Experimental studies of objective and subjective passenger response to various fore-and-aft, or longitudinal, vehicle acceleration transients are reviewed. It is found that the wide variability in type of study and form of results does not allow conclusive statements to be made regarding passenger acceptability of any specific acceleration—jerk profile in a given transportation system.
This work presents results of an experimental and theoretical study ofvibratory screening of bentonite/water drilling fluids containing amedium-fine fracturing sand to simulate granular drilled solids. Satisfactory solids conveyance off the screen can be obtained for flat decks if the vibrator is placed to yield proper phasing between the normal and tangential acceleration components at all points on the vibrating deck. Introduction Drilling fluids returning from a well during drilling are passed serially through a number of solid/liquid separation devices to maximize removal of drilledsolids from the fluid before reuse. The vibratingscreen or shale shaker, the first device to process thefluid, removes the largest particles. Othersolids-separation equipment in the surface mud system can operate efficiently only if the shale shaker is performing properly. Consequently, it often is considered the most important solids-control device on a drilling rig. Most, if not all, of the various shaker designs now available have evolved from vibrating screens used in other industries, primarily the mining industry. Because of its obvious importance in such industries, vibratory screening has been the subject of numerous studies and investigations. On the other hand, very little investigative work has been published on vibratory screening of drilling fluids. The essential difference between this type of screening and that in other industries is that most of the material processed by a drilling fluid screen is liquid, rather than solid. For example, a well-maintained drilling fluid could have less than 10% tool solids by volume. Consequently, much of the existingtechnology for vibratory screening of dry solids, or even very wet slurries, does not apply toscreening of drilling fluids. The importance of this problem has been recognized by the IADC, which recently sponsored a conference on vibrating screen separators. Because the screen cloth itself is critical in determining the amount and size of solids removed by a shale shaker, the API has published a recommended practice for designating shale shaker screen cloth. More recently, Cagle and Wilder reported results of an experimental comparison between two commercially available shakers, primarily to evaluate a new design in screening cloth. Beyond this study, however, comprehensive investigations of the problem apparently have not been published. JPT P. 1889^
This paper reports theory, procedure and results on the use of drilling parameters collected during typical drilling operations to predict bounds on minimum principal in-situ stress of rock. These predictions are desired in order that hydraulic fracturability of reservoir rock can be better determined and fracturing programs designed without the need for expensive fracturing stress tests, guesswork, or empiricism. A high fidelity tri-cone roller bit drilling model is used in an "inverted" mode to predict in-situ ultimate compressive rock strength. This compressive rock strength is a function of effective confining pressure available from published laboratory data for various rock types. Knowledge of the compressive rock strength failure as a function of confining pressure can be used to obtain the Mohr failure envelope at a given depth for rock. The angle of internal friction is determined from the Mohr failure envelope, which can be used to calculate a "coefficient for earth at rest." This coefficient, together with known overburden and pore pressure, can be used to calculate an upper bound on the minimum horizontal stress for each foot drilled. The calculated in-situ stress bound profiles are compared, with good results, with experimental field closure stress data obtained in 46 tests in four GRI (Gas Research Institute) wells, SFE (Staged Field Experiment) wells #I, 2, 3, and 4. Introduction In order to properly design and complete effective hydraulic fracturing operations, Voneiff and Holditch [1] and Holditch, et al [2] have shown that apriori knowledge of in-situ stress profiles is an extremely important ingredient. Typical methods for estimating such profiles have assumed elastic formation properties, and have used Poisson's ratio together with measurements taken from electric logs, with mixed results [3–4]. These procedures require expensive logging operations, which in shallow wells might constitute a large fraction of the total well cost. During the drilling of a well, drilling operating parameters, mud properties, and mudlogger samples are usually collected. By using such data in the approach proposed here, a potentially less expensive method is available for in-situ stress determination. Instrumentation for collection of drilling data is becoming more routine with most drilling operations, and will therefore add little extra cost. In what follows, we present a new method, using data collected during normal drilling operations, to estimate bounds on in-situ stress. The theoretical background is presented, a step-by-step procedure is listed, and results are compared with field data from four GRI SFE wells. DRILLING MODELS The use of drilling data to predict drilling rock strength has developed over a number of years as drilling models for various types of bits have steadily improved. Although penetration rate models have been proposed for polycrystalline diamond compact bits and natural diamond bits, the more traditional tricone roller bit has received the most attention [5–7] because of its widespread use. Consequently, penetration rate models of this bit are the most highly-developed, and a recent article by Winters, et al [8] has demonstrated high fidelity in predicting penetration rates. In this model, penetration rate of the drill bit is calculated as a function of known operating conditions, bit coefficients, mud properties and hydraulics, and ultimate compressive rock strength and ductility. P. 457^
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