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

Geofluids ◽  
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.

scholarly journals Influence of the Weakening Effect of Drilling Fluid on Wellbore Stability in Anisotropic Shale Formation

2021 ◽  
Vol 9 ◽  
Author(s):  
Fan Zhang ◽  
Hou-Bin Liu ◽  
Shuai Cui ◽  
Ying-Feng Meng ◽  
Jia-Jun Wang
Keyword(s):  
Shear Failure ◽  
Drilling Fluid ◽  
Great Influence ◽  
Pressure Rise ◽  
Wellbore Stability ◽  
Distribution Model ◽  
Longmaxi Formation ◽  
Collapse Pressure ◽  
Long Time ◽  
Shale Formation

For horizontal wells in Longmaxi Formation, oil-based drilling fluid that soaks for a long time is more likely to cause a wellbore collapse. Therefore, in this paper, the downhole core method of shale formation, in Longmaxi Formation, was adopted. First, rock samples were selected from different sampling angles and soaked with field drilling fluid. Second, a triaxial mechanics experiment was carried out. Based on the anisotropic wellbore stress distribution model, the stability of shale wellbore was calculated and analyzed. The results show that the compressive strength and cohesion of the shale are reduced after soaking in the drilling fluid. Hence, the reduction range of various sampling angles obviously differs as well. Shear failure occurs in vertical stratification; shear slip failure occurs along the weak plane, showing strong anisotropy. Combined with the experimental results, the collapse pressure is calculated, and it is found that the weakening effect of drilling fluid makes the overall collapse pressure rise by about 0.2 g/cm3. Finally, the shale bedding dip and dip direction have a great influence on the collapse pressure. The lower critical mud weight always takes the minimum value when the borehole axis is perpendicular to the bedding.

The Effects of Anisotropic Transport Coefficients on Pore Pressure in Shale Formations

2015 ◽  
Vol 137 (3) ◽  
Author(s):  
Vahid Dokhani ◽  
Mengjiao Yu ◽  
Stefan Z. Miska ◽  
James Bloys
Keyword(s):  
Pore Pressure ◽  
Fluid Transport ◽  
Drilling Fluid ◽  
Transport Coefficients ◽  
Electrical Potential ◽  
Three Dimensional ◽  
Bedding Plane ◽  
Wellbore Stability ◽  
Coupled Flow ◽  
In Situ Conditions

This study investigates shale–fluid interactions through experimental approaches under simulated in situ conditions to determine the effects of bedding plane orientation on fluid flow through shale. Current wellbore stability models are developed based on isotropic conditions, where fluid transport coefficients are only considered in the radial direction. This paper also presents a novel mathematical method, which takes into account the three-dimensional coupled flow of water and solutes due to hydraulic, chemical, and electrical potential imposed by the drilling fluid and/or the shale formation. Numerical results indicate that the presence of microfissures can change the pore pressure distribution significantly around the wellbore and thus directly affect the mechanical strength of the shale.

Realtime Drilling Geomechanics Aids Safe Drilling through Unstable Shales and Channel Sands of Wara Formations, Minagish Field, West Kuwait

2021 ◽  
Author(s):  
D.. Al Enezi ◽  
M.. AL Hajeri ◽  
S.. Gholum ◽  
S.. Nath ◽  
T.. Ahmad ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Bulk Density ◽  
Drilling Fluid ◽  
Poor Quality ◽  
Wellbore Stability ◽  
Quality Data ◽  
Earth Model ◽  
Empirical Correlations ◽  
Integrity Test ◽  
Pull Out

Abstract As part of any successful development plan of any hydrocarbon field, drilling boreholes safely is a key factor to make the entire process safe, economic and environmentally friendly. One of the main factors that dictates whether a borehole is going to be drilled safely or not is to understand the geomichanical behavior of the different formation to be penetrated. A definition of geomechanics could be stated as the science that studies the relationship between each of; in-situ stresses, rock mechanics, and the drilling fluid properties. In Kuwait and during the course of efforts to develop Wara channel sands in Minagish Field to the west of the country, Kuwait Oil Company (KOC) realized that continuing to drill development wells using conventional drilling practices is not any more an easy task. Considerable non-productive time has been recorded due encountering events such as shale carvings and pack off leading to stuck pipe. In addition, partial to total lost circulation were faced while drilling through Mutriba Formation which added to the complexity of problem. This study involved gathering data from offset wells to build a mechanical earth model for the area where the new well is going to be drilled. The main objective of having the model built is to perform wellbore stability analysis (WBS) and compute the quantitative mud window values to insure stable and safe borehole drilling. As the case of any study, performing reliable WBS analysis requires accurate modeling of earth stresses and rock mechanical properties. This process is primarily based on sonic logs (compressional and shear slowness), formation bulk density and lithology distribution. The study started with an audit of the available data sets in the region to select the best offset wells and generating empirical correlations to fill- up any missing and/or poor-quality data zones. Initially,7offset wells were identified, based on the geological distribution and data availability.Out of them, only four wells were found to have compressional slowness and three with bulk density measurements. However, it is worth mentioning that no shear slowness measurements were available in any of the offset wells in the region. Due to this, a correlation based compressional-shear relationship from nearby wells was proposed for the pre-drill study. The mechanical properties were characterized using the tri-axial core test results available from Wara and Burgan Formations. Empirical correlations were developed to obtain static mechanical properties from the dynamical mechanical ones and log responses. In addition, horizontal stresses in the region were constrained with formation integrity test data to have better control on the model. Finally, after the WBS model was built,it was compared to the available caliper data from the offset wells for calibration purposes. The resulted pre-drill geomechanics model was used to advise on the drilling parameters (mud weight) to be used in drilling the new development well. Moreover, and being the first realtime drilling geomechanics (RTDG) job in in Kuwait, an LWD sonic was used while drilling to supply the pre-drill model with realtime compressional and shear slowness measurements. Having the model updated in realtime with data from the formation at the borehole location resulted in optimizing the mud weight window limits by the geomechanics engineers as the well was being drilled. Following these mud weight recommendations based on the updated pre-drill model resulted in a smooth landing and horizontal sections in which all the wiper trips until the final pull out of hole were smooth.

Borehole Stability Analysis and its Application in Xujiahe Formation of ZJ Block

2012 ◽  
Vol 524-527 ◽  
pp. 1359-1362
Author(s):  
Kan Hua Su ◽  
Hong Liu ◽  
Jun Wang
Keyword(s):  
Mechanical Test ◽  
Drilling Fluid ◽  
Stress Test ◽  
Field Application ◽  
Wellbore Stability ◽  
Test Method ◽  
Borehole Stability ◽  
Xujiahe Formation ◽  
Ground Stress ◽  
Rock Mechanical Test

The mainly borehole problems are sticking (collapse) and circulation loss in Xujiahe formation of ZJ block, so the drilling rate is very low. In order to improve the penetration of rate of ZJ block, the rock mechanical test method, ground stress test method, well history statistics method, and logging data analysis method were adopted. The borehole stability mechanism of xujiahe formation was analyzed. Combined with the drilling fluid experimental evaluation, the measures of improve wellbore stability of xujiahe formation was Proposed. Field application tests show that, the borehole problems and its processing time are greatly reduced using those proposed measures. The penetration of rate in the Xujiahe formation of test well increased 20-30%, and the application effect is obvious.

scholarly journals Experimental studies of the cone index mechanical properties of weak peatland soils

2018 ◽  
Vol 7 (4) ◽  
pp. 167-174
Author(s):  
М. Дмитриева ◽  
M. Dmitrieva ◽  
Игорь Григорьев ◽  
Igor Grigorev ◽  
В. Лухминский ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Internal Friction ◽  
Shear Modulus ◽  
Physical And Mechanical Properties ◽  
Weak Soil ◽  
Angle Of Internal Friction ◽  
Satisfactory Accuracy ◽  
Modulus Of Deformation ◽  
Cone Index

The aim of the research, the results of which are set forth in this article, is to supplement the scientific description of the properties of the weakly bearing swampy surfaces of forest machinery movement. In the course of the experiments, the following tasks were set: to reveal the interrelationships of the physical and mechanical properties of weak soil; to test the possibility of expressing the specific cohesion, the angle of internal friction and the shear modulus through its modulus of deformation; to investigate the relationship between the cone index and physical and mechanical properties of weak soil. The experiments were carried out on the territory, leased by the LLC "Kupechesky Dom" (Pskov) in summer and autumn of 2016. To determine the angle of internal friction, specific adhesion, modulus of de-formation, shear modulus and cone index, methods that were regulated by the relevant standards were used. The article presents the main statistical data on the properties of samples of weak soil and information on the correlation of values of properties of weak ground. Based on the results of the study, close bonds of specific adhesion, the angle of internal friction, shear modulus and cone index with the modulus of deformation of weak soil were revealed. Based on the results of experimental data processing and values of the coefficients of determination of the formulas obtained for the properties of weak soil, it was confirmed that the values of specific adhesion, angle of internal friction, shear modulus and cone index are in practice expressed in terms of the deformation modulus with satisfactory accuracy. The calculated values of the conic index are compared with the previously known theoretical formulas and the experimental values measured during the experiments. It is shown that the results of the comparison make it possible to insist on the satisfactory accuracy of the theoretical approach to the determination of cone index of weakly bearing soil.

Mechanical properties of North Sea Tertiary mudrocks: investigations by triaxial testing of side-wall cores

Clay Minerals ◽  
1998 ◽  
Vol 33 (1) ◽  
pp. 171-183 ◽  
Author(s):  
L. Wensaas ◽  
P. Aagaard ◽  
T. Berre ◽  
E. Roaldset
Keyword(s):  
Mechanical Properties ◽  
North Sea ◽  
Drilling Fluid ◽  
Side Wall ◽  
Failure Criteria ◽  
Strength Properties ◽  
Wellbore Stability ◽  
Core Material ◽  
Elastic Behaviour ◽  
Triaxial Tests

AbstractIn the North Sea Tertiary section, wellbore instability problems are frequently reported in Palaeocene-Early Oligocene smectite-rich mudrocks. Analysis of the mechanical properties of these Tertiary mudrocks is generally hampered by the lack of suitable core material. This study represents an attempt to study the geomechanical behaviour of mudrocks by triaxial tests of side-wall cores obtained from the borehole wall. The tests performed include measuring the changes in pore pressure during shearing and undrained shear strength in specimens initially consolidated to in situ effective stress levels. The coefficients of permeability (kf), estimated from the consolidation time behaviour range from 2.6 x 10-11 to 2.4 x 10-12 m/s. The tested cores behaved like slightly overconsolidated to normally consolidated materials with an initial near constant volume (elastic behaviour) for low deviatoric load followed by an increasingly contractant behaviour approaching failure. Compared with results from onshore analogues, the strength properties of the investigated mudrocks appear to be related to their content of expandable clay minerals. A wellbore stability chart to forecast adequate drilling fluid pressures for future wells has been developed by the use of linear (Mohr-Coulomb) failure criteria based on the peak strength data. It is demonstrated that side-walt cores can provide satisfactory test materials for rock mechanical analysis, and their use may serve to improve our knowledge of the rock mechanical behaviour of typically troublesome mudrocks for which no conventional cores are available.

scholarly journals Mechanical properties of potato starch modified by moisture content and addition of lubricant

2014 ◽  
Vol 28 (4) ◽  
pp. 501-509 ◽  
Author(s):  
Mateusz Stasiak ◽  
Marek Molenda ◽  
Józef Horabik ◽  
Peter Mueller ◽  
Ireneusz Opaliński
Keyword(s):  
Mechanical Properties ◽  
Internal Friction ◽  
Moisture Content ◽  
Bulk Density ◽  
Modulus Of Elasticity ◽  
Potato Starch ◽  
Magnesium Stearate ◽  
Wall Friction ◽  
Considerable Influence ◽  
Angle Of Internal Friction

Abstract Laboratory testing was conducted to deliver a set of characteristics of structure and mechanical properties of pure starch and starch with an addition of a lubricant - magnesium stearate. Considerable influence of moisture content of potato starch was found in the case of density, parameters of internal friction, coefficients of wall friction and flowability. Elasticity was found to be strongly influenced by water content of the material. Addition of magnesium stearate affected density and parameters of flowability, internal friction and elasticity. Bulk density increased from 604 to 774 kg m-3 with decrease in moisture content of potato starch from 17 to for 6%. Addition of magnesium stearate resulted in approximately 10% decrease in bulk density. Angle of internal friction obtained for 10 kPa of consolidation stress decreased from 33 to 24º with increase in moisture content, and to approximately 22º with addition of the lubricant. With an increase of moisture content from 6 to 18% and with addition of the lubricant, the modulus of elasticity during loading decreased from approximately 1.0 to 0.1 MPa. Modulus of elasticity during unloading was found in the range from 19 to 42 MPa and increased with increase of moisture content and amount of lubricant.

Study of the Effect of Borehole Size on Wellbore Stability

2014 ◽  
Vol 574 ◽  
pp. 214-218
Author(s):  
Hao Yong Huang ◽  
Yuan Fang Cheng ◽  
Wei Zhao ◽  
Chong Cheng ◽  
Wen Biao Deng
Keyword(s):  
Drilling Fluid ◽  
Wellbore Stability ◽  
Borehole Diameter ◽  
Analysis Model ◽  
Borehole Stability ◽  
Collapse Pressure ◽  
Drilling Technology ◽  
Ground Stress ◽  
The One ◽  
Borehole Size

Based on the size effect of rock strength, the borehole stability analysis model is established, which the borehole size is taken into consideration. Through this model, the relation between borehole size and collapse pressure under borehole pressure, ground stress and drilling fluid flow function is analyzed. The analysis shows that with the increase of borehole diameter, collapse pressure increases significantly, and borehole stability becomes poor, but the variation of borehole size is not proportional to collapse pressure: the bigger the borehole, the smaller the variation. When borehole diameter increases from 152.4 mm to 444.5 mm, wellbore collapse pressure increases from 1.18g/cm3 to 1.315g/cm3 and the rate of the increase is 11.44%. When slimhole drilling technology is applied, the density of minimum fluid that maintains wellbore stability is lower than the one used in conventional wellbore drilling.

scholarly journals Coffee grounds as a soil conditioner: Effects on physical and mechanical properties – II. Effects on mechanical properties

2019 ◽  
Vol 52 (2) ◽  
pp. 277
Author(s):  
M-Naguib A. Bedaiwy ◽  
Yasmine S. Abdel Maksoud ◽  
Ahmed F. Saad
Keyword(s):  
Mechanical Properties ◽  
Internal Friction ◽  
Initial Stress ◽  
Calcareous Soil ◽  
Seedling Emergence ◽  
Physical And Mechanical Properties ◽  
Clayey Soils ◽  
Angle Of Internal Friction ◽  
Coffee Grounds ◽  
Resistance To Penetration

<p>Applying coffee grounds (CG) to sandy, calcareous, and clayey soils resulted in notable effects on soil expansion, cracking, cohesion, internal friction, initial stress and resistance to penetration. In sand, expansion upon saturation was greater after wetting-and-drying cycles. Highest increases were 15.71%, 16.14% and 31.86% for sandy, calcareous and clayey soils, respectively. Effect of CG on cracking was negligible in sand and very slight (&lt;1.0%) in the calcareous soil but marked in clay (14.18% at 10% CG). In sand, cohesion (c) increased significantly with CG up to the 10% content. Cohesion increased by 2.5-folds and 4.5-folds at 5% and 10% CG, respectively. The presence of fine CG grains among larger sand particles, boosted microbial activities, and the resulting cementing and binding effects resulted in increased cohesion. For calcareous soil, cohesion rose from 0.04 kg∙cm-2 to 0.13 kg∙cm-2 as CG increased from 0% to 15%. In clay, maximum cohesion (0.20 kg∙cm-2) was associated with the 10% CG and was highest of all soils. In sand, the angle of internal friction (φ) decreased notably as CG increased from 5% to 10% but there was no consistent pattern in any of the soils. An increase in initial stress (pi) was observed between 0% and 10% CG in sand and between 0% and 15% in calcareous soil while clay showed no particular trend. Patterns of pi were, thus, consistent with those of cohesion for all soils. Resistance to penetration increased substantially with CG in sand. The effect in calcareous and clayey soils took an opposite trend to that of sand and resistance was generally higher in calcareous soil. Overall effects of CG on resistance were desirable in all soils as far as agriculture (seedling emergence, crop growth, irrigation, etc.) is concerned.</p>

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