Gas hydrates are crystalline solids comprised of a lattice of water molecules that encapsulate natural gas molecules. Hydrates form under specific conditions of high pressure and low temperature when the supply of gas is sufficient to initiate and stabilize the hydrate structure. It is important to further our understanding of the geotechnical behaviours of hydrate-bearing soils during hydrate dissociation because of their potential to initiate and propagate submarine slope failure and be recovered as an energy resource.This thesis focuses on the pore pressure response and volume change of sands during isotropic undrained hydrate dissociation.Three groups of carbon-dioxide hydrate-bearing sand specimens were formed using a specialized triaxial test apparatus. The first group of tests included carbon-dioxide hydrate-bearing sand specimens formed under a cell pressure of 2.6 MPa at a temperature of 10 C, 2.3 ° C, 40 C. The cell pressure was increased to 2.8 MPa and 3 MPa for the second and third test group, respectively. Sample temperatures were raised to 260 C for complete dissociation of the carbon-dioxide hydrate.Physical effects, such as stress and deformation changes of carbon-dioxide hydrate dissociation on the surrounding sand are presented based on the results of this research.The triaxial test data indicate: 1) dissociation of even a small percentage of gas hydrate caused a dramatic reduction in the effective stress and lead to soil failure; 2) the specimen expanded even during isotropic undrained dissociation; 3) the higher the pressure, the viii 3.2.3 VOLUME CHANGE DEVICE 3.2.4 SCON-2000 DIGITAL CONTROLLER 3.2.5 WINDOWS BASED SOFTWARE 3.3 MODIFICATIONS TO THE SYSTEM 3.3.1 CIRCULATION SYSTEM 3.3.2 NEAR SAMPLE PORE PRESSURE TRANSDUCER 3.4 SUMMARY CHAPTER FOUR: LABORATORY TESTING 4.1 INTRODUCTION 4.2 GENERAL CONSIDERATIONS 4.2.1 MATERIALS 4.2.2 TARGET PRESSURES AND TEMPERATURES 4.3 SPECIMEN PREPARATION AND MOUNTING 4.4 CARBON DIOXIDE PURGING 4.5 SATURATION WITH WATER 4.6 RAMPING UP PORE PRESSURE AND CELL PRESSURE 4.7 CONSOLIDATION 4.8 B-TEST 4.9 SETTING UP THE CIRCULATION SYSTEM 4.10 PORE FLUID REPLACEMENT 4.11 FORMING GAS HYDRATE 4.12 DISSOCIATING GAS HYDRATE ix 4.13 ESTIMATING GAS HYDRATE CONTENT USING OUTLET BOTTLE 4.13.1 PRINCIPLE TO CALCULATE THE GAS HYDRATE CONTENT 4.13.2 VOLUME OF CARBON DIOXIDE GAS AT STP FROM UNIT VOLUME OF HYDRATE 4.13.3 VAN DER WAALS EQUATION OF STATE 4.13.4 GAS HYDRATE CONTENT 4.14 CALCULATION OF VOID RATIO 4.15 SUMMARY AND CONCLUSIONS CHAPTER FIVE: LABORATORY RESULTS 5.1 INTRODUCTION 5.2 SPECIMEN RESULTS 5.2.1 CELL VOLUME CHANGE RESULTS FOR THE DUMMY SPECIMEN 5,2.2 REFERENCE TEST RESULTS GAS HYDRATE TEST RESULTS

Considerable efforts have been devoted to the modeling of the results for the Leak-off Tests (LOT) in the past. Over the last decade, there are two major focuses in this field of research: the extended application of LOT models to horizontal wells and the theory of the fluid leakage during LOT. In the present study, an improved model has been proposed based on the original Altun's model: 1) the initial system volume is corrected after considering thermal and pressure effects as well as the geometry of the well path; 2) the casing expansion during LOT test is extended to directional wells with respect to pressure change; 3) a new leak volume model is developed to analyze the different flow behavior of fluid before and after the fracture initiation pressure (FIP). The data from a field example is used to validate the model. The predicted results demonstrate the improvement and accuracy of the model for the estimation of LOT values for horizontal wells.