Page 388 - Fundamentals of Gas Shale Reservoirs
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368   GAS SHALE CHALLENGES OVER THE ASSET LIFE CYCLE

                It is understood that most international horizontal shale   improvements in many drilling environments worldwide.
                wells will be probably be drilled with WBM.      Drilling optimization is based on the continuous improve-
                 • Mud weights depend on formation, which ranges from   ment cycle. Each well has slightly different challenges, but
                normal to overpressured.                         successive well captures additional drilling efficiency. Drilling
                 • In a cost‐sensitive environment, motors (positive dis-  shale wells presents technical challenges that impact the
                placement motors, PDM) are used to drill the curve and   overarching goal of optimizing drilling costs and reducing
                the lateral sections.                            days on wells. The quality of pre‐well planning impacts both
                 • Most operators use poly‐diamond crystalline (PDC)   drilling spend and ultimate recovery. Therefore, an integrated
                                                                 approach is required to ensure that all the available reservoir
                bits in the shale.                               data, geoscience, and geomechanical knowledge and down‐
                 • Early preference for drilling wells in the “toe up” atti-  hole conditions are well understood prior to planning the
                tude is gradually changing to drilling the lateral as flat   details of shale wells.
                as possible  and perfectly horizontal  (toe up attitude   The planning for the drilling pathway must take into
                selection based on fact that gravity would facilitate   account the need to maximize the contact of the well with
                drainage of any fluids collecting along the lateral into   the reservoir. It is recommended that the curve and lateral
                the mother hole, thus allowing production/lifting from   part of shale wells be drilled using rotary steerable systems
                the well).                                       (RSS) in order to reduce drilling risk, promote wellbore
                 • Wells are drilled in the direction of minimum horizontal   stability, increase rig efficiency, increase the contact of the
                stress.                                          well with the reservoir, and deliver holes of superior
                 • Typical drilling time in Barnett and Marcellus = 12   quality at a price comparable to motors. These new tools
                days, and Eagle Ford = 17 days.                  are becoming increasingly popular in shale plays.  The
                 • Typically,  wells  using  the plug‐and‐perf  method  are   importance of a high‐quality hole cannot be emphasized
                completed with a 4½″ or 5½″ production string.   too much. Poor quality boreholes will, in many cases, lead
                 • US operators are quickly adopting the practice of pad   to a poorly completed well or one where significant amount
                drilling (4–10 wells per pad), and currently over 60%   of repair must be undertaken prior to well completion. An
                of US shale wells are being drilled from pads. Savings   RSS is typically more efficient than using motors because
                are achieved from logistics and the operation protects   of the continuous near‐bit information and automatic
                the environment.                                 steering capability. Today with the advancement of modern
                 • The “drilling cost” constitutes 40–50% of the total well   drilling technology, it is possible to drill the build/curve
                                                                 section and the lateral section in “one single run” using
                cost (hydraulic fracture treatment cost is the major part   high build rate RSS.
                of a completed well cost).
                                                                   Some of the other drilling technological advances include
                                                                 Janwadkar et al. (2006), bottom assembly hole (BHA) and
            Due to the unique nature of shale, every basin, play, well,   drilling string modeling to optimize Barnett drilling
            and pay zone may require a different approach. Complex   performance; Janwadkar et al. (2007), advanced (LWD) and
            reservoir characteristics pose different drilling challenges   directional drilling technologies to overcome completion
            related to well placement, wellbore stability, higher torque   challenges in Barnett horizontals; Janwadkar et al. (2009),
            and drag, inconsistent buildup rates, geological uncer-  innovative rotary steerable system to overcome challenges
            tainties, lost circulation zones, and other issues.
                                                                 of the Woodford complex well profiles; Isbell et al. (2010),
                                                                 new use of PDC bits to improve performance in shale plays;
                                                                 and Janwadkar et al. (2010), using electromagnetic MWD to
            17.5.4  Design Wells and Optimize Drilling Costs—    improve Fayetteville drilling performance.
            Recommended Practice
                                                                   Once the target zone has been identified, it is important to
            Operators have already seen the benefits of horizontal   place the well bore in the optimal part of the reservoir fol-
            wells in US shale plays.  With the available modern   lowing the natural formation dip and moving to follow
            horizontal drilling technology, it is possible to efficiently   faults. With today’s modern MWD (measurement while dril-
            drill and complete these wells. This author supports fol-  ling) and LWD (logging while drilling) tools it is possible to
            lowing a strict regimen of careful planning and execution   use reservoir navigation services (Fig.  17.5) where engi-
            that is included in drilling optimization process. Drilling   neers use the shale analysis with available seismic and offset
            optimization involves a proven and highly disciplined pro-  well data to plan the trajectory of the well bore. During dril-
            cess that includes the following steps: (i) pre‐project anal-  ling, the LWD data are monitored by experts located in
            ysis, (ii) planning, (iii) implementation, (iv) detailed post   remote drilling centers and modifications are made to the
            well  analysis,  and  (v)  Knowledge  capture.  The  effective   trajectory to maintain the well bore in the optimal zone and
            application of this process has delivered substantial drilling   in the sweet spots.
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