Borehole stability analysis has been well studied in oil and gas. Problems generally build up over time, beginning with fragmentation at the borehole wall, followed by transfer of fragments to the annulus, and culminating in such problems if hole cleaning is insufficient as a sticky or tight hole, packing off, hole. Optimum hydraulics design and operation for extendedreach. Wellbore stability analysis to determine the safe mud weight window. Predrill wellbore stability analysis using rock physical.
Qra approach to stability analysis the range of safe mud weights to maintain wellbore stability lies between the wellbore. Stability analysis of vertical boreholes using a three. This paper mainly deals with borehole stability of transversely isotropic formation. This special laminar texture kind of formation bears the following characteristics. Wellbore stability modeling in vertical and horizontal. The derived wellbore stability model was calibrated using the drilling information, logging data and geological model. Horizontal borehole stability in naturally fractured. The important effects of filter cake, coal depth, and rock strength anisotropy are demonstrated with two different elastoplastic models. Analysis of wellbore stability shows that horizontal wells drilled in the direction of the maximum horizontal stress in this field are the most successful. Analysis of vertical, horizontal and deviated wellbores stability by analytical and numerical methods, journal of petroleum exploration and production technology, 2014, pp.
Our objective is to present a theoretical study of the problem of stability of a borehole drilled through a salt formation with the purpose of evaluating the optimal mud weight and avoiding creep effects. Moreover, it is aimed to monitor the changes around wellbore during production and with a view to optimizing well planning, construction and post evaluation procedures. After setting the first string to isolate a shallow hazard, the remaining casing depth points were selected based on drilling experience in an offset block, supplemented by pore pressures predicted using seismic data. Mitigation of wellbore instability in deviated wells by. Recognizing horizontal stress orientation for optimizing. The zagros fold and thrust belt zagros ftb is an approxi. The research on influence of unloading on borehole stability in. Finally, the results show that the collapse pressure will be underestimated if the conventional model is used in shale gas reservoirs improperly. Horizontal directional drilling 416 borehole on pullback. Recognizing horizontal stress orientation for optimizing well placement and well completion jobs r. The research on borehole stability in depleted reservoir and. Pdf on nov 1, 2000, jincai zhang and others published horizontal borehole stability in naturally fractured reservoirs find, read and cite all the research you need on researchgate. Wellbore instability prediction and performance analysis using. For this the borehole will be reamed to a minimum diameter of 8 or 10 inches and concrete grouting placed in the annular space between the casing and open borehole wall.
Because the largest of the in situ stress components, the overburden stress. Borehole stability free download as powerpoint presentation. Inclined wells drilled in the direction of minimum horizontal stress tend to be more stable in a normally faulted basin compared to those drilled in any other directions. By solving the stress distribution on the borehole wall, a new vertical borehole stability model was established. Stability analysis of a borehole wall during horizontal directional. Practical approach to solving wellbore instability problems. They are monitored throughout the process to make sure the bore stays open, pumps are not overworked, and. On the other hand, the reduction of pore pressure and the ratio between maximum and minimum horizontal stresses causes the smww to widen significantly. Borehole stability analysis of horizontal drilling in shale. Measurement of minimum horizontal stress from logging and drilling data in unconventional oil and gas unpublished masters thesis. Theory of borehole stability when drilling through salt.
The associated problems are pipe sticking and possible loss of well. A glossary of abbreviations and definitions used in permeability calculations k coefficient of permeability in feet meters per year under a unit gradient. Stability analysis of a borehole wall during horizontal directional drilling. Results for a horizontal well, along the minimum horizontal stress azimuth in. Geomechanical information is relevant to assure wellbore stability, i. Borehole stability analysis accounting for anisotropies in. Pdf stability analysis of a borehole wall during horizontal. There are some difficulties in drilling utype well, such as well bore stability, cutting carrying problem, large torque and friction at the horizontal section, and formation damage to coalbed. Jul 07, 2007 furthermore, as demonstrated using a western canadian example a shallow well in the ardley coal zone, relatively simple elastoplastic models can be used effectively for borehole stability analyses. There have been many articles written on the subject of wellbore stability. Fuh applied this research method to the horizontal boreholes, which. Stability analysis of a borehole wall during horizontal. A borehole is a narrow shaft bored in the ground, either vertically or horizontally.
For packer tests, determining the effective head is defined. Special considerations for the marcellus shale julie kowan1,2 and see hong ong1. Horizontal well drilling includes mwd, borehole trajectory control, borehole stability, drillingcompletion fluids, and other key techniques. Analysis of vertical, horizontal and deviated wellbores stability. Recognizing horizontal stress orientation for optimizing well.
Besides this, in hard rock underground mining, such as. Horizontal directional drilling manual 1 and the horizontal directional. A borehole may be constructed for many different purposes, including the extraction of water, other liquids such as petroleum or gases such as natural gas, as part of a geotechnical investigation, environmental site assessment, mineral exploration, temperature measurement, as a pilot hole for installing. Results show that horizontal borehole stability depends strongly on the in situ stress state, the borehole orientation, time, mud pressure and fracture characteristics. To address this issue, the dehydration from caprock to reservoir and roof effect of caprock are performed. Borehole stability analysis of horizontal drilling in. Stability of a borehole during horizontal directional. Serious wellbore instability occurs frequently during horizontal drilling in shale gas reservoirs. Understanding and implementing the basic principles of how drilling fluid or slurry stabilizes a hole in these types of formations can save a drilling contractor a lot of headaches, drill pipe, downhole. The influence of arching on the stability of a borehole filled with bentonite has been tested with the geotechnical centrifuge of geodelft in combination with the maximum mud pressure the borehole can withstand. Wiprut dj, zoback md 1998 high horizontal stress in the visund field, norwegian north sea.
Fracture mapping and determinationof horizontal stress field by borehole measurements in hdr drillholes soultz urach helmut tenzer stadtwerkebad urachgeothermicresearch 89, d72574 bad urach, germany tel fax key words. Observations of gas leakage along a normal fault which is optimally oriented for reverse failure in the current stress field are correlated with predictions of leakage. Borehole instability in shales is a major source of trouble, time, and cost during drilling. N2 borehole stability analysis plays an important role in the design of oil and gas well drilling.
A comprehensive modeling analysis of borehole stability and. The results obtained in this study showed that the anisotropy of the rock and the horizontal stress ratio greatly affect the stress distribution and the failure plane of vertical wellbores. Wellbore instability wi is recognized when the hole. How to create borehole stability using drilling fluid or. One consequence is that the fourth casing section has an extremely narrow mud window. Based on the theory of elasticity mechanics and some assumptions, the mechanical model taking into account of initial ground stress and mud pressure is established. For the collapse of the sand and gravel stratum in the process of trenchless drilling hole, based on elasticity analysis with the elasticity theory of horizontal directional drilling hole wall, the stress states under different lateral pressure coefficients are analyzed after reinforcing the sand and gravel stratum which is prone to collapse. Centrifuge tests on borehole stability during horizontal directional drilling were carried out by viehofer et. Pdf numerical simulations of wellbore stability in under. A wellbore stability analysis was carried out by fuf et al. A history match of the observed field wellbore stability cases with the coupled model was.
Jan 01, 2015 borehole stability in loose, unconsolidated soil conditions such as sand or gravel is essential to the overall success of a drilling project. Goodman and shi 1985, used for the stability of underground openings, suggests that only the removable blocks of the top section fail because of gravity, but the lower section remains in gauge despite having removable. Borehole stability analysis of horizontal drilling in shale gas. In the latter, the stability of horizontal boreholes at relatively shallow depths in loose soils is the issue. Measurement of minimum horizontal stress from logging and. Pdf horizontalwellbore stability and sand production in weakly. It is then compared with flac outputs, in order to show the accuracy of results and investigate the wellbore stability in different states of vertical, horizontal and deviated. Results of the centrifuge tests showed that a borehole is usually stable in normal soil types due to the mechanism of arching.
Predrill wellbore stability analysis using rock physical parameters for a deepwater high angle well. As part of well design, wellbore stability and pore pressure analysis are main. In this paper, numerical simulation strategies are proposed and numerical analyses are performed to investigate the stability of a borehole wall during horizontal directional drilling in loose sand with an emphasis on the role of the filter cake in borehole stability. The results obtained in this study showed that the anisotropy of the rock and the horizontal stress ratio greatly affect the stress distribution. Request pdf analysis of wellbore stability for horizontal wells in stratification shale based on the poroelastic mechanics and the single weakplane strength. Jan 22, 2014 figure 5 also shows that the stability of the horizontal borehole i 90 o is lower than the vertical one i 0. Stability analysis of horizontal directional drilling. Horizontal well borehole stability is analyzed by the new in situ stress prediction model in shale gas reservoirs yuan et al.
Furthermore, the borehole stability can be affected by insitu stresses changes. Drilling fluids range from water to oil to complex chemical systems with properties designed for specific site conditions to aid the drilling process. During horizontal directional drilling, the instability of borehole wall may lead to serious accidents such as too large torque, failure pullback of pipeline, abandonment of bore, etc. Stability analysis in determining safety drilling fluid. Well trajectory has a direct effect on wellbore stability when horizontal wells are drilled with ubd, where inclination angle, relative azimuthal angle and borehole curvature play crucial roles in different well sections vertical wellbore, deviated wellbore and horizontal wellbore. Underbalanced drilling can have some positive effects on borehole stability. Many of the drilling parameters, as mud weight or the optimal orientation of the borehole, require some knowledge of the mechanical behaviour of the rock. Wang and sterling 2007 performed numerical analyses named finite element to investigate the stability of a borehole wall during horizontal directional drilling in loose sand with an emphasis on. Assessing the mechanical stability of horizontal boreholes in. Psborehole stability and field stress analysis with azimuthal loggingwhiledrilling technology. Well orientation effect on borehole stability onepetro. T1 a comprehensive modeling analysis of borehole stability and productionliner deformation for inclined horizontal wells completed in a highly compacting chalk formation au furui, k. Our borehole stabilizers serve as preventive medicines that help operators avoid the difficult and expensive tasks associated with remediating an unstable formation. The impact of well trajectory on wellbore stability.
Predictions of borehole instability risks were made for a broad. Borehole stability analysis for underbalanced drilling. Analysis of wellbore stability for horizontal wells in stratification. Borehole collapse occurs when the drillingfluid pressure is too low to maintain the structural integrity of the drilled hole. Stability of highly inclined boreholes journal article.
Pdf assessing borehole instability risks for horizontal. Investigation of wellbore stability in a north sea. One of the early concerns in horizontal drilling was a borehole stability issue related to the way in which the in situ stress field is oriented to a horizontal borehole. Based on that, the influence scope and magnitude of horizontal stresses reduction in caprock above the depleted reservoirs are estimated. Based on this work, horizontal well borehole stability is analyzed by the new in situ stress prediction model. For example, shale formations containing reactive clays often suffer from hydrationrelated mechanical degradation, swelling, and pore pressure penetration when infiltrated by drilling muds that flow into the formation at overbalanced conditions. Knowledge of horizontal stress orientation can be utilized for addressing issues related to wellbore stability in any fault regime. In parallel bedding directions horizontal, its physical and mechanical properties are very close and can be approximately considered as the same. Analysis of borehole wall stability in horizontal directional. Horizontal drilling an overview sciencedirect topics. The smaller the radius of curvature from a vertical well section to a horizontal well section, the higher the construction difficulty. Directional drilling or slant drilling is the practice of drilling nonvertical wells.
The trenchless technique horizontal directional drilling. A group of dutch drilling contractors and engineering consultants are working together to enhance their knowledge on borehole stability during horizontal directional drilling hdd. Therefore, the safe mud weight should be greater than the pore pressure gradient and shear failure. Oct 08, 20 avoid borehole collapse for a well located in iran oil field. Maximum horizontal stress and wellbore stability while. The study shows that the borehole stability is controlled, under the normal condition, by the largest insitu stress in the radial borehole direction so that the borehole orientation effect for a horizontal well is not significant if two horizontal stresses are less than the vertical overburden pressure, however, if one horizontal stress is. Analysis of vertical, horizontal and deviated wellbores. H the effective head of water in the well in feet m. Pdf horizontal borehole stability in naturally fractured. Abstract maximum horizontal stress is a critical parameter used in drilling optimization and wellbore stability modeling. Stability of a borehole during horizontal directional drilling dec 20, 2005 the influence of arching on the stability of a borehole filled with bentonite has been tested with the geotechnical centrifuge of geodelft in combination with the maximum mud pressure the borehole can withstand before a blowout occurs.
Marcellus and utica point pleasant, pittsburgh, pennsylvania, june 1719, 2014 datapages. In all cases, the borehole stability was satisfied by minimum mud pressure formation pressure in the vertical well. The collapse pressure of a horizontal well is maximum at dip angle of 45. Depending on specific conditions, such effects may lead to collapse of the borehole or a reduction in the fractureinitiation pressure. Pdf longterm stability of horizontal wellbore completions with uncemented liners in weakly consolidated to unconsolidated sandstone formations e. Borehole stability an overview sciencedirect topics. Tiwari summary knowledge of horizontal stress orientation can be utilized for addressing issues related to wellbore stability in any fault regime. These problems can occur in a variety of forms including stuck pipe.
Geomechanical modeling of insitu stresses around a borehole. Results show that horizontal borehole stability depends strongly on the in situ. Due to the sensitivity of the horizontal wells, stability analysis will be performed specifically for the horizontal well in this study. Wang and sterling17 analyzed the stability of a horizontal well drilled into a loose sandstone formation, especially the effect of mud cake on wellbore stability. Current maximum horizontal stress prediction from wellbore breakout was based on the maximum tangential stress on the wellbore wall to be equal to. Borehole stability and field stress analysis with azimuthal. Borehole stability technology includes chemical as well as mechanical methods to maintain a stable borehole, both during and after drilling. Borehole stability is a continuing problem which results in. Wellborestability study for the safod borehole through the. Request pdf stability analysis of a borehole wall during horizontal directional drilling in this paper, numerical simulation strategies are proposed and. Early theoretical studies on borehole stability were based on models developed for underground salt cavities e. This paper describes the use of rock mechanics modeling of borehole stresses during offshore drilling in the gulf of mexico. Use of borehole stability analysis for successful drilling.
Horizontal borehole stability in naturally fractured reservoirs. Borehole stability modeling for drilling operations is primarily to create a safe mud weight mud pressure window such that the designed mud density will be high enough to ensure borehole stability and low enough to not fracture the formation i. Comprehensive wellbore stability analysis utilizing. Jul 24, 20 the second objective is application of finite difference method to estimate the mud pressure required to avoid borehole collapse for a well located in iran oil field. Wellbore stability analysis is based on rock mechanical property. The minimum overbalance pressure predicted by the mohrcoulomb criterion is 8. Analysis of the vertical borehole stability in anisotropic. In the finite element analysis, the common approach is to subtract the. T1 stability analysis of vertical boreholes using a threedimensional hoekbrown strength criterion. Pdf borehole stability analysis for underbalanced drilling. Numerical simulations of wellbore stability in underbalanceddrilling wells. Introduction borehole stability is a very important issue in the gas and oil industry as it can result in substantial expenditures having thus a significant impact on reservoir. In this paper, the borehole stability problem, from the collapse of granular soils near the borehole wall to the hydraulic fracturing induced by high drilling mud pressure. Before drilling, the rock strength at some depth is in equilibrium with the insitu rock stresses effective.
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