Economic and Physical Optimization of Hydraulic Fracturing

Abstract

Optimization has taken several different hues in all areas of engineering. Hydraulic fracturing, as applied to petroleum wells, has had its share. In the past, and before the maturing of high-permeability fracturing and the tip screen out techniques, this well stimulation procedure was limited to low-permeability reservoirs and unrestricted fracturing. In such cases, the fracture length would be an appropriate design optimization variable against an economic criterion, e.g., the Net Present Value (NPV). This involved the balancing of incremental future revenue against the cost of execution. Also interesting are parametric studies, allowing the variation of execution variables and the detection of differences in their respective design NPV. Such differences would be useful in decisions to measure a variable or stay within reasonable assumptions. The emergence of higher-permeability fracturing and the Unified Fracture Design (UFD) concept allowed two important notions. First, there is no difference between low and high-permeability reservoirs in terms of benefiting for fracturing. Just execution issues need to be resolved. Second, and more important, for any mass of proppant to be injected in any well, there exists only one fracture geometry that would maximize production. This geometry, consisting of length and propped width (with height as a parasitic variable) can be readily determined and, if placed, it will provide the maximum productivity index. All other configurations would result in lower productivity values. This is physical optimization.In this paper we combine the two: the economic and physical. For each proppant mass we first optimize the fracture physically and then we apply the NPV criterion. We perform a series of parametric studies for a range of reservoirs and we use economic variables that differ in various parts of the world. We show how to determine the optimum fracture size. We then show how fracture treatments may be attractive in certain reservoirs in mature areas but not attractive elsewhere. We also show that for a diversified company, given the choice, few successful fractures in high-permeability reservoirs are far preferable to fracturing large numbers of wells in lower permeability fields, although the latter can be made economically attractive only through hydraulic fracturing.

How to Decide Between Horizontal Transverse, Horizontal Longitudinal and Vertical Fractured Completion

“…Thus, it is once again clear that fracturing gas wells is beneficial not only for stimulation but also for reducing overall turbulence effects. As we have repeated before in other publication (Wang and Economides, 2004;Marongiu-Porcu et al, 2008;Marongiu-Porcu et al, 2009) one "cannot afford not to fracture" any gas well.…”

Purposefully built underground natural gas storage

“…The second is economic optimization and, again, the only way to accomplish it is to iterate on the mass of proppant, i.e. the fracture size, balancing incremental production and therefore, economic benefits against the costs of the treatment (Marongiu-Porcu et al, 2008).…”

Key issues in high-performance natural gas wells

“…If the cost of drilling vertical and horizontal wells is similar and the cost of fracturing is relatively small, multiple transverse fracturing of horizontal wells is attractive. This has been employed widely in North America and has been the reason for the major success in monetizing shale gas reservoirs (Marongiu-Porcu et al, 2009, 2008. If the cost of drilling horizontal wells is far larger than the cost of drilling vertical wells, then transverse fracturing may not be attractive at all above certain reservoir permeability, such as 0.5 md.…”