<p>U.S. domestic shale-gas production is economic owing to the new completion practice of horizontal wells and multiple hydraulic fractures. The performance of these fractures is improved through the placement of proppant. The change in the stress can affect fracture conductivity considerably. The objective of this study is to experimentally determine the impact of rock stress and time on aperture and permeability of hydraulic fractures in shale gas reservoirs. </p><p> Seven experiments were conducted to measure pressure and time dependent closure and permeability of hydraulic fractures created in Barnett shale under different confining pressure. Result shows that pressure dependence of permeability of these fractures obeys Walsh&rsquo;s permeability models. Time dependence of permeability at high stresses reveals that proppant embedment occurred to the Barnett shale cores. </p>

The continuous researvoir model updating is widely used to calibrate reservoir simulation models to production data, but many challenges remain. First, few real field data are available to test the new history matching method, and most of the data sets are synthetic cases. Second, computational cost may be high when using non-Gaussian priors or nonlinear models. Third, with large complex models, the simulation runs and history matching method require huge memory allocations. This dissertation achieves a continuous reservoir model updating workflow with a meter-scale , two-phase flow experiment. Both production and seismic data are collected in the experiment. Because the data are high-frequency sequential data with noise, the EnKF method is used to efficiently integrate them. To better understand the problem, scaling analysis is done on the capillary transition zone. Two new dimensionless numbers are introduced-capillary time and capillary length. We found that for different models, if their capillary time and gravity number are equal, the capillary length would be the same. The scaling analysis results help us find a proper flow rate for the sand tank experiment. Two experiments are conducted to test the workflow and the EnKF method. In the first one, both the production and seismic data are collected and analyzed. The production data have large errors in the flow rate and they are integrated to improve reservoir models using EnKF method. The history matching results are in an acceptable range which demonstrate that even if the observation data has large error, the EnKF method still works. In the second experiment, the errors of flow rate are reduced by measuring manually with a graduated cylinder. Because the data quality are much better in the second experiment, the observations can be matched easily.

Sustained Casing Pressure (SCP) is the undesirable casing head pressure of a well annulus that rebuilds when bled-down. As the conventional methods for SCP removal using rigs are expensive, there is a need for improvement. Annular intervention for replacing the fluid above the leaking cement with a heavier fluid to stop gas migration is a solution for SCP removal; however, previous attempts failed due to miscibility of injected fluids. Using hydrophobic heavy fluids for the purpose is a newly proposed technique to the technology. Potential of theoretically selected and produced immiscible heavy fluids are investigated in characterized annular fluids. A transparent laboratory scaled-down hydraulic analog of wells annulus provided visual evidence for displacement geometry and did the first stage testing of heavy fluid injection into clear synthetic-clay muds. A 20-foot physical model then tested the performance of the displacement process. Settling of various heavy fluids with densities from 11 to 23 ppg in drilling fluids with densities from 9 to 13 ppg provided quantitative bottom pressure data. Finally, a full-size test in 2750-foot well examined the viability of the technology. Visualization experiments proved that the counter-current flow in annulus leads to up-lifting of heavy fluid droplets and must be minimized for a desirable displacement process. Selection of injection geometry and rate are also essential to maintain a controlled transport of heavy fluid downwards. Pilot experiments developed mathematical correlations relating the process performance to fluid properties and rate. Full-size test shows that hydrophobic heavy fluids are able to slip in long columns; however, bridge-over of buoyant settling may occur due to high injection rates and/or flotation effect of migrating gas that was entrapped in annular fluid. The findings in this research present solid support to the viability of immiscible gravity displacement of annular fluid for remediating a well annulus affected with SCP. For given fluid properties and in confined annular space, injection rate is the key to a successful displacement. Finally, the research proved that the duration of a complete displacement process and required heavy fluid volume are inversely correlated. For any operation design; time and killing material restrictions must be considered.

Dispersion, deposition, and suspension of particulate materials in the carrier fluid play a significant role in the oil industry. Increasing the cuttings transport performance in deviated wells is difficult due to the rolling/sliding transport, and cuttings settling on the low side of the annulus. Insufficient cuttings transport may lead to some crucial problems such as pipe sticking, increasing in torque and drag, material damage and bed cementing quality. Increasing flow rates and improving mud properties may not be applicable for a proper hole cleaning because of the hydraulic and mechanical limitations. In such cases, additional pressure may be generated, and this causes formation fractures and drilling fluid losses. Under these circumstances, the other major contribution to cuttings transport is provided by drill-pipe rotation. In this study, the effect of drill-pipe rotation on cuttings transport behavior is investigated for eccentric horizontal wells. Whirling motion of drill-pipe is also analyzed. During drilling, drill-pipe is subjected to axial, lateral and torsional loads due to the dynamic vibrations. These loads cause that drill-pipe to lose its stability and generate snaking and/or whirling type of motion. Dynamic behavior of drill-pipe plays a significant role on cuttings transport and stationary bed removal. Turbulence modeling becomes very complicated when cuttings transport includes deposition and sliding effects. Advanced turbulence models are required to get accurate flow predictions while optimizing computational resources requirements. Unsteady SST k-ω turbulence model is applied due to its practicability and reliability in predicting cuttings transport behavior. Discrete phase is modeled with discrete element method (DEM) by including particle-particle and particle-fluid interactions with a commercial ANSYS FLUENTTM 15.0 CFD package using LSU high performance computing (HPC) resources. It is concluded that cuttings concentration significantly decreases with increasing flow rate. Drill-pipe rotation around its own axis causes cuttings swaying and distribute asymmetrically along the circumferential direction. Orbital motion of the drill-pipe contributes more to cuttings transport performance. Low whirling rotary leads to increase in annular pressure losses in low flow rates. In the turbulent flow regime, however, annular pressure losses increase with increasing whirling speed.

No description available.

The cement sheath failures and nearby wellbore failures may lead to upward flow of drilling fluid or formation fluid, which may have significantly adverse consequences like loss of reserve and environmental hazards. In order to maintain wellbore integrity in the long term, it is expedient to examine the causes of failures around the wellbore and propose suitable numerical models to predict annulus cracks around the casing. The complex failure behavior of cement/rock interfaces observed in the laboratory experiments does not look like the behavior of linear or simple nonlinear mechanical interfaces. Cohesive zone method (CZM) with BK-form bilinear traction separation law can be a good candidate to reproduce the complicated failure behavior around the casing. Then fracture critical energy, cohesive strength, and the deformability can be derived for cohesive zone constitutive equations by reproducing the loading-displacement curves from laboratory and inverse analyses. In this work, the comprehensive analysis for microannulus formation is presented by utilizing axisymmetric or three-dimensional poroelastic finite element models with CZM. This dissertation investigated these aspects: 1) Two and three-dimensional analysis of cement sheath integrity around wellbores due to presence of a leakage point; 2) Stimulation multi-zone fracturing and its cement sheath integrity during hydraulic fracturing. In this research, the physical mechanism of the loss of wellbore integrity is explained by the combined effects of fluid pressure, tensile and shear stresses, as well as failures. The excessive fluid pressure induced by leakage or hydraulic fracturing fluid acts as the drive for failures. The intensified tensile stress and shear stress occur at the crack tip initiate failures if they satisfy with the failure initiation criterion. Moreover, Lab and field scaled sensitivity analysis extract the influential parameters involved in failure development. Furthermore, the matching between failure patterns from numerical analysis and real field measurements using radioactive tracer-logs provides a comparison basis for model accuracy. Additionally, micro-annulus cemented systems are further analyzed by considering interface strength heterogeneity, anisotropic in situ stresses, wellbore inclination and eccentricity. The proposed approach provides a tool for more accurate predictions of cement integrity in the subsurface conditions to quantify the risk of wellbore integrity issues.

Thesis (PhD)--University of South Australia, 1996

Thesis (Ph.D.)--University of South Australia, 1995.

Thesis (B.S.)--University of Missouri, School of Mines and Metallurgy, 1914. / The entire thesis text is included in file. Typescript. Title from title screen of thesis/dissertation PDF file (viewed April 7, 2009) Includes bibliographical references (p. 10).

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1991. / Vita. Abstract. Includes bibliographical references (leaves 120-124). Also available via the Internet.