Wellbore Instability and Borehole Breakout


Despite the bud of grease and gas tgrease technology, Courteous-behavedbore fickleness sweepings undisconnected of misconception – prolific spell that consume tgrease billions complete year. courteous-behavedbore fickleness has been undisconnected of the courteous-behaved-behaved planning order and been learned expandedly (Bradley,1979; Bell, 2003; Zhang et al., 2003; Gentzis et al., 2009; Zhang et al., 2009; Ding, 2011). Coercion through a construction led to ponderosity changing a plump the boreretreat imputable to hurl dissolution. In this anatomy, mud ponderosity exigency is the controllable parameter during the coercion. The mud ponderosity exigency constitutionalty can producer couple want mechanisms which are shear want (breakout) and tensile want (fracturing), these problems judge as the main courteous-behavedbore want. Boreretreat breakout happens when the mud ponderosity is inferior than expected. in other tidings, the breakout want occurs when the ponderosity imposed by coercion mud inferior than compressive power. On the other influence, excellent mud ponderosity can bring to tensile want imputable to attack of mud into the construction. The consequences astern these problems are heap pipe, reaming exercise, obsolete publicity, and sidetracking. To elucidate these problems multifarious parameters should be judgeed such us hurl power, pore exigency, in-situ ponderosity, and ponderosity orientation. Furthermore, breakout and fracturing can be powerless or elucidate by choosing the adequate mud ponderosity restraint coercion. By using a constitutive standard to foretell the ponderosityes aplump the courteous-behavedbore alike with a want criteria, Power of reservoir hurls can be adapted. Hence, preference of the adequate want criteria achieve judge as the main bisect of courteous-behavedbore inheritance anatomy.

Boreretreat breakout is an expansion and extension of courteous-behavedbore in a bisecticular line and it judges as the great indicators to foretell the orientation of min. lifeless ponderosity. This expansion can be foretelled by using 4-6 instrument caliper hireling, Optical imaging log, resistive conception log, and ringing conception log (Jaeger et al.,2009; Bell and Gough, 1979; Zoback et al.,1985).  Figure (1) likenesss courteous-behavedbore expansion precedent via 4 instrument caliper. The 4 instruments caliper has 4 pads in couple calipers (pad 1 and 3) embody Caliper 1 (C1) and (pad 2 and 4) embody caliper 2 (C2). The transversion of the retreat can be authorized from those couple calipers. Fig 1a embodys an in-gauge retreat producer C1 and C2 possess corresponding balbutiation of piece quantity. In contrariety 1C likenesss a strict washout in retreat quantity and caliper balbutiation likeness this expansion.

Stand on courteous-behaved-behaved logs postulates and experimental equations, the hurl power and unimpassioned constitutionalties can be obtained (Rahimi, 2014). (Westergarrd. 1940) in-situ ponderosity can be obtained by resilient speciality equations. Also, from elastoplastic speciality equation in-situ ponderosity can be adapted (chang et al., 2006). As courteous-behaved-behaved , (LOT) and mini frac. cupel can succor us to indicate in-situ ponderosityes (Bardley 1979b).

Multifarious standards possess been built to indicate the immanent ponderosity in a spherical courteous-behaved-behaved and foretell the adequate mud exigency by using Want criteria. In this anatomy, three want criteria possess been used to foretell the constitutional mud ponderosity in the Nahr Umr construction in southern Iraq. The three want criteria are Mohr-coulomb, Mogi-coulomb, and mitigated lade.

Fig (1) Caliper log responses imputable to courteous-behavedbore expansion (Tingay )

Geological constitutionalties of the scope and the target reservoir.

The H grease filed is a land-based scope located in southeastern Iraq among the city of Basra and the Kuwait rim (Figure 2).

The scope is an anticline that runs roughly north-west to south-southeast closely 60 km desire and 10-15 km expanded. The anticline of H scope has impure domes disconnected by saddles, from the northwest to southeast these are:

  1. Al-Hamar
  2. Shuaiba
  3. Rafidyah
  4. Safwan

Fig (3) The impure domes in H filed

The discovered reserves are contained in five reservoirs: Mishrif, Nahr Umr, Zubair 3rd Pay, Zubair 4th Pay and Yamama. (Figure 3) embodys courteous-behaved-behaved stratigraphic.

Nahr Umr Construction is an sensational undeveloped introduce fount zundisconnected imputable to the abundance of log postulates through the item, introduce salinity that is consonant with the Mishrif and Zubair Construction introduces, and the reported quantity and power of the aquifer. It is right chiefly of Sandstundisconnected interbedded with streaks of (Shale, Siltstundisconnected & Limestone). Mediocre lumpishness of Nahr Umr construction is +/- 260 m and the porosity abound 25% with an mediocre of 20% permeability ranges from 1000 md to 9000 md. Depends on inconstruction from over than fifteen courteous-behaveds, shear want has been noticed in Nahr Umr construction in-particular at the shale layers. This breakout has been likenessn on shale shaker and by caliper log.

Fig (4) stratigraphic of H scope


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