In aspiration to educate its customers, European Geophysical Services has launched a narrow-targeted media campaign aimed at increasing the level of understanding of borehole drilling processes. Being an expert in geophysics, UK-based company has already implemented over 150 borehole drilling projects, which is eventually one of the main company’s specializations.
The basics of horizontal wells
Horizontal well type implies having a stem portion angled to 90° vertically, although other wells drilled at a sharper angle may also fall under this definition. Depending on the horizontal trajectory of the wellbore and drilling technology adopted, horizontal wells are arbitrarily divided into four groups.
Wells with a large radius of curvature of the set are drilled using conventional equipment for directional wells. They are characterized by a set tempo curvature of 1-2˚/10 m and horizontal trunks length of 1500m and more. These wells can be deep enough and have a trunk diameter of up to 444.49 mm.
Horizontal wells are drilled with an average radius of curvature of special downhole motors with bent sub and stabilizers. The pace for the curvature of these wells is set at 3 – 7710 m, the radius of curvature equals 45-300m, while the of diameter horizontal borehole is 311.2 mm.
Horizontal wells are drilled in small radius of curvature with special drilling systems of two types. In mechanical rotary systems composite curving drilling direction with an inner drive shaft to the bit is used. Horizontal wells of small radius of curvature are characterized by a set rate of curvature of 30-100° to 10 m; 90° tilt is gained within 6-12 m range. Horizontal wells of this type are limited by the diameter of the wells drilled by 114,3-165,1 mm diameter bit; the usual length of horizontal section is 180-300 m.
Ultrashort horizontal wells are designed for the development of heavy oil and tar sands technology sidetracking. The technology is based on the use of jetting a downhole drilling head lifting system placed in the reservoir against the expanded area of the vertical well. With such a system of vertical shaft can be quickly spudded several radial horizontal holes with a diameter of 100 mm and a length of 30-60 m.
Horizontal well profile
Horizontal well profile is composed of the guide portion and the horizontal portion. Horizontal profile well may include a vertical section, a portion of the initial curvature, tangential section and sections increasing zenith angle or consist only of the vertical portion and increasing zenith angle.
Horizontal well profile and its horizontal section may be calculated separately; however, they need to be paired with each other.
The purpose of the guide part of the profile of the horizontal well lies in the removal of the barrel at a certain angle to the point of producing formation with specified coordinates. Therefore, when calculating this part of the profile of the horizontal well except for the target depth and the deviation from the vertical wellbore setting the value of the zenith angle at the design depth is required. Moreover, as a rule, the radius of curvature of increasing zenith angle is set.
The method of calculating the guide part of the profile of the horizontal well is based on solving a system of equations projection of the profile on the vertical and horizontal axis. The calculation of the horizontal well profile reduces to determining the length of the vertical portion of horizontal well and the radius of curvature of one of the sections or lengths of the tangential portion.