Advancements in Extended Reach Drilling technology enable drillers to reach targets beyond imagination
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Advancements in Extended Reach Drilling technology enable drillers to reach targets beyond imagination

Saturday, 07 November 2015 17:34 Written by 

Understanding Extended Reach Drilling

Extended Reach Drilling (ERD) is a type of directional drilling where horizontal section is very long compared to vertical length of the well. In general the ratio of measured depth (MD) and true vertical depth (TVD) of extended reach wells is higher than 2.0. Through ERD the operators aims to reach larger length of the well from one drilling location and keep the well in the reservoir for a longer distance to maximise productivity. ERD show the utmost use of current technology advancements and precision of drilling a well. Wells are drilled to the target depth as per the drilling program. Extended reach drilling can be done on the new well or it can be done on the well which is already producing. Extended-reach wells are expensive and technically challenging thus planning for ERD is a very important step.

Logging while drilling, Measurement while drilling and Geo-steering plays a vital role in ERD as these technologies together guide the well in the right direction and keeps the well in the play area for maximum length and hence reaching the target finally. This real-time information bought from the subsurface helps the driller to achieve the desired results.

Scenarios where Extended Reach Drilling is preferred

One of the main reasons of adopting ERD by operators is to avoid offshore drilling. Currently operators are employing land rig to reach the offshore target by reducing the cost of drilling. This helps operator to reduce environmental impact, well site infrastructure and operational footprints. At the same time it gets the maximum reservoir exposure to produce Oil & Gas from the zone of interest.

Secondly, environmentally sensitive and protected areas (which are previously inaccessible) can be approached to reach reservoirs in developed through ERD technology. Under this scenario Artic is a good example where ERD technology is very appropriate. Recently it has been observed that ERD is used to improve recovery in offshore fields. Use of ERD in offshore operations reduces the field development cost.

Technological challenges

The main technological challenges faced in ERD include controlling torque and drag, fluid circulation, maintaining directional control, hole cleaning, managing the mechanical loads on the drill string, buckling, Limited WOB and downhole pressure etc.

Typically, the ERD operations are stopped when one or more of the following occurs:

  • 1. The hole becomes unstable, due either to time exposure, geomechanical interaction, adverse pressure differential, or drilling fluids interaction (or incompatibility). The onset of these conditions usually results in the sudden increase of torque and drag in the drill string not related to dogleg severity (DLS) of the hole or the length of the drilled section.
  • The drillstring no longer travels to the bottom of the hole due to excessive drag. This is differentiated from the preceding in that this effect is not related to the friction factor, which remains unchanged. Instead, it is related to the cumulative length drilled along with the DLS of the hole as drilled.
  • When rotation is used to overcome friction and advance the drillstring, such as in rotary steerable application. The limit is reached when you reach the torque capacity of the tubulars.

Current trend and ERD recod

In order to access reserves and extend the life of mature fields, a strong demand for cost effective ERD has increased currently. As the ERD envelope has rapidly evolved during the l990s, many operators are now reassessing field opportunities previously considered uneconomic, when an onerous capital investment in new equipment was necessary. The industry is looking into the possibility of doing highly deviated extended reach wells in deep water environments. Before doing so different simulations are done to investigate which factors will limit the maximum well trajectory and to figure out of far it is theoretically possible to drill in horizontal and vertical direction.

As per recent industry news, Rosneft (Russian oil and gas operator) has completed drilling world’s longest ERD well in Russian Sakhlain island. As revealed by Rosneft in April 2015, well O-14 in Chayvo field has reached a record breaking measured depth of 13,500 m with length of horizontal section is 12,033 m.

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