Experimental and Numerical Analysis of Flow Behavior for Reverse Circulation Drill Bit with Inserted Swirl Vanes

A swirling drill bit designed with an integrated vane swirler was developed to improve reverse circulation in down-the-hole hammer drilling. Its entrainment effect and influential factors were investigated by CFD simulation and experimental tests. The numerical results exhibit reasonable agreement with the experimental data, with a maximum error of 13.68%. In addition, the structural parameters of the swirler were shown to have an important effect on the reverse circulation performance of the drill bit, including the helical angle and number of spiral blades, swirler outlet area, and the flushing nozzles. The optimal parameters for the swirling drill bit without flushing nozzles include a helical angle of 60°, four spiral blades, and the area ratio of 2, while it is about 30°, 3, and 3 for the drill bit with flushing nozzles. Moreover, the entrainment ratio of the drill bit without flushing nozzles can be improved by nearly two times compared with one with flushing nozzles under the same conditions.

ANALISIS PRODUKTIVITAS PENGEBORAN TANAH MENGGUNAKAN ALAT RCD (REVERSE CIRCULATION DRILLING)

Proyek Kereta Cepat Jakarta Bandung merupakan mega proyek kereta cepat pertama di Indonesia. Kondisi tanah terdapat batu cadas yang keras, alat yang sudah tua dengan pemakaian yang terus menerus menyebabkan mesin mati tiba – tiba dan jenis tanah yang menjadi lengket bila bertemu dengan air yang dapat memperlambat proses pengeboran tanah. Berbagai cara pekerjaan pengeboran tanah dilakukan oleh kontraktor, salah satunya menggunakan alat RCD pada pier P 238. Tujuan dari karya ilmiah ini menganalisis produktivitaspengeboran tanah dengan menggunakan alat RCD. Langkah pengeboran dimulai dari pembersihan lapangan dan pembuatan dua buah kolam. Untuk mempermudah pengeboran tiang bor digunakanlah casing. Tinggi casing yang digunakan 4 m dan 6 m. Setelah itu melakukan pengeboran dengan tekanan air 0,2 Kg/cm2 atau dengan kecepatan aliran 7,5 cm/detik sehingga air akan keluar bersama dengan material lumpur melalui pipa di tengah alat bor . Hasil endapan lumpur (padatan) akan dibuang menggunakan truck sedangkan cairan akan dimasukan kembali kedalam lubang bor. Pruduktivitas alat bergantung pada empat faktor yaitu volume pekerjaan, waktu siklus, efisiensi alat dan kapasitas peoduksi. Pada pier 238 memiliki 8 borepile dengan diameter 1,25 meter dan kedalaman 90 meter dengan rata – rata produktivitas sebesar 2,851 m/jam.

Managed-Pressure Cementing in HPHT Well with Very Narrow Operating Pressure Window

A 7-in. liner was successfully cemented in the south east region of Mexico at 7530 m MD despite significant pressure and temperature challenges. The entire 1,370-m, 8.5" open hole section needed cement coverage and isolation to test several intervals. The challenge of the ultranarrow working pressure window was overcome by using managed pressure cementing (MPC) along with lost circulation solutions for the cement slurry and spacer. Due to the narrow pressure window (0.05 g/cc density gradient), mud losses could not be avoided during the cementing job. To limit and manage losses, an MPC placement technique was proposed, in conjunction with using lost circulation fiber technology in the cement slurry and spacer. After addressing the losses and narrow working pressure window, the next main challenge was the extremely high temperature (Bottom hole static temperature of 171°C). Extensive lab testing provided the fluid solution: HT formulations for cement slurry and spacer to maintain stability and rheology for placement and management of equivalent circulating density and set cement properties for long-term zonal isolation. After the liner was run to bottom, the mud density was homogenized from 1.40 g/cc to 1.30 g/cc (pore pressure: 1.38 g/cc). During this process, 32.5 m3 of mud was lost to the formation. During the previous circulation, the backpressure required to maintain the equivalent circulation density (ECD) above pore pressure, which was calculated and validated resulting in 1,100 psi annulus surface pressure (close to the limit of the equipment capacity) during the stopping time. The cementing job was pumped flawlessly with only 10 m3 of mud loss at the end of the job. During reverse circulation, contaminated spacer at surface indicated no cementing fluid had been lost to the formation and adequate open-hole coverage. The liner was successfully pressure tested to 4,500 psi, and cement logs showed that the cement had covered the open hole completely. MPC is not a conventional cementing technique. After the successful result on this job and subsequent operations, this technique is now being adopted to optimize cementing in even deeper wells in Mexico, where losses during cementing operations in the past had modified or limited the whole well construction and designed completion, and production of the well.

Simulation of ship handling in reverse

One of the main problems of seamanship is steering the boat in reverse modes. This skill can be achieved using simulators or simulators that work based on a mathematical model. This model should adequately describe all ship maneuvers, including simulation in reverse modes. The article deals with the mathematical modeling of maneuvering from a ship in reverse. The authors performed model calculations, basic test maneuvers, such as “Circulation”, “Exit Circulation” and “Zigzag”. The analysis of trajectories testifies to the qualitative correspondence of the calculation results according to the mathematical model to the practice of navigation, and this model can be used for automatic control of the vessel, for assessing the movement of the vessel in reverse, and teaching navigation skills on simulators and simulators. The vessel when moving in reverse, at low speeds obeys the steering organ, but at speeds greater than the average stroke on the backward shift, it leaves the circulation very slowly and sometimes becomes uncontrollable. The withdrawal of a reverse circulation vessel is extremely difficult and requires additional skills and abilities from the navigator.

A Bivariate Index Vector to Measure Departure from Quasi-symmetry for Ordinal Square Contingency Tables

This study proposes a bivariate index vector to concurrently analyze both the degree and direction of departure from the quasi-symmetry (QS) model for ordinal square contingency tables. The QS model and extended QS (EQS) models identify the symmetry and asymmetry between the probabilities of normal circulation and reverse circulation when the order exists for arbitrary three categories. The asymmetry parameter of the EQS model implies the degree of departure from the QS model; the EQS model is equivalent to the QS model when the asymmetry parameter equals to one. The structure of the EQS model differs depending on whether the asymmetry parameter approaches zero or infinity. Thus, the asymmetry parameter of the EQS model also implies the direction of departure from the QS model. The proposed bivariate index vector is constructed by combining existing and original sub-indexes that represent the degree of departure from the QS model and its direction. These sub-indexes are expressed as functions of the asymmetry parameter under the EQS model. We construct an estimator of the proposed bivariate index vector and an approximate confidence region for the proposed bivariate index vector. Using real data, we show that the proposed bivariate index vector is important to compare degrees of departure from the QS model for plural data sets.

Experimental and Numerical Study on Air Flow Behavior for a Novel Retractable Reverse Circulation Drill Bit of Casing-while-Drilling (CwD)

A reverse circulation Down-The-Hole (DTH) hammer drill bit in Casing-while-Drilling (CwD) processes is designed and applied to drilling under complicated formation. The drill bit is a special retractable drill bit with an exclusive reverse circulation gas channel. Using numerical simulations and experiments, the influence of the gas channel structure parameters of the drill bit, including the inner jet nozzles, flushing nozzles, suction channel, and other parameters, on its reverse circulation performance is analyzed, and the optimal gas channel structure parameters of the drill bit are determined to improve the reverse circulation effect. The results show that the flushing nozzles and inner jet nozzles have an important influence on entrainment performance. The entrainment rate η decreases as the flushing nozzle diameter increases and decreases as the inner jet nozzle diameter increases. An increase in the suction channel diameter can improve the reverse circulation effect of the drill bit. The spiral slot drill bit is more conducive to air being sucked into the central channel in the form of spiral flow, so it can improve the entrainment performance. The entrainment rate η can reach 23.4% with the optimum structured drill bit.

Analytical and Numerical Simulation of Asymmetric Converging Flow of Gas under Drill Bits in Reverse Circulation Gas Drilling

Reverse circulation gas drilling has been considered to solve engineering problems such as formation water influx, wellbore instability, and excess gas requirement in gas drilling. The performance of reverse circulation gas drilling depends to a large extent on the structure design of drill bit. An analytical model and a numerical model were developed in this study to simulate the asymmetric converging flow of gas under drill bit for reverse circulation gas drilling. The two models were compared and applied to the evaluation of a drill bit structure design for bottom hole cleaning capacity of gas flow. It was found that the pressure, velocity, and specific kinetic energy given by the analytical model are slightly lower than that given by the numerical model. The relative difference between the gas flow rates given by the analytical model and the numerical model is less than 5%. For the drill bit structure design considered in this study, the gas flow energy between the short blades is much higher than that between the long blades. A gas injection rate of 10 m3/min (360 ft3/min) is expected to clean the drill cuttings between the short blades, while a gas flow rate of 28 m3/min (990 ft3/min) is required to clean the drill cuttings between the long blades. Although the numerical model gives more accurate result than the analytical model in predicting hydraulics parameters, the analytical model is recommended for evaluating drill bit structure design because of its simplicity and conservativeness.