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1

Drilling large diameter intake wells with cutter bits in loose and weakly consolidated rocks

Macuda J., Macuda M.

AGH Drilling, Oil, Gas

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2016

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Vol. 33, no. 1

23--30

EN

Most of the useful aquifers in Poland occur in the Quaternary and Tertiary horizons, which are deposited at a depth of tens to hundreds of meters. Owing to the need of providing large quantities of water for municipal and industrial purposes, the aquifers are more and more frequently opened with large diameter wells of various designs. Such wells are mostly drilled with the rotary method with reverse mud circulation with the use of various bits. The Quaternary and Tertiary strata abound in loose and weakly consolidated rocks therefore cutter bits are predominantly used. They allow for high rates of drilling and shorter time of drilling of the well. This significantly influences the negative influence of drilling mud on the near screen zone of the aquifer and better hydraulic properties of the well. Drillability tests were performed with cutter bits of 0.86 and 0.67 m diameter for providing high rates of drilling of large diameter intake wells in loose and weakly consolidated rocks. The research was made for measurement sections 0.5 to 1.0 m long, and each of them was drilled at con- stant rotational velocity and axial weight on bit. Prior to the drillability tests the limitation of weight on bit and rotational velocity of bit imposed by the technical characteristic of Prakla B50 rig, strength of the string and butter bit were established. Various regression models were analyzed for the sake of finding a dependence between drilling rate and axial weight on bit and rotational velocity of bit for particular macroscopically homogeneous layers. The best results were obtained for the exponent model illustrating the influence of axial weight on bit and rotational velocity of bit on the drilling rate, which has been proved by the calculated regression coefficients and statistical parameters.

2

Efficiency of drilling large diameter wells with cutter bits on Szczerców opencast

Macuda J.

AGH Drilling, Oil, Gas

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2015

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Vol. 32, no. 2

405--413

EN

Drilling of large diameter wells to be used for dewatering of lignite deposits is inefficient due to the presence of large packages of loose Quaternary and Tertiary strata. Moreover, considerable dewatering of the rock mass favors serious complications and drilling break-downs connected with the sliding of wellbore walls. Accordingly, new technical and technological solutions, which enable faster drilling, are searched for. In this way the time of operation of drilling mud on the near-wellbore zone can be shortened and the safety of drilling works increased. For the sake of obtaining higher rates of drilling in large diameter dewatering wellbores a new cutter bit 0.96 m of diameter was designed. Drillability tests in industrial conditions followed. These tests were performed in separated, loose and low-compaction, macroscopically homogeneous rocks of similar drillability. The tests were performed on selected sections 0.3 to 1.0 m long, and each of the sections was drilled at constant rotational velocity and weight on bit. Prior to these tests there were established limitations regarding weight on bit and rotational velocity of the bit, in reference to the technical characteristic of the rig, strength of the string and the cutter bit. Two different regression models were considered to find a dependence of mechanical drilling rate on weight on bit and rotational velocity of the bit for selected macroscopically homogeneous strata. The most favorable results were obtained for a power model representing impact of axial stress and rotational velocity of the bit on the drilling rate. They have been confirmed by calculated regression coefficients and statistical parameters. Industrial tests were performed to assess the efficiency of drilling large diameter dewatering wells with a cutter bit of 0.96 m diameter on the basis of the presented model of average drilling rate. The results for the average drilling rate turned out to be much higher than the ones obtained so far.

3

Analysis of efficiency of drilling of large-diameter wells with a profiled wing bit

Macuda J.

Archives of Mining Sciences

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2012

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Vol. 57, no. 2

363--373

EN

In Poland all lignite mines are dewatered with the use of large-diameter wells. Drilling of such wells is inefficient owing to the presence of loose Quaternary and Tertiary material and considerable dewatering of rock mass within the open pit area. Difficult geological conditions significantly elongate the time in which large-diameter dewatering wells are drilled, and various drilling complications and break-downs related to the caving may occur. Obtaining higher drilling rates in large-diameter wells can be achieved only when new cutter bits designs are worked out and rock drillability tests performed for optimum mechanical parameters of drilling technology. Those tests were performed for a bit ø 1.16 m in separated macroscopically homogeneous layers of similar drillability. Depending on the designed thickness of the drilled layer, there were determined measurement sections from 0.2 to 1.0 m long, and each of the sections was drilled at constant rotary speed and weight on bit values. For finding the dependence of the rate of penetration on weight on bit and rotary speed of bit various regression models have been analyzed. The most satisfactory results were obtained for the exponential model illustrating the influence of weight on bit and rotary speed of bit on drilling rate. The regression coefficients and statistical parameters prove the good fit of the model to measurement data, presented in tables 4-6. Industrial tests were performed for assessing the efficiency of drilling of large-diameter wells with a cutter bit having profiled wings ø 1.16 m according to elaborated model of average rate of drilling. The obtained values of average rate of drilling during industrial tests ranged from 8.33×10-4 to 1.94×10-3 m/s and were higher than the ones obtained so far, i.e. from 181.21 to 262.11%.

PL

W Polsce wszystkie odkrywkowe kopalnie węgla brunatnego odwadniane są za pomocą studni wielkośrednicowych. Ich wiercenie jest mało efektywne ze względu na występowanie w profilu luźnych utworów czwarto i trzeciorzędowych oraz znaczne odwodnienie górotworu, które jest jedną z głównych przyczyn obwałów ściany otworów i tym samym powstawania trudnych do usunięcia awarii wiertniczych. W celu uzyskania większych prędkości wiercenia wielkośrednicowych studni odwadniających opracowano nową konstrukcję świdra skrawającego i wykonano w warunkach przemysłowych testy zwiercalności. Testy te wykonano dla świdra o średnicy 1,16 m w wydzielonych warstwach makroskopowo jednorodnych, charakteryzujących się zbliżoną zwieralnością. W zależności od projektowanej miąższości przewiercanej warstwy, wyznaczano odcinki pomiarowe o długości od 0,2 do 1,0 m, a każdy odcinek pomiarowy był wiercony przy stałych wartościach prędkości obrotowej i nacisku osiowego na świder. Dla znalezienia zależności mechanicznej prędkości wiercenia od nacisku osiowego i prędkości obrotowej świdra dla wydzielonych warstw makroskopowo jednorodnych, przeanalizowano różne modele regresyjne. Najbardziej zadawalające wyniki uzyskano dla potęgowego modelu wpływu nacisku osiowego i prędkości obrotowej świdra na prędkość wiercenia. Współczynniki regresji i parametry statystyczne potwierdzające bardzo dobre dopasowanie modelu do danych pomiarowych przedstawiono w tabelach 4-6. Dla dokonania oceny efektywności wiercenia wielkośrednicowych studni odwadniających świdrem skrawającym z profilowanymi skrzydłami o średnicy 1,16 według opracowanego modelu średniej prędkości wiercenia wykonano próby przemysłowe. Uzyskane wartości średniej prędkości wiercenia zawierały się w przedziale od 8,33×10-4 do 1,94×10-3 m/s i były wyższe od dotychczas uzyskiwanych od 181,21 do 262,11%.