A Low Cost Microproppant for Flattening Production Declines Using an Industrial Byproduct
Authors: Barba Robert , Crenshaw James , Wilie Curtis 
Published: September 2024

Unconventional reservoir production declines are notoriously steep in part due to up to 75% to 90% of the flow area being unpropped (Barba 2015 and Sharma 2015.) The second referenced study coined the term "induced unpropped" (IU) fractures to describe the flow path in the unpropped portions of the reservoir. As the closure stress on the reservoir increases with depletion these are more likely to close off than propped fractures and can result in a gradual reduction in total flow area. In addition to the steep declines there are two other indications that many of these IU fractures do not remain conductive as the effective stress increases. The first is that the production "bump" from an offset well FDI typically returns the to the original decline in approximately two to three years (Gupta 2012). A possible mechanism is the offset well was stimulated with the distal extent of a low or unpropped conductivity fracture that degraded with the effective stress increase from depletion. A second indication is the reduction in producing height in time lapse geochemical surveys (Ge 2022). With the low viscosity fluids, fracture widths are already challenged especially at as the distance from the lateral to the IU fractures increases with increasingly less hydraulic pressure due to friction losses. Natural fractures and induced microfractures have been shown to have aperture widths of generally less than 0.1 mm (Anders 2014). In theory, if these sub 100 mesh width (less than 0.15 mm) IU fractures can be propped with microproppant during the treatment to maintain conductivity flow can possibly be maintained. The P50 mesh size for fly ash is 320 mesh with a range from 800 to 200. There have been multiple studies done that show this can happen even with relatively small microproppant volumes and suggests this theory has credence. In spite of these largely positive results the use of microproppant has not been widely adopted in organic shale completions. In the case of one major operator that did several trials and published positive results they have cut back their microproppant use due to the high cost of the currently commercially available products. This study proposes that a significantly lower cost system is available with fly ash. Fly ash is an industrial byproduct from coal fired power plants. The P50 size is 320 mesh and has a similar mesh size distribution to the current commercially available ceramic products. It has been shown to create high conductivity fracture systems in over 70 wells as a stand-alone proppant. The delivered cost is approximately the same as Ottowa which is approximately half of the cost of the commercial ceramic products. With the higher cost commercially available microproppants operators typically pump relatively small volumes. The operator mentioned earlier that had seen success with microproppants in the Bakken had been pumping a maximum of 2% of the stage proppant volumes due to the high cost per pound. With the use of fly ash the microproppant cost per pound will not increase for operators already pumping Ottowa (as in the Bakken) and will only increase by a factor of plus or minus two for local sand treatments vs a factor of four for the ceramic products already on the market.