Fracturing Horizontal Transverse, Horizontal Longitudinal and Vertical Wells: Criteria for Decision

Abstract

Fracturing has become ubiquitous in the petroleum industry to the point that, at least in North America, almost all natural gas and the vast majority of oil wells are fractured. In fact there are more fracturing treatments than there are wells because of multiple treatments in many wells. Because of recent activities in shale gas, hydraulic fracturing of horizontal wells has become increasingly popular. However, not all reservoirs lend themselves to the same fracture and well architecture. Other than deviated wells which we do not recommend, to match proper well architecture (vertical versus horizontal) and number and size of treatments is a very important production engineering exercise. For gas wells one of the most important additional considerations is turbulence which happens in two places: the reservoir and then in the created fracture. This paper will discuss production from vertical, horizontal transverse and horizontal longitudinal fractured wells. Calculations of the incremental performance of each configuration are done for both oil and gas wells, using rigorous models for fractured well performance. There are physical and economic limits and criteria. For example, for gas wells in reservoirs above 0.5 md, there is an unacceptable reduction in the performance of each transverse fracture because of enhanced turbulence effects. In such case a vertical fractured well is preferable. There are also economic criteria for selecting which type of completion is the optimum choice. Very low permeability reservoirs while attractive in North America with its controlled costs, they may be very unattractive in other countries. We look at a range of reservoir and proppant pack permeabilities and discuss the optimization of fracture geometry. The paper not only delineates areas of indicated application of each well completion but it highlights the importance of considering the hydraulic fracturing process from the very start of wellbore planning. The processes involved in planning a wellbore for efficient decision making and maximum flexibility of choice are also described.

Performance Comparison of Transversely and Longitudinally Fractured Horizontal Wells Over Varied Reservoir Permeability

“…The fracture configuration is identified from the Barnett Formation stress map shown as Fig. 21b (Gale 2007).…”

“…In 2010, Economides et al continued the same comparison for oil and gas reservoirs with permeability ranging from 0.001 md to 500 md (Economides et al 2010). As in prior work, they compared horizontal wells with transverse or longitudinal fractures with vertical fractured wells by use of the unified fracture-design approach.…”

“…On the basis of these studies, Economides et al (2010) developed a series of recommendations for both gas and oil formations summarized in Table 1, which has been widely referenced in industry studies since. Generally, 10 md was suggested to be the point in oil formations where longitudinal fractured horizontal wells would be a better choice than transverse fractured horizontal wells.…”

Simulation of Fracturing Induced Formation Damage and Gas Production from Fractured Wells in Tight Gas Reservoirs

“…However, there is not a "standard" approach to provide these equivalent parameters, especially for finite conductivity fractured horizontal wells. For example, the analytical choke skin formula (Mukherjee and Economides, 1991;Economides et al 2010), which is proposed for accounting the radial flow around a horizontal well in the fracture plane, is not always suitable for numerical simulations in complex cases as shown in the examples hereafter. Gdanski et al (2006) proposed to use a face skin factor, which is a function of the saturation and the relative permeability, to take into account the fracturing fluid induced formation damage and cleanup effect.…”

Unified Fracture Design for very low permeability reservoirs

“…An important concept introduced by UFD is the Proppant Number, N p , which combines all of the given variables into a single dimensionless number that uniquely determines the optimal values of C fD and, by extension, x f , w f , and the maximum J D . Successful application of UFD has been demonstrated for reservoirs with low to high permeability (Daal and Economides, 2006;Demarchos et al, 2004Demarchos et al, , 2005Economides et al, 2010;Porcu et al, 2008Porcu et al, , 2009). However, UFD has not been applied to reservoirs with very low (nanodarcy) permeability, such as shales.…”