With the recent slump in the price of crude oil, it has become essential to improve the net present value (NPV) of unconventional reservoirs by intelligently down-spacing the horizontal wells with multistage fractures wells. Unconventional Liquid-Rich Shale (LRS) reservoirs, characterized by low permeability, require optimal well density in addition to stimulation for economic viability. Optimally designed multi-well facilities simplify well management and maintenance, prevent overcapitalization by eliminating redundant equipment and increase the overall long-term economic outlook of LRS plays.
This paper presents a systematic workflow to identify the best well spacing strategies for liquid rich shale (LRS) plays with multiple fluid gradients and significant multiphase flow. We analyzed the performance of wells with different spacing and fluid composition, ranging from volatile oil to rich gas condensate based on different initial in-situ solution gas oil ratios (GOR). Compositional reservoir simulation was performed on analog wells with drilling and completion techniques similar to several LRS plays to calculate EUR's for different well spacing scenarios. NPV analysis was performed for each case to identify the “cut-off' range, after which further down-spacing causes a negative NPV, with results varying for differen fluid compositions.
The results from the study show that the workflow presented in this paper provides a reliable tool to predict the performance of a various well-spacing conditions in a reservoir with multiphase flow. Well interference increased when well spacing was decreased below a certain threshold value, based on the initial fluid composition and other reservoir parameters. The wells cannibalized each other when they were too closely spaced resulting in lower per-well production. Furthermore, the increase in final cumulative production was negligible beyond a certain well spacing, making it economically unappealing. For gas condensates, reduced well spacing beyond a certain value showed a detrimental effect on final cumulative condensate production due to larger amounts of condensate dropout. We can conclude from the results that increases in NPV of LRS reservoirs require a careful implementation of optimal well spacing based on initial fluid and reservoir conditions.
This paper demonstrates that LRS reservoirs need optimal well spacing for optimum production and favorable NPV. It also provides a reliable methodology to identify proper well spacing for improved overall recovery based on different reservoir and fluid conditions.