Abstract
In order to weaken the influence of external groundwater on in situ pyrolysis exploitation, the flow characteristics of groundwater were studied according to the oil shale reservoir characteristics of Qingshankou Formation in Songliao Basin, China. In addition, the parameters of marginal gas flooding for water-stopping were optimized. Taking a one-to-one pattern and a five-spot pattern as examples, the characteristics of groundwater flow under the in situ process were studied. Under the one-to-one pattern, the external groundwater flows into the production well from the low-pressure side, and the water yield was basically stable at 1000 kg/d. In the five-spot pattern, the groundwater can flow into the production wells directly from the windward side, and the water yield of the production well on the leeward side mainly comes from the desaturated zone; the water yield of each production well remains at a high level. By setting water-stopping wells around the production well and keeping the gas flooding pressure slightly higher than the production well, the water yield of the production well can be reduced and stabilized within 100 kg/d under gas flooding pressures of 3 and 5 MPa. However, the gas yield of the production well slightly decreased when the gas flooding pressure reduced from 5 to 3 MPa. Therefore, the gas flooding pressure of water-stopping wells shall be determined in combination with the water yield and gas yield, so as to achieve the best process effect. It is expected that the results will provide technical support for large-scale oil shale in situ pyrolysis exploitation.
Highlights
Oil shale is a kind of solid combustible organic shale with high ash content
This paper focused on the flow characteristics of groundwater in the conventional oil shale in situ exploitation process and evaluated the groundwater infiltration behavior under different patterns by taking the water yield of production wells and groundwater flow trace as indicators
In order to weaken the influence of external groundwater on the in situ pyrolysis exploitation, the flow characteristics of groundwater were studied
Summary
The internal kerogen can be cracked to produce shale oil at a temperature above 350 ◦C [1]. If the global oil shale resources are converted into shale oil, its resources are three times those of the proven crude oil reserves. In situ pyrolysis is the most potential exploitation method of oil shale resources at present; this technology is used to heat the oil shale reservoir in situ to produce oil by kerogen cracking, and extracting the products to the surface [3,4,5]. One of the problems restricting the development of this technology is that it is difficult to cut off the connection between the pyrolysis zone and external groundwater, so that a large amount of injected heat is absorbed by the groundwater [5,6]. Reasonable measures should be taken to form a water-stopping effect in order to provide in situ pyrolysis space for oil shale
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