Downhole Conversion of Lloydminster Heavy Oil Using THAI-CAPRI Process

Abstract

Abstract THAI - ‘Toe-to-Heel Air Injection’ is a radically new process for therecovery and in-situ upgrading of heavy/medium crude oil and bitumen. It is anintegrated-horizontal wells process, which creates its own natural sealingmechanism (in the horizontal producer well), enabling stable combustion frontpropagation along the horizontal producer well to be achieved. CAPRI is anextension to the basic THAI (thermal) process, which involves the emplacement(‘gravel-packing’) of a standard refinery HDS catalyst, around the horizontalproducer well. A series 3-D combustion cell experiments were performed to physicallysimulate the THAI-CAPRI process, using Lloydminster heavy crude oil (11.9°API).In separate THAI and CAPRI experiments, high temperature combustion wassustained (500–550°C), achieving stable combustion front propagation. Very highoil recovery was achieved, exceeding 79% OOIP for THAI and CAPRI. Thefirst-stage of downhole conversion, or in-situ upgrading, is accomplished bythermal cracking (THAI), and thermally/catalytically, in the second stage(CAPRI). Thermal upgrading of the produced oil by THAI averaged 18.3 °API - anincremental conversion gain of 6.4 API points, with a maximum of 22 °API.Higher upgrading was achieved by CAPRI using a regenerated CoMo HDS catalyst.The produced oil averaged 23°API, essentially a light oil product. The oilviscosity produced by THAI or CAPRI was as low as 20 to 30 mPas. Introduction In-situ combustion (ISC) is an enhanced oil recovery method (EOR), in whichair is injected into an oil-bearing formation, so as to sustain stablepropagation of a combustion front and displacement of the oil. The oxidationreactions between hydrocarbons and oxygen generate heat and flue gas in-situ.Hence, if high temperature oxidation (HTO), or combustion, can be maintained, the temperature of the oil-bearing matrix will be greatly increased. Typically, for a heavy oil reservoir, this will be in the range 500–650°C. The largeincrease in temperature generated by ISC reduces the oil viscosity verysignificantly. The fuel availability, i.e. fuel deposited in the reservoir matrix as aresult of thermal cracking of the heavy residue, left behind after vaporisationand displacement of the lighter fractions of the crude oil, lies in the range10 to 100 kg/m3. Depending on the temperature, ISC reactions areusually divided into high temperature oxidation (HTO) and low temperatureoxidation (LTO):HTO: CHx + O 2 —> CO + CO2 + H2 O (1)LTO: CHx + O 2 —> CHx Oy(2) LTO produces more viscous oxidised hydrocarbons, which can cause severe oilblocking, ahead of the combustion front, in the colder, downstream region ofthe reservoir, if ISC process is operated in the conventional mode, using avertical injection-vertical producer (VIVP) pattern. Even if the producer is ahorizontal well for heavy oil reservoir, ISC should be engineered to avoid theLTO mode The necessary condition is to achieve high temperature ignition duringstartup and maintain stable combustion front propagation by means of a high airflux. The chemical mechanisms of fuel laydown and combustion in a heavy oilreservoir are complex, due to the large number of oil component and interactionwith the reservoir matrix. Pyrolysis of the heavy fractions of the residual oilultimately produces a coke-like fuel, when the combustion temperature is above450°C.Pyrolysis: CHx1 —> CH x2 + Coke(x2>x 1) (3)