The Rose field in central California produces oil from the McLure shale, a low permeability overpressured quartz-phase siliceous shale interval at 8,000 ft depth. The field has been developed with horizontal wells, completed with an uncemented liner and a single hydraulic fracture treatment to cover the average 2,500 ft lateral length. Based on initial vertical well experience in the adjoining North Shafter field, this horizontal well strategy greatly improves the ability to place hydraulic fracture treatments, and improves well economics by accessing a greater volume of reservoir rock per well. However, the half-mile-long completion interval and the uncemented liner unavoidably add uncertainty to fracture treatment distribution along the lateral.
Using limited entry perforation strategy, does the completion technique effectively stimulate the entire target lateral interval? To assist with answering this question, the fracture diagnostic of surface tiltmeter fracture mapping was used to evaluate fracture growth during the nine fracture treatments. Tilt results include fracture orientation and the approximate location and volume distribution of fracture components along the lateral.
The original intention of the uncemented liner strategy in the McLure shale was to align the wellbore with the preferred fracture orientation, thus resulting in the initiation and propagation of a simple longitudinal fracture along the entire lateral. However, the actual fracture growth pattern was found to be much more complex, with vertical fracture components in two orthogonal directions, and a significant horizontal fracture component. Considering overall averages, about 45% of fracture volume was contained in transverse fracture components (N60°W), while 35% of fracture volume was in longitudinal components (N30°E), and the remainder in horizontal fractures. This complex multiple-component fracture growth is believed to be due to a small in-situ stress bias, combined with the impact of the completion technique and the naturally fractured character of the McLure shale.
Fracture orientation and approximate component distribution along the lateral are compared and discussed for the nine treatments evaluated. Although the uncemented liner technique did not achieve the original intent of longitudinal fracture dominance, reasonable lateral coverage was achieved. Based on one-year cumulative production, the limited dataset is suggestive, but not conclusive, that horizontal and transverse fracture growth is preferable to longitudinal fracture growth.
Author(s): C.B. Lackey, W.A. Minner; StrataGen Engineering, J. Du; Pinnacle Technologies Inc., B.L. Ganong, EOG Resources Inc.; S.L. Demetrius; C.A. Wright; Pinnacle Technologies Inc.
Paper Number: SPE 83503