首页|Water-rock interaction during steaming of Clearwater oil sands.
Water-rock interaction during steaming of Clearwater oil sands.
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In the Cold Lake area of Alberta, cyclic steam stimulation (CSS) is commonly used to recover the highly viscous bitumen from the Clearwater oil sands. However, CSS can decrease permeability of reservoirs through the formation of clay minerals, precipitation of scale and physical migration of clay-size fines. This thesis studied such clay minerals using autoclave experiments, and pre- and post-steam cores from the Cold Lake area. The objective is to understand the behaviour of shaly, clayt-rich Clearwater oil sands during CSS and, in particular, poor hydrocarbon production at site D11.8.; Autoclave experiments (at 250°C) demonstrate that berthierine decomposes under steaming conditions to form mainly Fe-rich smectile (in neutral and alkaline solutions) or Fe-chlorite (in acidic solutions). Solids from these experiments show a marked decrease in δ<super>18</super>O and δD values following the experiments, but neither oxygen nor hydrogen isotopic equilibrium was established between the solids and solutions. More oxygen isotope exchange (44 to 58%) was obtained between the solids and solutions than was the case for hydrogen isotopes (23 to 50%). This behaviour likely indicates inheritance of part of the oxygen and hydrogen in post-experiment clays from precursor berthierine.; Pre- and post-steam cores obtained at site D11.8 from production Pad D11 (Imperial Oil Limited Cold Lake lease) were examined for possible causes of its poor hydrocarbon production. The post-steam core is located about 10 m from both its injection well and the available pre-steam core. The changes in the abundance of volcanic rock fragments and clay minerals in the injection zone following steaming strongly suggest that mineral reactions occurred to form smectitic clays at the expense of berthierine and kaolinite. These smectitic clays have higher Si and Fe, and lower Al contents than pre-steam smectitic clays, and may have inherited part of the compositions from precursor berthierine. The δ-values of post-steam clay minerals also suggest that steam temperatures were ≥200°C at site D11.8. Calcite cement with a curious “meniscus” texture and lower δ<super>18</super>O and δ<super>13</super>C values than pre-steam calcite were also deposited in post-steam sands within the injection zone, and calcite scale occurs in the near well-bore region at Pad D11 as well. Neoformation of smectite, calcite cementation and precipitation of carbonate scale in the near well-bore region are largely responsible for the permeability loss and hence poor hydrocarbon production obtained for Pad D11 at site D11.8. The decrease in δ-values of clay minerals in the injection zone following steaming suggested that physical migration of fines into the injection zone was not a major cause of the changes in clay mineralogy.; One pre-steam core (B5.08) and two post-steam cores (B5.28 and B5.33) were also examined from another pad (B05) within the Imperial Oil Limited Cold Lake lease. Clay minerals and calcite from these cores provided an opportunity to study the extent of interaction with steam at distances greater than 70m from the injection well. Post-steam smectitic clays have similar or slightly higher δ<super>18</super>O values than pre-steam clays, indicating that neoformation of smectitic clays was minimal. Disseminated calcite also retained its original isotopic compositions following CSS. Collectively, this behaviour suggests that temperatures in excess of 100°C were not achieved at these locations for a sufficient period of time to permit isotopic exchange between these minerals and steam.
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