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.