TRACKING FLUID MOVEMENT DURING CYCLIC STEAM STIMULATION OF CLEARWATER FORMATION OIL SANDS USING STABLE ISOTOPE VARIATIONS OF CLAY MINERALS

摘要

In situ thermal recovery methods such as cyclic steam stimulation (CSS) are required to extract highly viscous bitumen from the Clearwater Formation oil sands of Alberta, Canada. The injection of hot fluids during CSS has altered the mineralogy of the sands, resulting in the loss of some minerals (e.g. disseminated siderite, volcanic glass) and precipitation of others (e.g. zeolites and abundant hydroxy-interlayered smectite). The high temperatures and high water-rock ratios associated with CSS might also alter the oxygen and hydrogen isotopic compositions of pre-existing clay minerals even in the absence of mineralogical changes. The present study exploits this fact to track the movement of injected hot fluids during CSS. Berthierine, a common diagenetic clay mineral in the Clearwater sands, survived CSS but acquired substantially lower δ~(18)O and δ~2H values in cores located ≤10m from the injection well. In contrast, the oxygen and hydrogen isotopic compositions of berthierine in cores located further from the injection well were generally unaffected, except at the depth of steam injection where horizontal fractures facilitate greater lateral penetration of hot fluids. Smectitic clays in near-injector cores also acquired lower δ~(18)O values during CSS, but a systematic shift in δ~2H values was not observed. While hydrogen-isotope exchange undoubtedly occurred, the particular combination of temperature and H isotopic composition of the injected fluid used during CSS appears to have yielded post-steam δ~2H values that are indistinguishable from pre-steam values. Only samples from near-injector core G-0B3 that contain hydroxy-interlayered smectite have lower δ~2H values as a result of CSS.