A Case Study of Exploratory Horizontal Drilling in the en Formation; Ceylon en Sand Pool, Southeast Saskatchewan, Canada

Barry A. Hebner, David G. Campbell, Donald G. Bryan

In early 1992, PanCanadian Petroleum Limited drilled the first exploratory horizontal well in Southeast Saskatchewan at Ceylon. A second horizontal well was also drilled into the en formation at 2000 meters depth on the large Ceylon structure by late 1992.

The en formation consists of three informal units. Lower and upper organic rich shale units encase a middle sandstone and siltstone unit. The middle en sandstone development occurs primarily within the Saskatchewan section of the Williston Basin and is the reservoir target.

The Ceylon area was selected to evaluate the productive potential of the naturally fractured, thin pay section of the en formation with horizontal drilling technology. A large structural high at Ceylon, defined by 2D and 3D seismic, projects into the Hummingbird trough. Salt dissolution of the underlying Prairie Evaporite formation and orthogonal sets of strike-slip faults coincide with the margins of the structure. The 3D seismic shot over the structure was used to plan the well trajectories.

A drilling program was designed to minimize formation damage by drilling with invert mud at slightly underbalanced conditions. An oriented core in the vertical pilot hole and a horizontal core were cut in the second well for fracture information and to determine in-situ water saturation.

Intersection of a transitional oil/water contact resulted in high initial water cuts in both wells. Produced water chemistry and inert gases suggest the en fracture network is also connected to deep seated strike-slip faults and act as conduits to deeper formation waters.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995