|Theme||Visible||Selectable||Appearance||Zoom Range (now: 0)|
As tubular structures and wellbore conditions in drilling engineering become more complex, the integral mechanical problem of tubular strings with connectors becomes more complicated, and it exceeds the scope of conventional tubular mechanics. To solve this problem, the concept of local-integral coupling of tubular strings is presented, and a local-integral coupling model is built. The coupling model is obtained by introducing the amended factors from local model into the integral model. Next, the coupling model is applied to extended-reach drilling in the South China Sea. The main reason for a common problem in drilling 12¼-in. sections in X oilfield, named periodic sticking, is studied from qualitative and quantitative aspects. The mechanical drags on connectors when periodic sticking occurs and mechanical extending limits considering mechanical drags are analyzed. The results indicate that openhole keyseat is the main reason for periodic sticking in long openhole drilling in X oilfield. Openhole keyseats are formed by drillstring connectors grinding the borehole wall under rotary drilling mode. Reducing or eliminating openhole keyseats is very important for safe and efficient extended-reach drilling.
Mao, Shaowen (Texas A&M University) | Siddhamshetty, Prashanth (Texas A&M University) | Zhang, Zhuo (Texas A&M University) | Yu, Wei (University of Texas at Austin) | Chun, Troy (Texas A&M University) | Kwon, Joseph Sang-Il (Texas A&M University) | Wu, Kan (Texas A&M University)
Slickwater fracturing has become one of the most leveraging completion technologies in unlocking hydrocarbon in unconventional reservoirs. In slickwater treatments, proppant transport becomes a big concern because of the inefficiency of low-viscosity fluids to suspend the particles. Many studies have been devoted to proppant transport experimentally and numerically. However, only a few focused on the proppant pumping schedules in slickwater fracturing. The impact of proppant schedules on well production remains unclear. The goal of our work is to simulate the proppant transport under real pumping schedules (multisize proppants and varying concentration) at the field scale and quantitatively evaluate the effects of proppant schedules on well production for slickwater fracturing.
The workflow consists of three steps. First, a validated 3D multiphase particle-in-cell (MP-PIC) model has been used to simulate the proppant transport at real pumping schedules in a field-scale fracture (180-m length, 30-m height). Second, we applied a propped fracture conductivity model to calculate the distribution of propped fracture width, permeability, and fracture conductivity. In the last step, we incorporated the fracture geometry, propped fracture conductivity, and the estimated unpropped fracture conductivity into a reservoir simulation model to predict gas production.
Based on the field designs of pumping schedules in slickwater treatments, we have generated four proppant schedules, in which 100-mesh and 40/70-mesh proppants were loaded successively with stair-stepped and incremental stages. The first three were used to study the effects of the mass percentages of the multisize proppants. From Schedules 1 through 3, the mass percentage of 100-mesh proppants is 30, 50, and 70%, respectively. Schedule 4 has the same proppant percentage as Schedule 2 but has a flush stage after slurry injection. The comparison between Schedules 2 and 4 enables us to evaluate the effect of the flush stage on well production.
The results indicate that the proppant schedule has a significant influence on treatment performance. The schedule with a higher percentage of 100-mesh proppants has a longer proppant transport distance, a larger propped fracture area, but a lower propped fracture conductivity. Then, the reservoir simulation results show that both the small and large percentages of 100-mesh proppants cannot maximize well production because of the corresponding small propped area and low propped fracture conductivity. Schedule 2, with a median percentage (50%) of 100-mesh proppants, has the highest 1,000-day cumulative gas production. For Schedule 4, the flush stage significantly benefits the gas production by 8.2% because of a longer and more uniform proppant bed along the fracture.
In this paper, for the first time, we provide both the qualitative explanation and quantitative evaluation for the impact of proppant pumping schedules on the performance of slickwater treatments at the field scale by using an integrated numerical simulation workflow, providing crucial insights for the design of proppant schedules in the field slickwater treatments.
Grooving corrosion results in a decrease in the ability of the structure to resist external loads. In the present study, a new assessment method was developed to investigate the ultimate loading capacity of stiffened plates with grooving corrosion damage. First, the basic parameters of stiffened plates (including model range, boundary condition, welding residual stress, initial geometric imperfection, and size of finite element) were assumed. Second, the influences of corrosion parameters and geometrical parameters of stiffened plates (such as finite element type, groove width, groove depth, groove depth-to-width ratio, plate flexibility, stiffener flexibility, and number of stiffeners) were analyzed. Third, based on the data analysis from a large number of nonlinear finite element analyses, the ultimate strength reduction formula of stiffened plates was derived. Last, the correctness of the formula was verified by ultimate strength experiment.
The enhanced unified theory (EUT) has been used as a core theory in the integrated system developed at the Research Initiative on Oceangoing Ships (RIOS) of Osaka University for predicting the propulsion and seakeeping performance of a ship in actual seas. In this study, the EUT is modified by adopting partially the solution method in the rational strip theory of Ogilvie and Tuck as a particular solution in the inner problem, thereby a forward-speed effect in the convection term of the free-surface condition is incorporated in the inner solution. This forward-speed effect is analytically shown to contribute only to the cross-coupling radiation forces. Some other forward-speed and 3D effects important in a low-frequency range are also included in the homogeneous component of the inner solution through matching with the outer solution in a similar manner to the unified theory of Newman. Numerical computations are implemented for a slender modified Wigley model and the RIOS bulk carrier model. Good agreement is confirmed in a comparison with experimental data for the cross-coupling added mass and damping coefficients between heave and pitch and also for the resulting ship motions, particularly in heave near the resonant frequency. The added resistance around the motion-resonant wavelength is found to be improved but sensitive to a slight change in heave and pitch motions. Thus, it is stressed that accurate prediction of the ship motions and resultant Kochin function is critical for more accurate prediction of the added resistance in waves.
Gunawan, _ (Univeristas Indonesia, Indonesia) | Utomo, Allessandro Setyo Anggito (Univeristas Indonesia, Indonesia) | Hamada, Kunihiro (Hiroshima University, Hiroshima) | Ouchi, Kazetaro (Hiroshima University, Hiroshima) | Yamamoto, Hiroyuki (Tsuneishi Shipbuilding Co., Ltd.) | Sueshige, Yoichi (Tsuneishi Shipbuilding Co., Ltd.)
This article presents a new approach for engine room design based on the modularization concept including the part arrangement optimization. The characteristics of the proposed methods are as follows. First, attention was paid to piping systems of multiple bulk carrier series of different sizes. The cost and length of the piping system as well as the similarity and the commonness of the modules and arrangements were considered. Second, to define an effective module that could be commonly used in different ships, a design structure matrix was adopted. Third, in the arrangement design, an optimization system was developed using a genetic algorithm to obtain a similar pattern for module arrangement in multiple series ships with specific consideration toward cost and similarity. Some examples using the proposed method are shown at the end of article.
This paper presents a series of numerical investigations of the capacity of the foundations of a spudcan in clay after it penetrates through a sand layer and under planar combined loading. The model is validated against available relationships for uniaxial capacity of spudcan foundations on clay soils. The model is then used to investigate the uniaxial capacity and combined VH, VM, and HM capacity of spudcan foundations in the underlying clay of sand overlying clay soils. The results are presented in the form of failure envelopes. The effects of the embedment depth, undrained shear strength of clay, and sand plug thickness on the uniaxial and combined capacity are investigated and discussed.
Shimamura, Junji (JFE Steel Corporation) | Izumi, Daichi (JFE Steel Corporation) | Igi, Satoshi (JFE Steel Corporation) | Ishikawa, Nobuyuki (JFE Steel Corporation) | Ueoka, Satoshi (JFE Steel Corporation) | Ihara, Koichi (JFE Steel Corporation) | Kondo, Joe (JFE Steel Corporation)
From actual pipe investigations of Grade X65 UOE sour linepipe steels, the inner surface hardness of pipes increased by increasing the volume fraction of the lath bainite (LB) microstructure instead of the granular bainite (GB) microstructure. Four-point bend tests on sulfide stress cracking (SSC) revealed that SSC occurred when the inner surface hardness of a pipe increased by increasing the volume fraction of the LB microstructure over a 1 bar H2S partial pressure condition. Lowering the surface hardness less than 250 HV0.1kgf at 0.25 mm from the surface by suppressing the LB microstructure led to a good SSC-resistant property over the 1 bar H2S partial pressure condition.
Straight line path following of the underactuated ONR Tumblehome ship in the presence of ocean currents is studied. The maneuvering modeling group (MMG) model is used to simulate the motion of the vehicle, and a linearized model is constructed for controller design. A guidance strategy combining the line-of-sight (LOS) and integral line-of-sight (ILOS) guidance laws is proposed to compensate for the drift effect. Furthermore, to deal with the saturation of rudder angle and limitation of maximum rudder rate explicitly, the model predictive control (MPC) technology is utilized. Simulations are conducted, and the results show good path following performance of the guidance-based MPC controller.
Superhydrophobic surfaces have raised a great deal of attention in recent years because of their numerous potential applications. In this work, a method of manufacturing “large” superhydrophobic surfaces using very fine stainless steel mesh to “hot-emboss” hydrophobic polytetrafluoroethylene (PTFE) surfaces is provided. A high static contact angle and low contact angle hysteresis for these “xPTFE” superhydrophobic surfaces were measured as approximately 150. and 15., respectively. The surfaces’ structures were investigated via scanning electron microscopy (SEM). Otherwise, the slip-length was measured using a rheometer as approximately 30 lm, which indicates a great potential drag reduction. This easy and inexpensive method could be a great step to bring superhydrophobic surfaces into real-world use.
Kwon, Yong-Ju (Korea Research Institute of Ships and Ocean Engineering (KRISO)) | Jung, Dongho (Korea Research Institute of Ships and Ocean Engineering (KRISO)) | Park, Byeongwon (Korea Research Institute of Ships and Ocean Engineering (KRISO)) | Jung, Jae-Hawn (Korea Research Institute of Ships and Ocean Engineering (KRISO)) | Oh, Seunghoon (Korea Research Institute of Ships and Ocean Engineering (KRISO))
A series of model tests were performed to investigate the response characteristics of a free hanging riser under forced oscillation conditions. The boundary conditions were considered to be fixed/free (fixed at the top and free at the bottom). The top end of the riser was fixed to the forced oscillator to give the effects of horizontal vessel motion. The model test was performed at the Ocean Engineering Basin of the Korea Research Institute of Ships and Ocean Engineering (KRISO). In this study, the displacements along the riser length were measured using underwater camera systems. Various oscillation conditions were considered in order to investigate the effects of period and amplitude. The oscillation period was determined considering the eigenvalues in the in-line (IL) response. The IL responses of the experiment were compared with the time simulation results of OrcaFlex. The responses of two results had a good agreement on time series, statistical value, and snapshot. The cross-flow (CF) responses along the riser length in the experiment were determined by the Keulegan-Carpenter number at each point of the riser. A comparison result of the IL and CF responses shows that they were excited by different dominant frequencies from the top-end motion and vortex shedding, respectively. While one top-end oscillation frequency appeared in the IL, multi-peak frequencies were investigated at all positions along the riser length in the CF, which is induced by traveling waves.