Thesis (Ph. D.)--Oregon State University, 1984. / Typescript (photocopy). Includes bibliographical references (leaves 222-232). Also available on the World Wide Web.

Thesis (Ph. D.)--University of Washington, 1985. / Vita. Bibliography: leaves [274]-283.

The purpose of this study is to determine if there is an alternative analysis method that can provide an estimate of fracture toughness for specimens that failed to meet all of ASTM E 1820 requirements. This study will look at three alternative analysis methods and evaluate each method’s ability to accurately and easily estimate the elastic-plastic fracture toughness. The standard method of analysis is long and complicated which leads to a number of validity requirements that many tests fail to meet. The objective is to find an easier and reasonably accurate estimate of elastic-plastic fracture toughness. This study has shown that there are two useful means of directly measuring the toughness from the load versus displacement record. It has also shown that there is a method of substituting a linear regression for the power law regression which yields good estimates of fracture toughness. All three methods have been estimating JQ which is a provisional measure of elastic-plastic fracture toughness. The first direct method uses an integral of the area up to the maximum load point to acquire the JQ. The second direct method uses a conversion of the linear elastic fracture toughness which only uses the crack growth and the maximum load from the load versus displacement record. The final method substitutes a linear regression of the two J-R points on either side of the JQ line to determine the JQ point. Each alternative analysis was able to acquire J values with varying degrees of accuracy. The linear substitution was the most accurate. The first direct method using an area integral tended to over predict the true J value. The second direct method using a conversion formula had a tendency to under predict the true J value. None of these methods could substitute for the ASTM standard; however, each provided a usable estimate of elastic-plastic fracture toughness.

The high incidence of long bone fractures and appreciable rate of delayed and non-union (5-10%) necessitates the development of non-invasive tools to monitor healing progression. The objective of this study was to develop a novel µCT-based measure of three-dimensional bone connectivity and to compare its ability to assess fracture callus mechanical stability to previously described measures. Bone connectivity parameters local to the failure surface were found to significantly correlate with mechanical stability, and proved superior to previously developed measures of torsional rigidity. Visualization of the failure surfaces demonstrated a consistent failure pattern indicative of the applied torsional loading, however the locations of the failure surfaces showed varying levels of fracture callus involvement. The results of this proof of concept work indicate the potential utility of bone connectivity analysis in non-invasive assessment of fracture callus stability.

Objectives: The objectives of this study were two-fold: (1) to describe the epidemiology of childhood fractures in Ontario; (2) to determine if having a fracture in childhood is associated with an increased risk of having a future fracture. Methods: This was a population-based retrospective cohort study using Ontario health administration data. Children aged 0 to 15 years were grouped according to baseline fracture status. Associations between predictors and future fracture were assessed using Poisson and Cox PH regression. Results: 43,154 Ontario children experienced a baseline fracture (17.5 per 1000 child years). Children with a baseline fracture had a 60% higher rate of fracture during 7 years of follow-up after adjustment for sex, rurality, history of previous fracture and the occurrence of head injury and soft-tissue injury. Conclusions: The occurrence of a baseline fracture is associated with an increased rate of future fracture irrespective of age at time of baseline fracture.

The high incidence of long bone fractures and appreciable rate of delayed and non-union (5-10%) necessitates the development of non-invasive tools to monitor healing progression. The objective of this study was to develop a novel µCT-based measure of three-dimensional bone connectivity and to compare its ability to assess fracture callus mechanical stability to previously described measures. Bone connectivity parameters local to the failure surface were found to significantly correlate with mechanical stability, and proved superior to previously developed measures of torsional rigidity. Visualization of the failure surfaces demonstrated a consistent failure pattern indicative of the applied torsional loading, however the locations of the failure surfaces showed varying levels of fracture callus involvement. The results of this proof of concept work indicate the potential utility of bone connectivity analysis in non-invasive assessment of fracture callus stability.

Objectives: The objectives of this study were two-fold: (1) to describe the epidemiology of childhood fractures in Ontario; (2) to determine if having a fracture in childhood is associated with an increased risk of having a future fracture. Methods: This was a population-based retrospective cohort study using Ontario health administration data. Children aged 0 to 15 years were grouped according to baseline fracture status. Associations between predictors and future fracture were assessed using Poisson and Cox PH regression. Results: 43,154 Ontario children experienced a baseline fracture (17.5 per 1000 child years). Children with a baseline fracture had a 60% higher rate of fracture during 7 years of follow-up after adjustment for sex, rurality, history of previous fracture and the occurrence of head injury and soft-tissue injury. Conclusions: The occurrence of a baseline fracture is associated with an increased rate of future fracture irrespective of age at time of baseline fracture.

Hydraulic Fracturing stimulation technology is used to increase the amount of oil and gas produced from low permeability reservoirs. The primary objective of the process is to increase the conductivity of the reservoir by the creation of fractures deep into the formation, changing the flow pattern from radial to linear flow. The dynamic conductivity test was used for this research to evaluate the effect of closure stress, temperature, proppant concentration, and flow back rates on fracture conductivity. The objective of performing a dynamic conductivity test is to be able to mimic actual field conditions by pumping fracturing fluid/proppant slurry fluid into a conductivity cell, and applying closure stress afterwards. In addition, a factorial design was implemented in order to determine the main effect of each of the investigated factors and to minimize the number of experimental runs. Due to the stochastic nature of the dynamic conductivity test, each experiment was repeated several times to evaluate the consistency of the results. Experimental results indicate that the increase in closure stress has a detrimental effect on fracture conductivity. This effect can be attributed to the reduction in fracture width as closure stress was increased. Moreover, the formation of channels at low proppant concentration plays a significant role in determining the final conductivity of a fracture. The presence of these channels created an additional flow path for nitrogen, resulting in a significant increase in the conductivity of the fracture. In addition, experiments performed at high temperatures and stresses exhibited a reduction in fracture conductivity. The formation of a polymer cake due to unbroken gel dried up at high temperatures further impeded the propped conductivity. The effect of nitrogen rate was observed to be inversely proportional to fracture conductivity. The significant reduction in fracture conductivity could possibly be due to the effect of polymer dehydration at higher flow rates and temperatures. However, there is no certainty from experimental results that this conductivity reduction is an effect that occurs in real fractures or whether it is an effect that is only significant in laboratory conditions.

The key to producing gas from tight gas reservoirs is to create a long, highly conductive flow path, via the placement of a hydraulic fracture, to stimulate flow from the reservoir to the wellbore. Viscous fluid is used to transport proppant into the fracture. However, these same viscous fluids need to break to a thin fluid after the treatment is over so that the fracture fluid can be cleaned up. In shallower, lower temperature (less than 250oF) reservoirs, the choice of a fracture fluid is very critical to the success of the treatment. Current hydraulic fracturing methods in unconventional tight gas reservoirs have been developed largely through ad-hoc application of low-cost water fracs, with little optimization of the process. It seems clear that some of the standard tests and models are missing some of the physics of the fracturing process in low-permeability environments. A series of the extensive laboratory “dynamic fracture conductivity” tests have been conducted. Dynamic fracture conductivity is created when proppant slurry is pumped into a hydraulic fracture in low permeability rock. Unlike conventional fracture conductivity tests in which proppant is loaded into the fracture artificially, we pump proppant/ fracturing fluid slurries into a fracture cell, dynamically placing the proppant just as it occurs in the field. Test results indicate that increasing gel concentration decreases retained fracture conductivity for a constant gas flow rate and decreasing gas flow rate decreases retained fracture conductivity. Without breaker, the damaging effect of viscous hydraulic fracturing fluids on the conductivity of proppant packs is significant at temperature of 150oF. Static conductivity testing results in higher retained fracture conductivity when compared to dynamic conductivity testing.

Shale gas formation exhibits some unusual reservoir characteristics: nano-darcy matrix permeability, presence of natural fractures and gas storage on the matrix surface that makes it unique in many ways. It’s difficult to design an optimum fracture treatment for such formation and even more difficult is to describe production behavior using a reservoir model. So far homogeneous, two wing fracture, and natural fracture models have been used for this purpose without much success. Micro seismic mapping technique is used to measure the fracture propagation in real time. This measurement in naturally fractured shale formation suggests a growth of fracture network instead of a traditional two wing fractures. There is an industry wise consensus that fracture network plays an important role in determining the well productivity of such formations. A well with high density of fracture networks supposed to have better productivity. Shale formations have also exhibited production pattern which is very different from conventional or tight gas reservoir. Initial flow period is marked by steep decline in production while the late time production exhibits a slow decline. One of the arguments put for this behavior is linear flow from a bi-wing fractured well at early time and contribution of adsorbed gas in production at late time. However, bi-wing fracture geometry is not supported by the micro-seismic observation. A realistic model should include both the fracture network and adsorbed gas property. In this research we have proposed a new Power Law Permability model to simulate fluid flow from hydraulically fractured Shale formation. This model was first described by Valko & Fnu (2002) and used for analyzing acid treatment jobs. The key idea of this model is to use a power law permeability function that varies with the radial distance from well bore. Scaling exponent of this power law function has been named power law index. The permeability function has also been termed as secondary permeability. This work introduces the method of Laplace solution to solve the problem of transient and pseudo steady-state flow in a fracture network. Development and validation of this method and its extension to predict the pressure (and production) behaviour of fracture network were made using a novel technic. Pressure solution was then combined with material balance through productivity index to make production forecast. Reservoir rock volume affected by the fracture stimulation treatment that contributes in the production is called effective stimulated volume. This represents the extent of fracture network in this case. Barnett shale formation is a naturally fractured shale reservoir in Fort Worth basin. Several production wells from this formation was analysed using Power Law Model and it was found that wells productivity are highly dependent on stimulated volume. Apparently the wells flow under pseudo steady state for most part of their producing life and the effect of boundary on production is evident in as soon as one months of production. Due to short period of transient flow production from Barnett formations is expected to be largely independent of the relative distribution of permeability and highly dependent on the stimulated area and induced secondary permeability. However, an indirect relationship between permeability distribution and production rate is observed. A well with low power law index shows a better (more even) secondary permeability distribution in spatial direction, larger stimulated volume and better production. A comparative analysis between the new model and traditional fracture model was made. It was found that both models can be used successfully for history matching and production forecasting from hydraulically fractured shale gas formation.