Trajectory Of Horizontal Wells Research Articles

Research on the Pass Capacity Model of Logging Tools for Complex Horizontal Wells

Shale gas, which exists in organic-rich shale or mud shale formations primarily in adsorbed or free states, poses significant development challenges due to the low permeability of shale formations. Traditional vertical wells are ineffective for shale gas extraction, making horizontal wells and large-scale hydraulic fracturing essential for efficient development. However, the complexity of the formation can lead to casing deformation, severely impacting the pass capacity of plug and perforation gun strings in the wellbore. This study analyzes the causes of casing deformation and discusses the rapid development of the cluster perforating technology in perforation operations, and discusses the challenges that might encountered during the process of wireline conveying or pumping. The irregular trajectory of horizontal wells and the high dogleg deflecting severity in the deviated sections can cause cluster perforating strings to suddenly get stuck during the downhole process, leading to a sudden increase in pumping pressure, which may result in premature seating of the fracturing bridge plug, or pull-off accidents at the weak point of the wireline. This research aims to improve engineering efficiency and prevent engineering accidents by conducting a pass capacity analysis of the perforating tool string, which is of significant engineering importance for shale gas development.

Optimization of cementing displacement efficiency based on circulation pressure of a shale gas horizontal well in low pressure and leakage formations

The well trajectory of horizontal wells are constantly changing due to the variation of well inclination and azimuth with depth, leading to a large difference of displacement efficiency in the annulus compared to a vertical well. In low pressure and leakage formations, optimizing injection parameters to improve displacement efficiency is a hot and difficult research topic for researchers and field engineers, particularly the complex well. A fluid flow model inside the casing and annulus was established during primary cementing under an eccentric casing. Pressure distribution in the eccentric and concentric annuli were compared with the field data. Based on the principle of the maximum circulation pressure being lower than formation leakage pressure, the injection rate and fluid density were optimized to improve displacement efficiency, using Computational Fluid Dynamics (CFD) methods and investigating the mud retention volume on the wall. The results indicated that the pressure model in a casing eccentricity with an error of 1% to 3.5% is in good agreement with the actual pump pressure. Frictional pressure loss in the eccentric annulus was 13% to 25% lower than in the concentric annulus. Appropriately increasing the fluid density difference (spacer and lead slurry), the mud retention volume in the annulus of the horizontal section decreased significantly, while increasing the injection rate at the wellhead had little influence on displacement efficiency. The sequence of displacement efficiency from high to low was horizontal section > deflecting section > vertical section. The results of this study allow a better understanding of casing eccentricity effect on circulation pressure and equivalent circulation density (ECD) distributions in the annuls. The complex displacement mechanism analysis for the horizontal, deflecting, and vertical sections provides practical guidance in improving displacement efficiency by optimizing the most effective operation parameters.

Application of Point-by-Point Vector Synthesis in Walkaway VSP Logging Data Processing

At present, it is necessary to use Walkaway VSP logging imaging data to drill horizontal shale gas wells in exploration areas lacking three-dimensional seismic data. Walkaway VSP logging imaging profile can delineate the formation structure around wells, obtain detailed information of dip, inclination and fault around wells, and guide the trajectory design of horizontal wells. But VSP logging is richer and more complex than conventional seismic data. The precondition of up-going wave imaging is to separate up-going P-wave or converted S-wave from complex wave field. Nowadays, most vector synthesis techniques can not completely separate up-going P-wave from up-going converted wave, which affects the accuracy of final imaging results. In order to achieve the best wave field separation effect of VSP logging data, the point-by-point vector synthesis technique is adopted. Firstly, the directional rotation synthesis of horizontal components is carried out according to the maximum energy criterion. Then the rotational synthesis of horizontal and vertical components uses ray tracing based on velocity model to estimate the polarization angle of time-varying upward reflected P-wave or converted wave. The method of “velocity fine-tuning scanning” is applied to search for the best synthesis angle, and the point-by-point vector synthesis is carried out by calculating the time-varying polarization angle. Finally, the best separation effect data are selected as the final vector synthesis result. This technique solves the problem that conventional vector synthesis cannot completely separate up-going P-wave from up-going converted S-wave. Upward P-waves acquired after separation has clear characteristics, more continuous phase axis and good fidelity processing effect, which lays a solid foundation for fine imaging of target formation in the study area and has become an indispensable key supporting technology for optimizing the trajectory of horizontal wells in shale gas development in Sichuan Basin.

水平井井眼轨迹控制误差分析

随着诸多新型定向井、水平井(如分支井、丛式井、大位移井、绕障井、SAGD水平井、火驱井等井型)的应用，所钻遇的地质环境日趋复杂，在井眼密集的老区和超薄边际油层钻井中，对水平井井眼轨迹监测与控制的精度要求越来越高。由于随钻测量仪器在测量过程中由于受到环境、仪器精度、磁场变化等因素影响，实钻井眼轨迹就会与设计轨道产生偏差。认识测量仪器误差对轨迹控制的重要性，减小井眼轨迹控制的误差，提高井眼轨迹的控制精度，可以有效降低井眼防碰的风险，也可以提高水平井的中靶精度，对水平井的现场施工具有重要的指导意义。 With many new directional wells and horizontal wells (such as Multilateral wells, Cluster wells, ERW, SAGD, Fire Flooding wells) application, the geological environment is becoming more com-plex. The accuracy requirement of monitoring and controlling the trajectory of horizontal well in drilling is higher and higher, especially in the old wells and ultra dense marginal reservoirs wells. Due to the environment, the precision of the instrument, the change of the magnetic field, and so on, the influence of the factors on the measuring instrument in the measuring process is measured. So there is deviation between the real drilling trajectory and design trajectory. By recognizing the importance of measuring instrument error on trajectory control, this error can be reduced in slim hole trajectory control, and it also can improve the control precision of the well trajectory. It can reduce the risk of well drilling and improve the accuracy of the target. It has great realistic significance to field operation.

Shale gas in China: Characteristics, challenges and prospects (I)

Abstract This paper mainly discusses the industrialization progress, “sweet spot” evaluation criterion, E&P technologies, success experiences, challenges and prospects of China's shale gas. Based on the geologic and engineering parameters of the Fuling, Changning and Weiyuan shale gas fields in the Sichuan Basin, this paper points out that China's shale gas has its particularity. The discoveries of super-giant marine shale gas fields with high evolution degree (R o =2.0%−3.5%) and ultrahigh pressure (pressure coefficient=1.3−2.1) in southern China is of important scientific significance and practical value to ancient marine shale gas exploration and development to China and even the world. It's proposed that shale gas “sweet spots” must be characterized by high gas content, excellent frackability and good economy etc. The key indicators to determine the shale gas enrichment interval and trajectory of horizontal wells include “four highs”, that is high TOC (>3.0%), high porosity (>3.0%), high gas content (>3.0 m 3 /t) and high formation pressure (pressure coefficient>1.3), and “two well-developed” (well-developed beddings and well-developed micro-fractures). It's suggested that horizontal well laneway be designed in the middle of high pressure compartment between the Upper Ordovician Wufeng Formation and Lower Silurian Longmaxi Formation. The mode of forming “artificial shale gas reservoir” by “fracturing micro-reservoir group” is proposed and the mechanisms of “closing-in after fracturing, limiting production through pressure control” are revealed. Several key technologies (such as three-dimensional seismic survey and micro-seismic monitoring of fracturing, horizontal wells, “factory-like” or industrialized production mode, etc.) were formed. Some successful experiences (such as “sweet spot” selection, horizontal well laneway control, horizontal length optimization and “factory-like” production mode, etc.) were obtained. The four main challenges to realize large-scale production of shale gas in China include uncertainty of shale gas resources, breakthroughs in key technologies and equipment of shale gas exploration and development below 3 500 m, lower cost of production, as well as water resources and environment protection. It is predicted that the recoverable resources of the Lower Paleozoic marine shale gas in southern China are approximately 8.8×10 12 m 3 , among which the recoverable resources in the Sichuan Basin are 4.5×10 12 m 3 in the favorable area of 4.0×10 4 km 2 . The productivity of (200−300)×10 8 m 3 /a is predicted to be realized by 2020 when the integrated revolution of “theory, technology, production and cost” is realized in Chinese shale gas exploration and development. It is expected in the future to be built “Southwest Daqing Oilfield (Gas Daqing)” in Sichuan Basin with conventional and unconventional natural gas production.

Optimizing the Method Used to Design the Trajectory of a Horizontal Well

The aim of this study is to optimize a method used to design the trajectory of horizontal wells. Many of the well-known can be used for various types of well (directional, horizontal, extended-reach, sidetrack horizontal, etc.) and for various curvature radii (long, medium, short, and ultrashort), but while the resulting trajectories meet standard field operation requirements they are still suboptimal. The research done here not only optimizes the angle of inclination of the linear (tangent) section of the well but also accounts for the forces created by rock debris and the equivalent circulating density (ECD) of the drilling fluid.

Application of Research of the Relationship between Ground Stress and Fractures in the Trajectory Optimization of Horizontal Wells

From the perspective of improving single well production and wellbore stability, stress field and natural fractures are the factors which have to be taken into account in the development of horizontal wells of the complex carbonate oil and gas fields in Kuqa piedmont and platform-basin transitional area. On the one hand, as the present stress field is the key factor to control fracture permeability, the trajectory of horizontal wells should pass through fracture system with good permeability as much as possible, being conducive to the effective stimulation of the reservoir. On the other hand, at the state of specific stress, the stability of well trajectory varies with directions. Therefore, before drilling horizontal wells, it is necessary to fully analyze the quantitative relationship between the present stress state and natural fracture occurrence and mechanical characteristics, etc., to optimize and determine a well trajectory conducive to high yield and wellbore stability. In this study, firstly, the fundamental principles for evaluating the present stress state and analyzing the relationship between the stress and fractures were described. Then based on the relationship between them, the occurrence and longitudinal positions of permeability fractures were analyzed. Apart from that, the stability index and fracture opening pressure distribution of wells in different directions at given stress state and fracture system were also analyzed. Finally, the optimization scheme for trajectory of horizontal wells under complex conditions was discussed with three aspects taken into account, i.e. best drilling in permeability fractures, wellbore stability and drilled reservoir stimulation.

Impulsive optimal control model for the trajectory of horizontal wells

This paper presents an impulsive optimal control model for solving the optimal designing problem of the trajectory of horizontal wells. We take fully into account the effect of unknown disturbances in drilling. The optimal control problem can be converted into a nonlinear parametric optimization by integrating the state equation. We discuss here that the locally optimal solution depends in a continuous way on the parameters (disturbances) and utilize this property to propose a revised Hooke–Jeeves algorithm. The uniform design technique is incorporated into the revised Hooke–Jeeves algorithm to handle the multimodal objective function. The numerical simulation is in accordance with theoretical results. The numerical results illustrate the validity of the model and efficiency of the algorithm.

Stochastic optimal control and algorithm of the trajectory of horizontal wells

This paper presents a nonlinear, multi-phase and stochastic dynamical system according to engineering background. We show that the stochastic dynamical system exists a unique solution for every initial state. A stochastic optimal control model is constructed and the sufficient and necessary conditions for optimality are proved via dynamic programming principle. This model can be converted into a parametric nonlinear stochastic programming by integrating the state equation. It is discussed here that the local optimal solution depends in a continuous way on the parameters. A revised Hooke–Jeeves algorithm based on this property has been developed. Computer simulation is used for this paper, and the numerical results illustrate the validity and efficiency of the algorithm.

Optimization model and algorithm of the trajectory of horizontal well with perturbation

In order to solve the optimization problem of designing the trajectory of three-dimensional horizontal well, we establish a multi-phase, nonlinear, stochastic dynamic system of the trajectory of horizontal well. We take the precision of hitting target and the total length of the trajectory as the performance index. By the integration of the state equation, this model can be transformed into a nonlinear stochastic programming. We discuss here the necessary conditions under which a local solution exists and depends in a continuous way on the parameter (perturbation). According to the properties we propose a revised Hooke-Jeeves algorithm and work out corresponding software to calculate the local solution of the nonlinear stochastic programming and the expectancy of the performance index. The numerical results illustrate the validity of the proposed model and algorithm.

Multi-objectives fuzzy models for designing 3D trajectory in horizontal wells

In this paper, multi-objective models for designing 3D trajectory of horizontal wells are developed in a fuzzy environment. Here, the objectives of minimizing the length of the trajectory and the error of entry target point are fuzzy in nature. Some parameters, such as initial value, end value, lower bound and upper bound of the curvature radius, tool-face angle and the arc length of each curve section, are also assumed to be vague and imprecise. The impreciseness in the above objectives have been expressed by fuzzy linear membership functions and that in the above parameters by triangular fuzzy numbers. Models have been solved by the fuzzy non-linear programming method based on Zimmermann [1] and Lee and Li [2]. Models are applied to practical design of the horizontal wells. Numerical results illustrate the accuracy and efficiency of the fuzzy models.