Horizontal Well Infill Development of the Manor Spearfish Field

Abstract

Abstract The Manor Spearfish Field, located in Southeast Saskatchewan, was originally discovered in 1987, with the drilling of several vertical wells that encountered remnant Spearfish sands on top of the Alida carbonates. A few vertical wells were produced at low rates. In 1992, several companies aggressively developed the pool entirely through horizontal drilling. Production peaked at 1,100 m3/d, then declined to just over 110 m3/d. The pool has been the target of recent horizontal infill drilling. Several successful wells have been drilled, and Spearfish production from Crescent Point Energy operated wells has doubled from under 100 m3/d to almost 200 m3/d. Additional infill locations remain, both with new stand-alone horizontal wells and with horizontal re-entry wells. This paper reviews the predicted and actual results of five horizontal infill wells drilled in 2002. The methodology used in prioritizing the infill locations is also intended to illustrate the basic principles of reservoir engineering, and how they can be applied through simple analytical methods to yield favourable results. The paper, as such, provides a review of the basic engineering steps needed in a successful infill well development project. Background The Manor Spearfish Field is located approximately 3 km southwest of the town of Manor, Saskatchewan. It consists of Triassic aged Spearfish sands, [also called Lower Watrous or Amaranth sands(1)], which on-lap the Mississippian erosional surface and form reservoir grade sand bodies up to 8 m in thickness. The primary sands are the P-2 Lower or "C" sand and the P-2 Upper or "B" sand. The two sand layers vary from 1 to 3 m, with the thinner sands having more anhydrite occlusion and dolomite cementation. Porosity varies between 15 - 18%, and permeability varies between 5 - 25 mD. The top seal is formed by the impermeable overlying terrestrial Red Beds. Oil is sourced and charged from the underlying Alida beds, due to the absence of effective Mississipian cap-rock. The target of horizontal drilling is the P-2 Upper sand. There is some separation between the Upper and Lower P-2 sands in places, but it appears that there is likely communication through the barrier. There are also various amounts of separation between the Alida and the Lower P-2 sand. Pool Performance The pool was discovered in 1987 and production commenced from several vertical wells. Production was never very prolific, due to the low permeability nature of the reservoir. Figure 1 illustrates a map of the field and outlines the location of the horizontal infill wells. During the horizontal drilling boom of the early 1990s, the pool was aggressively developed, entirely with horizontal wells. Production dramatically increased and peaked in 1992, at approximately 1,100 m3/d. It should be noted that total production presented here is for Crescent Point Energy operated wells, only because the data is more current. Thus, the Spearfish production operated by Crescent Point peaked at 950 m3/d. Production then declined in an apparent harmonic fashion; rapidly at first, then leveling off at slower decline rates.