Post-Stimulation Diffusion Time Assessment on Early Hydrocarbon Breakthrough and Initial Water Recovery of Unconventional Wells

Abstract Post-stimulation diffusion time is defined as the time period at which hydraulic fracturing fluids diffuse into the formation after the completion of pumping operations. It is measured from the conclusion of stimulation operations until the well is first opened for post-stimulation flowback operations. The primary objective of this paper is to comprehensively study the impact that diffusion time has on hydrocarbon breakthrough and initial water recovery, and to thoroughly investigate any potential association with overall well performance. The onset of production from unconventional wells that underwent stimulation through hydraulic fracturing is dominated by high water cut, starting from 100% and gradually dropping with time as the well cleans up and hydrocarbons breakthrough into the production stream. The process followed in this paper starts with a broader review on a large group of wells looking at two main parameters with time: water production rate which is expected to peak at the start of production and progressively drop, and the percentage of water recovery after a fixed period of time. After that, the process takes a closer look into a sample set of closely-placed wells that have similar formation properties, to quantify the impact on well performance, specifically through the use of hydrocarbon production and productivity index normalized by lateral length versus time. The first part of the paper investigates a wide spectrum of unconventional wells to establish a baseline understanding on the impact of diffusion time. Looking at initial water production rates, both peak water production and water production profiles were lower with higher diffusion time, indicating an inverse relationship between the two. Similarly, Hydrocarbon breakthrough had an inverse relationship with diffusion time, where gas/oil breakthrough was faster when diffusion time was longer. The second part of the paper looked into the impact of diffusion time on well performance, where a group of wells within close proximity were evaluated. Results from that comparison indicated the absence of a correlation between diffusion time and well performance. Results from this study addressed potential concerns related to shutting in wells post-stimulation in the application area, especially on wells within close proximity where formation properties are relatively homogenous. The novelty of this paper resides in its in-depth examination of a critical transition period between stimulation and production of unconventional wells, which might have been overlooked the past. The approach adopted in this paper can be readily implemented at any unconventional basin, to provide a comparison with the findings from this paper. This in turn broaden its practical application and relevance to the field of unconventional oil and gas production.