Advances in Drilling Technology

Experience With Rotary Steerable System For Reservoir Drilling In Iranian Offshore Oilfields

By: Akshit Patel 11BPE0266th SEM (Upstream)SPT, PDPUContentDirectional Drilling- ApplicationRotary Steerable SystemTypesWorkingBit SelectionField Case HistoryAdvantages and LimitationsSummary

Directional DrillingDirectional Drilling is the science of Deviating a wellbore along a Planned Path to a target located a given lateral distance and direction from vertical.

Reasons for Drilling DIRECTIONAL WELLS

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Source : http://images.pennwellnet.com/ogj/images/ogj2/9651jwa01.gif

Rotary Steerable SystemRSS is a new form of drillingtechnology used in directional drilling.

A tool is designed to drill directionally with continuous rotation from the surface.

Rotary steerable systems have Minimal Interaction with theBorehole, thereby preserving borehole quality.

Steerable without sliding (100% rotation).

Combined with logging tools in the drill string close to the bit, allowing a continuous optimization of the well trajectory.

TypesTwo methods used in RSS:

Push-the-bitPads on the outside of the tool which press against the well bore causing the bit to press on the opposite side resulting in a direction change.

Point-the-bit

Cause the direction of the bit to change relative to the rest of the tool by bending the main shaft running through it.

Require some kind of non-rotating housing or reference housing in order to create this deflection within the shaft.

Push-The-Bit Method

Comprises of TWO units.Bias Unit-Located directly behind the bit which applies force to bit in a controlled direction during rotation of drill string.Control Unit-Resides behind the bias unit , contains self powered electronics, sensors and a control mechanism to provide magnitude and direction to bit. CONTROL UNITBIAS UNITPush-the-bit systemssteer the bit by applying a side load that forces the bit laterally inthe direction of the desired curve11Working Principle

The BIAS UNIT consists of Three Pads that are activated by controlled mud flow.

When the push point comes, the disk valve actuates each pad by diverting the mud flow into the piston chamber of each pad.

When the push point passes the valve cuts off the mud supply and the mud escapes through the bit.

If no change in the direction is required, each pad extends so that pads push in all direction and effectively cancel each other. Each pad cant extend more than 1 cm(3/8 in.).If no change in the direction is required, each pad extended so that pads push in all direction and effectively cancel each other.

13Point-The-Bit Method

Fig: Point the bit system in bent modeDivided into TWO Sub-Assemblies The steering sectionControl section Electronics and Sensor Section Power Generation SectionPoint-the-bit systems steer thebit by tilting the bit in the direction of the desired curve14Working PrincipleThe steering section contains a universal joint, which transmits torque and weight on bit, but permits the axis of the bit to be at an angular offset from the axis of the tool. The offset allows for the directional drilling tendency of the system to be controlled through 3-point contact with the well bore.

The axis of the bit shaft is kept offset by a mandrel, which is maintained geostationary during collar rotation.

To drill straight, the bit-shaft offset rotates at a rate that differs from that of the tool.

The result is a slightly over gauged hole.Fig: Point the bit system in Straight modeIn both the methods, the control unit is mounted on the bearings that allow to rotate freely.

It maintains the proper angle of shaft relative to formation as well as azimuth and inclination of the bit.A control unit near the bit ensures that the hole angle is not increased or decreased rapidly creating dog legs which will result in excessive torque and drag.

Bit SelectionNo matter which method has been selected, the drill bit selection must be done very carefully.Ultimate goal HIGH ROP LOW COSTBit Selection includes factors such as lateral and axial drilling efficiency, gauge pad length and durability.

For PUSH THE BITRequires laterally aggressive bit and also there is less concern about bit induced torque and there is plenty of power available for more aggressive design.

It is important for Every driller to select right drill bit for any roatary steerable system. Because the ultimate goal of driller is to high ROP because high ROPs shorten drilling time and therefor reduces overall costs.

Laterally aggressive bits with little or no passive gauge area in high steerability applications to yield the highest degree of dogleg severity,18For POINT THE BIT

Requires Long Gauge Length and utilize bit tilting for changing direction

steer by tilting the bit, bit designs may feature longer gauge lengths ( for stability purpose)

relationship between applied WOB and the resulting reactive torque.19Field Case HistoryPEDCO is a branch of NIOC formed in 1999. PEDCO has started to improve the Production from one of the biggest Persian golf offshore oilfields since 2002.

It includes drilling new wells or re-entering the well.

Typically re-entry wells takes about 35 days from start of re-entry till completion with conventional mud motor.

So they want to MINIMIZE the NO. of DAYS by increasing ROP.

Sosolution isRSS PEDCO used PUSH The BIT Technology for drilling 1142 m.

Just simply achieving HIGH ROP is not useful, unless and until it is justified both ECONOMICALLY and TIME SAVING. AdvantagesCutting the cost of staying vertical.

Reducing upper-hole collision risk.

Minimizing sticking and borehole stability problems.

Significant time saving through ROP improvementsContinuous effective hole cleaning Drilling of a hole with lower Tortuosity.

Drilling of much more ambitious well trajectories (either complex 3D and/or ERD) with lower technical risk

When drilling vertical wells through dipping beds, especially in tectonically stressed environments, the drilling assembly often tends to build angle along the path of leastresistance. The Revolution V technology is set to maintain zero-degree inclination automatically to prevent any deviation. This feature ensures that vertical wells canbe drilled on target with higher weight on bit, thereby increasing the ROP

drilling multiple directional wells from a single location. While drilling the upper-hole sections of these wells to kick-off point, well teams runthe risk that the wells will collide or tangle. By maintaining verticality, the collision risk is minimized.

Continuous drillstring rotation reduces the risk of stuck pipe and potential resulting wellbore stability issues24Limitation

SummaryDrilling industry is continuously evolving day by day

Rotary Steerable System is the best deflection tool available

This technology will help in planning the well bore geometry even better.

Usage and availability of RSS must increase to make drilling process more accurate and fast

RefrencesMolayee, A., & Teymoori, A. (2006). Experience with Rotary Steerable System for Reservoir Drilling in Iranian Offshore Oilfields. SPE Asia Pacific Oil & Gas Conference and Exhibition. Adelaide: SPE 100917.

http://images.pennwellnet.com/ogj/images/ogj2/9651jwa01.gif

Geoff Downton, A. H. (2000). New Directions in Rotary Steerable Drilling. Oilfiled Review , 18-29.

http://www.weatherford.com/weatherford/groups/web/documents/weatherfordcorp/WFT111035.pdf

Questions?Thank You