Changes

* Low-permeability reservoirs. Where an interval shows low permeabilities, horizontal wells can make up for this by maximizing the contact length with the reservoir. This means that low-permeability rocks such as chalk can produce at economic rates that would be marginal to uneconomic with conventional wells.

* Low-permeability reservoirs. Where an interval shows low permeabilities, horizontal wells can make up for this by maximizing the contact length with the reservoir. This means that low-permeability rocks such as chalk can produce at economic rates that would be marginal to uneconomic with conventional wells.

* Reservoirs prone to coning. Because of the lower drawdown, horizontal wells may be less prone to water or gas coning behavior. For example, horizontal wells have been drilled in the Widuri field, offshore Sumatra, so as to minimize water coning. High vertical permeabilities and viscous oil are factors likely to promote coning behavior in the vertical wells in the field (Carter et al., 1998).

* Reservoirs prone to coning. Because of the lower drawdown, horizontal wells may be less prone to water or gas coning behavior. For example, horizontal wells have been drilled in the Widuri field, offshore Sumatra, so as to minimize water coning. High vertical permeabilities and viscous oil are factors likely to promote coning behavior in the vertical wells in the field (Carter et al., 1998).

 

* Similarly, individual horizontal wells produce more oil in heavy oil reservoirs because the lower pressure drawdown tends to keep water and gas away from the well longer. For example, a total of 110 horizontal wells had been drilled prior to 2002 in the Hamaca field in Venezuela's Orinoco Heavy Oil Belt. The development plan is to ultimately drill over 1000 horizontal laterals to produce the 8–10deg API gravity oil (Tankersley and Waite, 2002).

Similarly, individual horizontal wells produce more oil in heavy oil reservoirs because the lower pressure drawdown tends to keep water and gas away from the well longer. For example, a total of 110 horizontal wells had been drilled prior to 2002 in the Hamaca field in Venezuela's Orinoco Heavy Oil Belt. The development plan is to ultimately drill over 1000 horizontal laterals to produce the 8–10deg API gravity oil (Tankersley and Waite, 2002).

* ''Oil rims,'' thin oil columns typically lying below a gas cap, can be targeted with horizontal wells. The reduced drawdown minimizes the chances of coning water up from the water leg or drawing gas down from the gas cap.

 

Oil rims, thin oil columns typically lying below a gas cap, can be targeted with horizontal wells. The reduced drawdown minimizes the chances of coning water up from the water leg or drawing gas down from the gas cap.

In certain parts of the world, horizontal wells are the well type of preference, whereas conventional wells are much less common. This is true of the Danish North Sea, where chalk is the main reservoir interval, and also in parts of the Middle East such as Qatar, Abu Dhabi, and Oman (Nurmi, 1996).

In certain parts of the world, horizontal wells are the well type of preference, whereas conventional wells are much less common. This is true of the Danish North Sea, where chalk is the main reservoir interval, and also in parts of the Middle East such as Qatar, Abu Dhabi, and Oman (Nurmi, 1996).