| dc.description.abstract | Onshore Oil and Gas production in the United States today primarily consists of exploiting unconventional shale reservoirs. Due to the low permeability of this type of formation, a stimulation method is required. A very common and effective method is hydraulic fracturing. The costs of hydraulic fracturing is highly variable and is dependent on many criteria, such as the cost of pumping proppant. Proppant in hydraulic fracturing maintains the fracture network open once the closure stress of the reservoir is applied, allowing for the flow of fluids to the wellbore. The mass quantity of proppant is dependent of the size of the hydraulic fracturing job. The cost of a fracture treatment can fluctuate due to the location, quantity, and quality of the proppant. The objective of this study is to find alternative proppants that can provide technical merit and economic benefits.
A multitude of proppants were tested for this study including local and premium sands, as well as taconite tailings, which is a low-grade iron ore. These proppants were tested in a variety of mesh sizes. The fracture conductivity and the strength of each proppant were compared under idealized conditions, utilizing the standard API conductivity test cell.
Fracture conductivity is the ability of a proppant pack to transport fracture fluid to through the fracture. Thus, a measurement of this value can provide insight into the effectiveness of the stimulation. The testing of fracture conductivity regarding all proppants will be adhered to by the API RP 61 procedure. This procedure is the recommended practice for evaluating short term proppant pack conductivity and has been put in place by the American Petroleum Institute. Proppant is the solids used in hydraulic fracturing that maintains the fracture open once the pumping is stopped and the reservoir closure stress is applied to the fracture. Proppant can be natural sands or man mad materials, such as ceramics.
As per the recommendation of API RP 61, a series of closure stresses is utilized ranging from 1000 psi – 6000 psi, in 1000 psi intervals, in order to test the fracture conductivity. To obtain results that relate to the strength of an individual proppant, a sieve analysis is conducted before and after a fracture conductivity test is completed. The sieve analysis provides a size distribution of the proppant ranging from 20 mesh-170 mesh. Thus, once the proppant has been exposed to very high closure stress, it experiences crushing of some sort. The size distribution of the proppant after crushing is then be compared to the initial distribution.
As can be expected, all proppants display a higher conductivity when a larger proppant mesh size is used. The strength of the proppant, relating to the Young’s modulus of the material, as well as the shape, help to further validate the results of the testing. Overall, conventional sand provided better and more consistent conductivity. The conductivity of the taconite shows a wide range of results that is highly dependent on the purity of the proppant sample. | |
