The Influence of Wellbore Stability on the Feasibility of Extended Reach Drilling Wells: A Case Study from Offshore Vietnam

Gui, Feng; Khaksar, Abbas; Gilmore, Todd Gerard

doi:10.2118/156221-ms

All Days 2012

DOI: 10.2118/156221-ms

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The Influence of Wellbore Stability on the Feasibility of Extended Reach Drilling Wells: A Case Study from Offshore Vietnam

Feng Gui

Abbas Khaksar

Todd Gerard Gilmore³

Abstract: Wellbore stability is important for successful horizontal and extended reach drilling (ERD) wells. Hole instability problems associated with ERD wells can sometimes change the original development plan because of complications and unforeseen operational and geomechanical issues.This paper presents a case study from offshore Vietnam, where historically, no significant wellbore stability problems had been reported for vertical and low-angled wells. There were plans to develop the field by drilling highly deviate… Show more

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Cited by 7 publications

References 6 publications

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Investigation of the Failure Mechanism and Complicated Wellbore Instability Issues in the Drilling of the Extra Deep Fractured Carbonate Reservoirs in Shunbei Field, NW China

Chen

Wang

et al. 2020

SPE Asia Pacific Oil &Amp; Gas Conference and Exhibition

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The Ordovician fractured carbonate reservoir in the Shunbei field is buried ~7300m below ground level and has presented great challenges for the drilling of extra deep, deviated development wells. Borehole instability-related drilling problems including pipe stuck, pack-off, and mud losses have been experienced frequently during drilling, with many wells being sidetracked three or four times before reaching the target. To understand the failure mechanism and optimize the drilling design to mitigate the drilling risk has become crucial for the field development. As the basis of the investigation, detailed geomechanical modelling was conducted for a selected area with the most representative drilling problems. Laboratory core tests, wireline logs, image data and drilling experiences were used to build geomechanical models characterizing the in situ stress, pore pressure and rock mechanical properties in both the overburden and reservoir sections. Stress-induced borehole failures observed in the image logs were analysed to help diagnose the failure mechanisms together with the cavings recovered from the problematic wells, which provided significant insights into the likely nature of instability problems in the wells. The geomechanical modelling from a series of wells revealed that the stress magnitudes in the selected area vary based on the structural location. The wells near the major fault system appear to be in a normal faulting stress regime in the Ordovician reservoir, while the wells nearby the secondary fault system are in a strike-slip faulting stress regime. Different stress regimes and horizontal stress anisotropies have resulted in different behaviors during drilling, with breakouts seen in some vertical wells while not in other vertical wells despite using similar mud weights. during drilling. The variable stress conditions plus the highly developed fractures have caused serious borehole collapse in some wells, but reasonably good hole condition in other wells. Wells using higher mud weight are not necessarily the ones having fewer drilling problems. Although the complex lithology, great depth, and unpredictable distribution of intrusive rocks has complicated the drilling problems, a proper definition of suitable mud weight to control borehole collapse and understanding of the natural fractures might play a bigger role in maintaining borehole stability and mitigating drilling risk. A good understanding of the stress condition and rock mechanical properties appears to be helpful in defining the proper mud weights and optimizing other drilling parameters to help mitigate the complex drilling problems encountered during drilling in the Shunbei field. However, additional work on the fracture distribution and trend of stress change in the field might be required to help investigate the problem further.

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Investigation of the Failure Mechanism and Complicated Wellbore Instability Issues in the Drilling of the Extra Deep Fractured Carbonate Reservoirs in Shunbei Field, NW China

Chen

Wang

et al. 2020

SPE Asia Pacific Oil &Amp; Gas Conference and Exhibition

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Integrated Multidisciplinary Solution for Improving Wellbore Stability and Drilling Efficiency in a Conglomerate Reservoir, a Case Study from North-West China

Shi²,

Zhang³

et al. 2021

SPE/IATMI Asia Pacific Oil &Amp; Gas Conference and Exhibition

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Drilling long horizontal development wells in a conglomerate reservoir with strong heterogeneity has been challenging in the Junggar Basin, onshore China. To develop the fields economically, rapid and safe drilling with minimal non-productive time (NPT) is required. However, various drilling problems such as stuck pipe, mud losses have been experienced in the build-up section while the horizontal conglomerate section experienced an extremely low rate of penetration (ROP). To overcome the drilling challenges, a thorough understanding of the subsurface characteristics of the formations is critical to develop effective engineering solutions. To improve drilling efficiency, an integrated multidisciplinary approach was applied to derive an effective drilling solution. Drilling experiences from offset wells were reviewed systematically to identify the possible reasons that have caused the drilling problems. This diagnostic approach helped to identify appropriate drilling solutions for mitigating the different drilling risks. Detailed geomechanical models were also constructed to understand the stress state and rock mechanical properties of the conglomerate reservoir and the overburden formations so that proper mud weights can be defined for each section to control both wellbore collapse and mud losses. Mud weight recommendations and failure mechanism diagnosis also provided the basis for drilling fluids designs. Additionally, in order to achieve a better hole quality as well as increase the reservoir contact and ROP, advanced rotary drilling systems were also used with real time monitoring. The latter enabled the tracking of rock property and ECD changes as well as other drilling parameters during the drilling process. This integrated solution was applied in the drilling of several horizontal wells. One typical case is presented in this paper. In this well, the risk of hole instability was very high because the well was targeting a deeper formation with a few shaly intervals in the build-up section which are known to cause serious wellbore stability problems. The safe mud weight window inferred from geomechanical analyses appears to be very narrow, particularly at the casing shoe where the mud weight required to control borehole collapse is very close or even higher than the fracture gradient. To help with drilling the well cost-effectively, drilling fluid was designed to perform three (3) critical functions - 1) maintaining wellbore stability, 2) increasing ROP and 3) broadening the mud weight window to minimize mud losses. The successful drilling of this well broke the drilling record in the same block. The integrated multidisciplinary approach successfully reduced the occurrence of borehole instability related problems and NPT in the study well. Following the same methodology, the drilling efficiency will improve with more experience and understanding obtained from continuous drilling. This continuous learning process will be the key aspect of this project, eventually contributing to the success of the field development.

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An Integrated Approach in Pore Pressure Prediction Contributes to Drilling Success of a HPHT Wildcat Well in South China Sea

Guan¹,

Xiannan²,

Wang

et al. 2022

SPE Asia Pacific Oil &Amp; Gas Conference and Exhibition

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An accurate pore-pressure prediction plays an important role in well planning as exploration targets shift to deeper over-pressured reservoirs. Pore pressure related problems in high-pressure high-temperature (HPHT) wells include well control, lost circulation, formation breathing, differential sticking, reduced penetration rate, and reservoir damage, many of which can potentially lead to expensive sidetracks, underground blowouts and early well abandonment. An integrated approach can help with better understanding the pore pressure regimes, including generating mechanisms as well as pressure preservation and dissipation processes through geologic time. This improved understanding provides invaluable insight into the different drilling challenges and the strategy to mitigate or minimize pore pressure related problems. Once the pore pressure model is established, the in-situ stress tensor needs to be constrained following a well-developed geomechanical modeling workflow. Both the pore pressure and in-situ stress models are required for wellbore stability analyses to understand wellbore failure mechanisms as well as the design of optimum mud weights. Additional considerations include drilling through faults, which due to the field's unique structural characteristics could further complicate the already difficult drilling condition in a HPHT environment. This paper presents a case study to highlight the utilization of an integrated approach for pore pressure prediction to reduce drilling risks and costs of a HPHT well located in South China Sea. Prior to drilling, the major risk anticipated for this well, which was required to explore a deep-play at 5 Km MD, was high-pressure (1.53 sg at 4800 m TVD) and high-temperature (172 ºC at 4800 m) with narrow margin drilling conditions. Geomechanical studies that include both pre-drill and real-time (RT) drilling components provided inputs for effective well designs and drilling operation supports. Compared to the drilling of an offset well which had to be prematurely terminated due to continuous high total gas encountered despite increased mud weights, the planned well was successfully drilled to the target zone with no issues even drilling at high rate of penetrations (ROP). This new drill was the best well ever recorded in the block. The adaptation of the integrated approach in pore pressure prediction has successfully reduced the occurrence of borehole instability related problems and the associated non-productive time (NPT). The drilling performance and well delivery efficiency of future wells will improve with additional operational experience and geomechanical understanding obtained from additional drilling. This continuous learning process will be the key aspect of this project, ultimately contributing to the overall success of the field development.

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The Influence of Wellbore Stability on the Feasibility of Extended Reach Drilling Wells: A Case Study from Offshore Vietnam

Cited by 7 publications

References 6 publications

Investigation of the Failure Mechanism and Complicated Wellbore Instability Issues in the Drilling of the Extra Deep Fractured Carbonate Reservoirs in Shunbei Field, NW China

Investigation of the Failure Mechanism and Complicated Wellbore Instability Issues in the Drilling of the Extra Deep Fractured Carbonate Reservoirs in Shunbei Field, NW China

Integrated Multidisciplinary Solution for Improving Wellbore Stability and Drilling Efficiency in a Conglomerate Reservoir, a Case Study from North-West China

An Integrated Approach in Pore Pressure Prediction Contributes to Drilling Success of a HPHT Wildcat Well in South China Sea

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