Research on Wellbore Pressure in the Dynamic Killing Process for Complex Structure Wells Based on the Wellbore Multiphase Flow Theory

Enhancing the production capacity of natural gas hydrates (NGHs) is critical for its commercial development. Complex structure wells may efficiently increase drainage areas while enhancing exploitation efficiency. Based on the field data of China’s first offshore NGH test production, the numerical method was used to analyze the production performance of different complex structure well types by continuous depressurization production for 360 days under the preconditions of fixed effective completion length of 300 m and a pressure difference of 6 MPa. Results indicated that the complex structure well types deployed at the three-phase layer demonstrated superior production performance within 240 days of production; the DLW2 and HW2 well types stood out, with an average gas production rate Qg reaching 43,333 m3/d and a specific production index J of 24.1. After 360 days of production, benefiting from multi-layer combined production, the Cluster vertical well deployed at the multi-layer had the best production performance, with an average Qg of 34,444 m3/d and a J-index of 19.1. The research results provided insights into the complex structure well-type selection strategy for NGH depressurization in this sea area.

Application of the enlarged wellbore diameter to gas production enhancement from natural gas hydrates by complex structure well in the shenhu sea area

About 90% of the world’s natural gas hydrates (NGH) exist in deep-sea formations, a new energy source with great potential for exploitation. There is distance from the threshold of commercial exploitation based on the single well currently used. The complex structure well is an efficient and advanced drilling technology. The improvement of NGH productivity through various complex structure wells is unclear, and there is no more complete combing. Thus, in order to evaluate their gas production characteristics, we establish a mathematical model for exploitation of NGH, and then 13 sets of numerical models based on the geological parameters of the Nankai Trough in Japan are developed and designed, including a single vertical well, a single horizontal well, 1~4 branch vertical wells, 1~4 branch horizontal wells, and 2~4 branch cluster horizontal wells. The research results indicate that wells with complex structures represented by directional wells and multilateral wells can significantly increase the area of water and gas discharge, especially cluster wells, whose productivity can be increased by up to 2.2 times compared with single wells. Complex structural wells will play an irreplaceable role in the future industrialization of NGH.

Laboratory research on degradable drilling-in fluid for complex structure wells in coalbed methane reservoirs

Complex structure wells are now widely used in the development of marine oilfield, old oilfield and low permeable oilfield. During drilling operations, if the fluid velocity is lower than a critical value in annulus, cuttings in the highly-deviated segments and horizontal segments will accumulate and eventually develop cuttings bed, which affects the rate of penetration (ROP) and downhole safety. As a result, numerous inventions which show different hole-cleaning detection methods can be applied to determine cuttings concentration or hole-cleaning efficiency, and there are three methods for good hole-cleaning condition. The fluid rate control methods include increasing flow rate and injecting slug. The chemical methods include changing the rheology of drilling fluid and adding fiber sweep into drilling fluid. The mechanical methods include using pipe joint, annulus reducer, and different types of blades tool for rotary drilling, and centralizer and fluid velocity shift device for non-rotary drilling and rotary drilling. This review presents a summary of the main United States and Chinese patents available on hole-cleaning techniques.

This article briefly introduces the completion structure and key support technologies of drilling, conventional horizontal Wells, lateral horizontal Wells and branch horizontal Wells under computer data evaluation. The problems existing in the process of well completion in complex structure Wells and the development direction in the future are put forward.

Effect of variable drill pipe sizes on casing wear collapse strength

State-of-the-art cuttings transport with aerated liquid and foam in complex structure wells

The use of a vertical well pattern results in productivity deficiency and poor development effect when developing buried hill reservoirs with complex properties. In this work, experiments are conducted to determine the best pattern for complex structure wells in buried hill reservoirs. Discretization is employed in an experimental method that uses unit cubic rocks with a size of 5 cm × 5 cm × 5 cm. The rocks are bonded in a spotty or reticular design to form a macroscopic model. Based on water flooding similarity criteria of fractured reservoir, an experimental model similar to a quarter of a five-spot unit in an actual reservoir is designed and manufactured. By selectively plugging wells in the model, various well patterns are established. Simulation results indicate that the vertical–vertical well pattern exhibits the fastest water breakthrough, fastest increase in water cut, and lowest recovery under the same pressure difference and well spacing. The horizontal–horizontal well pattern has the slowest water cut increase and the highest final oil recovery. For fishbone wells, this pattern facilitates an ideal development effect when the percolation direction is perpendicular to the plane determined by the mother bore and branch. When liquid rate, water cut, and recovery are considered, the horizontal–horizontal well pattern is recommended when conditions allow.

Effective cuttings transport is one of the most major concerns in designing hydraulic parameters during drilling complex structure wells. It is important and essential to study critical parameters how to influence cuttings bed development, especially the drillpipe rotation effects on cuttings transport behavior. In this study, cuttings transport simulations were carried out for inclinations from 45° to 90°, for pipe rotation speeds from 80 to 240 rpm, and for flow rates from 30 to 50 L/s. Annular cuttings volume, pressure drop, and cuttings distribution are recorded simultaneously within the simulation proceeding. The CFD simulations show that pipe rotation makes cuttings presented in asymmetric distribution along the wellbore and significantly improves the drag effects on drilling fluid in the tangential direction. At a low or medium flow rate, pipe rotation has a significant impact on annular cuttings volume and pressure drop. However, there is no additional contribution of pipe rotation after reaching critical speed at high flow rates. Buckingham-π theorem combined with least square method was applied to establish the empirical correlations for estimating cuttings concentration and annular pressure drop.

As cutting-edge technology, cluster wells can substantially enhance wells production and oil recovery. Rotating Magnet Ranging System (RMRS) is critical technology to ensure precise ranging and accurate interconnecting target of complex structure wells. The magnetic signal of RMRS is a sinusoidal signal of frequency-varying, narrow band, and its intensity attenuates rapidly with cube of the propagation distance. When the distance is far away, the weak magnetic field signal is completely submerged by the environmental electromagnetic interference and the inherent noise of the detection circuit, which can not be detected accurately. According to the narrow band and varying frequency characteristics of rotating magnetic signal, a signal acquisition and processing system is designed for RMRS in order to track the varying frequency accurately and extract the weak amplitude precisely. System hardware included preamplifier, narrow band filter circuit, high precision A/D conversion circuit, control circuit and peripheral circuit. System software included digital filter algorithm and PC interface designing. A novel IQuinn-Rife method is proposed to effectively estimate the frequency of signal for RMRS under a strong interference background. Simulation results indicate IQuinn-Rife algorithm can improve the frequency resolution, avoid collecting useless frequency points, advance efficiency of the calculation speed and enhance accuracy of the results. The experiment verifies that the instrument is stable and reliable to quickly process the magnetic field signals while drilling in strong noise environment. The results indicate that the maximum effective ranging distance can be up to 50m for the adjacent well distance detection signals acquisition system, which can fulfill the requirements of drilling engineering in complex structure wells.

Fully transient coupled prediction model of wellbore temperature and pressure for multi-phase flow during underbalanced drilling

Gas kick simulation in oil-based drilling fluids with the gas solubility effect during high-temperature and high-pressure well drilling

To solve the insufficient energy for reverse circulation fishing tools in complex structure wells, it is necessary to further optimize the design of the tools to improve the impurity salvage efficiency. In this work, a three‐dimensional (3D) flow field simulation model of reverse circulation fishing tool with venturi negative pressure is employed to identify the vortex zone of circulation channel and to investigate the negative pressure and jet velocity distribution around the spray nozzle based on the ANSYS‐CFX. The effects of the spray angle, diameter of the suction nozzle, and the nonstructural parameters on negative pressure and jet velocity are investigated through sensitivity analysis. As revealed from the results, there may be an optimum value for the spray angle, and the nozzle jet direction can indeed affect the propagation and attenuation of the bottom hole flow field greatly. The combination of the inner diameter of the nozzle outlet and that of the nozzle inlet (Φ + Φ′ = 3 mm + 6 mm) is the best design solution when the negative pressure at the nozzle outlet can be the highest. The negative pressure and jet velocity increase with the increasement of the inlet flow rate. The comparative analysis of different bottom hole impurity mass in the cases of the borehole inner diameter 5′ and 8.5″ on the salvage efficiency are conducted numerically. It is observed that the impurity mass salvaged and salvage time are not directly related to its total amount, but only related to the flow rate of the sucked fluid flow. The impurity salvage efficiency can be as high as 95.4%, which meets the engineering requirements in the field. This work improves the working performance of the reverse circulation fishing tool and provides theoretical guidance for well washing.

A variety of possible well types and so many complex drilling variables and constraints make the wellbore optimization problem a very challenging work. Several types of well are listed as directional wells, horizontal wells, redrilling wells, complex structure wells, cluster wells, and extended reach wells etcetera. Over the recent few years, the number of unconventional wells including deviated wells, highly deviated wells are steadily increasing. Directional drilling has some advantages over vertical drilling though it is more expensive. In drilling engineering, the optimization of wellbore plays an important role, which can be optimized based on minimization of length, mud pressure, critical pressure, etc. Till today so many approaches and methods are used to optimize this wellbore trajectory. From those methods in this study, we have focused on metaheuristic approaches based on PSO (particle swarm optimization) which will be used to optimize wellbore trajectory. This reduction of the wellbore length helps in establishing cost-effective approaches that can be utilized to resolve a group of complex trajectory optimization challenges. For smooth and effective performance (i.e. quickly locating global optima while taking the shortest amount of computational time) we must identify flexible control parameters. Later this parameter can be effectively fixed to tune different algorithm. This research will propose a new neighborhood function with Particle swarm optimization(PSO) algorithm for minimizing the true measured depth (TMD). In this paper, the authors have proposed a particle swarm optimization with neighbourhood function to solve this problem. Later the authors will compare this method with conventional methods.