Wellbore Strengthening and Borehole Stability: A Geomechanical Model to Increase the Thin Mudweight Window in Vertical and Deviated Wellbores

Bassey, Akong; Dosunmu, Adewale; Buduka, Stanley; Alabi, Tunde

doi:10.2118/151078-ms

Cited by 3 publications

References 26 publications

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Influence of depth on induced geo-mechanical, chemical, and thermal poromechanical effects

Ezendiokwere

Aimikhe

Dosunmu

et al. 2021

J Petrol Explor Prod Technol

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Delivering efficient and cost-effective drilled and excavated holes require effective prediction of instability along the hole profile. Most drilled and excavated hole stability analyses in the literature are performed for a given zone without considering the influence of depth. This study focused on determining the influence of depth on induced geo-mechanical, chemical, and thermal stresses and strains in drilled or excavated holes. To this end, a new porochemothermoelastic model was developed based on extended poroelastic theory, and the developed model was employed in determining induced strains and stresses for an oil and gas well case study, using data from the literature. The study delineated the different significance levels of geo-thermal-, chemical-, and thermal-induced strains and stresses as depth increased. From the results obtained, it was clear that at shallow depths, chemically induced strains and stress were the most significant formation perturbations responsible for instability of drilled and excavated holes. On the other hand, at deeper depths, geo-mechanical-induced strains and stress were the most predominant. Comparatively, thermally induced strains and stresses were found to be the least significant formation perturbations responsible for instability of drilled and excavated holes. For this case study, the results indicated that chemical strains and stresses were more prominent at depths below 170 m, accounting for more than 50% of the total stresses and strains. At 170 m, both chemical and geo-mechanical stress and strain had equal contributions to the overall stress and strain. However, as depth increased, the percentage contribution of the geo-mechanical component increased and accounted for about 80% of the total strains and stresses at 1000 m, which increased to 98.48% at depths of 6000 m and beyond. The findings of this study will provide guide for future studies on the application of extended poroelasticity theory in solving instability problems of drilled and excavated holes.

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Influence of depth on induced geo-mechanical, chemical, and thermal poromechanical effects

Ezendiokwere

Aimikhe

Dosunmu

et al. 2021

J Petrol Explor Prod Technol

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A New Approach in Rock Strength Constraining Using Petrophysical Logs for Effective Real-Time Wellbore Stability Management in Normal Stress Regimes

Bassey¹,

Usim²,

Otutu³

et al. 2016

All Days

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The geomechanical knowledge of rocks physical and mechanical properties could reduce the NPT incurred while drilling and production of a reservoir to a large extent by selection of proper/optimum operating envelope. Hence, a field development plan for each oil/gas field may contain optimized geomechanical procedures that take into accounts the rock mechanical principles and failure scenarios. "The unconfined compressive strength (UCS) and internal frictional interplays of rocks is the important rock mechanical parameters that plays crucial role when drilling an oil or gas wells". "(UCS) is the stress level at which rock is broken when it is under a uniaxial stress state (Bruce et al 2004)"; it can be used for real – time wellbore stability evaluation, bit selection management, and design of enhanced geomechanical earth models and cap integrity evaluation. Rock strength can be estimated along drilled wellbore using different approaches, including laboratory tests, core – log relationships and rate of penetration models. The benefit of a petrophysical log- derived method is that, it provides continuous strength profiles with depth. This is useful in delineating differences between near uniform zones, and identifying weaker zones. There is also a cost advantage in obtaining these data without having to perform extensive laboratory testing throughout the core interval. "In this study, new equations for estimation of rock strength in Niger Delta formations are formulated based on empirically derived models that accommodate petrophysical log information such as the degree of shaliness detected over the entire logged interval, corresponding to shale and sand units (Fjaer, et al. 1990), lithology index etc., hence they are utilized for estimation of the rock strength profile for easy and effective geomechanical evaluations" (Dosunmu 2007). A geomechanical enhanced framework coupled with discrete finite element analysis is utilized for prediction of UCS in any predefined well trajectory and batch depth analysis on the course of this research (study). Cross/post – validation shows that, the results from the formation discretization were compatible with realities (based on MEM utilization). This approach has proven to be useful for estimation of rock strengths and frictional interplays in any design well trajectory prior to drilling (predrill scenarios). Above all, it helps to determine the minimum and optimum mudweights required for real – time wellbore stability management during drilling, POOH, casing running and cementing, helps in preventing unplanned events leading to outrageous NPT's (Otutu 2013)

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Borehole Stability Management Using the New Mudweight Window Concept; A Case Study of Well KTY 02, KTY 03 and KTY 04

Bassey¹,

Dosunmu²,

Otutu³

et al. 2016

All Days

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Borehole instability is one of the major factors that contribute significantly to additional unplanned cost in drilling operations irrespective of the wellbore inclination. Problems generally build up in time, starting with the tensile or compressive failure of the borehole wall, followed by transfer of fragments to the annulus and finally-if hole cleaning is insufficient-culminating in such difficulties as tight hole, breakouts, caving, pack off, borehole collapse and stuck pipe. Horizontal and highly deviated wells in normal faults stress regimes present more difficult challenges than low inclined wells due to compressive or shear failure of the wellbore. Wellbore stability issues are more pronounced as the wellbore stress difference reaches at maximum with increase in inclination. Proper planning of the well trajectory and mud weights are crucial to avoid such complexity which causes huge rig downtime, NPT and cost. With the aid of in-situ stress, pore pressure and rock strength analysis the wellbore stability can be assured with suggested optimum deviation profile and mud weights window for different inclinations and azimuths. An attempt has been made to perform the wellbore stability analysis for three high angle and three horizontal wells (with drain-extension of about 500ftahd) development wells in Niger Delta which is planned for production in near future. In our workflow, the seismic data and offset well information have been incorporated to generate pore pressure, optimum mudweight, shear failure (minimum envelope) and fracture pressure gradient. Rock physical parameters have been calculated from the offset well's logs and calibrated with laboratory tested dataset to use in the stability analysis for well KTY 02, KTY 03 and KTY 04. In the study area, wellbore stability analysis was carried out in both the pilot and drain hole sections of the horizontal wells. However, because of horizontal drilling plan in drain holes, differences in principal stresses in the wellbore and their physical implication on stability was plotted and interpreted through stress concentration plot and safe MW window analyzer extensively. The stresses and the rock strength datasets input were used to derive the collapse failure gradient curve (CFG) using the Mogi failure criteria. The wellbore circumferential and radial stress distribution analysis has been done for different depths with the inputs from stresses and the corresponding cohesive strengths and the Frictional Angles. With these analytical results, we have recommended the wellbore trajectory along Shmin and SHmax direction and along the maximum good reservoir facies with corresponding mud weight (window) profile required to drill these wells with NPT as a result of instability consequences such as stuck pipes and jeopardizing wellbore integrity during logging, casing running and completions.

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Wellbore Strengthening and Borehole Stability: A Geomechanical Model to Increase the Thin Mudweight Window in Vertical and Deviated Wellbores

Cited by 3 publications

References 26 publications

Influence of depth on induced geo-mechanical, chemical, and thermal poromechanical effects

Influence of depth on induced geo-mechanical, chemical, and thermal poromechanical effects

A New Approach in Rock Strength Constraining Using Petrophysical Logs for Effective Real-Time Wellbore Stability Management in Normal Stress Regimes

Borehole Stability Management Using the New Mudweight Window Concept; A Case Study of Well KTY 02, KTY 03 and KTY 04

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