Horizontal Drilling TechnologyTue, 01/22/2013 - 17:15
The first horizontal well was drilled in 1929 in Texon, Texas at a depth of around 500 feet (152.4m), when horizontal drilling did not really have any true practical applications. Nonetheless, due to the fact that most oil and gas reservoirs are more extensive in their horizontal dimensions than in their vertical thickness, horizontal drilling exposes more reservoir rock to the well bore and thus brings more financial and production benefits to oil and gas operators.
However, even though horizontal wells generally offer more benefits and a higher production rate than vertical wells, they come at a cost of around 300% more than vertical wells. For this reason, even though they offer more benefits, they are only used in places where vertical wells
would not offer the production needed to make the well profitable. For example, in a reservoir with a high matrix permeability, no gas cap, and no water intrusion, drilling a horizontal well would not be recommended, because a vertical well would offer similar productivity at a lower cost. But if an oil reservoir has low matrix permeability and there is no potential gas and/or water interference, then a horizontal well could offer more profitability because it could increase well productivity by 2.5 to 7 times the rate of a vertical well.
In essence, horizontal drilling is the process of drilling a vertical well from the surface to a target just above the oil and/or gas reservoir – called the kickoff-point – and then changing direction to penetrate the reservoir horizontally – called the entry-point – until the bottom-hole location is reached. The first section of the well is usually drilled using the same technique as a vertical well, where the drill string is rotated at the surface and consists of multiple joints of steel alloy drill pipe, drill collars, and the drill bit itself. However, in order to begin drilling the horizontal well the drill bit is rotated using a hydraulic motor and through a steerable downhole motor the steering of the hole is accomplished.
In order to make sure the well is being drilled in the right direction, depth, and at the right speed, downhole instrument packages that have azimuth sensors provide inclination and directional information and transmit the information wirelessly to the operator at the surface. These state-of-the-art sensors and mechanisms allow operators to calculate the exact position of the drill bit at all times, and depending on the types of sensors, they could also include information on the downhole environment, such as temperature, pressure, and weight, rotational speed, and torque of the drill bit.
Besides the financial and technological benefits of horizontal drilling, this technique also allows operators to develop oil and gas reservoirs with a significantly smaller number of wells, due to the fact that each horizontal well has the capability to drain a larger rock volume than a vertical well. Additionally, horizontal drilling also offers the benefit of reducing the footprint of oil and gas operations and they reduce production obstacles and challenges that may cause low production rates, low recovery efficiencies, and premature well abandonment.