A Study of Transversely vs Longitudinally Fractured Horizontal Wells ina Moderate-Permeability Gas Reservoir
- Tianyu Liu (Texas A&M University) | Matteo Marongiu-Porcu (Economides Consultants) | Christine A. Ehlig-Economides (Texas A&M University) | Michael J. Economides (University of Houston)
- Document ID
- Society of Petroleum Engineers
- SPE Kuwait International Petroleum Conference and Exhibition, 10-12 December, Kuwait City, Kuwait
- Publication Date
- Document Type
- Conference Paper
- 2012. Society of Petroleum Engineers
- 2.5.1 Fracture design and containment, 2 Well Completion, 4.6 Natural Gas, 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 2.5.2 Fracturing Materials (Fluids, Proppant), 1.6 Drilling Operations, 5.8.2 Shale Gas
- Hydraulic Fracturing, transverse fracture, Gas reservoir, net present value, longitudinal fracture
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Transverse fractures created from horizontal wells are a common choice in tight and shale gas reservoirs. Previous work has shown that proppant pack permeability reduction due to non-Darcy flow in a transverse fracture from a horizontal well causes significant reduction in the fracture performance when the gas formation permeability exceeds 0.5 md. There are other configurations and architectures such as aligning the well trajectory with the fracture, either by drilling horizontal wells in the direction that results in longitudinal fractures or by just sticking with drilling vertical wells. However, when drilling and fracturing costs are considered, productivity is not the only optimization consideration.
The field example illustrates a case when the apparent choice to use transverse fractures from horizontal wells proved to be suboptimal from the productivity perspective, but fundamental considering economics. Parametric studies for permeability ranging from 0.01 to 5 md illustrate the importance of economics in addition to physical performance. For similar reservoir characteristics, the optimum fractured well architecture varies considerably, and therefore an extensive reservoir engineering approach may be necessary beyond the well completions and/or current prejudices and inadequate understanding.
The Unified Fracture Design (UFD) approach was introduced by Economides et al. (2002a), using the Proppant Number, Np, as the important correlating parameter. It generates a powerful output: for a given mass of proppant injected which fracture geometry would maximize well performance. As such it constitutes a physical optimization scheme.
Previous studies have addressed both vertical and horizontal wells considering both oil and gas production. For gas production there is a need to adjust the fracture design to account for non-Darcy flow, especially for transverse hydraulic fractures created in horizontal wells. Economides and Martin (2010), indicated that vertical wells with vertical fractures outperform multiple transverse fractures in horizontal wells for permeability above 0.5 md. However, another possibility would be to create longitudinal fractures from horizontal wells drilled in the direction normal to minimum stress.
This paper begins by reviewing the UFD approach, how it is adjusted for gas reservoirs, and how non-Darcy flow impacts both transverse and longitudinal fractures in horizontal wells. Then a field example contrasts well performance for wells with transverse fractures with that of wells with longitudinal fractures for reservoir permeability ranging from 0.01 to 5 md. Our conclusion is that completion strategies with highest productivity may not provide the best value.
|File Size||470 KB||Number of Pages||14|