Mist Drilling Research Articles

Experimental study on effects of drilling parameters on respirable dust production during roof bolting operations

ABSTRACTUnderground coalmine roof bolting operators exhibit a continued risk for overexposure to airborne levels of respirable coal and crystalline silica dust from the roof drilling operation. Inhaling these dusts can cause coal worker's pneumoconiosis and silicosis. This research explores the effect of drilling control parameters, specifically drilling bite depth, on the reduction of respirable dust generated during the drilling process. Laboratory drilling experiments were conducted and results demonstrated the feasibility of this dust control approach. Both the weight and size distribution of the dust particles collected from drilling tests with different bite depths were analyzed. The results showed that the amount of total inhalable and respirable dust was inversely proportional to the drilling bite depth. Therefore, control of the drilling process to achieve proper high-bite depth for the rock can be an important approach to reducing the generation of harmful dust. Different from conventional passive engineering controls, such as mist drilling and ventilation approaches, this approach is proactive and can cut down the generation of respirable dust from the source. These findings can be used to develop an integrated drilling control algorithm to achieve the best drilling efficiency as well as reducing respirable dust and noise.

Effects of lubrication modes on part quality during drilling 6061-T6 aluminium alloy

The main objective of this research is to investigate the effects of the cutting fluid and application mode (dry, mist and flood drilling) and its interaction with cutting parameters on part quality during the drilling of 6061-T6 aluminium alloys. The part quality criteria include the burr form and sizes, and surface finish as well as the cutting forces generated. A multi-factorial design (DOE) is used to plan test and statistical analyses are used to determine the effects of lubrication and cutting parameters on part quality. The parameters governing the part quality are different from those governing the cutting force; the burr height and the surface roughness are mostly influence by cutting speed, cutting fluid modes and feed rate while the cutting force is mainly determined by the feed rate. It is found that dry machining and mist machining can produce parts whose quality is comparable to what is obtained in wet machining, when optimal cutting conditions are used.

Temperature Measurement of Cutting Edge in Drilling -Effect of Oil Mist-

In drilling, the temperature of the cutting edges of a drill is measured using a two-color pyrometer with an optical fiber. A cemented carbide drill with a diameter of 10 mm is used as a cutting tool, and carbon steel, cast iron and aluminum die-cast alloy are used as work materials. The temperature distribution along the cutting edge of a drill is measured and the influence of spindle speed and feed rate on the tool temperature is investigated. The maximum tool temperature is observed during the drilling of carbon steel. The effect of oil mist supplied from oil holes in the drill on the tool temperature is examined and the result is compared to that in turning and end milling. The temperature reduction in oil mist turning is approximately 5%, while in oil mist end milling it is 10–15% and that in oil mist drilling is 20–25% compared to the temperature in dry cutting.

Volumetric Requirements for Foam and Mist Drilling Operations

Summary State-of-the-art foam and mist drilling suggests a need for predictive models for volumetric requirements that properly account for frictional losses caused by the solid phase in solids/foam slurry flow, settling velocities of such solids, and pressure drop across bit nozzles during foam flow. The objective of this paper is to fulfill this need. A model that predicts pressure drop across bit nozzles for foam and mist is presented. It accounts for the compressibility of foam but assumes negligible pressure losses resulting from friction and change in elevation. A model has been developed for predicting minimum volumetric requirements for foam and mist drilling operations. It accounts for the frictional losses caused by the solid phase, pressure drop across bit nozzles, and particle-settling velocity. The technique offers a high degree of flexibility in the selection of wellhead injection pressures and volumetric injection rates. Field application of this work can be accomplished by two primarily graphical methods that depend on compressor specifications: variable-backpressure and constant-backpressure schedules. Charts are presented for 7.875- and 9.00-in. [20.0- and 22.9-cm] hole sizes, and for 0.500-, 0.75-, and 1.00-in. [1.27-, 1.91-, and 2.54-cm] cutting sizes. Penetration rates range from 30 to 90 ft/hr [9 to 27 m/h]. Results indicate that volumetric requirements increase with increasing hole size, depth, and particle size. Increases in penetration rate cause only minor increases in volumetric requirements. All foam-drilling and well-cleanout operations can be accomplished within the laminar flow region with adherence to 0.55 minimum bottomhole and 0.96 maximum annular foam quality. Annular backpressures greater than atmospheric pressure are needed to maintain a bottomhole foam quality of 0.55 or more while reaching reasonable depths. To maintain constant depth as backpressure increases, however, both wellhead injection pressure and gas injection rate must be increased, and liquid flow rate decreased.

Simulation of Air and Mist Drilling for Geothermal Wells

Summary An improved method for calculating downhole temperatures, pressures, fluid densities, and velocities during air drilling has been developed. Improvements on previous methods include the following.A fully transient thermal analysis of the wellbore and formation is used to determine the flowing temperatures.The effects of flow acceleration are included explicitly in the calculation.The slip velocity between the gas and the cuttings is determined by the use of a separate momentum equation for the cuttings.The possibility of critical flow in the wellbore is tested and appropriate changes in the volume flow rate and standpipe pressure are made automatically.The standpipe and flowing pressures are predicted.The analysis is conservative. The effect of the cuttings on the wellbore flow will tend to overpredict the required volume flow rates. In this paper, the basic equations of fluid flow for a gas with cuttings and mist are presented along with a numerical method for their solution. Several applications of this calculational method are given, showing the effect of flow rate and standpipe pressure in typical air and mist drilling situations. Introduction Air and mist drilling have several advantages over conventional drilling fluids for geothermal drilling. The principal advantages are higher penetration rates, longer bit life, and no lost-circulation problems. The usual disadvantages, such as control of fluid influx and high pressure zones, are not normally a factor in geothermal well drilling. To realize these advantages, it is important to maintain adequate circulation. Determining the required volume flow rate to maintain this "adequate" circulation has always been difficult. The best available technique has been the analysis developed by Angel. This analysis allows estimation of volume circulation rates for various hole sizes. drillpipe sizes, and penetration rates. One difficulty with Angel's result is that the equation giving the volume flow rate must be solved by trial and error. This difficulty is avoided by use of the charts prepared by Angel, provided the case of interest is tabulated or can be estimated from similar cases. A second difficulty is that the drill cuttings are assumed to travel at the same velocity as the air. Angel notes that this is not a conservative assumption, and the analysis presented here demonstrates that the flow rates he predicts are 20 to 30% low. The downhole temperatures used for Angel's chart are assumed to be 80 degrees F at the surface, increasing 1 degrees F/100 ft of depth. There is no convenient way to convert to other temperatures. A final consideration is that the Angel charts do not apply to mist drilling. The addition of water to the air requires increases in both the volume flow rate and standpipe pressures to maintain the same penetration rate. The flow model discussed here was developed for Sandia Laboratories by Eneriech Engineering and Research Co. for use in a general purpose wellbore thermal simulator called GEOTEMP. Some features of GEOTEMP have been described in previous papers; however, the major technical features are summarized as follows. JPT P. 2120^

A Laboratory Method for Screening Foaming Agents Used in Air-Gas Drilling Operations

Abstract An apparatus has been designed and built for the purpose of studying factors affecting the foaming performance of available and potential air-drilling surfactants. The principal feature of the apparatus is a constant-head device which allows foaming of test liquid in a chamber at a constant rate, called carry-over rate; this rate is determined by direct measurement of the volume of liquid supplied to the test chamber in any given time interval to replace test-chamber liquid having been converted to foam and carried out of the test chamber by air or other compressed-gas stream. A study of variables connected with the apparatus and composition of test solutions and effects on various air-drilling surfactants has resulted in development of a laboratory screening method which has correlated with observed results during field testing in gas-mist drilling operations. Laboratory foaming performance data, collected by the constant-rate method and by the standard Bureau of Mines carry-over method, are compared with observed field results. A theory is developed connecting foaming performances of surfactants directly to type of injection water used in air-gas mist drilling, as opposed to the type of formation water being produced in the drilled well and commonly thought to be responsible for adverse effects on foaming surfactants. Background Since the advent of air-drilling operations, large numbers of surfactants have appeared on the market for use as "foaming agents". That such agents have been found useful is attested to by the fact that, in 1955, only a few air-drilled wells employed them, whereas today several thousand air-drilled wells employ these agents; and, in addition, they are being used to increase gas production in water-logged wells. Some surfactants do a "cleaner" job than others on an equal-concentration or an equal-cost basis. Therefore, methods are needed (such as bottle-testing techniques in treating oilfield emulsions) which would enable surfactants to be "screened" systematically and significantly. Several methods have been used to screen surfactants for potential use as air-drilling foaming agents. Although no standard method exists in the air-drilling industry for such screening, the Ross-Miles method has been widely accepted in the screening of foaming detergents. This method involves measurement of the height of foam generated by dropping a test liquid into another portion of the test liquid from a specified height at a specified temperature, and also measuring relative foam stability by observing height readings at given time intervals. A laboratory modification of this method has involved high-speed Waring-Blendor agitation of test liquid containing surfactant, pouring foam into a large graduated cylinder, measuring foam volume and measuring the time required for a certain body of liquid to be broken from the foam. A gas-lift type of screening method has been employed by Dunning, et al, of the U. S. Bureau of Mines. In this method, test liquids are foamed out of a column by gas, and the foam is broken; liquid collected at various intervals is used to establish a relative carrying capacity of a foam generated by surfactants in a wide variety of test liquids. A modification of this type of carryover testing has been described by Lummus and Randall: the gas-lift operation is carried out in an apparatus similar to field air-drilling design as various test media are converted to foam and carried out of an annulus along with drill solids for measurement. A fixed quantity of liquid is involved in this operation, which closely resembles conditions encountered in a gas-well clean-out because hydrostatic head continuously decreases as liquid is foamed-out. Air drilling involving slugging or misting presents different conditions than found in clean-out operations. Here, one might consider that the mixture of produced (formation) water and/or oil and injected water containing foaming agent (mist) being carried steadily out of the hole with high air-gas velocities constitutes a dynamic system with a reasonably constant balance of pressures; i.e., there is essentially no hydrostatic-head variation. As air-drilling technology advances, the trend is toward mist drilling and away from slugging operations because air drillers are learning where to mist successfully, thus avoiding those locations which produce copious amounts of water. JPT P. 143^

A Water Shut-Off Method for Sand-Type Porosity in Air Drilling

Published in Petroleum Transactions, AIME, Volume 216, 1959, pages 163–167. Abstract A new type water shut-off for use in air drilling has been developed. The method has been 99 to 100 per cent effective in several different formations of intergranular-type porosity. Since costs for materials, time and equipment used are relatively small, the process should extend economies of air drilling to many new areas. The treatment involves a new technique for forming a water-insoluble precipitate within the pores of a rock. Advantage is taken of the difference in mobility of a liquid and a gas in porous media to achieve the greatest volume of precipitate in a given pore. Reactants selected for the laboratory and field tests were aluminum sulfate solution and gaseous ammonia. This process has been tested in both intergranular and fractured-type porosities. It has consistently shut-off between 99 and 100 per cent of the water flowing from formations having intergranular-type porosity and permeabilities ranging from a few millidarcies to over a darcy. The treatment is not particularly suitable for shutting-off water from fractured formations although plugging of the order of 50 per cent or greater has been achieved in all such applications. Among advantages of the treatment are:no reaction waiting time after a relatively short placement time,a low materials' cost of about $3/ ft of hole treated,use of common service-type equipment for treatment, andno unusual requirements for mixing and placement. Introduction In rotary drilling with air or gas it has been possible to increase bit life by tenfold and more than double rate of penetration over corresponding performance when drilling with mud. These factors have amounted to as much as 22 per cent savings on total cost of drilling a well. However, these advantages are rapidly lost when water is encountered in an air- or gas-drilled well because water interferes with the removal of cuttings from the hole and also gives rise to other difficulties. In attempting to combat water troubles, operators have commonly resorted to such measures as mist drilling, treatment with cement or chemicals, converting to conventional mud drilling, or setting casing. In many cases these measures have either been costly or ineffective.