Abstract
With complex fractured-vuggy heterogeneous structures, water has to be injected to facilitate oil production. However, the effect of different water injection modes on oil recovery varies. The limitation of existing numerical simulation methods in representing fractured-vuggy carbonate reservoirs makes numerical simulation difficult to characterize the fluid flow in these reservoirs. In this paper, based on a geological example unit in the Tahe Oilfield, a three-dimensional physical model was designed and constructed to simulate fluid flow in a fractured-vuggy reservoir according to similarity criteria. The model was validated by simulating a bottom water drive reservoir, and then subsequent water injection modes were optimized. These were continuous (constant rate), intermittent, and pulsed injection of water. Experimental results reveal that due to the unbalanced formation pressure caused by pulsed water injection, the swept volume was expanded and consequently the highest oil recovery increment was achieved. Similar to continuous water injection, intermittent injection was influenced by factors including the connectivity of the fractured-vuggy reservoir, well depth, and the injection–production relationship, which led to a relative low oil recovery. This study may provide a constructive guide to field production and for the development of the commercial numerical models specialized for fractured-vuggy carbonate reservoirs.
Highlights
Carbonate reservoirs are the important sources of hydrocarbons, accounting for half of world’s oil and gas reserves (Li and Chen 2013; Yousef et al 2014)
In this paper, based on a geological example unit in the Tahe Oilfield, a three-dimensional physical model was designed and constructed to simulate fluid flow in a fractured-vuggy reservoir according to similarity criteria
Similar to continuous water injection, intermittent injection was influenced by factors including the connectivity of the fractured-vuggy reservoir, well depth, and the injection–production relationship, which led to a relative low oil recovery
Summary
Carbonate reservoirs are the important sources of hydrocarbons, accounting for half of world’s oil and gas reserves (Li and Chen 2013; Yousef et al 2014). A fractured-vuggy unit is considered as the basic production unit during the exploitation of these carbonate reservoirs (Yi et al 2011; Rong et al 2013). This type of reservoir is characterized by serious heterogeneity, random distribution, and complex co-location of fractures and vugs, and various filling types. Cruz et al (2001) performed water-displacing oil experiments using a two-dimensional vuggy fractured porous cell, took photographs of the water front, measured the flow area corresponding to oil and water, and developed a theoretical model based on the experimental results. The experimental results may provide an insight into the later production with water injection and numerical simulations of fractured-vuggy carbonate reservoirs
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