Deviated wells

Deviated well (tick marks every 500ft) TD Total depth ft tvss Clay / claystone... 

Horizontal wells were drilled as far back as the 1950s, but have gained great popularity in the last decade, as lower oil prices have forced companies to strive for technologies which reduce the cost of oil and gas recovery. Horizontal wells have potential advantage over vertical or deviated wells for three main reasons ... 

Figure 4-284. Density comparison in a deviated well. (Courtesy Anadrill...

Finally, inadequate hole cleaning results in an overloading of the annulus with cuttings, especially in very high penetration rate, poor mud properties, and insufficient annular velocity or circulation time. Inadequate hole cleaning can also be experienced in deviated wells with the formation of cutting beds on the low side migrating in a sand dune fashion. 

The weight transfer is also an important parameter that can decrease the rate of penetration. In deviated wells, up to 20,000 lb of weight and 25,000 ft-lb of torque can be lost to drag and friction. Figure 4-312 shows the improvement that can be caused by an 11-stand short trip and circulating a mud pill of 15 Ib/bbl of Barafiber. 

Figure 4-320 shows the data recorded in a highly deviated well. 

A. Donche, A. Vaussard, and P. Isambourg. Use of scleroglucane muds for drilling deviated wells (application des boues au scleroglucane au forage des puits devies). Patent FR 2670794, 1992. 

With increased development work from offshore platforms, more non-vertical (deviated) wells are being drilled. Settling of mud solids to the low side of the well bore can result in a continuous channel of undisplaced drilling mud solids in the casing annulus... 

The best gas production well in the world is not a horizontal well but a simple deviated well located in Norge UGS (close to Groningen in Netherlands) with a maximum daily deliverability over 12 MMcm/d. 

Deviations from expected additive effects can be assessed in terms of synergism or antagonism. In only a few cases are the mechanisms underlying such deviations well understood. Interaction typically occurs when 1 substance induces toxifying (or detoxifying) steps effective for another mixture component, which in turn alters profoundly the efficacy of the second chemical. 

Table II. Comparison of Sand-Control Methods for Horizontal and Highly Deviated Wells...

The rapid expansion of horizontal drilling has accelerated the development of numerical methods to calculate the responses of 3D induction logging models that include anisotropic bedding and deviated boreholes with invasion. Indeed, in deviated well with noncylindrical invasion caused by gravity segregation, it is practically impossible to interpret induction responses without 3D modeling. 

In highly deviated wells the readings of conventional induction tools depend on resistivity anisotropy, which was undetectable in vertical wells. To perform the interpretation of logs in horizontal wells it is therefore important to have a modeling code making it possible to take anisotropy into account. 

Shale is strongly anisotropic in diffusivity and O-E as well as strength parameters. Deviated wells encounter anisotropy in any orientation. 

The foregoing simple example serves to introduce the main concepts of statistical analysis of experimental data but is inadequate in dealing with real-world data from chemical analyses. Assumptions (i) and (iii) together imply that the separate experimental values (x and Xj jt) obtained for x are examples of values randomly drawn from an assumed normal distribution with standard deviation well estimated by the experimental parameter Sx. This combined assumption is reasonable (but even then not necessarily valid) if the number of replicate measurements is sufficiently large, as exemplified by the (fictitious) data used to obtain the histograms shown in Figure 8.7 even for 1000 data points the distribution is not well defined and certainly the width parameter s will itself be subject to considerable uncertainty. In real life... 

At present, systematic errors tend to limit the accuracy of electron-dififraction studies more than do random errors. The probability of introducing a serious error by accident seems higher than in other methods for structure determination. Particularly it has too often happened that the scale error has been considerable. To keep the effect of systematic errors under control, it is necessary to study well-known standard compounds rather frequently. If this is done, and especially if the electron-diffraction investigation is combined with spectroscopic data as discussed in Chapter 4, standard deviations well below 0.001 A are obtainable for many compounds with photographic recording. It is possible that counting techniques may reduce the errors still further and also make the method more useful for electron density and energy determinations than it is today. 

Run 2. Next we terminate the steady-state simulation, begin another where we retain that geology (although we need not), and change the shape of Well 2 and other inputs. The re-drilled, more deviated well follows. 

The simulator informs you that you have brought a new well on stream and that the number of wells has increased to two. This drill new wells option always appears in the runtime menu so long as the total number of well clusters is less than the maximum allowable of nine. At this point, you will have separately determined that six blocks, say, are required to define the deviated well needed to penetrate the pay zone. Incidentally, the maximum number of grid blocks supported by the prototype PC simulator is 20 x 20 x 9, or approximately 4,000. The number of well clusters supported is 9, with a maximum number of 200 blocks defining each cluster. The total number of character based lithologies supported is 31. These numbers are easily increased by redimensioning. 

Chin, W.C., 3D/S1M 3D Petroleum Reservoir Simulation for Vertical, Horizontal, and Deviated Wells, Petroleum Engineering Software for the IBM PC and Compatibles, Gulf Publishing, Houston, 1993. 

It is a deviated well (and not a horizontal well) making interpretation of pressure fall offs less uncertain It was already drilled and tested allowing reliable data for designing the injectivity test sequence A significant water injection base line was available at the time of the injectivity test... 

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