defining

1930s, a controlled directional well was drilled in Huntington Beach, California, USA, from an onshore location to target offshore oil sands.

Today, operators use sophisticated drilling assemblies to drill complex geologic structures identi?ed from 3D seismic data. Previously unreachable reserves have become accessible and economical to produce.

Directional drilling includes three main specialized applications: extended-reach drilling (ERD), multilateral drilling and short-radius drilling. Operators have used ERD to access offshore reservoirs from land locations, sometimes eliminating the need for a platform. As of 2013, the world’s longest ERD well is the 12,345-m [40,502-ft] well drilled from Sakhalin Island, Russia, to the offshore Odoptu ?eld. Multilateral drilling helps increase wellbore con-tact with hydrocarbon-producing zones by branching multiple extensions off a single borehole. The ?rst multilateral well was drilled in 1953 at Bashkiria capability and drilling ef?ciency of a BHA.

By varying stabilizer placement in the drillstring, directional drillers can alter side forces acting on the bit and the BHA, causing it to increase, main-tain or decrease inclination, commonly referred to as building, holding or dropping angle, respectively (below).

? To build angle, the directional driller uses a BHA with a full gauge near-bit stabilizer, another stabilizer between 15 to 27 m [50 to 90 ft] above the ?rst and a third stabilizer about 9 m [30 ft] above the second. This BHA acts as a fulcrum, exerting a positive side force at the bit. ? To hold angle, the directional driller uses a BHA with 3 to 5 stabilizers, placed about 9 m apart. This packed BHA is designed to exert no net side force.? To drop angle, the directional driller uses a BHA with the ?rst stabilizer 9 to 27 m behind the bit. This BHA acts as a pendulum, exerting a negative

Kicking off—Diverting a well path from one trajectory to another iscalled kicking off. The number of KOPs in a single well path depends on thecomplexity of the planned trajectory.

Sidetracking—De?ecting a well path from an existing wellbore, or side-tracking, is performed for a variety of reasons such as avoiding a well col-lapse, a zone of instability or a section of previously drilled wellborecontaining unretrieved?sh (junk or tools left in the well). This technique isalso used to initiate multilateral drilling operations. Operators also drill ver-tical pilot holes to con?rm reservoir true vertical depth (TVD), then side-trackhorizontallytomaximizereservoirexposure.Theysometimessidetrack wells when expected targets are not encountered.

Whipstockoperations—Awhipstockisawedge-shapedsteeltooldeployed downhole to mechanically alter the well path. The whipstock isoriented to de?ect the bit from the original borehole at a slight angle and inthe direction of the desired azimuth for the sidetrack. It can be used incased or open holes.

Geosteering—Geosteeringusesformationevaluationdataobtainedwhile drilling—primarily through measurements-while-drilling (MWD) orlogging-while-drilling (LWD) sensors—to provide real-time input for steer-ing decisions in horizontal and high-angle wells. Recent improvements intelemetry allow MWD and LWD data to be transmitted faster and withgreater data density than in the past, greatly increasing the accuracy withwhich the well trajectory can be controlled.

Advances in Directional Drilling

The development of reliable mud motors provided an important advance indirectional drilling technology. Wellbore direction could then be controlledusing a bent motor housing, which was oriented to point the drill bit in thedesired direction. Mud motors use the mud pumped through a rotor and statorassembly to turn the bit without rotating the drillstring from the surface. Byalternating intervals of rotating mode and sliding mode, the directional driller

can control the wellbore trajectory and steer it in the desired direction. Inrotatingmode, the drilling rig’s rotary table or its topdrive rotates the entiredrillstring to transmit power to the bit. By contrast, inslidingmode, the bendand bit are ?rst oriented in the desired direction, then the downhole mudmotor alone powers the bit, with no rotation of the drillstring above the bit.Drilling motors and rotary steerable systems (RSSs) presented direc-tional drillers with an ef?cient way to steer wells—and to do so with greateraccuracy. The RSS enables wells to be drilled directionally while the drill-string continuously rotates. The advantages of this method are improvedwell cleaning through rotation, a smoother wellbore and more accuratedirectional control. To steer the RSS, the directional driller transmits com-mands from the surface using pressure ?uctuations in the mud column.Today, hybrid RSSs use pads inside the tool to push against an internalsleeve that pivots and points the bit in the desired direction. These tools candeliver DLS of up to 18°/30 m. Hybrid RSS tools enable directional drillersto kick off from vertical at greater depths andland, or transition the well tohorizontal, more quickly than was previously possible. This techniqueincreases wellbore exposure to the reservoir(above).

Advanced steering systems use a system-matched mud motor in combi-nation with an RSS tool below it. This BHA design enables higher revolu-tions per minute at the bit, enhanced steering control and increased rateof penetration.

Future Developments

The introduction of fully automated downhole control systems is likelywithin the near future. Such advances, however, do not herald the removalof directional drillers from the process; their experience will always beneeded to oversee the full scope of directional drilling operations. Thefuture promises to be fast moving and technologically groundbreaking forthis highly specialized niche within the oil and gas industry.

Winter 2013/201455

久久建筑網i5h4u.cn提供大量：建筑圖紙、施工方案、工程書籍、建筑論文、合同表格、標準規(guī)范、CAD圖紙等內容。