Research On Core Drilling In Loose Formation From In-Situ Leaching Sand Uranium Deposit

In the early 1990s, the focus of Uranium prospecting has been changed from Southern toNorthern China, from magmatic-rocks type uranium to basin in-situ leaching type uranium in thenuclear industry. At the present time, in-situ leaching sand type uranium deposit has alreadybecome very important in the uranium prospecting of our country.The prospecting area of in-situ sand type uranium deposit is mainly distributed in the basin ofNeozoic era. Drilling in the formation proves to have many difficulties which are as follows: (1)there is very low core recovery; (2) the hole wall is very difficult to be protected and the hole isdifficult to be constructed;(3) there are high possibility of accidents in the hole; (4) there are verylow drilling efficiency and high construction cost; (5) drilling in the cobble formation is verydifficult. To sum up, coring in the loose formation and drilling in the cobble strata are the twodifficulties in the construction of drilling in the in-situ leaching sand.The theme of the dissertation stems from the tenth-five-year geological research project"research on core drilling in the loose formation from in-situ leaching sand uranium deposit". Inthis dissertation, which are divided into four chapters, among them chapter 1 is the introduction,chapter 2 is about core drilling technology, chapter 3 is about the technology of drilling in thecobble, chapter 4 is the conclusions, the achievements about coring in the loose formation anddrilling in the cobble are introduced.In the second chapter, the importance of core recovery and coring quality is reviewed. Aseries of measures of improving core recovery and coring quality is also described in detail. Todeposit a filter cake, the width of which is proper and has a certain amount of structure strength, onthe surface of the core has the function of protecting core. Through analyzing the conditions of thecore in the swivel-type double-tube core barrels, rigid-type double-tube core barrels andsingle-tube core barrels, Relative mechanic models have been established and the functionrelationship between the footage per run in the coring drilling and rock yield strength, the diameterof inner tube, dynamic pressure of circulating fluids, friction coefficient between rock and theinner wall of core barrel, annular clearance, the properties of drilling fluids.The target formation in the in-situ leaching uranium drilling is the loose sand formation withwater and ore, which has the characteristics of low cement strength and fracture, in the drillingprocess the loose core is easy to be flushed and worn away if it is not protected properly. Inaddition, coring operation is difficult to master because loose sand formation and clay formationexchange frequently and exist the inhomogeneous in rock hardness. In the second chapterball-input single-tube core barrels, ball-input rigid-type double-tube core barrels, HD-216 corebarrels, HD-216A core barrels, jetting core barrels, double-valve swivel-type double tube corebarrels, jetting-and-reverse-circulation swivel-type double-tube core barrels etc. are introduced,among them ball-input single-tube core barrels, ball-input rigid-type double-tube core barrels,HD-216 core barrels, HD-216A core barrels are focused in terms of their structure, operationtechnology, drilling regimes, applicable formations and production tests in the big basins of Northern China.How to extract the loose core well from core barrels on the earth surface should be alsonoticed in the coring drilling. In the second chapter the technology of core extracting by pumppressure is explained in details in terms of working principles, connection methods ofcore-extracting apparatus, operation regimes and their real application effect.In the second chapter the common carbide-insert drill bits, PDC drill bits and their applicableformations are introduced as well in drilling of in-situ leaching uranium deposit. The drilling fluidswith the functions of core-protecting and wall-protecting are suggested in terms of their formula,working principles of additives in the drilling fluids. Through field production tests andapplication, they are approved with the following functions: (1)their application can improve corerecovery in the loose formation, decrease the fluids soaking effect on the loose core and then keepits original shape; (2) their application can realize the bare drilling without casing in the wholehole, save a large number of casing, lower construction cost and improve production efficiency;(3)their application can shorten the time of changing the drilling fluid before logging at the end ofdrilling, and then make well logging easy. Compares with applying the common drilling fluid, thelogging time is decreased by 40％.Drilling in the cobble formations, which exist extensively in the drilling of in-situ leachinguranium deposit, meets many difficulties such as shorter bit life, high drilling cost, low drillingefficient, lots of mechanical troubles, frequent hole accidents and bad drilling quality. The cost ofabrasive materials in the cobble drilling accounts for about 80％total cost of abrasive materialsconsumed in the drilling. The time of drilling in the cobble is many times as that of drilling theother formations of the same thickness. The difficulty is becoming more and more obvious inaffecting drilling construction due to rapidly increasing of working amount of drilling production.In the third chapter there are the following contents of three aspects: (1) research on specialcarbide-insert drill bits for drilling the cobble formations; (2) research on the bits of compositebuttons of diamond and tungsten carbide; (3)research on the bits of impregnated diamond andhard-metal bars.In the third chapter curing, pressing out and catching in etc. three working states, the first twoamong which exist in the most of conditions, of the carbide-insert drill bit rotating in thedown-hole are clearly suggested through analyzing the drilling features in the cobble formations.The plotted state diagrams of bits rotating and drilling in the down-hole reflect their real workingstates in the direct way.Through analyzing rotary drilling characteristics in the cobble, rock fracture mechanism, andthe bits failure conditions, the writer suggested the ideas that "pressing out and catching in is themain way, cutting is the second", make a breakthrough in the condition of high drillingconsumption and show us the clear direction for the consecutive relative research.In the third chapter there is a main research line through the whole chapter, that is, problemsextracted from core drilling in the cobbles——complex analyzing and research——to suggest theideas that "pressing out and catching in is the main way, curing is the second"——button drillbits with high impact toughness——composite button bits of diamond and tungsten carbide——composite coring drill bit of impregnated diamond and hard-metal bars.In the drilling in-situ leaching sand-type uranium The common carbide-insert bits,chilled-steel shot drilling, PDC drill bits and common impregnated diamond bits are not adapt todrilling the cobble formation, which has the characteristics of high hardness, high drill-ability,varied diameter and irregular shapes of cobbles.In this dissertation the writer suggests the ideas of improving the mean penetration rate andservice life of carbide-insert bits through bettering the bits structures, selecting tungsten carbidetypes and their combining forms on the base of considering the historical problems of drilling thecobbles in details. There are the following two detailed measures: (1) to select Q-type and S-typebuttons with high impact toughness as main cutters of drill bits; (e) to increase properly the innerdiameter of the bits. The field production tests show that the service life of the designed mix-setcarbide-insert bits can be improved by more than 7 times as compared with common octagonalcarbide-insert bits, the drilling cost per meter can be decreased by 75%.Although Q-type and S-type button hard-metal bits have high drilling efficient and longservice life in drilling the cobbles of small diameter, they exhibit low drill efficient in drilling thecobbles of large diameter. Due to the reason the composite button bits of diamond and tungstencarbide has been developed.The developed composite button bits of diamond and tungsten carbide have the followingadvantages as high wear resistance, high hardness and high impact toughness. Their super-hardcomposite parts can cut hard rock such as large diameter cobbles like impregnated diamond bits.The field production tests show us that the footage per run can be improve by more than one times,drill efficient can be improved by more than 1.5 times, service life improved by more than 2.5times, and drill cost per meter has been decreased by 35% as compared with those of the commonhard-metal bits.Although the composite button bits of diamond and tungsten carbide can drill effectively inthe large diameter cobbles, they are very difficult or are expensive to manufacture and there arelots of further research works to do. In order to solve the problem of drilling cobbles further, thewriter suggested another idea and got the fund from Geological Bureau of Nuclear Industry todevelop composite coring bits of impregnated diamond and tungsten carbide bars.In drilling cobbles, composite coring bits of impregnated diamond and tungsten carbide canstand high percussive load and have the strong ability against impact due to tungsten bars in thematrix, which make the good base for diamond working and prevent diamonds from impactingload. In general, the matrix of impregnated diamond bits will be abraded quickly in drillingcobbles, the existence of tungsten carbide bars can reduce the changing velocity of diamonds, keepthe constant contact area between matrix and rock in drilling, and so can keep higher drill efficientand improve service life of the bits.Composite coring bits of diamond and tungsten carbide have both high wear resistance ofimpregnated diamond bits and high impact toughness of tungsten carbide. Field drilling tests showus that the kind of bits can drill cobbles effectively and has obvious economic benefits that the costper meter is only 1/5 of that of drilling of common carbide-insert bits. The successful development of composite coring bits of diamond and tungsten carbideprovides effective drill tools for in-sire leaching uranium sand drilling, coal field geologicaldrilling and engineering geological drilling etc. and they have good potentials for promotion.