A very important but often difficult question to answer when dealing with gas reservoirs is: to drill or not to drill? Why are some gas pools only drilled at two wells per section and some drilled up to 16 wells per section? How do you decide whether downspacing will be beneficial? An accurate assessment of important factors such as capacity (kh), original gas-in-place (OGIP), and reservoir continuity is required. This paper describes a set of techniques that can be used to confidently assess kh, OGIP, and continuity in a gas reservoir. This information is then used to help determine if infill drilling has the potential to be beneficial. The following diagnostic techniques are simple to use and do not require a lot of time to perform. These techniques let the historical production/pressure data do the talking, so detailed geological modelling/mapping is not required. This fact, in combination with their effectiveness, makes them a must-have tool in any reservoir engineer's repertoire. The techniques include: Using the inflow equation coupled with simple gas material balance to determine the effectiveness of recent infill wells, along with the determination of kh and OGIP; Looking at initial productivities or initial measured pressure vs. on-production data for a group of wells in the same formation to determine continuity and heterogeneity; and, Calculation of the "depletion index," which is an innovative tool in which the level of depletion is quantified, and can then be used to compare to other pools. The techniques are described in detail and then applied in a case study where infill drilling was successful, and one in which it wasn't so successful, to illustrate how they work.
