectable ceramics, such as calcium-aluminate. In this in vitro study human osteoblast-like cells, MG-63, were cultured on three different injectable biomaterials based on: Ca-aluminate, Bis-GMA (bisphenol A-glycidylmethacrylate) and PMMA, to investigate the cellular response elicited by these materials. Cell proliferation was measured by the NucleoCounter® system, cell viability was investigated by LDH (lactate dehydrogenase) analysis, cell differentiation and mineralization was evaluated by mRNA gene expression of the osteoblastic markers: ALP (alkaline phosphatase), OC (osteocalcin) and COLL-I (collagen type I) by qPCR (quantitative polymerase chain reaction) analysis. Two control materials were used: TCP (tissue culture polystyrene, negative control) and PVC (polyvinyl chloride, positive control). The results showed that all the bone cement materials were non-toxic and biocompatible, i.e. they provided good cell viability and proliferation of the MG-63 cells. They are specific for bone cells, since they expressed high values of the osteoblast-specific differentiation markers, and are thus promising as injectable bone cement materials. Among the bone cements, Xeraspine appears to be the most biocompatible material for bone cells. It is followed by Cortoss and then Vertebroplastic.</p>

Reproduction de : Thèse d'exercice : Médecine : Nancy 1 : 2003. / Thèse : 03NAN1117. Titre provenant de l'écran-titre.

Diss. (sammanfattning) Stockholm : Karolinska institutet, 2009.

SAMMANFATTNING Patienter som drabbas av höftfrakturer är en vårdkrävande och utsatt patientgrupp inom sjukvården. Riktlinjer för handläggning av misstänkta höftfrakturer har utformats för ett snabbare omhändertagande, så kallat snabbspår. Dessa används för att optimera och förkorta handläggningstiden, förbättra behandlingen samt minska risken för komplikationer. I Västernorrlands län tillämpas detta snabbspår, vilket medför att delar av den behandling som tidigare utfördes på akutmottagningen, nu utförs av ambulanssjuksköterskor redan i den prehospitala vården. Dessa medicinska och omvårdnadsmässiga åtgärder utförs i varierande och ibland svåra vårdmiljöer. Därför finns ett behov av att studera ambulanssjuksköterskornas upplevelser och erfarenheter av att vårda patienter med misstänkt höftfraktur. Syftet med studien var att beskriva ambulanssjuksköterskors upplevelser och erfarenheter vid omhändertagande av patienter med misstänkt höftfraktur. Kvalitativ ansats användes och designen var semistrukturerade intervjuer som analyserades med kvalitativ manifest innehållsanalys. Studiepopulationen bestod av åtta ambulanssjuksköterskor stationerade i Ångermanland. I resultatet framkom att ambulanssjuksköterskorna innehar både positiva och negativa erfarenheter av att arbeta med misstänkta höftfrakturer. Äldre människor utgjorde den största patientgruppen och dessa patienter led ofta av demenssjukdomar samt andra sjukdomar och tillstånd som försvårade kommunikation och interaktion, vilket skapade svårigheter i handläggningen av dessa patienter. Vårdmiljön försvårade arbetet ytterligare för ambulanssjuksköterskorna och innebar ofta svåra förflyttningar och lyft. Positivt för både patienten och ambulanssjuksköterskorna var att det strukturerade omhändertagandet gav en snabbare vårdkedja och likvärdig vård för patienterna samt mer tid för omvårdnad. Andra aspekter som framkom var att ambulanssjuksköterskorna hade en del förutfattade meningar gällande patientgruppen och svårigheter att få patienten tillräckligt smärtlindrad. Själva omhändertagandet uppgavs vara alltför strukturerad, handläggningen tog lång tid och att det var svårt att få patienten tillräckligt smärtlindrad utan biverkningar. Slutsatsen var att ambulanssjuksköterskorna hade både positiva och negativa erfarenheter kring det strukturerade omhändertagandet, samt en del förutfattade meningar. Samtliga informanter ansåg att de hade mer tid för omvårdnaden och att de på så vis fick lära känna patienten bättre, därför kunde de enklare utvärdera behandlingsresultatet. De positiva erfarenheterna var att omhändertagandet gav en snabbare handläggning med bättre struktur och därigenom en likvärdig vård i hela länet gällande denna patientgrupp. Det accepterades att uppdragen tog längre tid och därför fick personalen även mer tid tillsammans med patienterna. Ambulanssjuksköterskorna kunde se ett konkret resultat av omhändertagandet. De negativa erfarenheterna innefattade att patientgruppen var svårbedömd på grund av eventuella tidigare sjukdomar och läkemedelsbehandlingar. Att anhöriga och vårdpersonal ibland trängde sig in i vårdrummet, med syfte att vara behjälplig, men flyttade istället fokus från patienten. / ABSTRACT Patients with hip fractures are a care-intensive and vulnerable patient population in health care. Guidelines for dealing with suspected hip fractures have been designed for a faster disposal, so-called fast track. These are used to optimize and shorten the processing time, improve treatment and reduce the risk of complications. Västernorrland county has applied a fast track, which means that parts of the processing previously performed in the emergency department, now is performed by ambulance nurses already in the prehospital care. These medical and nursing activities performed in varying and sometimes difficult healthcare environments. Therefore there was a need to study the ambulance nurses' experiences of caring for patients with suspected hip fracture. AIM: The aim of the study was to describe Ambulance nurses experiences of treatment of patients with suspected hip fracture. Qualitative approach was used and the design was semi-structured interviews were analyzed using qualitative manifest content analysis. The study population consisted of eight ambulance nurses stationed in Ångermanland, Sweden. The result showed that ambulance nurses possess both positive and negative experiences of working with suspected hip fracture. Older people represented the largest group of patients and these patients often suffered from dementia and other diseases and conditions that impeded communication and interaction, which created difficulties in dealing with these patients. The healthcare environment complicated the work further for the ambulance nurses and often includes difficult movements and lifting. Positive for both the patient and ambulance nurses was that it structured the care provided faster care chain and equivalent care for patients as well as more time for care. Other aspects that emerged were that the ambulance nurses have some preconceptions regarding the patient group and the difficulties in getting the patient adequate pain relief. The fast track was described to be too structured, the processing takes a long time and that it was difficult to get the patient enough pain relief without side effects. The conclusion was that it emerged that the ambulance nurses had both positive and negative experiences of the structured care, and had some preconceptions. All the respondents felt that they had more time for care, and that they got to know the patient better, because they could more easily evaluate the treatment outcome. The positive experience was that the fast track provided faster processing with better structure and thereby an equal treatment throughout the county regarding this population. It was accepted that missions took longer therefore the staff spent more time with the patients. The ambulance nurses could see concrete result of the fast track. The negative experiences included that the patient group was difficult to assess because of past illnesses and drug treatments. Relatives and caregivers are sometimes forced into the nursing room, with the aim to be helpful, but instead moved focus from the patient.

ABSTRACT Aquifer storage and recovery (ASR) is used world-wide to supplement available water supplies by storing surplus water in aquifers and recovering it during periods of drought and increased demand. The use of ASR as an option for increasing available municipal irrigation and fresh water supplies is threatened as a result of the mobilization of arsenic in some aquifers during ASR. Arsenic is liberated from arsenic-bearing sulfide minerals as a result of the mixing of oxidizing injected water with reducing insitu groundwater. Fracture networks can have significant influence on the migration and distribution of arsenic in the Upper Floridan Aquifer (UFA) during ASR operations through effects on fluid flow, chemical reactions, and transport characteristics. To characterize fracture flow and associated mass transport, numerical three-dimensional models constructed with MODFLOW and FracMan are used to represent fractures in equivalent continuum, discontinuum, and stochastic discontinuum or discrete fracture network (DFN) dual porosity or hybrid models. The geochemical reaction (PHREEQC-2) and transport (MT3DMS) models are coupled to the three dimensional numerical flow model (MODFLOW 2000) as PHT3D- 2003, and utilized to simulate the flow, transport, and inorganic reactions associated with the injection of oxidized water into the UFA of Southwest Florida during ASR cycles. The discrete fractures, implicitly simulated in MODFLOW as high flow zones, are model layers of varying thicknesses with uniform hydraulic conductivity and storage parameters, and as stochastically-generated horizontal and vertical fractures with varying physical attributes including orientation, aperture widths, fracture intensity, and fracture distributions, distributed within a lower conductivity matrix. Discrete fracture networks are simulated with FracMan and the results imported into MODFLOW. Although each fracture zone layer is assigned a unique stochastic distribution of hydraulic conductivity, each model represents a single realization. The FracMan output of stochastic distributions of hydraulic conductance and storage parameters is "upscaled" for use in MODFLOW. The vertical migration of solute due to variations in the density of injectate and groundwater does not appear to be a significant characteristic of the modeled flow system. The modeling results support the hypothesis that arsenopyrite, which is stable under reducing conditions, liberates arsenic during recharge cycles as a result of oxidation. The results also indicate that fracture flow significantly controls the distribution of all solutes affected by the ASR flow system due to the significantly higher transmissivity of the fractures compared to the matrix. The simulated distribution of arsenic in the matrix is significantly less than in the fractures as a result of the limited penetration of oxidized recharge waters into the inter-fracture matrix. Under the simulated aquifer and geochemical conditions, arsenic travels farther from the injection well via fractures than is observed in monitor wells, suggesting that the partially-penetrating monitoring well network does not intercept many of the fractures. The modeled increases in concentrations of arsenic in the ASR wells during the recovery cycles are also consistent with observations. Explicit representation of fracture zones in numerical transport models provides an increased understanding of the flow system and the potential occurrence and distribution of arsenic in groundwater.

Sets of natural opening-mode fractures in sedimentary rocks may show a variety of types of aperture-size distributions. A frequently documented size distribution type, in the literature and in data presented here, is the power law. The emergence of power-law distributions of fracture aperture and length sizes has been simulated using various quasi-mechanical fracture-growth routines but models based on linear-elastic fracture mechanics rarely produce such patterns. I collected a fracture-size dataset of unprecedented size and resolution using core and field methods and scanning electron microscope-based cathodoluminescence (SEM-CL) images. This dataset confirms the prevalence of power laws with a narrow range of power-law exponents among fractures that contain synkinematic cement. Organized microfractures are ubiquitous in sandstones. A fracture-growth simulation I devised reproduces observed size-scaling patterns by distributing fracture-opening increments among actively growing fractures. The simulated opening increments have a uniform size, which can be specified; uniform opening size is consistent with observations of narrow ranges of micron-scale widths of opening increments within crack-seal texture in natural fractures. Thus power-law size scaling of natural fractures can be explained using non-power-law (uniform-sized) opening increments, arranged using rules designed to simulate the effects of cement precipitation during fracture opening. A fundamental shortcoming of previous models of fracture-set evolution is the absence of a test because only natural fracture end states, not growth histories, could be measured. Using a technique to constrain fracture timing based on fluid inclusion microthermometry and thermal history modeling, I tested growth models by reconstructing the opening history of a set of natural fractures in the Triassic El Alamar Formation in northeast Mexico. The natural-fracture data show that, consistent with simulations, new microscopic fractures are continually introduced during natural fracture pattern evolution. As well, larger fractures represent sites of concentrated reactivation, although smaller fractures may be reactivated after long periods of quiescence. The pattern likely arises through feedback between fracture growth and the mechanically adhesive effects of contemporaneous fracture cement deposition. The narrow range in power-law exponents documented among fractures can help improve estimates of meter-scale large-fracture spacing where limited fracture samples are available. / text

Although many fracture models are based on two-dimensional plane strain approximations, accurately predicting fracture propagation geometry requires accounting for the three-dimensional aspects of fractures. In this study, we implemented 3-D displacement discontinuity (DD) boundary element modeling to investigate the following intrinsically 3-D natural or hydraulic fracture propagation problems: the effect of fracture height on lateral propagation of vertical natural fractures, joint development in the vicinity of normal faults, and hydraulic fracture height growth and non-planar propagation paths. Fracture propagation is controlled by stress intensity factor (SIF) and its determination plays a central role in LEFM. The DD modeling is used to evaluate SIF in Mode I, II and III at the tip of an arbitrarily-shaped embedded crack by using crack-tip element displacement discontinuity. We examine the accuracy of SIF calculation is for rectangular, penny-shaped, and elliptical planar cracks. Using the aforementioned model for lateral propagation of overlapping fractures shows that the curving path of overlapping fractures is strongly influenced by the spacing-to-height ratio of fractures, as well as the differential stress magnitude. We show that the angle of intersection between two non-coincident but parallel en-echelon fractures depends strongly on the fracture height-to-spacing ratio, with intersection angles being asymptotic for "tall" fractures (large height-to-spacing ratios) and nearly orthogonal for "short" fractures. Stress perturbation around normal faults is three-dimensionally heterogeneous. That perturbation can result in joint development at the vicinity of normal faults. We examine the geometrical relationship between genetically related normal faults and joints in various geologic environments by considering a published case study of fault-related joints in the Arches National Park region, Utah. The results show that joint orientation is dependent on vertical position with respect to the normal fault, the spacing-to-height ratio of sub-parallel normal faults, and Poisson's ratio of the media. Our calculations represent a more physically reasonable match to measured field data than previously published, and we also identify a new mechanism to explain the driving stress for opening mode fracture propagation upon burial of quasi-elastic rocks. Hydraulic fractures may not necessarily start perpendicular to the minimum horizontal remote stress. We use the developed fracture propagation model to explain abnormality in the geometry of fracturing from misaligned horizontal wellbores. Results show that the misalignment causes non-planar lateral propagation and restriction in fracture height and fracture width in wellbore part. / text

Naturally fractured reservoirs (NFRs) hold a significant amount of the world's hydrocarbon reserves. Compared to conventional reservoirs, NFRs exhibit a higher degree of heterogeneity and complexity created by fractures. The importance of fractures in production of oil and gas is not limited to naturally fractured reservoirs. The economic exploitation of unconventional reservoirs, which is increasingly a major source of short- and long-term energy in the United States, hinges in part on effective stimulation of low-permeability rock through multi-stage hydraulic fracturing of horizontal wells. Accurate modeling and simulation of fractured media is still challenging owing to permeability anisotropies and contrasts. Non-physical abstractions inherent in conventional dual porosity and dual permeability models make these methods inadequate for solving different fluid-flow problems in fractured reservoirs. Also, recent approaches for discrete fracture modeling may require large computational times and hence the oil industry has not widely used such approaches, even though they give more accurate representations of fractured reservoirs than dual continuum models. We developed an embedded discrete fracture model (EDFM) for an in-house fully-implicit compositional reservoir simulator. EDFM borrows the dual-medium concept from conventional dual continuum models and also incorporates the effect of each fracture explicitly. In contrast to dual continuum models, fractures have arbitrary orientations and can be oblique or vertical, honoring the complexity and heterogeneity of a typical fractured reservoir. EDFM employs a structured grid to remediate challenges associated with unstructured gridding required for other discrete fracture models. Also, the EDFM approach can be easily incorporated in existing finite difference reservoir simulators. The accuracy of the EDFM approach was confirmed by comparing the results with analytical solutions and fine-grid, explicit-fracture simulations. Comparison of our results using the EDFM approach with fine-grid simulations showed that accurate results can be achieved using moderate grid refinements. This was further verified in a mesh sensitivity study that the EDFM approach with moderate grid refinement can obtain a converged solution. Hence, EDFM offers a computationally-efficient approach for simulating fluid flow in NFRs. Furthermore, several case studies presented in this study demonstrate the applicability, robustness, and efficiency of the EDFM approach for modeling fluid flow in fractured porous media. Another advantage of EDFM is its extensibility for various applications by incorporating different physics in the model. In order to examine the effect of pressure-dependent fracture properties on production, we incorporated the dynamic behavior of fractures into EDFM by employing empirical fracture deformation models. Our simulations showed that fracture deformation, caused by effective stress changes, substantially affects pressure depletion and hydrocarbon recovery. Based on the examples presented in this study, implementation of fracture geomechanical effects in EDFM did not degrade the computational performance of EDFM. Many unconventional reservoirs comprise well-developed natural fracture networks with multiple orientations and complex hydraulic fracture patterns suggested by microseismic data. We developed a coupled dual continuum and discrete fracture model to efficiently simulate production from these reservoirs. Large-scale hydraulic fractures were modeled explicitly using the EDFM approach and numerous small-scale natural fractures were modeled using a dual continuum approach. The transport parameters for dual continuum modeling of numerous natural fractures were derived by upscaling the EDFM equations. Comparison of the results using the coupled model with that of using the EDFM approach to represent all natural and hydraulic fractures explicitly showed that reasonably accurate results can be obtained at much lower computational cost by using the coupled approach with moderate grid refinements. / text

This dissertation presents an experimental investigation of fluid flow, proppant settling and horizontal proppant transport in hydraulic fractures. The work is divided into two major sections: investigation of proppant settling in polymer-free surfactant-based viscoelastic (VES) fluids and development of a new method of proppant injection, referred to as Alternate-Slug fracturing. VES fluid systems have been used to eliminate polymer-based damage and to efficiently transport proppant into the fracture. Current models and correlations neglect the important influence of fracture walls and fluid elasticity on proppant settling. Experimental data is presented to show that elastic effects can increase or decrease the settling velocity of particles, even in the creeping flow regime. Experimental data shows that significant drag reduction occurs at low Weissenberg number, followed by a transition to drag enhancement at higher Weissenberg numbers. A new correlation is presented for the sphere settling velocity in unbounded viscoelastic fluids as a function of the fluid rheology and the proppant properties. The wall factors for sphere settling velocities in viscoelastic fluids confined between solid parallel plates (fracture walls) are calculated from experimental measurements made on these fluids over a range of Weissenberg numbers. Results indicate that elasticity reduces the retardation effect of the confining walls and this reduction is more pronounced at higher ratios of the particle diameter to spacing between the walls. Shear thinning behavior of fluids is also observed to reduce the retardation effect of the confining walls. A new empirical correlation for wall factors for spheres settling in a viscoelastic fluid confined between two parallel walls is presented. An experimental study on proppant placement using a new method of fracturing referred to as Alternate-Slug fracturing is presented. This method involves alternate injection of low viscosity and high viscosity fluids into the fracture, with proppant pumped in the low viscosity fluid. Experiments are conducted in Hele-Shaw cells to study the growth of viscous fingers over a wide range of viscosity ratios. Data is presented to show that the viscous finger velocities and mixing zone velocities increase with viscosity ratio up to viscosity ratios of about 350 and the trend is consistent with Koval’s theory. However, at higher viscosity ratios the mixing zone velocity values plateau signifying no further effect of viscosity contrast on the growth of fingers and mixing zone. The plateau in the velocities at high viscosity ratios is caused by an increase in the thickness of the displacing fluid and a reduction in the thin film of the displaced fluid on the walls of the Hele-Shaw cell. Fluid elasticity is observed to retard the growth of fingers and leads to growth of multiple thin fingers as compared to a single thick dominant finger in less elastic fluids. Observations show the shielding effect is reduced by fluid elasticity. Elastic effects are observed to reduce the thickness of thin film of displaced fluid on the walls of Hele-Shaw cell. The dominant wave number for the growth of instabilities is observed to be higher in more elastic fluids. At the onset of instability, the interface breaks down into a greater number of fingers in more elastic fluids. Experiments are performed in simulated fractures (slot cells) to show the proppant distribution using alternate-slug fracturing. Observations show alternate-slug fracturing ensures deeper placement of proppant through two primary mechanisms: (a) proppant transport in viscous fingers formed by the low viscosity fluid and (b) an increase in drag force in the polymer slug leading to better entrainment and displacement of any proppant banks that may have formed. The method offers advantages of lower polymer costs, lower pumping horsepower, smaller fracture widths, better control of fluid leak-off and less gel damage compared to conventional gel fracs. / text