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 [[Production_problems#Water-gas_coning|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.<ref name=Carteretal_1998 />

* Reservoirs prone to [[Production_problems#Water-gas_coning|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.<ref name=Carteretal_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 8–10&deg; API gravity oil.<ref name=Tankersleyandwaite_2002>Tankersley, T. H., and M. W. Waite, 2002, [https://www.onepetro.org/conference-paper/SPE-78957-MS Reservoir modeling for horizontal exploitation of a giant heavy oil field-Challenges and lessons learned]: Presented at the SPE International Thermal Operations and Heavy Oil Symposium and International Horizontal Well Technology Conference, November 4-7, 2002, Calgary, Canada, SPE Paper 78957, 6p.</ref>

* 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 8–10&deg; [[API gravity]] oil.<ref name=Tankersleyandwaite_2002>Tankersley, T. H., and M. W. Waite, 2002, [https://www.onepetro.org/conference-paper/SPE-78957-MS Reservoir modeling for horizontal exploitation of a giant heavy oil field-Challenges and lessons learned]: Presented at the SPE International Thermal Operations and Heavy Oil Symposium and International Horizontal Well Technology Conference, November 4-7, 2002, Calgary, Canada, SPE Paper 78957, 6p.</ref>

* 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.