Abstract
As unconventional reserves, oil shale deposits require additional oil recovery techniques to achieve favorable production levels. The efficiency of a shale reservoir development project is highly dependent on the application of enhanced oil recovery (EOR) techniques. There are many studies devoted to discrete investigations of each EOR method. Most of them claim that one particular method is particularly effective in increasing oil recovery. Despite the wealth of such research, it remains hard to say with certainty which technique would be the most effective when applied in the extraction of unconventional reserves. In this work, we aim to answer this question by means of a comparative study. Three EOR methods were applied and analyzed in the same environment, a single target object—an oil field in Western Siberia characterized by ultra-low permeability (0.03 mD on average) and high organic content. Methods involving huff-and-puff injection of a surfactant solution, hydrocarbon gas, and hot water were studied using numerical reservoir simulations based on preceding laboratory experiments. A single horizontal well having undergone nine-stage hydraulic fracturing was used as the field site model. The comparative calculations of cumulative oil production over an 8-year period revealed that the injection of hot (supercritical) water led to the highest oil recovery in the target shale reservoir. Each EOR method was implemented using the best operation scenario. All three cases resulted in an increase in cumulative oil production compared to the depletion mode, though the efficiency was distinctly different. Twenty-six percent more oil was obtained after hot water injection, 16% after hydrocarbon gas, and 12% after a surfactant solution. Simulation of a hot water huff-and-puff operation over a longer period (43 years) led to a level of oil production 3 times higher than depletion. The drawbacks of each EOR method on the shale site are discussed in the results. A possible solution was proposed for preventing the negative effects of heat loss and water blockage incurred from hot water injection. The comparative study concludes that hot water injection should lead to the highest volume of oil recovery. The conclusions drawn are suggested to be relevant for similar shale fields.
Highlights
At present, the development of prospective unconventional oil reserves is one of the highest-profile topics in the oil industry.According to various sources, the Bazhenov formation in Western Siberia holds between 65 and 500 × 109 tons of oil in place.[1−3] The shale reserves within the Bazhenov formation contain light low-sulfur tight oil and a significant amount of solid organic matter kerogen,[4] which can adsorb oil, making it more difficult to recover
Various enhanced oil recovery (EOR) techniques can be applied for the efficient extraction of shale oil
This study aims to investigate the efficiency of EOR methods for developing a single shale field in Western Siberia
Summary
The development of prospective unconventional oil reserves is one of the highest-profile topics in the oil industry. Waterflooding could potentially be effective in lowand ultra-low-permeability reservoirs,[9,10] other oil recovery agents should lead to a better result, especially for tight reservoirs with mosaic hydrophobization.[11] Various enhanced oil recovery (EOR) techniques can be applied for the efficient extraction of shale oil. The main constraints on the efficiency of surfactant injection in shale deposits are the ultra-low matrix permeability of the surfactant blend, the adsorption of the surfactant on the surface of the rock, clay swelling, and the surfactant’s instability under reservoir conditions (i.e., the temperature and composition of reservoir water).[37,38] the success of surfactant EOR is dependent upon developing a surfactant composition and concentration suited to the specificities of the particular target shale reservoir. Most of the data used in the numerical experiments were obtained from laboratory tests
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