New Methods for Determining Infill Drilling Potential in Large Tight Gas Basins
Authors: Guan L. , Gao H. , Du Y. , Wang Z. 
Published: March 2010

Abstract
It has been acknowledged that infill drilling can improve the recovery of hydrocarbons by accelerating production as most reservoirs in the world are not homogeneous. With the increasing demand for energy and higher oil and gas prices, more and more fields all over the world are undergoing infill drilling.
This paper discusses two recently developed techniques to determine the infill drilling potential in large tight gas reservoirs and it summarizes what petroleum engineers have learnt about the application of those two techniques. Field examples are also included in this paper to demonstrate the usefulness, as well as the limitations, of these techniques to help independent operators develop operation and design strategies for current and future infill drilling projects in large tight gas basins.

Introduction
The importance of enhanced oil recovery (EOR) technology cannot be overemphasized, especially in the context of a country, such as the U.S., with declining domestic petroleum production and increased imports. Combine this with the fact that the probability of finding new petroleum discoveries continues to decrease, which only reinforces the need for EOR technology.
The significance of EOR lies in the promise it holds for increasing the expected production from existing oil fields. In mature petroleum reservoirs, such as those U.S. onshore fields, the growth of reserves in existing oil fields typically contributes more to the industry's continued viability than the discovery of new fields. In other words, in thoroughly explored reservoirs, better technology, more accurate reservoir characterization and more effective production from known fields add new reserves faster than does exploration for new fields.
It has been known that infill drilling can improve the recovery of hydrocarbons by accelerating hydrocarbon production because most reservoirs in the world are not homogeneous(1–7). Driscoll(1), Gould and Munoz(2) and Gould and Sarem(4) summarized the various factors that contribute to increased recovery after infill drilling:Improved areal sweepArea heterogeneityImproved vertical sweepLateral pay connectivityRecovery of ‘Wedge-edge’ oilReduced economic limits
Infill drilling of additional wells after initial development (primary and/or secondary) played an important role in improving the oil and gas recovery in tight hydrocarbon reservoirs(6). Generally speaking, the reservoir heterogeneity and layer continuity can be changed by the well spacing. The infill drill wells reduce the well spacing of the hydrocarbon fields and then enhance the well connectivity. Wu et al.(7) reported the results of their study to determine the impact of infill drilling on waterflood recovery in a West Texas carbonate reservoir. Their study shows a certain degree of correlation between waterflood recovery and well spacing.
Recently, with the increasing demand for energy and favorable oil and gas prices, more and more fields all over the world are undergoing infill drilling. The advances in reservoir management provide a much clearer picture of hydrocarbon distribution in reservoirs which helps petroleum engineers to plan highly effective well profiles and advanced imaging technologies allow hydrocarbon field operators to select the best locations for infill drilling to optimize well placement.