* Change in gas volume = (''GB''<sub>gi</sub> – ''GB''<sub>g</sub>) + [''N''<sub>p</sub>''R''<sub>p</sub> ''(N'' – ''N''<sub>p</sub>) – NR<sub>si</sub>]''B''<sub>g</sub> due to gas produced, evolved, and encroached from a gas cap | * Change in gas volume = (''GB''<sub>gi</sub> – ''GB''<sub>g</sub>) + [''N''<sub>p</sub>''R''<sub>p</sub> ''(N'' – ''N''<sub>p</sub>) – NR<sub>si</sub>]''B''<sub>g</sub> due to gas produced, evolved, and encroached from a gas cap |