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Drilling deviated wells in a highly unstable gas field in southern part of Iran
Published in Vladimir Litvinenko, EUROCK2018: Geomechanics and Geodynamics of Rock Masses, 2018
Seyedalireza Khatibi, Azadeh Aghajanpour, Mehdi Ostadhassan, Yulia Kovaleva
Offshore fields are often developed based on a platform supporting different directional wells which are targeting reservoirs for a better drainage area. However, directional wells suffer from few severe problems such as excessive drag and torque of drilling strings, cuttings transportations, casing wear and wellbore instability (Zhang et al., 2014; Ma et al., 2015) among which wellbore instability is the most important problem, costing more than 100 million dollars per year worldwide (Fjar et al., 2008). These problems may become more severe when horizontal and deviated boreholes are drilled in poorly consolidated formations (Roegiers and Detoumay, 1998). Drilling fluid invasion into fractured formations can also create severe formation damage around the wellbore and reduce the productivity of the well. Therefore, minimizing fluid invasion in this type of reservoir is very important.
Drilling deviated wells in a highly unstable gas field in southern part of Iran
Published in Vladimir Litvinenko, EUROCK2018: Geomechanics and Geodynamics of Rock Masses, 2018
Seyedalireza Khatibi, Azadeh Aghajanpour, Mehdi Ostadhassan, Yulia Kovaleva
Offshore fields are often developed based on a platform supporting different directional wells which are targeting reservoirs for a better drainage area. However, directional wells suffer from few severe problems such as excessive drag and torque of drilling strings, cuttings transportations, casing wear and wellbore instability (Zhang et al., 2014; Ma et al., 2015) among which wellbore instability is the most important problem, costing more than 100 million dollars per year worldwide (Fjar et al., 2008). These problems may become more severe when horizontal and deviated boreholes are drilled in poorly consolidated formations (Roegiers and Detoumay, 1998). Drilling fluid invasion into fractured formations can also create severe formation damage around the wellbore and reduce the productivity of the well. Therefore, minimizing fluid invasion in this type of reservoir is very important.
Damage-control technology of oil-based drilling fluid for Kuqa piedmont structure
Published in Geosystem Engineering, 2018
Peng Xu, Zhengwu Tao, Xiao Liu, Zhihang Yan, Mingbiao Xu
In the process of drilling, fluid invasion changes the surface wettability of pore and cracks, wettability reversal damage is great when water-wet of rock change to oil-wet. Unlike other damages, wettability change would not decrease rock absolute permeability. Compared to conventional damage, it is extremely concealed, and easy to be ignored in drilling fluid. Experiments measured contact angle, surface tension, interfacial tension of oil-based drilling fluid at the rock sample of Keshen Block. The results are shown in Table 1.
Granular LCM migration and plugging behavior in shear-slip fractures
Published in Particulate Science and Technology, 2023
Baiyu Zhu, Hongming Tang, Wu Youxin, Chen Gongyang, Feng Zhao
The stress redistribution around the wellbore when drilling in the fractured reservoir will cause deformation of fractures, especially fractures that obliquely intersect with the fracture near the wellbore, thus making the fluid flow and particle migration in the fractures change. With lost circulation, the drilling fluid and bottom-hole pressure will propagate to the tip of the fracture, and possibly cause fracture tip breaking and therefore fracture growth (Dupriest et al. 2005; Razavi et al., 2016; Dudley, Fehler, and Zeilinger 2020). When the fluid pressure in a natural fracture is small, the normal stress on the fracture surface is compressive stress, and the fracture is in a close state. If a hydraulic fracture connects with a natural fracture during propagation, the stress exerted on the natural fracture may change. Once shear stress exceeds the frictional resistance between the natural fracture surfaces, the fracture surfaces will slip (Gao et al. 2020). Furthermore, with drilling fluid invasion, the fluid lubrication, strength weakening of micro-bumps on the fracture, falling of skeleton particles, and increase of pressure inside the fracture will make the fracture surfaces more likely to slip (You et al. 2018). At present, it is commonly believed that the slipped fractures can be self-supported by their surface roughness, resulting in a permanent permeability increase of the fractures (Ye and Ghassemi 2018). That is to say, shear-slip is one of the important factors aggravating lost circulation and adding reservoir plugging difficulty. According to statistics, the success rate of one-time bridge plugging in shale gas reservoirs of the Sichuan Basin is less than 40%. One of the important reasons for the low success rate of one-time plugging is the decrease of plugging formula suitability caused by shear slip. In this case, the shear slip of fracture surfaces would lead to changes in flow rate and direction, and thus changes in plugging and migration behaviors of drilling fluid and LCMs (Figure 1; Lee and Babadagli 2021). But studies on LCMs adaptability taking shear slip into account are rare, especially studies on microscopic mechanisms of migration and plugging of LCM particles in shear slip fracture.