Changes

==Success rate vs. depth==

==Success rate vs. depth==

[[file:evaluating-top-and-fault-seal_fig10-45.png|thumb|{{figure number|1}}After .<ref name=ch10r47 /> Copyright: Oil & Gas Journal.]]

[[file:evaluating-top-and-fault-seal_fig10-45.png|thumb|300px|{{figure number|1}}Distribution of oil and gas production from more than 20,000 wells.<ref name=ch10r47 /> Copyright: Oil & Gas Journal.]]

The chance of finding an economically successful accumulation in the Gulf Coast decreases with depth. This decrease is a result of several changes, including [[reservoir quality]] and [[migration pathway]]s. Most importantly, however, the distribution of hydrocarbons is closely related to the top of the overpressure zone. [[:file:evaluating-top-and-fault-seal_fig10-45.png|Figure 1]] shows the distribution of oil and gas production from more than 20,000 wells. Most hydrocarbons are found near or slightly above the top of the overpressured zone. The chance of success is reduced by 90–95% at depths of 2,000–5,000 ft below the top of overpressure.<ref name=ch10r47 />

The chance of finding an economically successful accumulation in the Gulf Coast decreases with depth. This decrease is a result of several changes, including [[reservoir quality]] and [[migration pathway]]s. Most importantly, however, the distribution of hydrocarbons is closely related to the top of the overpressure zone. [[:file:evaluating-top-and-fault-seal_fig10-45.png|Figure 1]] shows the distribution of oil and gas production from more than 20,000 wells. Most hydrocarbons are found near or slightly above the top of the overpressured zone. The chance of success is reduced by 90–95% at depths of 2,000–5,000 ft below the top of overpressure.<ref name=ch10r47 />

==[[Hydrocarbon distribution]] vs. overpressure==

==[[Hydrocarbon distribution]] vs. overpressure==

[[file:evaluating-top-and-fault-seal_fig10-46.png|thumb|{{figure number|2}}After .<ref name=ch10r47 /> Copyright: Oil & Gas Journal.]]

[[file:evaluating-top-and-fault-seal_fig10-46.png|thumb|300px|{{figure number|2}}Distribution of hydrocarbons relative to the top of overpressure changes as reservoir depth changes.<ref name=ch10r47 /> Copyright: Oil & Gas Journal.]]

The distribution of hydrocarbons relative to the top of overpressure changes as reservoir depth changes is shown in [[:file:evaluating-top-and-fault-seal_fig10-46.png|Figure 2]]. This pattern is consistent with loss of top seal integrity because of hydrofracturing rather than a simple loss of reservoir quality or other variable. Deeper reservoirs have the peak gas occurrence below the top of overpressure. This is consistent with the changing P_f with depth. As depth increases, confining pressure increases and thus the amount of pressure required to fracture the top seal (P_f) increases. As fracture pressure increases, the depth of the first intact top seal increases.

The distribution of hydrocarbons relative to the top of overpressure changes as reservoir depth changes is shown in [[:file:evaluating-top-and-fault-seal_fig10-46.png|Figure 2]]. This pattern is consistent with loss of top seal integrity because of hydrofracturing rather than a simple loss of reservoir quality or other variable. Deeper reservoirs have the peak gas occurrence below the top of overpressure. This is consistent with the changing P_f with depth. As depth increases, confining pressure increases and thus the amount of pressure required to fracture the top seal (P_f) increases. As fracture pressure increases, the depth of the first intact top seal increases.