# Extended-Reach Drilling (ERD)--The Main Problems and Current Achievements
###### Abstract  
With the development of different segments within the drilling technology in the last three decades, well drilling has become possible in harsh downhole conditions. The vertical well provides access to oil and gas reserves located at a certain depth directly below the wellsite, and a large number of vertical wells are required for the exploitation of hydrocarbons from spatially expanded deposits. However, the borehole can deviate from the vertical well, which means that the target zone can be reached by a horizontal directional well. With this type of well, especially in the case of drilling an extended-reach well (ERW), the length of the wellbore in contact with the reservoir and/or several separate reservoirs is significantly increased, therefore, it is a much better option for the later production phase. Unfortunately, the application of extended-reach drilling (ERD technology), with all of its advantages, can cause different drilling problems mostly related to the increased torque, drag, hole cleaning and equivalent circulation density (ECD), as well as to an increase in the well price. Overcoming these problems requires continuous operational change to enable operators to address downhole challenges. Today, the longest well reaches 15,240 m (50,000 ft), which raises the question of the technological and economic feasibility of this type of drilling project, especially with the lower oil price on the energy market. This paper provides a comprehensive overview of extended-reach drilling technology, discusses the main problems and analyzes current achievements. well design; extended-reach drilling (ERD); torque; drag; hole cleaning +
Footnote †: journal: selected topics  
breaking in terms of drilling the longest wells. Today, engineers are capable of designing and successfully drilling wells deeper (or rather longer) than 15,240 m (50,000 ft), onshore or offshore. Although extended-reach technology provides numerous benefits over conventional vertical or directional drilling technology, it simultaneously presents a kind of engineered challenge. Hole cleaning problems, an increase in drag and torque an an increased equivalent circulation density are just some of the problems encountered by engineers and, unfortunately, with an increase in wellbore length, the problems become more challenging and difficult to overcome. Today, reservoirs can be developed by wells with a different well construction (Figure 1), even on the same field, and the construction of the particular well depends on numerous factors, such as the reservoir depth and type, local lithology, proven reserves, expected problems, costs, etc. Extended-reach drilling (ERD) technology is essentially an advanced form of directional drilling or horizontal drilling technology. Extended-reach drilling employs both directional and horizontal drilling techniques. It has the ability to achieve horizontal well departures and total vertical depth-to-horizontal distance ratios well beyond conventional directional drilling [3]. An extended-reach well is defined as a well where the ratio between the horizontal reach (departure) and true vertical depth (TVD) is larger than 2, or where the horizontal displacement is greater than 20,000 (6096 m) [4; 5; 6; 7]. With today's industry challenges in meeting ever-increasing production targets and maximizing the full potential from maturing fields, horizontal or complex trajectories are now accepted as standard practice or warranted as a viable design for field development [8]. Figure 2 shows the ratio of the well length vs. the true vertical depth and the reach for wells such as BD-04, M-16, OP-11 and Z-44, which have recently been drilled. When the ratio between the measured depth of wells and the true vertical depths of the wells in Figure 2 is compared with the value mentioned just above, it can be assumed that the aforementioned claim must be revised. Today, we are already distinguishing between low-reach, medium-reach, extended-reach and ultra-extended-reach wells.