Optimizing a Deepwater Subsalt Drilling Program by Evaluating Anisotropic Rock 
Strength Effects on Wellbore Stability and Near-Wellbore Stress Effects on the 
Fracture Gradient

Brehm, Andrew; Ward, Christopher; Bradford, Dale; Riddle, Darrell

doi:10.2523/98227-ms

Cited by 3 publications

(5 citation statements)

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“…In general, Figures 12-14 show that the mud pressures required to maintain the stability with the imposed in situ state of stress are quite high, and can be close to the minimum in situ stress when δ = δcrit; this in agreement with the field experience reported by Brehm et al [7]. We observed that, for a given rock, the difference between the mud pressure peaks at different δ ranges from 5 MPa to 10 MPa, which is a considerable gap.…”

Section: Mud Pressures To Prevent Slipsupporting

confidence: 87%

“…For our purposes, we selected the weakness plane model which is linear and characterized by two constant strength parameters: the cohesion and the friction angle of the weakness planes. To date, the weakness plane model seems to be the most widely used for predicting mud pressures in wellbores drilled in anisotropic rocks ( [4][5][6][7][8][9][11][12][13][14][15][16][17][18][19][20]). This is probably because the cohesion and the friction angle of the discontinuities can be directly determined by direct shear tests.…”

Section: Selection Of Strength Criteria For Rocks With Strength Anisomentioning

confidence: 99%

“…Figure 16a The results shown in Figures 12-14 indicate the mud pressures to avoid slip change with δ. As the inclination of the weakness planes can vary over relatively short sections of the wellbore [5,7], the definition of the minimum mud pressures to avoid slip should take into account more than one inclination of these planes. To this end, we analyzed the peaks of the mud pressures calculated with the Hoek and Brown criterion in the range δ = 0°-90°.…”

Section: Energies 2018 11 X For Peer Review 18 Of 31mentioning

confidence: 99%

“…Brehm et al [7] reported wellbore instabilities in the Shenzi Field (Gulf of Mexico), characterized by weakly bedded rocks. They observed that while drilling the first wells, instability grew when drilling down-dip at low attack angles, but was almost non-existent when drilling up-dip (nearly On the other hand, we needed to verify if these high mud pressures could cause the occurrence of tensile failure (fracturing).…”

Section: Introductionmentioning

confidence: 99%

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Prediction of Mud Pressures for the Stability of Wellbores Drilled in Transversely Isotropic Rocks

Deangeli

Omwanghe

2018

Energies

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Serious borehole instability problems are often related to the presence of weakness planes in rock formations. In this study, we investigated the stability of wellbores drilled along a principal direction and parallel to the weakness planes. We used three different strength criteria (weakness plane model, Hoek and Brown and Nova and Zaninetti) to calculate the mud pressures to avoid slip and tensile failure along the weakness planes. We identified the orientation of the weakness planes that generate the most critical slip condition as a function of the friction angle of the planes. We also identified the range of orientations of the weakness planes that corresponds with the lower mud pressure window. We confirmed the validity of the proposed relationships with comparative stability analyses by using analytical solutions and numerical simulations (Ubiquitous Joint Model, FLAC). We found that the mud pressures calculated with the Hoek and Brown criterion show a particular trend, which cannot be predicted by the weakness plane model. We provided two normalized stability charts to predict mud pressures to prevent slip along the weakness planes in the critical slip condition. Finally, we corroborated our findings by simulating the stability of wellbores drilled in the Pedernales Field (Venezuela) and in oil fields located in Bohai Bay (China).

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Section: Mud Pressures To Prevent Slipsupporting

confidence: 87%

Section: Selection Of Strength Criteria For Rocks With Strength Anisomentioning

confidence: 99%

Section: Energies 2018 11 X For Peer Review 18 Of 31mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Prediction of Mud Pressures for the Stability of Wellbores Drilled in Transversely Isotropic Rocks

Deangeli

Omwanghe

2018

Energies

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“…Numerous wellbore instability problems have been reported when drilling through thinly laminated rock formations Zoback, 1990, 1992;Mastin et al, 1991;Last et al, 1995;Skelton et al, 1995;Okland and Cook, 1998;Willson et al, 1999Willson et al, , 2003Willson et al, , 2007Beacom et al, 2001;Edwards et al, 2003;Brehm et al, 2006;Lang et al, 2011). Therefore, maintaining wellbore stability is one of the major tasks encountered in the CBM industry, considering that wellbore instability-related problems will result in additional high drilling costs and have a severe impact on the drilling schedule.…”

Section: Introductionmentioning

confidence: 94%

An elastoplastic model of collapse pressure for deep coal seam drilling based on Hoek–Brown criterion related to drilling fluid loss to reservoir

Zhang

Yan

Yang

et al. 2015

Journal of Petroleum Science and Engineering

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Assuring Stability in Extended-Reach Wells—Analyses, Practices, and Mitigations

Willson

Edwards²,

Crook

et al. 2007

SPE/IADC Drilling Conference

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Whilst the step-out lengths of proposed ERD wells are becoming more and more challenging, wellbore stability assurance technologies - both in the pre-planning and execution phases - are developing at an equal pace. In this paper we describe several new developments in theoretical understanding and predictive capability of rock failure surrounding wells drilled at high-angle to bedding that are required to solve the problems encountered in these challenging environments. Rig-site processes for the integration of this new understanding with real-time diagnostic measurement and monitoring provide the means to deliver borehole stability assurance for ERD wells drilled in the most challenging environments. Introduction It has been 10 years since the temporary suspension of the extended reach drilling (ERD) program in the Niakuk field, North Slope, Alaska, due to the severe wellbore instability problems in the 8.5-in sections of successive ERD wells. The peer review1 and studies2,3 that were commissioned to investigate these problems highlighted the importance of integrating, in a holistic way, results of wellbore stability prediction, drilling fluid optimization, hydraulics and cuttings transport, operational practices and PWD tool utilization. Since the Wytch Farm, UK and Niakuk, Alaska, ERD well drilling campaigns in the mid-'90s, there has been a steady progression in the vertical depth and horizontal departure length of ERD wells drilled world wide (Figure 1)4. Wells with horizontal departures in excess of 40,000 feet (12 km) at vertical depths of less than 10,000 feet (3 km) are now being actively considered as a viable way of accessing satellite reserves from existing facilities or, in the case of environmentally-sensitive arctic environments, to develop offshore fields from onshore locations. A review of the recent SPE conference literature reveals that the challenges of ERD well feasibility planning and execution identified at Niakuk persist to the present day. Notable case history summaries have been presented by ExxonMobil for their Sakhalin-1 development in the Russian Far East. Here the offshore Chayvo field reservoirs are being accessed from an onshore location using ERD wells with reaches of 9 to 11 km5,6. In the Norwegian part of the North Sea, ExxonMobil again are using ERD drilling technology to access multiple independent reservoirs from their Ringhorn development, requiring well departures of up to 8 km7. Elsewhere in the Norwegian sector, Statoil have successfully drilled ERD wells with up to 7593 m (24911 ft) departure from their Visund platform; a record from a floating installation8,9. The reader is particularly directed to these papers, plus their associated references and bibliography, for a recent compilation and discussion of drilling engineering aspects of ERD well construction. In the rest of this paper, the authors will focus on the wellbore stability aspects of ERD wells. Particularly, new understanding and predictive capability for assessing instability in wells drilled at high angles to bedding are presented. Real-time drilling monitoring and operational practices are discussed, as are approaches that can be applied to minimize the risk of incurring wellbore instability problems in extended reach and high-angle wells. Wellbore instability in ERD wells - what's different about it? One can legitimately question whether wellbore instability in ERD wells differs significantly from instability occurring in near-vertical wells and in high-angle wells of lesser departure. It is the authors' opinion that there are differences in assessing and addressing wellbore instability in ERD wells. The additional considerations are more subtle in relation to conventional high-angle wells, but extra assurance steps are considered necessary. The list below summarizes particular issues that should be addressed when planning ERD wells.

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Optimizing a Deepwater Subsalt Drilling Program by Evaluating Anisotropic Rock Strength Effects on Wellbore Stability and Near-Wellbore Stress Effects on the Fracture Gradient

Cited by 3 publications

References 0 publications

Prediction of Mud Pressures for the Stability of Wellbores Drilled in Transversely Isotropic Rocks

Prediction of Mud Pressures for the Stability of Wellbores Drilled in Transversely Isotropic Rocks

An elastoplastic model of collapse pressure for deep coal seam drilling based on Hoek–Brown criterion related to drilling fluid loss to reservoir

Assuring Stability in Extended-Reach Wells—Analyses, Practices, and Mitigations

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