ABSTRACT: Horizontal Hole Drilling Increases Recovery and Production in a Pinnacle Reef

Graeme Bloy, Richard Davis

In 1989, a horizontal hole was successfully drilled in northern Alberta through the Keg River "G" pool, a Rainbow member limestone pinnacle reef. This pool has a 2.3 · 10⁶ m³ (14.5 × 10⁶ bbl) of original oil in place and has been on secondary solvent miscible flood for most of its production history. Production has decreased from 500 m³ of oil/day (3145 bopd) to 150 m³ o/d (944 BOPD) from two wells. The production decline was due to high solvent coning. The pool became a candidate for a horizontal hole to improve recovery of its remaining reserves and to increase oil production rates by the reduction of solvent coning. Placement of the horizontal hole had to be as structurally low as possible, leaving little cellar oil unrecovered. Understanding facies distribution and their diagenesis within the reef was important in determining the hole placement.

This pinnacle reef is composed of three stages of growth: (1) lower Middle Keg River mud mound, (2) upper Middle Keg River reef, and (3) upper Keg River shoal. Each stage is composed of a number of facies and represents the changes in depositional environment within the Rainbow basin. Dolomitization overprints the margin facies of stages 1 and 2. Each facies has unique reservoir characteristics, most importantly the mud mound lagoon facies has little vertical permeability. The horizontal hole was drilled 2 m above this facies.

The hole was drilled 178 m horizontally through the reef, and open-hole completed. Presently, the horizontal hole is capable of producing in excess of 400 m³ of oil/day (2515 BOPD), with one-fifth the drawdown of a conventional vertical hole, and incremental oil recovery is estimated at 115000 m³ (723,270 bbl) of oil.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990