Study on the Seepage Force-Induced Stress and Poroelastic Stress by Flow Through Porous Media Around a Vertical Wellbore

2021 ◽  
Author(s):  
Haiyang Wang ◽  
Desheng Zhou ◽  
Qian Gao ◽  
Xin Fan ◽  
Jinze Xu ◽  
...  
Keyword(s):  
Fluid Flows ◽  
Fracture Initiation ◽  
Surface Force ◽  
Wellbore Stability ◽  
Tensile Failure ◽  
Seepage Force ◽  
Breakdown Pressure ◽  
Induced Stress ◽  
Lower Permeability ◽  
Rock Skeleton

Fluid flowing through reservoir pores not only generates poroelastic stress but also exerts seepage force on rock skeleton. However, the mechanism of seepage force is not clear. Traditional methods of analyzing wellbore stability and hydraulic fracture initiation are mainly focused on the poroelastic stress without the effects of seepage force. Based on the linear elasticity and consolidation theory, this paper analyzed the mechanism of seepage force and poroelastic stress, and presented an analytical solution for seepage force-induced stress around a vertical wellbore. It also introduced how to calculate poroelastic stress by exerting hypothetical body force and surface force. Through comparison and superposition of stress fields, this paper studied the change characteristics of the poroelastic and seepage force-induced stress under different borehole pressures and the effects of seepage force on the wellbore tensile failure. Numerical simulation results show that when fluid flows through the rock, using traditional models without considering, the effect of seepage force to calculate the borehole pressure-induced stress will result in lower calculation results. Compared with the traditional model, seepage force-induced circumferential tensile stress is larger, and the seepage force significantly reduces the formation breakdown pressure. Rocks near the borehole wall with lower permeability and larger Poisson’s ratio have a greater action of seepage force. When fluid flows through the reservoir, the effects of seepage forces cannot be ignored in the analysis of hydraulic fracturing and wellbore stability.

scholarly journals Effect of Seepage Force on the Wellbore Breakdown of a Vertical Wellbore

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Desheng Zhou ◽  
Haiyang Wang ◽  
Yafei Liu ◽  
Shun Liu ◽  
Xianlin Ma ◽  
...  
Keyword(s):  
Hydraulic Fracturing ◽  
Fluid Flows ◽  
Seepage Force ◽  
Breakdown Pressure ◽  
Principal Stresses ◽  
Rock Permeability ◽  
Linear Elasticity Theory ◽  
Reservoir Permeability ◽  
The Matrix ◽  
The Media

As a fluid flows through a porous media, a drag force, called seepage force in the paper, will be formed on the matrix of the media in the fluid flowing direction. However, the seepage force is normally ignored in the analysis of wellbore fracturing during hydraulic fracturing operation. In this paper, an analytical model for seepage force around a vertical wellbore is presented based on linear elasticity theory, and the effect of the seepage force on wellbore breakdown has been analyzed. Also studied are the effects of the two horizontal principal stresses and the reservoir permeability on the action of seepage force. The paper proves that seepage force lowers formation breakdown pressure of a vertical wellbores; the deeper a formation is, the greater action of the seepage force; seepage force contributes more to breakdown formation with small difference of the two horizontal stresses such as unconventional reservoirs; seepage force increases as rock permeability decreases, and it should not be ignored in hydraulic fracturing analysis, especially for low-permeability formation.

Wellbore Geomechanics of Extended Drilling Margin and Engineered Lost-Circulation Solutions

SPE Journal ◽  
2017 ◽  
Vol 22 (04) ◽  
pp. 1178-1188 ◽  
Author(s):  
Amin Mehrabian ◽  
Younane Abousleiman
Keyword(s):  
Mechanical Properties ◽  
Stability Analysis ◽  
Analytical Approach ◽  
Wellbore Stability ◽  
Tensile Failure ◽  
Mechanical Interaction ◽  
Lost Circulation ◽  
Drilling Operations ◽  
Secondary Fractures ◽  
Lost Circulation Materials

Summary Wellbore tensile failure is a known consequence of drilling with excessive mud weight, which can cause costly events of lost circulation. Despite the successful use of lost-circulation materials (LCMs) in treating lost-circulation events of the drilling operations, extensions of wellbore-stability models to the case of a fractured and LCM-treated wellbore have not been published. This paper presents an extension of the conventional wellbore-stability analysis to such circumstances. The proposed wellbore geomechanics solution revisits the criteria for breakdown of a fractured wellbore to identify an extended margin for the equivalent circulation density (ECD) of drilling. An analytical approach is taken to solve for the related multiscale and nonlinear problem of the three-way mechanical interaction between the wellbore, fracture wings, and LCM aggregate. The criteria for unstable propagation of existing near-wellbore fractures, together with those for initiating secondary fractures from the wellbore, are obtained. Results suggest that, in many circumstances, the occurrence of both incidents can be prevented, if the LCM blend is properly engineered to recover certain depositional and mechanical properties at downhole conditions. Under such optimal design conditions, the maximum ECD to which the breakdown limit of a permeable formation could be enhanced is predicted.

A Novel Method and its Application to Define Maximum Horizontal Stress and Stress Path

2021 ◽  
Author(s):  
Jianguo Zhang ◽  
Karthik Mahadev ◽  
Stephen Edwards ◽  
Alan Rodgerson
Keyword(s):  
Fracture Initiation ◽  
Stress Path ◽  
Horizontal Stress ◽  
Geomechanical Model ◽  
Breakdown Pressure ◽  
In Situ Stresses ◽  
Fracture Closure ◽  
Minimum Horizontal Stress ◽  
Maximum Horizontal Stress

Abstract Maximum horizontal stress (SH) and stress path (change of SH and minimum horizontal stress with depletion) are the two most difficult parameters to define for an oilfield geomechanical model. Understanding these in-situ stresses is critical to the success of operations and development, especially when production is underway, and the reservoir depletion begins. This paper introduces a method to define them through the analysis of actual minifrac data. Field examples of applications on minifrac failure analysis and operational pressure prediction are also presented. It is commonly accepted that one of the best methods to determine the minimum horizontal stress (Sh) is the use of pressure fall-off analysis of a minifrac test. Unlike Sh, the magnitude of SH cannot be measured directly. Instead it is back calculated by using fracture initiation pressure (FIP) and Sh derived from minifrac data. After non-depleted Sh and SH are defined, their apparent Poisson's Ratios (APR) are calculated using the Eaton equation. These APRs define Sh and SH in virgin sand to encapsulate all other factors that influence in-situ stresses such as tectonic, thermal, osmotic and poro-elastic effects. These values can then be used to estimate stress path through interpretation of additional minifrac data derived from a depleted sand. A geomechanical model is developed based on APRs and stress paths to predict minifrac operation pressures. Three cases are included to show that the margin of error for FIP and fracture closure pressure (FCP) is less than 2%, fracture breakdown pressure (FBP) less than 4%. Two field cases in deep-water wells in the Gulf of Mexico show that the reduction of SH with depletion is lower than that for Sh.

Calculation and Implications of Breakdown Pressures in Directional Wellbore Stimulation

2015 ◽  
Author(s):  
Robert D. Barree ◽  
Jennifer L. Miskimins
Keyword(s):  
Shear Failure ◽  
Growth Parameters ◽  
Vertical Plane ◽  
Longitudinal Direction ◽  
In Situ Stress ◽  
Tensile Failure ◽  
Petroleum Engineering ◽  
Breakdown Pressure ◽  
Cascading Effects ◽  
Wellbore Pressure

Abstract In 1898, Kirsch published equations describing the elastic stresses around a circular hole that are still used today in wellbore pressure breakdown calculations. These equations are standard instruments used in multiple areas of petroleum engineering, however, the original equations were developed strictly for vertical well settings. In today's common directional or horizontal well situations, the equations need adjusted for both deviation from the vertical plane and orientation to the maximum and minimum horizontal in-situ stress anisotropy. This paper provides the mathematical development of these modified breakdown equations, along with examples of the implications in varying strike-slip and pore pressure settings. These examples show conditions where it is not unusual for breakdown pressure gradients to exceed 1.0 psi/ft and describes why certain stages in "porpoising" horizontal wells experience extreme breakdown issues during hydraulic fracturing treatments. The paper also discusses how, in most directional situations, the wellbore will almost always fail initially in a longitudinal direction at the borehole wall, after which the far-field stresses will take over and transverse components can be developed. Tortuosity and near wellbore friction pressure can actually add to forcing the initiation of such longitudinal fractures, which can then have cascading effects on other growth parameters such as cluster-to-cluster and stage-to-stage stress shadowing. Special considerations for highly laminated anisotropic formations, where shear failure of the wellbore may precede or preclude tensile failure, are also introduced. Such failure behaviors have significant implications on near wellbore conductivity requirements and can also greatly impact well production and recovery efforts.

Influence of Oriented Perforation Design on Refracture Reorientation: Simulation and Experiment

2018 ◽  
Vol 140 (8) ◽  
Author(s):  
Minhui Qi ◽  
Mingzhong Li ◽  
Tiankui Guo ◽  
Chunting Liu ◽  
Song Gao ◽  
...  
Keyword(s):  
Hydraulic Fracturing ◽  
Large Scale ◽  
Simulation Models ◽  
Fracture Initiation ◽  
Simulation Method ◽  
Induced Stress ◽  
Study Results ◽  
Simulation Results ◽  
Fracturing Experiments ◽  
The Impact

The oriented perforating is the essential technique to guide the refracture reorientation, but the influence of the oriented perforation design on the refracture steering radius is still unclear. In this paper, the factors influencing the refracture reorientation were studied by simulation models and experiments. The effects of initial fracture, well production, and perforations on the refracture initiation and propagation were analyzed. Three-dimensional finite element models were conducted to quantify the impact of perforation depth, density, and azimuth on the refracture. The large-scale three-axis hydraulic fracturing experiments guided by oriented perforations were also carried out to verify the fracture initiation position and propagation pattern of the simulation results. The research results showed that perforations change the near-wellbore induced stress distribution, thus changing the steering radius of the refracture. According to the simulation results, the oriented perforation design has a significant influence on the perforation guidance effect and refracture characteristics. Five hydraulic fracturing experiments proved the influence of perforating parameters on fracture initiation and morphology, which have a right consistency between the simulation results. This paper presents a numerical simulation method for evaluating the influence of the refracture reorientation characteristics under the consideration of multiple prerefracturing induced-stress and put forward the oriented perforation field design suggestions according to the study results.

Uncertainty Evaluation of Wellbore Stability Using Comparative Rock Strength Criterions

2020 ◽  
Author(s):  
Rasool Khosravanian ◽  
Bernt Sigve Aadnøy
Keyword(s):  
Sensitivity Analysis ◽  
Wellbore Stability ◽  
Tensile Failure ◽  
Rock Properties ◽  
Uncertainty Evaluation ◽  
Fluid Loss ◽  
Real Problem ◽  
Wellbore Integrity ◽  
Drilling Operation ◽  
Geomechanical Analysis

Abstract The requirement of uncertainty analysis has shifted the transformation of sensitivity analysis from the deterministic area to the stochastic area.Geomechanical wellbore integrity problems during drilling operation can occur due to wellbore shear failure or tensile failure. To guarantee wellbore integrity, breakout and fracture geomechanical analysis is essential to estimate the Safe Mud Weight Window (SMWW). Wellbore stability problems causes many challenges in a drilling operation, such as pipe sticking, wellbore collapse, fluid loss and poor cement jobs. A drilling engineer must minimize the risk of these problems, however, there is a considerable uncertainty of different parameters such as geomechanical rock properties of drilled formation, and, data and parameters gathering are often incomplete. This uncertainty of main parameters have impact on the resulting SMWW.This paper perform an uncertainty evaluation of wellbore stability and its effect on the optimum interval of SMWW. The SMWW Uncertainty Evaluation of Wellbore Stability assessment for two failure criteria are compared, Mohr-Coulomb and Modified Lade criterion. We apply Monte Carlo simulations to investigate the uncertainty of the models and we do a sensitivity analysis and confidence level analysis. The paper will show the advantage of including uncertainty evaluation when determining the optimum SMWW window, as opposed to classical deterministic analysis. A case study is presented to draw a perfect understanding of the foundation of the MCS approach with practical and good results. It confirmed the capability of the proposed approach in solving such a strong-nonlinear, complex real problem.

Time-Dependent Initiation of Multiple Hydraulic Fractures in a Formation With Varying Stresses and Strength

SPE Journal ◽  
2015 ◽  
Vol 20 (06) ◽  
pp. 1317-1325 ◽  
Author(s):  
Andrew P. Bunger ◽  
Guanyi Lu
Keyword(s):  
Tensile Strength ◽  
Hydraulic Fracture ◽  
Fracture Initiation ◽  
Time Frame ◽  
Hydraulic Fractures ◽  
Static Fatigue ◽  
Breakdown Pressure ◽  
Initiation Point ◽  
Delayed Failure ◽  
Wellbore Pressure

Summary The premise of classical hydraulic-fracture-breakdown models is that hydraulic-fracture growth can only start when the wellbore pressure reaches a critical value that is sufficient to overcome the tensile strength of the rock. However, rocks are well-known to exhibit static fatigue; that is, delayed failure at stresses less than the tensile strength. In this paper, we explore the consequences of delayed failure on axially oriented initiation of multiple hydraulic fractures. Specifically, given a certain breakdown pressure, we investigate the conditions under which subsequent hydraulic fracture(s) can begin within the time frame of a stimulation treatment in regions of higher stress and/or strength because of delayed-failure mechanisms. The results show that wells completed in shallower formations are more sensitive to variations in strength, whereas wells completed in deeper formations are more sensitive to variations in stress. Furthermore, cases in which all hydraulic fractures break down according to the same pressurization regime—that is, all are “fast” (nonfluid-penetrating) pressurization or else all are “slow” (uniformly pressurized fluid-penetrating) pressurization cases—are highly sensitive to small stress/strength variability. On the other hand, if the first hydraulic-fracture initiation is in the “fast”-pressurization regime and subsequent fracture(s) are in the “slow”-pressurization regime, then the system is robust to a much-higher degree of variability in stress/strength. Practically, this work implies that methods aimed at moderately reducing the variability in stress/strength among the possible initiation points (i.e., perforation clusters) within a particular stage can have a strong effect on whether multiple hydraulic fractures will begin. In addition, this analysis implies that pumping strategies that encourage “fast,” nonpenetrative breakdown of the first initiation point followed by the opportunity for fluid-penetrating, “slow” breakdown of subsequent initiation points could be effective at encouraging multiple-hydraulic-fracture initiation.

RESERVOIR GEOMECHANICS APPLIED TO DRILLING AND COMPLETION PROGRAMS IN CHALLENGING FORMATIONS: NORTHWEST SHELF, TIMOR SEA, NORTH SEA AND COLOMBIA

2000 ◽  
Vol 40 (1) ◽  
pp. 507
Author(s):  
D.A. Castillo ◽  
D. Moos
Keyword(s):  
Stress Field ◽  
North Sea ◽  
Sedimentary Basins ◽  
Wellbore Stability ◽  
Tensile Failure ◽  
Drilling Process ◽  
Natural Fractures ◽  
Fracture Permeability ◽  
Lost Circulation ◽  
Timor Sea

It has become increasingly clear to the oil and gas community that earth stresses at depth in sedimentary basins have a profound effect on wellbore stability. Drilling problems frequently occur due to severe mechanical instabilities at the borehole wall where stress amplification has exceeded the strength of the rock. This is because the rock surrounding the hole must support the stress previously supported by the material removed in the drilling process. Drilling problems associated with lost circulation often occur where the borehole has intersected critically-stressed natural fractures that are inherently prone to high fracture permeability. In order to design a drilling and completion program that eliminates or minimises these mechanical instabilities in the borehole, it is essential to understand the interaction between the stress field, pore pressure, natural fractures, rock strength, mud weight, and borehole trajectory.In some cases wellbore performance can be maximised by selecting an optimal trajectory through the reservoir that can be drilled near balanced or under-balanced to minimise the formation damaging effects of mud infiltration, while other trajectories may require more aggressive drilling parameters. In these situations a well-constrained stress field is essential for determining the appropriate mud window to control compressive failure leading to the development of wellbore breakouts and, at the same time, prevent catastrophic tensile failure leading to formation breakdown or fluid losses through natural fractures.This paper serves to illustrate how a well-constrained geomechanical model can be used to address a suite of drilling and completion problems. Case studies reviewed include; wellbore stability and completion practices in extended reach wells (North West Shelf), wellbore stability in vertical and deviated wells (North Sea); drilling and completions in complex geological environments associated with steeply-dipping bedded shales (Colombia), and lost circulation in highly fractured regions (Timor Sea).

A Semianalytical Modeling Approach for Hydraulic Fracture Initiation and Orientation from Perforated Wells

2021 ◽  
pp. 1-15
Author(s):  
Andreas Michael ◽  
Ipsita Gupta
Keyword(s):  
Tensile Strength ◽  
Closed Form ◽  
Hydraulic Fracture ◽  
Fracture Initiation ◽  
Barnett Shale ◽  
Transverse Fracture ◽  
Breakdown Pressure ◽  
Analytical Approximations ◽  
Wellbore Pressure

Summary Accurate prediction of fracture initiation pressure and orientation is paramount to the design of a hydraulic fracture stimulation treatment and is a major factor in the treatment's eventual success. In this study, closed-form analytical approximations of the fracturing stresses are used to develop orientation criteria for relative-to-the-wellbore (longitudinal or transverse) fracture initiation from perforated wells. These criteria were assessed numerically and found to overestimate the occurrence of transverse fracture initiation, which only takes place under a narrow range of conditions in which the tensile strength of the rock formation is lower than a critical value, and the breakdown pressure falls within a “window.” For a case study performed on the Barnett Shale, transverse fracture initiation is shown to take place for breakdown pressures below 4,762 psi, provided that the formation's tensile strength is below 2,482 psi. A robust 3D finite volume numerical model is used to evaluate solutions for the longitudinal and transverse fracturing stresses for a variable wellbore pressure, hence developing correction factors for the existing closed-form approximations. Geomechanical inputs from the Barnett Shale are considered for a horizontal well aligned parallel to the direction of the least compressive horizontal principal stress. The corrected numerically derived expressions can predict initiation pressures for a specific orientation of fracture initiation. Similarly, at known breakdown pressures, the corrected expressions are used to predict the orientation of fracture initiation. Besides wellbore trajectory, the results depend on the perforation direction. For the Barnett Shale case study, which is under a normal faulting stress regime, the perforations on the side of the borehole yield a wider breakdown pressure window by 71% and higher critical tensile strength by 32.5%, compared to perforations on top of the borehole, implying better promotion of transverse fracture initiation. Leakage of fracturing fluid around the wellbore, between the cemented casing and the surrounding rock, reduces the breakdown pressure window by 11% and the critical tensile strength by 65%. Dimensionless plots are employed to present the range of in-situ stress states in which longitudinal or transverse hydraulic fracture initiation is promoted. This is useful for completion engineers; when targeting low permeability formations such as shale reservoirs, multiple transverse fractures must be induced from the horizontal wells, as opposed to longitudinal fracture initiation, which is desired in higher permeability reservoirs or “frac-and-pack” operations.

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