Laboratory surveys of bottom-hole pressures under a tricone bit when one, two or three nozzles are used indicate that hole cleaning and drilling rate should improve as the number of nozzles is decreased. Tests also show that these should improve as the length of the nozzle is increased. Introduction Minimum-cost well drilling demands the best possible use of the time and energy involved. One place where much energy is expended is at the bit. As the mud flows through the nozzles, across the bottom of the hole, and starts back toward the surface, friction and turbulent mixing dissipate a large amount of energy. In any general attempt to cut drilling costs, this part of the operation must be considered important. part of the operation must be considered important. There is no universal agreement as to what are the most important factors at and below the bit. Present-day ideas on this subject have come to us either from jet hydraulics studies or indirectly from other studies such as of rock mechanics. With regard to jet hydraulics studies, Kendall and Goins have outlined hydraulics programs for maximum jet velocity, maximum jet impact, and maximum jet horsepower. They did not define which of these has the greatest effect on drilling rate. Van Lingen found that drilling rates increased if the bit nozzles were extended toward the bottom of the hole. Feenstra and van Leeuwen showed that, for impermeable rock drilling, increasing the jet velocity influences drilling rate more than increasing the flow rate. Both of these laboratory studies were made with a full-size bit. Using a microbit and low-permeability rock, Eckel has shown that drilling rate is a function of a Reynolds number involving flow rate, nozzle diameter, and fluid density and viscosity. He has also concluded that for a given viscosity drilling rate is not related to the mud solids content or the fluid loss. All of the studies mentioned thus far suggest that jet velocity plays an important role in establishing the drilling rate. Feenstra and van Leeuwen state "jet action" (a more inclusive term than jet velocity) keeps the bit teeth and hole bottom clean and overcomes the "chip hold down effect." In a more basic study, McLean measured the impact pressure and crossflow on a simulated hole bottom under a jet bit. Concluding that crossflow (velocity) was the more important, he determined the relationship between crossflow and vertical velocity distribution, kinetic energy flux, and shear stress. All of these, he says, may have an effect on the cleaning of the hole bottom and the bit teeth. The works of Maurer and Myers show that bottom-hole pressure has an effect on drilling rate. They found pressure has an effect on drilling rate. They found that as the difference between the mud pressure and the formation pressure increases the bit tooth forms a smaller crater. From this it appears that drilling rates should decrease as this pressure difference increases. Field data indicate that this is not universally true. Considering the evidence presented thus far, it is apparent that the fluid velocity through and beyond the nozzles and the pressures existing at and near the bottom of the hole both play important roles in the drilling process. Our goal, then, is to study the bottom-hole pressure distribution as it is affected by nozzle velocity and to demonstrate the influence of different nozzle sizes, extensions, and numbers. JPT P. 1299
Bit hydraulics play an important role in the drilling process. The beneficial action of the fluid's impacting, cleaning the bottom of the hole and the bit teeth, and carrying particles into the annulus is well established. What is not well known or commonly agreed upon is bow this beneficial action can be made most effective. To understand better the drilling hydraulics phenomenon, laboratory tests were carried out with phenomenon, laboratory tests were carried out with full-scale bits and a simulated hole bottom. An earlier paper described the pressure distribution on the hole bottom as it varied with nozzle size, number, and extension. This paper discusses the way the force acting on a stationary chip varies with these same parameters and also includes The effect of chip size and fluid density and viscosity. The results show that closing one or two nozzles or extending the nozzles increases chip removal force and should assist is cleaning the hole and, in some cases, increase penetration rate. Fluid velocity, nozzle diameter, and chip size are the most important factors affecting chip removal force. Fluid viscosity plays a minor role. These findings reinforce and broaden the conclusions reached in the pressure distribution studies. It was also found that chip removal force correlates more closely with jet impact and horse power than with velocity or nozzle Reynolds number. Introduction Bit hydraulics are difficult to study. If tests are carried out in the field, there are uncertainties regarding down-hole conditions and whether these conditions change during a test. If the tests are carried out in the laboratory, results are usually more clear-cut, but then there is the question of how well the tests simulate field conditions. The most reliable insight into the over-all hydraulics problem is probably reached by blending the results problem is probably reached by blending the results of all types of work; no single study fits together more than a few pieces of the intricate puzzle. Past work in drilling hydraulics has been in the following categories: field testing, similar to that of Thompson, Spear, and Eckel; drilling tests in the laboratory, similar to those of Horner el al, van Lingen, Feenstra and van Leeuwen, and Eckel; and laboratory nondrilling tests like those of McLean and Cheatham and Yarbrough. other significant work includes the Kendall and Goins theoretical paper on optimization and that portion of Bingham's series on "a new approach portion of Bingham's series on "a new approach to interpreting rock drillability" that deals with bit hydraulics. The work reported here fits in the category of laboratory nondrilling. It is aimed at explaining how nozzle size, jet velocity, fluid properties, etc., affect tat takes place as the fluid leaves the nozzle impinges on the hole bottom, and begins to return to the surface. This work differs from Refs. 4 through 7 in that no actual drilling took place. In a sense, this detracts from its usefulness; on the other hand, we feel that we were able to maintain closer control over test conditions because we did not have the problems of rock variability, drilling fluid problems of rock variability, drilling fluid contamination, and the other phenomena involved in drilling tests. The work in Refs. 8 and 9 described the measurement of velocities and pressures under a jet bit. Maximum jet velocity was 171 ft/sec. The work reported in this paper describes the forces caused by fluid velocities and pressures as they act on a chip. Maximum jet velocity was 286 ft/sec. An earlier paper, described the pressure distribution on the bottom of the hole as it is affected by nozzle size, number, and extension. Conclusions included the desirability of plugging one or two nozzles, using extended nozzles and a correlation of pressure distribution with jet velocity, nozzle diameter, and the distance between the nozzle and hole bottom. The present work is a continuation of the same study and was set up to find out what happens when fluid moving across the hole bottom meets an object in its path. In a sense, it a basic attempt to study hole cleaning under closely controlled conditions. SPEJ P. 233
There is a need in the offshore industry for a means of protecting certain operations and for reducing time lost because of weather. A floating breakwater may be the answer in many cases. A laboratory study is presented that establishes the most important parameters affecting a breakwater's performance. Introduction There is a need in the offshore petroleum industry for a means of protecting certain operations and for reducing the time lost because of weather. Among these operations are platform setting, pipeline laying, tanker loading and unloading, and transferring personnel and equipment between platform and boat. One way this need could be met is with a floating breakwater. A breakwater interferes with incoming waves and thus provides a sheltered area in its lee. In the process of interfering, it reflects, dissipates, and transmits certain portions of the wave energy. The amount of energy reflected, dissipated, or transmitted depends on the particular breakwater involved, the mooring system, wave height and period, and the water depth. Rigidly fixed breakwaters, such as the rubblemound or masonry type, provide the highest level of protection. They are very expensive to build and install and are not mobile. Floating breakwaters, on the other hand, provide lesser protection; but they are less expensive and can be moved from one location to another. It is possible that floating breakwaters could be used in locations where a rigid, bottom-founded structure would be out of the question. Potential benefits from the use of floating breakwaters includecost savings because of a reduction in down-time for tanker terminals, and platform setting and pipeline laying operations, platform setting and pipeline laying operations,protection for loading and unloading men and supplies, andreduced likelihood of pollution. There has been a considerable amount of experimental work done on floating breakwaters. Included is that of Kato et al., in which the effects of four different breakmeter shapes (cross-sections) were evaluated. Their work indicated that an inverted trapezoid gave the lowest wave transmission and that the natural frequency of rotation about an axis parallel to the wave front was an important variable. Two excellent sources became available after the beginning of this study. "Transportable Breakwaters - A Survey of Concepts" gives a review, in outline form, of published and unpublished reports and data on 106 breakwater concepts. Also discussed are the effectiveness and potential of specific breakwater classes. "Recent Designs of Transportable Wave Barriers and Breakwaters" gives the status of portable breakwaters, with emphasis on recent designs. It reviews the performance studies for several breakwater types and describes the important parameters on the basis of past theoretical work. Both papers give extensive lists of additional references. The performance of a floating breakwater is influenced by a large number of variables; i.e., shape, mooring type, weight distribution, submergence, skin permeability, and size. This work was set up to define permeability, and size. This work was set up to define the effects of these variables on wave transmission, reflection and dissipation, and mooring-line force. Tests were made over a range of wave heights and periods. periods. JPT P. 269
This paper compares measured hole angle changes and predicted angles between bit force and hole direction. The predictions were made using an analytical program that assumes the drillstring is a static beam with varying properties constrained by borehole geometry. Data were taken from a field study conducted in Dubai. Agreement was good for 8 of 12 cases and improved with use of an interpretive length. Introduction Directional drilling continues to play an important part in offshore field development. A more thorough and firmly based understanding of the factors affecting hole angle and direction are needed so that drilling can be done as economically as possible and so that overall drilling technology can advance at a uniform rate.Probably the most concentrated recent effort toward a logical and thorough understanding of the factors involved in directional drilling is that of Millheim. Among his works are a series of articles dealing with proper use of directional tools, bottomhole assembly (BHA) mechanics, and behavior of single- and multiple-stabilizer BHA's. In the first of these articles, he lists 46 references but states that there is still much to learn. Later in the series, he presents material derived from postanalysis of more than 70 wells in the U.S. and overseas, field tests, computer analyses, literature, and research.In other articles, Millheim et al. describe a finite-element method of analyzing BHA's and Millheim discusses hole curvature as it relates to hole trajectory. Among the conclusions reached are that reaction forces at the bit can be calculated, the dropping or building tendencies of various assemblies can be assessed, and hole curvature can play a significant role in deviation and deviation control. Walker and Friedman present a three-dimensional force and deflection analysis of a drillstring and state that the use of the model can improve the understanding of how various assemblies compare and can assist in determining the direction the bit will drill. Fischer describes an analysis of a drillstring in a curved borehole and concludes that valuable insight into the mechanical performance of drillstrings can be gained using such an analysis. In discussing the factors that affect the control of borehole angle in straight and directional wells, Bradley gives information relating to the location of drillstring tangency, drill collar stiffness and weight, placement of stabilizers, and downhole motor case flexibility. He emphasizes the need for additional research into the bit/rock interaction as it affects the deviation process.Analytical programs like those in Refs. 1 through 6 calculate the force acting at the bit. Although it generally is agreed that the bit tends to drill in the direction of this force, Millheim and Warren indicate that no method is available to predict rates of build, drop, or turn for a particular set of conditions. JPT P. 2090^
Present-day drilling hydraulics can be made more efficient. The methods discussed in this paper result in lower cost and better use of hydraulic ener~y. These findtngs are based on using two nozzles instead of three and, in some cases, lowering the annular velocity, New data is also presented on borehole wall erosion and on better hole bottom cleaning with extended nozzles, especially when the nozzle angle is increased.
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