Reinterpretation of Performance of Horizontal Well Pilot No. 1 (HWPI) 1980 - 1989
Authors: Ito Y. , Singhal A.K. 
Published: March 2010

The performance of Imperial Oil Resources Ltd.'s Horizontal Well Pilot No.1 (HWPI) was reinterpreted using numerical simulation. It appears plausible that the performance was significantly influenced by geomechanical deformation of the reservoir.

The project is a successful thermal horizontal well pilot that has recovered more than 50,000 m3 of 10 ° API Cold Lake Clearwater bitumen over the last decade at an oil-steam ratio of over 0.35. Steam is injected via a vertical injector, and oil produced via a horizontal producer. It was observed that oil rates, as well as oil cuts improved when steaming was discontinued. Consequently, the bulk of the oil was recovered when steam was not being injected.

This behaviour could not be explained by any of the conventional theories regarding thermal operations. It is speculated that geomechanical effects (namely, increases and decreases in porosity with pressurization and depressurization, creation of flow channels due to formation-dilation upon steam injection, transport of heat and fluids deep into the reservoir via these channels, etc.), as first proposed by Ito, and termed "Sand Deformation," may be responsible for this production behaviour. To test this hypothesis, the performance of the pilot for the first eight years was simulated.

Excellent history matches were obtained. Many interesting field observations were made, such as (1) oil production improved when steaming was stopped, (2) low fluid production was seen for the first two and a half years of operation, and (3) lower than expected amount of energy was produced.

Changes in porosity, permeability and relative permeability to water with pressure, as required for obtaining a satisfactory history match, are larger than those determined in the laboratory. This discrepancy needs to be investigated by further research.

Introduction

The first horizontal well in the oil sands was drilled in 1978 at Cold lake by Imperial Oil. It was drilled from the surface and has a horizontal slotted section of 245 m total length. It served as a production well. A vertical injection well was located over the horizontal well at a distance of 45 m from the toe end of the slotted section. Over 50,000 m3 of bitumen has been recovered at a cumulative oil-steam ratio (OSR) of over 0.35 during the first eight years of operation.

Performance during the first eight years of operation, as well as data for comprehensive field monitoring program, including bottom hole pressures and reservoir temperatures, were presented by Adegbesan et al.(1) Analytical models were developed and recovery mechanisms were also investigated. It was concluded that recovery mechanisms changed with elapsed time of the project. The results of a numerical history match of the subject well pair were presented by Adegbesan(2). Many interesting concepts, including geomechanical deformation, were used for obtaining the history match. A good match of the cumulative oil production was obtained. According to Butler(3), during the Steam Assisted Gravity Drainage (SAGD) process, production rates will increase as a steam chamber spreads along a horizontal production well with a vertical injector. He developed equations to calculate oil production rate during the spreading period.