Is there a "Silver Bullet Technique" For Stimulating California's Monterey Shale?

Abstract

AbstractA large number of California's Central Valley, coastal, and offshore oilfields produce from the Miocene Monterey shale formation. Example oilfields with productive Monterey intervals include offshore and inland fields such as Hondo, Point Arguello, Lost Hills, Elk Hills, Belridge, and North Shafter/Rose. Example productive formation members that produce from the Monterey shale would include the Antelope Shale, McLure shale, McDonald Shale, and the Reef Ridge. The Monterey shale is both a reservoir and hydrocarbon source rock. There are large variations in reservoir properties and general interval behavior due to differences in the lithology, diagenetic state, mechanical properties, and the stress state. Generally the Monterey shale has a low matrix permeability of 0.01–1.0 md, but effective permeability can be higher due to natural fracture conductivity. Porosity spans a huge range – from as low at 10% to as high as 70%.One illustrative example is in Southeast Lost Hills, where vertical wells are drilled and hydraulically fractured to target thick Opal-CT and the deeper cherty/quartz-phase Monterey pay intervals. The design and placement of multiple fracture treatment stages with appropriate conductivity and half-length is a requirement for a successful field development. In contrast, offshore Monterey developments have usually targeted intersecting the conductive natural fracture network in quartz-phase intervals. For this flavor of the Monterey, an acid job can effectively stimulate production by removing the drilling/completion damage and dissolving the calcite filling in natural fractures.A significant thickness of Monterey siliceous shale is present across a large area in California. The oil industry has learned much from unconventional shale reservoir development elsewhere in the country. Is it possible that Monterey siliceous shale will be transformed into the California version of an ‘unconventional’ shale resource? The key will be to identify the Monterey intervals with the most potential, and apply the proper development drilling and completion strategy, with changes made to accommodate the low-mobility multiphase liquid flow. General Monterey development challenges include: a) defining the structure, b) identifying the target pay intervals within the thick depositional intervals, c) understanding the lithology and the reservoir / rock properties of the different pay zones, d) understanding and designing the optimum stimulation treatment(s) and e) determining the optimum well development pattern and completion strategy to incorporate all the above requirements. Is there a "silver bullet" strategy that will enable success in the pervasive Monterey siliceous shale? The purpose of this paper is to stimulate industry thought and discussion.