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Rock mechanical property testing for petroleum geomechanical engineering applications
Published in Xia-Ting Feng, Rock Mechanics and Engineering, 2017
The lowest well pressure, or mud weight, required to drill a section of a well is one that exceeds the formation pore pressures (overbalanced drilling) and minimizes compressive failure. The largest recommended mud weight avoids tensile hydraulic fracturing of the wellbore wall or fracture propagation away from the wellbore, against the far-field minimum stress. These upper and lower mud weights define the useable wellbore pressures or ‘mud weight window’.
Numerical modelling of wellbore instability: a review
Published in Wang Yuehan, Ge Shirong, Guo Guangli, Mining Science and Technology, 2004
Guangquan Xu, Hai-Sui Yu, David J. Reddish
During drilling, the wellbore is temporarily supported by the drilling mud pressure. Mud weight is to keep the pressure which it provides slightly above the formation pore pressure to prevent kicks and blow outs. On the other hand, high mud pressure may cause differential pressure sticking problems and can create large washouts in fractured rocks. In general, the safe mud weight window is narrowed and it needs to be determined by accurate models.
Measuring stiffness of soils in situ
Published in Fusao Oka, Akira Murakami, Ryosuke Uzuoka, Sayuri Kimoto, Computer Methods and Recent Advances in Geomechanics, 2014
Fusao Oka, Akira Murakami, Ryosuke Uzuoka, Sayuri Kimoto
Borehole instability during drilling can cause millions of dollars lost. It is one of the most studied topics of petroleum geomechanics (Fjaer et al. 2008). In drilling, as the rock is removed, the stresses that were originally supported by the intact rock are now re-distributed to the rock formation surrounding the borehole. As a result, near wellbore rock formation experiences changes in tension, compression, and shear loadings. Chemical reactions also occur with exposure to the drilling fluid and may further destabilize the borehole (Heidug and Wong 1996). Under these conditions, the rock surrounding the wellbore may deform, fracture, and cave into the wellbore. Borehole collapse refers to the situation when the total volume of cuttings and failed material in the hole cannot be effectively cleaned out by drilling mud circulation. This type of failure is due to compressive shearing of rock. Increasing drilling fluid pressure by increasing fluid density (also known as mud weight) can mitigate against borehole collapse. This is achieved by reducing the compressive stress concentration or hoop stress as the drilling fluid pressure is increased. The lowest drilling fluid pressure needed to prevent the wellbore collapse is called the lower limit mud pressure to prevent collapse, or simply the collapse pressure. As the drilling fluid pressure increases, the hoop stress on the borehole wall becomes more tensile until it reaches the upper limit where inadvertent hydraulic fracturing of the near wellbore rock formation can occur. This is potentially a serious drilling problem which could lead to the loss of well control and the well itself. The pressure at which this unstable on-set of fracture propagation is often called the breakdown pressure. When the collapse pressure is lower than the breakdown pressure, a stable borehole drilling mud weight/pressure window can be defined. Both the lower and upper limits of mud pressure can be estimated by linear elastic theory and an appropriate failure criterion (e.g., Huang et al. 2012). This provides a rather conservative estimate of collapse pressure. For many field conditions, this approach often suggests that it is not possible to have a feasible drilling mud weight window, which is not supported from experience. Wong et al. 1993 proposed a lower collapse pressure based on elasto-plastic theory and finite element method (FEM). In that approach, near wellbore rock failure is not synonymous with borehole failure. As mud pressure increases, the maximum principal stress (i.e. the radial stress) is becoming more compressive and the other two principal stresses become less compressive. If the rock shear strength is low, it is very well possible that the near wellbore stress condition reaches yield or shear failure condition before the least principal stress becomes tensile. In other words, the borehole may experience 'failure' at a drilling fluid pressure just lower than the upper limit breakdown pressure, which means a stricter upper limit should be imposed. This paper shows in details an example when shear failure occurs before tensile failure at high drilling fluid pressure.
A multi-objective optimisation algorithm for a drilling trajectory constrained to wellbore stability
Published in International Journal of Systems Science, 2022
Wendi Huang, Min Wu, Jie Hu, Luefeng Chen, Chengda Lu, Xin Chen, Weihua Cao
As for constraint conditions, we mainly consider the wellbore stability (indicated by mud weight) to reduce the risk of accidents. During the drilling process, the original stress balance of the formation will be destroyed. Therefore, suitable mud weight is crucial to avoid wellbore instability. When the mud weight is too low, a collapse will occur due to a shear failure; when the mud weight is too high, a wellbore fracture will occur due to a tension failure. For the same formation conditions, the ultimate pressures for shear or tension failure depend on drilling directions. Therefore, considering the mud weight constraints in drilling trajectory design is beneficial to reduce the risk of accidents.
Determination of drilling mud weight using deep learning techniques
Published in Petroleum Science and Technology, 2023
Aref Khazaei, Reza Radfar, Abbas Toloie Eshlaghy
The wellbore stability is one of the most important issues during the drilling operation. Instability of wellbore can lead to interrupt the drilling operation and waste time and money (Zeynali 2012). Two main problems that may occur for the stability of the wellbore are: 1- break-out; 2- fracture. In the drilling industry, the drilling mud is used to keep up the stability of the wellbore; and the mud weight is an important and controllable factor to take care of the hydrostatic pressure and stability of the well (Barton, Zoback, and Burns 1988).
Chemical and mechanical model to analysis wellbore stability
Published in Petroleum Science and Technology, 2023
The wellbore instability is the biggest challenge impacting the petroleum industry operations, especially in production and drilling (Allawi and Al-Jawad 2021, 2022a). Especially when Water-based drilling mud is used because it is associated with many drilling problems, it loses its properties with high pressure and high temperature in certain circumstances (Gao et al. 2021; Hakim et al. 2018; Heshamudin et al. 2019; Katende et al. 2019; Majid et al. 2019; Majidi et al. 2008; Wise et al. 2022; Yeu et al. 2019; Yi et al. 2017) . The instability problem is considered a significant drilling problem because it caused costs over 500–1,000 million dollars each year in the oil industry (Liu et al. 2021; Mansourizadeh et al. 2016). It is reported that the shale represents more than 75% of all formations, which causes 90% of wellbore stability problems. Moreover, the drilling fluid will be in non-reactive soft form and implying within the hydrated cement matrix, which leads to lousy cement (R. Ahmed, Salehi, and Srivastava 2022; De Andrade and Sangesland 2016; Didier, Radonjic, and Du 2018; Duguid, Radonjic, and Scherer 2011; Jimenez, Darbe, and Pang 2019; Katende et al. 2020; Massion et al. 2022; Mayibeki et al. 2021; Ritchie et al. 2019; Vissa and Radonjic 2020; Wu, Salehi, and Khalifeh 2022). Failure mechanisms can be divided into breakout and tensile failures detected in a borehole (B. Aadnoy and Looyeh 2019). Using light mud weight (less than breakout pressure) can cause shear failure and cause fluid flow into the well because of the dominant compression condition. Using heavy mud weight (higher than the minimum horizontal in-situ stress) can cause a tensile failure that led to mud loss and drilling induced tensile fracture initiations. In this case, formation permeability may affect by mud loss. So, the horizontal stress orientation is estimated based on the borehole breakouts and induced fractures (M. Abdideh and Amanipoor 2012; Hedayatikhah and Abdideh 2019). Several parameters affect wellbore stability: in-situ stress, mechanical rock properties, formation pressure, drilling mud, and drilling operations. In addition, the well’s direction may be impacted by the stress regime which is based on the formations (Mohammad Abdideh and Dastyaft 2022).