Lateral O&G drilling

Most people have heard of fracking in the context of oil and gas (O&G) drilling and maybe a few of them know that this can be done in horizontal drilling at a distance from the surface well hole. Explosives or hydraulic pressure is used to fracture a section of rock formation surround the drill hole and then frac sand is forced into the fractures to prop them open. Sometimes the sand is referred to as a proppant. This increases the permeability of the formation and, hopefully, increases the productivity of the well.

The first directional drilling was performed in 1930 from shore at Huntington Beach, CA, into an offshore deposit of oilsands.

The fracking controversy stems from evidence that fracturing can lead to O&G migration into ground water and then into drinking water. This essay does not address this matter.

Within the O&G drilling world is the question of how far laterally a hole can be drilled and to what extent it pays. According to one source, in 1997 the lateral distance stood at about 500 ft to completion. At present it stands at 3 miles with 4 miles becoming more common. Greater length requires an upgrade in drilling equipment to handle the extra power demands.

Today there are steerable down-hole mud motors that can rotate the drill bit independent of the drill string. Mud is pumped downhole at high pressure to rotate a rotor connected to the bit. The rotor fits in a stator near the end of the drill string. A steerable feature is able to bend ~3 to 4 degrees.

In the literature there is mention of the issues in vertical drilling through a steeply inclined fault. As the bit penetrates a steep fault surface it could slip and lead to damage of the drill string and casing. Better to penetrate a fault perpendicular to the fault plane with directional drilling.

There are many good reasons for a driller to use directional drilling.

• A borehole that has gone off-course can be redirected to the desired direction from the same borehole.
• From a single drilling site multiple boreholes can be drilled, each going to a different part of the formation.
• During a well blow-out or fire, a new borehole can be drilled from a distance to intercept the blown-out borehole and pump material into it to control the blow-out.
• A drilling site can be situated away from a settlement or body of water and still get to the oil reservoir by directional drilling.
• Directional drilling can be performed in an existing well where equipment or debris is blocking the original bore hole.
• Drilling through a salt dome is problematic for several reasons. A soft formation like a salt dome can result in bit balling where the tricone bit packs with debris and the wheels quit turning. Wellbore erosion, salt creep, and excessive mud losses can occur as well.

Salt domes form from plastic deformation of an underlying low density and ductile salt layer (90 to 99 % halite) into a fault or fracture where it is subject to movement by lateral forces of the surrounding sediment layers. These lateral forces push the salt formation in the direction of weakest forces which is generally upwards. Irregular features in the salt dome can lead to collection of oil and gas pockets. Lateral drilling can be used to access the reservoirs, bypassing the salt formation.