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RESEARCH PAPERS

J. Energy Resour. Technol. 1990;112(3):157-162. doi:10.1115/1.2905752.

A technique is presented for the determination of the size of a horizontal permeability barrier (plug) that can be displaced from the wellbore to suppress cone-fluid production in individual oil wells with coning problems. Details are given concerning the computation of the plug size for any well with known wellbore and completion constants. Also discussed are materials which can be used to create the plugs. Based on literature data and rock stress considerations, plugging by fluid injection is found to be much more practical and general in application than methods based upon hydraulic fracturing technology. Two types of plugging fluids are recommended for injection into the formation as a function of pressure and flow rate conditions. The injected plug-fluid penetrates the reservoir rock surrounding the wellbore to the radial distance given by a predetermined radius of the plug. Predictive calculations show that production of cone-fluid-free oil can be enhanced by as much as 100 percent after a successful plugging job is done using the method presented.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1990;112(3):163-169. doi:10.1115/1.2905753.

A common assumption for annular flow used in the petroleum industry is that the inner pipe is concentrically located inside the flow geometry; however, this is rarely the case, even in slightly deviated wells. Considering the increasing number of directional and horizontal wells, the flow behavior of drilling fluids and cement slurries in eccentric annuli is becoming particularly important. In this paper, the governing equation of laminar flow is numerically solved using a finite differences technique to obtain velocity and viscosity profiles of yield-power law fluids (including Bingham plastic and power law fluids). Later, the velocity profile is integrated to obtain flow rate. Results show that the velocity profile is substantially altered in the annulus when the inner pipe is no longer concentric. Stagnant regions of flow were calculated in the low side of the hole. Viscosity profiles predicted for an eccentric annulus show how misleading the widely used single-value apparent viscosity term can be for non-Newtonian fluids. Profiles of velocity and viscosity in concentric and varying eccentric annuli are presented in 3-D and 2-D contour plots for a better visualization of annular flow. Frictional pressure loss gradient versus flow rate relationship data for power law fluids is generated using the computer program. Later, this data is fitted to obtain a simple equation utilizing regressional analysis, allowing for a quick calculation of friction pressure losses in eccentric annuli. For a given flow rate, frictional pressure loss is reduced as the inner pipe becomes eccentric. In most cases, about a 50-percent reduction in frictional pressure loss is predicted when the inner pipe lies on the low side.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1990;112(3):170-173. doi:10.1115/1.2905754.

Probability distribution functions, mean upcrossing rates and other descriptors are developed for the power that can be potentially extracted from the wind. Wind power is proportional to the cube of the wind velocity. The wind velocity is modeled as a stationary Gaussian process. The distribution of the extreme power is developed from mean upcrossing rates and the assumption that crossings of high thresholds follow a Poisson probability law. The results obtained are valid for any amount of the mean wind speed.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1990;112(3):174-182. doi:10.1115/1.2905755.

In bolted or riveted joints where the interfacial pressure is not uniform, the total resistance to heat flow in a vacuum is the result of two separate components: the microscopic resistance, which arises due to the constraint of the heat flow through the actual microscopic contact spots, and the macroscopic resistance, which exists because the contact zone, over which these microscopic contact spots are located, is only a fraction of the total interfacial area. Presented here is a review of the recent literature addressing the interfacial pressure distribution and the size of the contact zone, in so far as they affect the heat transfer at these interfaces. A survey of the experimental work on contact pressure and the associated heat transfer in bolted joints is presented, along with the size of the actual contact zone which was identified as an important parameter affecting both the microscopic and the macroscopic resistances. An analysis is performed in which it is formally shown that the exact form of the stress distribution within the contact zone is immaterial for the computation of the total microscopic conductance if the available theoretical results for local solid spot conductance are used. If experimental correlations for local solid spot conductance are used, however, the computed total microscopic conductances may differ about 5 to 10 percent, depending on the type of stress distribution chosen. It is also shown that, for a given load, the total microscopic conductance may be increased by increasing the loading radius and/or the plate thickness.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1990;112(3):183-187. doi:10.1115/1.2905756.

The background knowledge of jackup structures, current methods and procedures for moving and positioning of jackups practiced by the industry and related safety performance (analysis of accident records) are reviewed. Floating stability and motion response are identified as important factors contributing to fatal accidents and weather is found to be, in general, responsible for delays in ocean transit. An improved criterion is suggested for assessing the capability of jackup structures to be moved and positioned safely. This also includes the procedure for selection of towing power in order that a move not be unduly delayed by its mobility to make desired speed.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1990;112(3):188-199. doi:10.1115/1.2905757.

General equation for the tensioner cable forces and for the forces exerted on the riser upper ball joint by the ship joint-tensioner system are derived. An analysis of the variation of forces acting on the upper ball joint of a riser string due to drill ship motion and riser tensioner dynamic has been conducted. The analysis includes the effect of breakaway torque on the tensioner sheaves while assuming vessel and upper ball joint motion to be independent.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1990;112(3):200-207. doi:10.1115/1.2905758.

An analysis of the variation of forces acting on the upper ball joint of a riser string due to the drill ship motion and riser tensioner dynamic has been conducted. The analysis includes the effect of breakaway torque on the tensioner sheaves while assuming vessel and upper ball joint motion to be independent. General equation for the tensioner cable forces and for the forces exerted on the riser upper ball joint by the ship joint-tensioner system derived in Part I are solved. The variation in the tensioner cable forces is compared to data generated in field operation.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1990;112(3):208-212. doi:10.1115/1.2905759.

An elasto-viscoplastic constitutive model for frozen sand is proposed based on the elasto-viscoplasticity theory incorporating the new time measure. The proposed model can describe a number of features of the mechanical behavior of the medium, such as rate sensitivity and strain softening under the triaxial compression test loading conditions. The effects of temperature, ambient pressure and the concentration of soil particles are also discussed.

Commentary by Dr. Valentin Fuster

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