The principal function of leak-off tests is to assess casing integrity, but the test data are commonly used beyond this original purpose, for stress estimations in exploration and drilling. The value of leak-off test data for stress estimation is questionable and extended leak-off tests have been proposed as a more appropriate method for stress estimation. The paper for the first time compares leak-off test (LOT) and extended leak- off test (ELOT) data from two areas, the North West Self of Australia and the Norwegian North Sea. Standard LOTs have a characteristically large scatter associated with the leak-off pressures (Plo), minimum stress and fracture gradient estimates in both areas. However, the minimum stress determined from ELOTs are consistent and form a lower bound to the standard fl0 data in both areas. The ELOT takes about an hour to perform, but provides far superior data than that obtained from a LOT, and is recommended where stress data are required. P. 131

No abstract

Tfds paPIJr was~lW waenfafion at h SWSRMEurti 'W hatd in T~m, -y, 8-10 Juty 1996 s paper w =bded & Pfewnfatiin by an SW Program Ccinmillee foflwi~revi.awof .9fti d~~h M Wafracf *KOd by W aul~($) Contents Of Ihe paper, as ti~. ha~~~n C*VW by the SWbtY of pairohw Ew!neers ati are subtecl tõ by tha adti(s) W material, as Ws.nred dws no! n.ussarily re~any wsillon of tha Smty d Petroti Ew-rs, its ofhcart, w membrs Papers wesenled @ SPE m-s w s~I~10 tir~cw mvk by Etitwial Committees of tfw Swiely of Petroleum =ti E~ic~M, distr~ti, or storaga of any pan of !hIs w for wifhouf fha written -sent of the Scciety of Petroleum Eng-rs is Pemi$sti 10 m~m m ml is restricted lo an abstract of mt mcfe than 3C0 -s,~alis may w m IXQM Ttm abstrna must mntam WSPIWOUS acknowld~wt of whom d by % the pqr was pesen!ed WTife L!brar!an SPE, P O Box 833836 Rti~, TX 7SC33.SJ3SSU S A fw Ilf-972-952-9435 AbstractThe principal finction of leak-off tests is to assess casing integri~, but the test data are commonly used beyond this original purpose, for stress estimations in exploration and drilling, The value of Ieak-off test data for stress estimation is questionable and extended leak-off tests have been proposed as a more appropriate method for stress estimation. The paper for the fwst time compares leak-off test (LOT) and extended leakoff test (ELO~data from two areas, the North West Self of AustraIia and the Norwegian North Sea. Standard LOTS have a chrrracteristicaIly large scatter associated with the leak-off pressures (~. ), minimum stress and fracture gradient estimates in both areas. However, the minimum stress determined from ELOTS are consistent and form a lower bound to the standard fio data in both areas. The ELOT takes about an hour to perform, but provides far superior data than that obtained from a LOT. and is recommended where stress data are required.

The historical and theoretical backgrounds of standard and extended leak-off tests with respect to in-situ stress measurement are discussed and compared with hydraulic fracture stress measurement as practised in other industries. The relative advantages of extended leak-off tests compared with standard tests in this context are discussed and a case made for the extended test procedure. The diagnostics of pressure records obtained from extended leak-off tests are discussed in light of extensive experience obtained from hydraulic fracture stress measurement, with reference to a number of extended leak-off tests conducted in Australia. A conclusion is reached that extended leak-off tests can potentially provide data of quality comparable with that obtained from ideal hydraulic fracture stress measurement, allowing resolution of the in-situ stress field with reasonable reliability in many cases. The results of some Australian extended leak-off tests are discussed and contrasted with corresponding data obtained from standard leak-off tests. A trend is revealed from this data for extended leak-off tests to produce a lower estimate of the minimum stress magnitude than standard leak-off tests.

This papr was prepared for presentation at the fAOC/SPE Asia Pacific Drilling Tetinology '98Cmfefence and Exhibition held in Jakarta, Indonesia, 7-9 September 1998, This pa~r was selected for prasantation by an SPE program Commitfae foll~~g ravi~~f information contalnad in an abstract submitted by the author(s). Contents of the paper, as presented, hava not ben reviewad by the Swiety of Pa!roleum Engineers and are subjact to mrraction by the author(s). The material, as presentad, does not necessarily reflect anỹ ifion of the S%iety of Pakolaum Engineers, ita ofimrs, or members. Pa~rs presented at SPE meetings are subject to publication review by Editorial Committaaa of the Society of Pebu[eum Engineers, Electronic reprcdutilon, distribution, or storage of any part of this paper for coinmercial pu~aes withoul the written consent of the Society of Petroleum Engineers is titsd.Permission to reproduce in print is restricted to an abstract of not more than 3c0 words; il[uatrations may not ba copied. The abstract must contain conspicuous awledgment of where and by whom the paper was presentad. Wte Librarian, SPE, P.O. Box 833S38, Ri~ardaon, TX 750S3-3S3S, U,S.A, fax 01-972-952-9435. AbstractAn efficient approach to wellbore stability analysis and management of shale instability by taking into consideration the dominant instability mechanism(s) has been developed. The mechanism(s) is dependent on the type of shale, in-situ stress environment and drilling fluid system used. These factors determine whether a drilling fluid program can be developed using a mechanical (stress-induced) wellbore stability analysis or complex time-dependent drilling fluidshale interaction and thermal mechanisms need to be taken into account.A range of wellbore stability analytical tools for efficient management of shale instability is presented. A pragmatic approach to use drilling fluid design charts together with a shale property database and property correlations for designing optimal drilling fluids to manage shale instability efficiently is described. me utilisation of the tools is demonstrated through a field case study in which strategies are developed to control wellbore instability in horizontal wells. Parametric analyses conducted demonstrate the effects of shale and drilling fluid properties on time-dependent wellbore (instability. They highlight the conditions in which the drilling fluid-shale interaction mechanisms are critical and need to be incorporated in the analysis.