Husky Oil has been active with the combustion process in the Lloydminster heavy nil area since 1968. Projects have been developed in depleted and virgin reservoirs with net pay from 3 to 8 metres.
The typical facility and well designs for firefload operations in the Lloydminster area are reviewed along with solutions to operational difficulties associated with the combustion process. Operating problems are caused by combustion gas, emulsified fluids. corrosion from combustion products, and sand production.
The recent development of enriched air, or oxygen injection, required modification to conventional fireflood facility and well design, as well as operating procedures. Thepotential benefits of oxygen injection provide further encouragement for the in situ combustion process.
Husky Oil Operations has operated five insitu combustion projects in the Lloydminster area as indicated in Figure 1. The experiences gained in these projects form the basis of this paper.
Combustion has been initiated in both depleted and virgin reservoirs. Reservoir thickness varies from 3 to B metres; oil densities are 950 - 9BO kg/m3 with viscosities from 1000 to 6000 MPa.S. All projects have been combination thermal drive using produced water as well as fresh water injection. Size of projects has varied from 12 to 250 hectares with a variety of pattern arrangements and sizes.
In the Lloydminster area the major operating difficulties are caused by:
Combustion gas production which can limit inflow into the wellbore and cause reduced productivity.
Emulsified produced fluids which cause rod fall problems and high flowline pressure because of their viscosity and treating difficulties because of their stability.
Corrosive products which cause or contribute to reduced life of pumping equipment and surface facilities.
Sand production which causes pumping difficulties and erosion in pumpline and surface equipment.
In all the projects developed each of these have been present, however, the extent of the operating problem varied between wells and projects. This paper outlines some general solutions to adapt to specific conditions.
A typical fireflood completion is shown in Figure 2. Thermal completions are only utilized if steam stimulation may be beneficial. The lower suction of thermal pipe provides protection to about 500 ° F if the well should get hot. Bottom-hold temperatures are also monitored where heat is suspected. Type L thermocouples are utilized in a stainless steel filled with magnesium oxide insulator. They can be run either attached to tubing or inside a hollow rod string; a thermocouple or thermowell run outside the casing has been tested with several new wells. Although all systems have operated satisfactorily, the preferred option is a thermocouple attached outside the tubing.
Venting at the well head has been the usual method of handling the gases with gas collection being installed on recent projects. A produced gas control system is installed, which allows the gas vent rate to be set, controlled and metered automatically.