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Nowadays, horizontal wells are one of the most common methods in the development of oil and gas fields. But Heel-Toe Effect phenomenon and non-uniform production influx along the well have caused early unwanted fluid production and reduced the performance of these. Application of inflow control devices (ICDs) is one of the most appropriate ways to solve these problems, which can ultimately improve the efficiency of horizontal wells both in production and injection. But some of the crucial questions in designing horizontal well completion using ICDs are determining the number of ICDs, identifying their location, and calculating required pressure drop imposed by these ICDs. This research seeks to develop a novel method that uses reliable data with low uncertainty and develops an integrated algorithm to answer these questions rapidly and analytically. This novel method introduces three key parameters in designing horizontal well completion: length of ICD associated well segment, equalized production influx, and the minimum length of ICD associated well segment. Then a novel and fast integrated workflow have been developed that uses the previous key parameters to determine the number of well segments, number of ICDs & AFIs, ICDs & AFIs location, and ICD’s strength.

The low permeability of silty hydrate reservoirs in the South China Sea is a critical issue that threatens safe, efficient, and long‐term gas production from these reservoirs. Hydraulic fracturing is a potentially promising stimulation technology for such low‐permeability reservoirs. Here, we assess the gas production potential of a depressurization horizontal well that is assisted by the hydraulic fracturing using numerical simulation according to field data at site SH2 in this area. In addition, the number of horizontal wells drilled is discussed if commercial production is to be performed at this site. The results show that the production potential can be significantly stimulated at the early production stage by adopting hydraulic fracturing in this reservoir due to a better depressurization effect. However, the increase in gas recovery gradually decreases with the continuous dissociation of gas hydrates, and the evolution trend is similar to that in a reservoir without stimulation during later periods of gas production because the dissociation front gradually moves away from the fractures. From the perspective of production potential, using a horizontal well scheme assisted by the hydraulic fracturing technology for gas recovery from a hydrate deposit can sharply reduce the number of operation wells, shorten the drilling operation time, and boost the economic efficiency. The horizontal well scheme may be an effective way to increase the gas yield if the application of quickly deployed horizontal wells and hydraulic fracturing techniques in such hydrate reservoirs greatly increases in the near future. The effect of hydraulic fracturing on gas recovery and the needed minimum number of horizontal operation wells are evaluated for gas hydrate reservoirs in Shenhu area of the South China Sea. The horizontal well scheme may be an effective way to increase the gas yield if the horizontal wells and hydraulic fracturing techniques in such hydrate reservoirs are adopted in the near future.

Sinusoidal buckling of drill strings will be easily caused during drilling process of extended-reach horizontal wells due to the factors such as excessive well length and larger friction torque, which will cause measurement errors of well depth and vertical depth and furthermore influence the accurate calculation of ECD. We have corrected the traditional ECD calculation model, considered the measurement errors of well depth and vertical depth caused by the sinusoidal buckling of drill strings, and established a set of equivalent circulating density (ECD) calculation model suitable for extended-reach horizontal wells to meet the requirements for fine ECD control during the drilling operation. We have combined the data from an extended-reach horizontal well in the East China Sea and compared the ECD data obtained from the recorded stand pipe pressure with the prediction results from Landmark commercial software、the model in this work and the conventional model. Results show that the prediction results by the model in this work are closest to the recorded values when drill string sinusoidal buckling occurs. Besides, the ECD value predicted by the model considering the measurement errors of well depth and vertical depth caused by the sinusoidal buckling of drill strings is smaller due to the factor that the length of drill strings with sinusoidal buckling is larger than the actual well depth. With the identical case well data, the larger the sinusoidal buckling degree of downhole drill strings, the smaller the predicted ECD value. The model can reduce risks for drilling operations of extended-reach horizontal wells and provide more accurate reference data for their well control operations.

To address the challenges of high running friction and limited depth extension caused by the heavy weight of traditional carbon steel casings in extended-reach horizontal wells, this study conducts a comparative analysis of titanium alloy and carbon steel casings using WellLead drilling software in a deep-water shallow-soft formation well (with a water-to-vertical ratio of 2.36 and maximum dogleg severity of 15°/30m). The friction sensitivity curve model reveals that the titanium alloy casing reduces static hook load by 13.2% (73 kN), significantly mitigating pipe sagging risks. Notably, under a high external friction co-efficient of 0.6, the titanium alloy casing achieves a hook load margin of 142.6 kN—107% higher than that of carbon steel casing (68.7 kN), thereby fully avoiding critical running failures. Simulation of a 5,000-meter lateral section demonstrates that the titanium alloy casing extends the maximum running depth by 2.4% (high friction: 0.6) to 27.4% (low friction: 0.6) compared to carbon steel. Field tests confirm superior running stability of titanium alloy casings in irregular wellbores, though wellbore reconditioning remains necessary for localized obstructions. This study quantifies the relationship between lightweight design and friction sensitivity, providing a reliable basis for casing selection in complex horizontal wells. Future research should also examine potential risks of titanium alloy casings, particularly weldability and long-term durability.

Horizontal wells play an often overlooked role in hydrogeology and aquifer remediation but can be an interesting option for many applications. This study reviews the constructional and hydraulic aspects that distinguish them from vertical wells. Flow patterns towards them are much more complicated than those for vertical wells, which makes their mathematical treatment more demanding. However, at some distance, the drawdown fields of both well types become practically identical, allowing simplified models to be used. Due to lower drawdowns, the yield of a horizontal well is usually higher than that of a vertical well, especially in thin aquifers of lower permeability, where they can replace several of the latter. The lower drawdown, which results in lower energy demand and slower ageing, and the centralized construction of horizontal wells can lead to lower operational costs, which can make them an economically feasible option.

The stimulation of coalbed methane (CBM) through multi-branch horizontal wells has been widely used in China. However, its effectiveness in high-order coal reservoirs in the Wenjiaba area of the Zhina Coalfield, Guizhou Province, requires further investigation. This paper develops a numerical model to evaluate CBM recovery and optimize wellbore structural parameters for the 16# coal seam. Firstly, CBM production, content, and gas pressure were selected for an integrated evaluation of extraction applicability. Then, an optimization study concerning structural parameters was conducted, such as branch length, branch angle, and branch spacing. Results show that multi-branch horizontal wells significantly enhance extraction efficiency of CBM. Notably, there is a negative correlation between the CBM content and the distance from the main branch well and this decrease rate exhibits attenuation over distance; A pronounced depressurization zone forms around these multi-branch wells; At greater distances along the wellbore, the CBM flow velocity diminishes leading to a relatively slower pressure relief rate, due to the frictional resistance. Optimizing branch length and angle significantly improves recovery performance.

Block A has developed narrow channel sand bodies, and over 30 years of efficient development experience, the main target of oil field exploration has gradually shifted from overall exploration to the fault edges and top of oil layers where residual oil is locally enriched. The ultra short radius horizontal well technology has the advantages of small turning radius, accurate target insertion, and simple construction [1] . It has become an important method for tapping the remaining oil in narrow river sand bodies in special well types [2] . This article summarizes the formation of a narrow channel sand body tapping method that combines well seismic prediction with reservoir sand body prediction and trajectory optimization design. Reasonable main design parameters have been determined. The research results indicate that the angle between the design trajectory and the mainstream should be between 120 ° and 150 º. When the angle is 135 °, the production is highest, and the horizontal section length should be between 70m-200m. When the length is 200m, the recovery rate and economic benefits are the best. The interlayer distance should be kept above 50m, and the horizontal section position should be designed in the middle part of oil reservoir. This method was applied to 8 wells in Block A, with an average initial daily oil production of 3.5 tons and an average cumulative oil production of 1053 tons per well. The residual oil tapping effect is significant.

A flexible drilling tool is a special drilling tool for ultrashort-radius radial horizontal wells. This tool is composed of many parts and has the characteristics of a multibody system. In this paper, a numerical method for the dynamic analysis of flexible drilling tools is proposed. The flexible drill tool is discretized into spatial beam elements, while the multilayer contact of the flexible drilling tool is represented by the multilayer dynamic gap element, and the dynamic model of the multibody system for the flexible drilling tool’s multilayer contact is established, considering the interaction force between the drill bit and the rock. The nonlinear dynamic equation is solved using the Newmark method and Newton–Raphson method. An analysis of the dynamic behavior of a flexible drilling tool is conducted. The results indicate that the flexible drilling tool experiences vortex formation due to the interaction between the flexible drilling pipe and the guide pipe, leading to increased friction and wear. This situation hinders safe drilling operations with flexible drilling tools. The collision force of the flexible drilling tool near the bottom of the hole is more severe than that of the other tool types, which may lead to failure of the connection.

The effectiveness of horizontal well multi-stage and multi-cluster fracturing in the fractured soft coal seam roof for coalbed methane (CBM) extraction has been demonstrated. This study focuses on the geological characteristics of the No. 5 and No. 11 coal seams in the Hancheng Block, Ordos Basin, China. A multi-functional, variable-size rock sample mold capable of securing the wellbore was developed to simulate layered formations comprising strata of varying lithology and thicknesses. A novel segmented fracturing simulation method based on an expandable pipe plugging technique is proposed. Large-scale true triaxial experiments were conducted to investigate the effects of horizontal wellbore location, perforation strategy, roof lithology, and vertical stress difference on fracture propagation, hydraulic energy variation, and the stimulated reservoir volume in horizontal wells targeting the soft coal seam roof. The results indicate that bilateral downward perforation with a phase angle of 120° optimizes hydraulic energy conservation, reduces operational costs, enhances fracture formation, and prevents fracturing failure caused by coal powder generation and migration. This perforation mode is thus considered optimal for coal seam roof fracturing. When the roof consists of sandstone, each perforation cluster tends to initiate a single dominant fracture with a regular geometry. In contrast, hydraulic fractures formed in mudstone roofs display diverse morphology. Due to its high strength, the sandstone roof requires significantly higher pressure for crack initiation and propagation, whereas the mudstone roof, with its strong water sensitivity, exhibits lower fracturing pressures. To mitigate inter-cluster interference, cluster spacing in mudstone roofs should be greater than that in sandstone roofs. Horizontal wellbore placement critically influences fracturing effectiveness. For indirect fracturing in sandstone roofs, an optimal position is 25 mm away from the lithological interface. In contrast, the optimal location for indirect fracturing in mudstone roofs is directly at the lithological interface with the coal seam. Higher vertical stress coefficients lead to increased fracturing pressures and promote vertical, layer-penetrating fractures. A coefficient of 0.5 is identified as optimal for achieving effective indirect fracturing. This study provides valuable insights for the design and optimization of staged fracturing in horizontal wells targeting crushed soft coal seam roofs.