Effective Hydraulic Fracturing Of The Lower Amaranth Formation In Southern Manitoba

Abstract

Abstract The Spearfish, or more properly, Lower Amaranth Formation in southwest Manitoba is a low permeability sandstone reservoir containing low GOR light oil. Wells drilled into this formation are generally not capable of commercial production until after a hydraulic fracturing stimulation. Factors such as an underlying water zone, along with an unconfined producing interval, have resulted in numerous hydraulically fractured Lower Amaranth wells producing water rather than-oil, limiting potential field development. Following the unsuccessful stimulation of several wells in the South Pierson field where hydraulic fractures propagated into the underlying water zone, a comprehensive re-evaluation and detailed design effort was implemented to minimize the potential for water production. The project incorporated geological studies; reservoir rock elastic properties determination and correlation with wireline logging techniques; determination of horizontal in situ stresses; reservoir performance testing; in situ fracture fluid performance evaluations; and two- and three-dimensional fracture geometry modelling techniques. It has resulted in new treatment designs incorporating fracture diversion anti-net pressure control techniques. This paper discusses the general stratigraphy of the Lower Amaranth zone and the completion requirements. Presented are the design concepts, data analyses and results of a number of Lower Amaranth Formation stimulations. Optimal treatment considerations and guidelines are provided to minimize the probability of water production following hydraulic fracture stimulation. Introduction Hydraulic fracturing has long been the most economic technique for the purpose of stimulating low permeability reservoirs and providing for commercial production of oil and gas. The success of fracture stimulation treatments depends primarily on achieving large contact area with the production interval and providing a large permeability contrast and high flow capacity within the fracture. Ideally, the hydraulic fracture created should extend laterally within the zone of interest, however, it is well known that substantial vertical fracture propagation may also occur, significantly impacting the success of the treatment. Complicating factors such as underlying water zones or overlying gas sections can be easily penetrated and subsequently reduce or eliminate any sought after oil production. BenNaceur and Touboul(12) considered the problem of a vertical fracture intersecting a formation with the underlying water zone. Several factors have been shown to influence the production of such a system, including the fracture extent and its distance from the water transition zone, its dimensionless conductivity, the vertical permeability or absence thereof, the relative permeability curves, and finally the mobility ratio between oil and water. It was shown that in addition to the benefit of increasing productivity, hydraulic fracturing resulted in a significant delay of the water breakthrough, even with values of vertical permeability being one-tenth the horizontal one. The major concern in the current study was to avoid any fracture propagation through an underlying low-permeability interval downward into a porous dolomite section that would have resulted in water breakthrough using the fracture as a flow path. Additional motivation for control of fracture height growth was to increase the effectiveness of the treatment by decreasing the extension into non-producing intervals and to reduce the over-all cost of the treatments.