Effect and mechanism of microbial solid-free drilling fluid for borehole wall enhancement

Borehole stability analysis has been well studied in oil and gas exploration when drilling through rock formations. However, a related analysis of ice borehole stability has never been conducted. This paper proposes an innovative method for estimating the drilling fluid pressure window for safe and sustainable ice drilling, which has never been put forward before. First, stress concentration on a vertical ice borehole wall was calculated, based on the common elastic theory. Then, three failure criteria, the Mogi–Coulomb, teardrop, and Derradji-Aouat criteria, were used to predict the stability of the ice borehole for an unbroken borehole wall. At the same time, fracture mechanics were used to analyze the stable critical pressure for a fissured wall. Combining with examples, our discussion shows how factors like temperature, strain rate, ice fracture toughness, ice friction coefficient, and fracture/crack length affect the stability of the borehole wall. The results indicate that the three failure criteria have similar critical pressures for unbroken borehole stability and that a fissured borehole could significantly decrease the safety drilling fluid pressure window and reduce the stability of the borehole. The proposed method enriches the theory of borehole stability and allows drillers to adjust the drilling fluid density validly in ice drilling engineering, for potential energy exploration in polar regions.

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A thermomechanical technology of borehole wall isolation using a thermoplastic composite material

E3S Web of Conferences ◽

10.1051/e3sconf/201910900098 ◽

2019 ◽

Vol 109 ◽

pp. 00098

Author(s):

Andrii Sudakov ◽

Andrii Dreus ◽

Yurii Kuzin ◽

Diana Sudakova ◽

Boranbay Ratov ◽

...

Keyword(s):

Composite Material ◽

Polyethylene Terephthalate ◽

Thermophysical Properties ◽

Drilling Fluid ◽

Melting Rate ◽

Thermoplastic Composite ◽

Borehole Wall ◽

Innovative Technology

Loss of drilling fluid in wells is one of the most important drilling challenges. To prevent this problem an insulation of borehole wall is requiring. The results of study of an innovative technology of isolation of borehole using a new thermomechanical plugging material are presented herein. The material considered is solid composite consisting secondary polyethylene terephthalate and gravel. Theoretically and experimentally shown the possibility to use this material to borehole isolation. The technology of manufacturing and isolation of absorbing horizons by thermomechanical material has been developed. Dependence of the regime parameters of thethermomechanical process melting of material on the thermophysical properties and technical characteristics was established. Dependence of the penetrating ability of material melt on the fractures was established. The results of work can be used to recommend technology parameters providing the efficient melting rate.

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Study on Wellbore Stability and Failure Regions of Shale considering the Anisotropy of Wellbore Seepage

Geofluids ◽

10.1155/2021/6694689 ◽

2021 ◽

Vol 2021 ◽

pp. 1-13

Author(s):

Fan Zhang ◽

Houbin Liu ◽

Yingfeng Meng ◽

Shuai Cui ◽

Haifeng Ye

Keyword(s):

Mechanical Properties ◽

Internal Friction ◽

Drilling Fluid ◽

Bedding Plane ◽

Wellbore Stability ◽

Borehole Wall ◽

Distribution Model ◽

Longmaxi Formation ◽

Angle Of Internal Friction ◽

Ground Stress

The hard and brittle shale formation is prone to collapse and instability, and the penetration of drilling fluid along the bedding reduces the mechanical properties of rock near the borehole wall, resulting in serious downhole accidents. Therefore, in this paper, the geomechanical parameters of the reservoir in the Longmaxi formation of Jiaoshiba were determined by field hydraulic fracturing and laboratory experiments. Then, the stress distribution model of borehole wall under the condition of underbalanced seepage flow is established based on the experimental results obtained by mechanical experiments on underground cores. The instability zone of borehole wall under the condition of underbalance is calculated and analyzed. The results show that the two-way horizontal ground stress of the Longmaxi formation is higher than 2.2 MPa/100 m, and the original ground stress is high. Moreover, the mechanical parameters of the stratified shale stratum matrix and weak surface are significantly different. The cohesion (4.7 MPa) and the angle of internal friction (26.9°) of bedding plane are significantly lower than that of the matrix (7.77 MPa) and the angle of internal friction (46.7°). Hard and brittle shale is easy to be destroyed along the stratification. Under the condition of underbalanced seepage, the mechanical properties of borehole shale can be stable. It is found that when the borehole axis is vertically stratified, the collapse pressure is the lowest, while in other drilling directions, the drilling fluid density needs to be increased by 0.5 g/cm3 to maintain the borehole stability. With the increase of the inclination angle of bedding plane, the wall failure area increases. The results of this study can provide guidance and suggestions for drilling in Jiaoshiba block and other permeable hard and brittle shale formations.

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Parameter substantiation of supra bit jet pump for productive formation opening

Earth sciences and subsoil use ◽

10.21285/2686-9993-2021-44-4-433-440 ◽

2021 ◽

Vol 44 (4) ◽

pp. 433-440

Author(s):

A. P. Melnikov ◽

N. A. Buglov

Keyword(s):

Hydrostatic Pressure ◽

Drilling Fluid ◽

Drill String ◽

Borehole Wall ◽

Circulation Loop ◽

Annular Space ◽

Jet Pump ◽

Mixing Chamber ◽

Jet Pumps ◽

Unsteady Operation

The purpose of the study is to develop a supra bit jet pump taking into account the unsteadiness of low-speed drilling for crushing the cuttings injected from the annular space under productive formation opening. The article proposes a device for drill string bottom assembly intended for the initial opening of the productive formation. The device includes a supra bit jet pump and a colmatator. The jet pump creates an additional circulation loop of the drilling fluid above the well bottom, crushes the cuttings injected from the annular space in the mixing chamber and delivers it to the colmatator. An additional circulation loop above the well bottom creates a local drawdown of the formation while maintaining the hydrostatic pressure in the well. Crushing of cuttings in the mixing chamber of the jet pump occurs due to the creation of cross flows in the jet pump. The cross flows are provided due to the angular and eccentric displacement of the working nozzle of the jet pump relative to the mixing chamber. The colmatator creates an impermeable screen on the borehole wall for temporary isolation of the productive formation under initial opening. The conducted study allowed the authors to propose head characteristics of the jet pump taking into account the angular, eccentric displacement of the working nozzle. The head characteristic of the jet pump has been developed for the unsteady operation of the jet pump in the drill string bottom assembly. The head characteristics take into account the roughness of the flow path of the jet pump. Using the head characteristics, the permissible displacements of the working nozzle of the jet pump have been determined. Recommendations for the design of jet pumps for drill string bottom assemblies are proposed.

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