Guidelines for Economic Design of Multistage Hydraulic Fracturing, Yanchang Tight Formation, Ordos Basin

Abstract

It is common practice to exploit tight oil resources with the assistance of techniques such as horizontal drilling and multistage hydraulic fracturing (MHF). Due to the high capital costs of such techniques and rapid oil decline rates of wells in tight oil reservoirs, the economic performance of a well, which is commonly evaluated by payback period and net present value, becomes crucial in the early stage of exploiting tight oil resources. A reasonable MHF design is one key factor that can benefit a well in both production and economic perspectives. Although many optimization studies have been conducted on MHF designs, hardly any focus has been given to the optimum design of total fracture length, number of stages and number of clusters per stage in the economic perspective for tight oil formations. In this work, economic performances under different MHF designs were studied through a series of numerical simulations and a statistical study for the Yanchang tight formation, Ordos Basin. Three matrix permeability levels (0.06 md, 0.10 md and 0.22 md) were considered in a single-well simulation model. In total, 264 MHF designs were investigated. The results showed that the production in the first 5 years was significant for a well to make a profit for a tight formation with a permeability less than 0.22 md. With a higher matrix permeability, the payback period became shorter under the same MHF design. This study also found that the NPV of a well with MHF can be expressed as a quadratic function of the fracture half-length. R2 values of parabolic correlations were more than 0.91 for all three permeability levels. With increasing matrix permeability, the R2 value increases. For tight formations with similar reservoir properties, this type of correlation can be used to evaluate MHF designs under the given economic parameters. It is worth noting that the optimal MHF design from the production perspective does not always lead to that from the economic perspective. Therefore, the economic optimization of MHF designs is necessary for tight oil formations. A rule of thumb for designing MHF is to have a longer fracture half-length, a smaller number of clusters and a smaller number of stages for tight oil formations with permeabilities in the range of 0.06 to 0.22 md.