scholarly journals Alkali Solution Erodes Shale: Influencing Factors and Structural Damage Characteristics

2018 ◽  
Vol 2018 ◽  
pp. 1-8
Author(s):  
Jiping She ◽  
Hao Zhang ◽  
Ying Zhong ◽  
Yang Yuan ◽  
Jiachun You
Keyword(s):  
Corrosion Rate ◽  
Shale Gas ◽  
Structural Damage ◽  
Reaction Rate ◽  
Fracture Propagation ◽  
Drilling Fluids ◽  
Gas Wells ◽  
Wellbore Instability ◽  
High Ph ◽  
Bedding Planes

High-pH drilling fluids are often used for drilling shale gas wells. Alkali erosion of shale is one of the important factors of wellbore instability. Alkali erosion experiments of different kinds of minerals and shale were conducted in this paper. Experimental results show that the corrosion rate of kaolinite is the highest when the pH is 9, the corrosion rate of smectite is the highest when the pH is 10 or 11, and the corrosion rate of the quartz is the highest when the pH is 12. Both shale particle size and concentration of hydroxide ion all affect the reaction rate, and the former has a negative correlation with the reaction rate, and the latter has a positive correlation with the reaction rate. In addition, alkaline erosion can lead to the fracture propagation along the bedding planes of shale, which can easily result in wellbore instability. This study may offer some theoretical basis for wellbore instability induced by high-pH drilling fluids.

Wellbore instability in shale gas wells drilled by oil-based fluids

2014 ◽  
Vol 72 ◽  
pp. 294-299 ◽  
Author(s):  
Lijun You ◽  
Yili Kang ◽  
Zhangxin Chen ◽  
Qiang Chen ◽  
Bin Yang
Keyword(s):  
Shale Gas ◽  
Gas Wells ◽  
Wellbore Instability

scholarly journals Oil-Based Drilling Fluid Plugging Method for Strengthening Wellbore Stability of Shale Gas

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-13
Author(s):  
Pengcheng Wu ◽  
Chengxu Zhong ◽  
Zhengtao Li ◽  
Zhen Zhang ◽  
Zhiyuan Wang ◽  
...  
Keyword(s):  
Shale Gas ◽  
Drilling Fluid ◽  
Wellbore Stability ◽  
Drilling Fluids ◽  
Fluid System ◽  
Horizontal Drilling ◽  
Wellbore Instability ◽  
Filtration Loss ◽  
Treatment Agent ◽  
Stability Method

Finding out the reasons for wellbore instability in the Longmaxi Formation and Wufeng Formation and putting forward drilling fluid technical countermeasures to strengthen and stabilize the wellbore are very crucial to horizontal drilling. Based on X-ray diffraction, electron microscope scanning, linear swelling experiment, and hot-rolling dispersion experiment, the physicochemical mechanism of wellbore instability in complex strata was revealed, and thus, the coordinated wellbore stability method can be put forward, which is “strengthening plugging of micropores, inhibiting filtrate invasion, and retarding pressure transmission.” Using a sand bed filtration tester, high-temperature and high-pressure plugging simulation experimental device, and microporous membrane and other experimental devices, the oil-based drilling fluid treatment agent was researched and selected, and a set of an enhanced plugging drilling fluid system suitable for shale gas horizontal well was constructed. Its temperature resistance is 135°C and it has preferable contamination resistibility (10% NaCl, 1% CaCl2, and 8% poor clay). The bearing capacity of a 400 μm fracture is 5 MPa, and the filtration loss of 0.22 μm and 0.45 μm microporous membranes is zero. Compared with previous field drilling fluids, the constructed oil-based drilling fluid system has a greatly improved plugging ability and excellent performance in other aspects.

scholarly journals Overview and prospect of fracture propagation and conductivity characteristics in deep shale gas wells

2017 ◽  
Vol 47 (11) ◽  
pp. 114603 ◽  
Author(s):  
TingXue JIANG ◽  
Jian ZHOU ◽  
Xu ZHANG ◽  
Lei HOU ◽  
Bo XIAO
Keyword(s):  
Shale Gas ◽  
Fracture Propagation ◽  
Gas Wells

Effect of Weak Bedding Planes on Wellbore Stability for Shale Gas Wells

2012 ◽  
Author(s):  
Yufei Li ◽  
Yongqiang Fu ◽  
Geng Tang ◽  
Chaoyi She ◽  
Jianhua Guo ◽  
...  
Keyword(s):  
Shale Gas ◽  
Wellbore Stability ◽  
Gas Wells ◽  
Bedding Planes

Coupled Thermal-Hydro-Mechanical-Chemical Modeling for Time-Dependent Anisotropic Wellbore Stability Analysis

2021 ◽  
Author(s):  
Jingyou Xue ◽  
Kenji Furui
Keyword(s):  
Stability Analysis ◽  
Chemical Potential ◽  
Bedding Plane ◽  
Wellbore Stability ◽  
Time Dependent ◽  
Drilling Fluids ◽  
Shale Formations ◽  
Wellbore Instability ◽  
Bedding Planes ◽  
Stress Changes

<p>Wellbore instability is one of the most serious drilling problems increasing well cost in well construction processes. It is widely known that many wellbore instability problems are reported in shale formations where water sensitive clay mineral exist. The problems become further complicated when the shale exhibits variation in strength properties along and across bedding planes. In this study, a coupled thermal-hydro-mechanical-chemical (THMC) model was developed for time-dependent anisotropic wellbore stability analysis considering chemical interactions between swelling shale and drilling fluids, thermal effects, and poro-elastoplastic stress-strain behaviors.</p><p>The THMC simulator developed in this work assumes that the shale formation behaves as an ion exchange membrane where swelling depends on chemical potential of drilling fluids invading from the wellbore to the pore spaces. The time-dependent chemical potential changes of water within the shale are evaluated using an analytical diffusion equation resulting in the evolution of swelling strain around the wellbore. On the other hand, the thermal and pressure diffusion equations are evaluated numerically by finite differences. The stress changes associated with thermal, hydro, and chemical effects are coupled to the 3D poroelastoplastic finite element model. The effects of bedding planes are also taken into account in the FEM model through the crack tensor method in which the normal and tangential stiffnesses of the bedding planes have stress dependency. The failure of the formation rock is judged based on the critical plastic strain limit.</p><p>The numerical analysis results indicate that the rock strength anisotropy induced by the existence of bedding planes is the most important factor influencing the stability of the wellbore among various THMC process parameters investigated in this work. The numerical results also reveal that an established theory to orient the wellbore in the direction of the minimum principal stress is not always a favorable option when the effect of the anisotropy of in-situ stresses and the distribution angle of bedding planes cancel out each other. Depending on both the distribution angle of bedding plane and ratio of the vertical to the horizontal stress, the trend of minimum mud pressure showed a great variation as predicted by the yield and failure criterion implemented in the model. Furthermore, the analysis results reveal that the distribution and evolution of plastic strains caused by the THMC processes have the time dependency, which can be controlled by the temperature and salinity of the drilling fluids.</p><p>The numerical wellbore stability analysis model considering shale swelling and bedding plane effects provides an effective tool for designing optimum well trajectories and determining safe mud weight windows for drilling complex shale formations. The time-dependent margins of safe mud weight window of drilling can be fine-tuned when the interaction among various parameters is fully considered as the THMC processes.</p>

Evaluation of High Dissolving-Power Retarded Acid Recipes for Carbonate Acidizing

2021 ◽  
Author(s):  
Norah Aljuryyed ◽  
Abdullah Al Moajil ◽  
Saeed Alghamdi ◽  
Sajjad AlDarweesh
Keyword(s):  
Hydrochloric Acid ◽  
Corrosion Rate ◽  
Carbonate Rock ◽  
Reaction Rate ◽  
Oil And Gas ◽  
Gas Wells ◽  
Low Viscosity ◽  
Oil And Gas Wells ◽  
Carbonate Acidizing ◽  
Acid Retardation

Abstract Development of retarded acid recipes that can have both adequate dissolving power and controllable reaction rate is desired to maximize the effectiveness of matrix stimulation treatments for oil and gas wells. Hydrochloric acid (HCl) has high dissolving power, however, the reaction rate with carbonate rock is uncontrollable and can cause face dissolution. Organic acids have low dissolving power and controllable reaction rate. The objective of this paper was to compare the effectiveness of three low viscosity retarded acid recipes with dissolving powers of 15 wt% and >20 wt% HCl equivalent. The examined acid recipes were 15/28 wt% emulsified acids, retarded acid recipes #1, #2 and #3, and 15/26 wt% HCl. The emulsified acids were at 30:70 ratio of diesel to acid. The retarded acid recipes were prepared at different dissolving power. Retarded acid recipe #3 was equivalent to 15 wt% HCl while retarded acid recipes #1 and #2 were equivalent to >20 wt% HCl. The calcite disc dissolution rate with retarded acids #1 and #2 was significantly lower than 26 wt% HCl and comparable to 15 wt% HCl at 75°F. The solubility of calcite discs in the retarded acid recipe #3 showed acid retardation higher than retarded acid recipes #1 and #2. The corrosion rate of retarded acid recipes #1 and #2 were 0.003-0.015 lb/ft2 at 250°F and 6 hrs, lower than both examined 26-28 wt% HCl and emulsified acids. The pitting indices of retarded acid recipes #1, #2, and #3 were 4, 2, and 1 respectively at 300°F. The pore volumes to breakthrough (PVBT) of retarded acid recipes #1 and #2 were slightly higher than retarded acid recipes #3 at 200°F. The PVBT values for 15 wt% and 28 wt% emulsified acid was comparable to retarded acid recipes #1, #2, and #3, confirming their retardation was effective.

A Methodology to Quantify the Volume-of-investigation in DFIT Design for Shale Gas Wells

2019 ◽  
Author(s):  
Zhiming Chen ◽  
Hongyang Chu ◽  
Xuefeng Tang ◽  
Lingyu Mu ◽  
Peng Dong ◽  
...  
Keyword(s):  
Shale Gas ◽  
Gas Wells
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