TABLE OF CONTENTS Horizontal wells are suitable for gas reservoirs. They are applicable in low-permeability reservoirs as well as in high-permeability gas reservoirs.
In the low-permeability reservoirs, it is difficult to drain large volumes using vertical wells. For example: reservoirs with permeabilities of less than 0.01 md may need vertical wells with less than 40-acre spacing to drain them effectively in a reasonable time frame. Fracturing vertical wells does help drainage, but creating long fractures in a tight reservoir is difficult. Horizontal wells provide an alternative to achieve long penetration lengths in the formations.
In high-permeability gas reservoirs, wellbore turbulence limits the deliverability of a vertical well. To reduce turbulence near the wellbore, the only alternative is to reduce the gas velocity around the wellbore. This can be partly achieved by fracturing a vertical well. However, fracturing is not very effective in a high-permeability reservoir, because proppants themselves have a limited flow capacity, which may be comparable to that of the reservoir rock. The most effective way to reduce gas velocity around the wellbore is to reduce the amount of gas production per unit well length. This can be accomplished by using horizontal wells. The long wells may produce less gas per unit well length than a vertical well, but total horizontal-well production can be higher than for a vertical well because of the long length. Thus, horizontal wells provide an excellent method to minimize near-well-bore turbulence, and at the same time, enhance total gas production from a well.
