Impact of Ash Beds on Production in Eagle Ford Shale

Abstract

The Eagle Ford shale contains both kaolinite-and smectite-rich altered ash beds that present challenges for completion and production. Considering the five Eagle Ford units (A-E), the ash beds occur in the B unit. The B unit is divided into five subunits; B1 and B2 are characterized by the highest total organic carbon (TOC) whereas B3-B5 have a higher frequency of ash beds. The impact of these ash beds is not yet fully understood, but acquired horizontal production log measurements indicate that the production performance of stages landed in the B3-B5 units, with high ash bed frequencies, are poor compared to other stages landed in a different unit. Some operators are vertically staggering laterals to effectively drain the reservoirs, partially due to the lack of vertical connection in the production phase. Thus, to increase the effectiveness of the completion strategy and ultimately the well performance, methods must be developed to quantify the impact of ash beds on production and to mitigate the negative impact. An integrated hydraulic fracture-reservoir modeling workflow was applied on an Eagle Ford shale lateral with part of the lateral crossing an ash bed in B3-B5 units. The subject well was completed with 15 stages. The simulation results demonstrate that the ash beds in B3-B5 units restrict part of the created hydraulic fracture height and create conductivity pinch points, thus reducing the effective fracture height connected to the wellbore. This, in turn, affects the potential well productivity. Based on the simulated results, the optimum lateral landing location is within the B1-B2 interval. The analysis also showed that targeting the hydrocarbons in these units requires a different completion strategy. Use of a crosslinked fluid carrying higher proppant concentrations will facilitate the creation of larger fracture widths to withstand the negative impact of the ash beds isolating a certain portion of the created fracture height.

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“…The other application known to the authors is in unconventional shale gas samples, sometimes volcanic ash beds are found (can be mm or meters thick) and these are known to fluoresce easily under UV excitation. A well-known example are the ash beds found in the Cretaceous Eagle Ford Shale of Texas, USA; studies indicate it has 55-110 volcanic ash beds and has been the topic/mentioned in multiple studies because of its impact on petroleum production (Amin et al, 2021;Lehrmann et al, 2019;Zeng et al, 2018;Xu et al, 2016;Lock, 2014) because it affects the fracture propagation that result from fracking and is easily detected/verified by fluorescence in drill core or outcrop.…”