Theoretical and statistical methods of determining recovery factors ofsolution, associated and non-associated natural gas, including gas condensate, are presented as a set of practical tools. The effects of recovery mechanisms and pool and gas-well performance on gasrecovery are examined for conditions applying to constant volume, water drive, gravity segregation and secondary recovery. Ways of recognizing such cases areindicated. The supporting techniques comprise material balance calculations, performance predictions and statistical analyses of depleted pool and predictedrecovery data. In material balance calculations, the gas recovery is consideredin terms of either:initial gas in place multiplied by a recovery factor orinitial gas in place less the gas remaining at abandonment. Performance predictions are based on geological, engineering and economic factors. The background study dealt with explicit correlations between:recovery factor, abandonment pressure or related expressions and pool depth, pay thickness, initial reservoir pressure, flow capacity and size of gas accumulation; andequivalent residual gas saturation and formation water saturation, porosity, permeability and specific surface area. The format for several correlationspresented is predetermined by theoretical considerations. Existing short-cutmethods are also evaluated. Easy-to-use approximations readily yield reliableestimations despite their simplicity and can be of considerable significance;however, the practicing engineer is urged to recognize and understand their limitations. An extensive review of methods of determining recovery and an analysis ofmany evaluations by industry form the foundation for the recommended guidelinesto serve the engineer. The methods of determining recovery factors areconsidered according to their practicality; i.e. the availability ofdata and the complexity of implementation. Useful relationships are classified, important steps of the proposed procedures are outlined and severalapplications are illustrated.
On March 7, 1978, a successful field test of the recovery of oil from under river ice was conducted on the North Saskatchewan River in Alberta, Canada. The ice was 28 inches (70 cm) thick, the water depth ranged from 1.5 to 7.9 ft (0.5 to 2.4 m) and the average water current was 1.3 ft/second (40 cm/sec). Dyed vegetable oil and crude oil were released under the ice upstream of a recovery slot which was 4 ft (1.2 m) wide, 400 ft (122 m) long, and placed at an angle of 30 degrees to the current. Almost all the vegetable and crude oil that was released under the river ice was intercepted by the slot and diverted to the slower current at the downstream end of the slot where it was readily recovered with a specially-constructed weir skimmer. From experiments in small 4 ft by 4 ft (1.2 m by 1.2 m) slots cut in the ice, it was determined that a slot would hold about a 5 inch (12 cm) layer of oil on the water surface for an ice thickness of 28 inches (70 cm) and an average current of 1.6 ft/sec (50 cm/s). A trenching machine (Ditch Witch) proved effective for cutting the ice. Ice blocks about 3 ft by 4 ft (1 m by 1.3 m) were formed and pushed along the slot to the river bank. There, each ice block was lifted with a mobile crane by means of a cable and T-bar inserted through a 6 inch (15 cm) diameter hole drilled in the centre of the block. The load bearing capacity of the ice was critical in determining the type and size of equipment that could operate safely on the ice. The project was conducted by the Prairie Region Oil Spill Containment and Recovery Advisory Committee and was financed by the Canadian Petroleum Association, Environment Canada, and the Petroleum Association for the Conservation of the Canadian Environment.
ABSTRAS'I' continued drilling and recent oil and gas discoveries in the arctic have increased the need for an improved under-standing bfor design purposes) of the thermal disturbance." in permafrost caused by drilling and production operations. Techniques have been developed for fabricating a multi-conductor cable with thermistors for measuring downhole temperatures. These thermistor cables have been success-fully placed in the permafrost zone at several arctic Well locations by strapping the cable to the surface casing as it is being run. This monitoring has provided useful informa-tion on the wellbore temperature profile during drilling, the thermal behaviour during placing and setting of cement, and the rate of freezeback in the permafrost zone. Thermistors can be used also to measure thermal distur-bances resulting from oil or gas testing or production operations, to obtain data for checking the accuracy of thermal simulation programs and, at equilibrium condi-tions, to establish the base of the permafrost and the geo-thermal gradient through the permafrost. N. M. KLJUCEC A. TELFORD N. -M. KLJUCEC holds Dipl. degree in Chemical Engineering from the University of Zagreb (Yugoslavia) and M.Sc. degree in Physics from the University of Man-itoba. He joined Imperial Oil Limited in 1968 and worked as a research engineer at their Production Research and Technical Service Iaboratory in Calgary. Recently he has heen transferred to Field Services Department (Dril-ling Engineeriing Section) in Edmonton. Mr. Kljucee is a member of CIM and the Association of Professional Engineers of Alberta. ALAN S. TELFORD is a section leader at Imperial Oil Limited's Technical Service and Production Research Lab-oratory in Calgary. He holds a B.Sc degree from the -University of Manchester, England, and a M.Se. from the University of Calgary in chemical engineering. Mr. Telford is a Member of CIM. , Montreal INTRODUCTION REcentOil AND and gas DISCOVERIES in the arctic have in-creased the need, for design purposes, for an im-proved understanding of the thermal disturbances in permafrost by drilling and production opera-thickness can vary from a few feet to I,500 feet or more. Permafrost depth and tempera-ture regime are influenced by topography, climate, vegetation and formation type. Equilibrium temperatures of permafrost can range from 5'F to 32'F; seasonal temperatures changes affect only the upper-50 to 100 feet. The presence of massive ground ice, ice lenses and wedges is generally restricted to the 100 feet. Above the permtfrost is a thin eictive layer, I to 3 feet thick, which thaws in summer and refreezes each winter.Drilling, completion and production operations in permafrost areas pose unique problems. Ice-consolid-ated silt, sand and gravel can cause drilling difficulties when thawed. Ice forming in casing annuli can result in casing collapse. Considerable research is being di-rected at these and related problems of artic oper-tions and several novel solutions have already been developed Special cements that will set at subfre...
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