Directional Drilling For Shale Gas
WHAT IS DIRECTIONAL DRILLING?
If a wellbore is intentionally deviated, the result is a directional well. Deviated wells are commonplace in shale gas plays such as the Barnett Shale and Marcellus Shale.
The reason is that shale traps a tremendous amount of natural gas but is not very permeable.
To combat this problem, fracking has been combined with horizontal drilling.
First a horizontal well bore is drilled into the shale formation. Second, the well is fracked. Fracking is a process in which water, sand and chemicals are imploded in the shale, creating holes that the natural gas can flow through in to the well.
The combination of horizontal drilling and fracking has made possible the extraction of shale gas at a cost reasonable to producers. It is estimated that the US has enough shale gas to last for 110 years.
Deviated wells begin with a straight wellbore drilled to a predetermined depth called the "kick off point". It is at this point that the directional company arrives at the drilling rig location.
The concept behind horizontal drilling is simple: point the rock drill bit in the direction you want it to go. The most common way to accomplish this is to place a bend near the bit in the downhole steerable motor. As mud pumps through the motor, the drill bit rotates but the drill string does not.
If the intention is to drill a straight hole but the geological formations are unpredictable or dip extremely, drilling tools can be added to the BHA to control deviation.
Directional drillers can make or break a bit run. Fatigue, experience and personal bias for or against the particular drill bit being run all play an important role in drill bit performance.
Typically, either a button bit or a PDC drill bit is used in horizontal drilling. Manufacturers have designed specific button bits that run on a motor, taking into consideration many design factors that affect the bit's performance.
If RSS (rotary steerable system) is used, a rotary steerable drill bit specifically designed for the particular system should be used as well. All major bit companies including Halliburton, Reed, Hughes Christensen and Smith have designed RSS drill bits.
BHA or Bottom Hole Assembly
BHA is extremely important as it definitely has an impact on drill bit performance. For instance, mud motor failure can cause impact damage to a PDC bit. Heavyweight drill pipe is also important as it provides a flexible transition from the drill collars and drill pipe. It also is used to provide additional weight on bit (WOB).
BHA is the section of downhole tools that connects the drill pipe to the rock bit. A slick BHA has no stabilizers. Stabilizers are considered an important drilling tool to avoid deviation in the well hole.
When drilling a straight hole rather than a deviated one, fewer BHA components are needed. Standard drilling tools are: rock bit, bit sub, jars, various crossovers, stabilizers and heavy weight drillpipe. A downhole motor may be used as well. The motor can be either a high speed or a low speed motor.
Horizontal drilling applications require additional drilling tools. Mud motors, MWD (measurement while drilling) tools, logging-while-drilling tools are just a few. Additionally, a directional driller (knowledgeable person trained in directional drilling and the tools used) is a must.
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Related Pages: Bakken Shale: The Bakken Shale was at one time considered to be a marginal find because the oil was trapped in such low permeable shale. Deepwater Horizon: Transocean's Deepwater Horizon burned for two days and then sank - an equipment loss of over $200 million. Directional Drilling: Directional drilling is common practice in shale gas plays such as the Bakken and Barnett Shale, and the selection of drilling tools is critical. Drilling Mud: Drilling mud can be oil, air, or water based. It cools and cleans the bit, stabilizes the well bore, and creates wallcake. Exxon Valdez: The effects of the Exxon Valdez oil spill are still being felt almost 30 years later. Natural Gas Drilling: Natural gas drilling looks to continue because the natural gas reserves of the United States are large enough to fuel our needs for many years to come. Oil Well Drilling: Oil well drilling requires many pre-drilling decisions, such as whether to reverse circulate and which type of drilling mud to use. Shale Oil: Shell Oil Company's in-situ conversion process requires a "freeze wall" around the outside perimeter of the shale oil extraction zone to prevent groundwater contamination. Spindletop: The oil revolution began when Spindletop gushed black gold 150 feet in the air for nine days in 1901, and Howard Hughes invented the roller cone bit. Tar Sands: Tar sands are a black, tar-like combination of clay, sand, water, and bitumen. They are sometimes called "oil sands" to make them seem more appealing. |
