Abstract

The performance of Horizontal Well Pilot No.1 (HWPI) was reinterpreted usingnumerical simulation. It appears plausible that the performance wassignificantly influenced by geomechanical deformation of the reservoir.

The project is a successful thermal horizontal well pilot that has recoveredmore than 50,000 ml of 10 ° API Cold Lake Clearwater bitumen over the lastdecade at an oil-steam ratio of over 0.35. Steam is injected via a verticalinjector, and oil produced via a horizontal producer. It was observed that oilrates, as well as oil cuts improved when steaming was discontinued. Consequently, the bulk of the oil was recovered when steam was not beinginjected.

This behavior could not be explained by any of the conventional theoriesregarding thermal operations. It is speculated that geomechanical effects(namely, increases and decreases in porosity with pressurization anddepressurization, creation off low channels due to formation dilation uponsteam injection, transport of heat and fluids deep into the reservoir via thesechannels, etc.), as first proposed by Ito, and termed "Sand Deformation ", maybe responsible for this production behavior. To test this hypothesis, theperformance of the pilot for the first eight years was simulated.

Excellent history matches were obtained. Many interesting field observationswere 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 withpressure, as required for obtaining a satisfactory history match, are largerthan those determined in the laboratory. This discrepancy needs to beinvestigated 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 slottedsection of 245 m total length. It served as a production well. A verticalinjection well was located over the horizontal well at a distance of 45 m fromthe end of the slotted section. Over 50,000 m3 of bitumen has beenrecovered at a cumulative oil-steam ratio (OSR) of over 0.35 during the firsteight years of operation.

Performance during the first eight years of operation, as well as data forcomprehensive field monitoring program, including bottom-hole pressures andreservoir temperatures, were presented by Adegbesan et al. (1). Analyticalmodels were developed and recovery mechanisms were also investigated. It wasconcluded that recovery mechanisms changed with elapsed time of the project. The results of a numerical history match of the subject well pair werepresented by Adegbesan (2). Many interesting concepts, including geomechanicaldeformation, were used for obtaining the history match. A good match of thecumulative oil production was obtained. According to Butler (3), during the Steam Assisted Gravity Drainage (SAGD) process, production rates will increaseas a steam chamber spreads along a horizontal production well with a verticalinjector. He developed equations to calculate oil production rate during thespreading period. A good history match in cumulative oil production was alsoobtained using his approach.

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