Study On Gas Injection Mechanism Of Fractured Metamorphic Rock Reservoir In Xinghe 7 Of Liaohe River

Gas injection technology has been widely used at home and abroad to enhance oil recovery, which is beneficial for low-viscosity crude oil to reach nearly miscible even miscible displacement, thus representing a substantial increased oil recovery. The main ways of immiscible flooding are:limited evaporation and extraction; reducing oil viscosity; crude expansion; dissolved gas driving caused by pressure drop; reducing the interfacial tension. It is also a viable EOR development way for those oilfields unfit for water injection (low permeability, high water sensitivity reservoir, etc.).This paper is supported by a research program from Xinggu oil reservoir in Liaohe Oilfield. The gas injection technology is important to make Liaohe Oilfield as ten million tons oilfield, because of a natural gas pipeline near the reservoir, which provides a rich source of natural gas. Research shows that top vertical gravity gas flooding technology can improve oil recovery for thick block reservoir,compared with water flooding. The OOIP of thick block reservoir in Liaohe Oilfield is more than400million tons,accounting for34.3%of light oil and high freezing point oil,which was developed by water flooding. Gas injection dimensional development is an important technology to enhance oil recovery.The conclusions obtained are as follows:1)Caprock test results showed that caprock is suitable for the top gas injection, as it is sealed good and a high breakthrough pressure.2)The phase behavior and gas injection expansion experiments imply that Xinggu oil is characterized by black oil, with original formation pressure of38.6MPa, current formation pressure of31.8MPa, and bubble point pressure of20.663MPa.3)The gas injection slimtube experiment indicate that the miscible pressure is45.27MPa. And non-miscible flooding can be conducted under current formation pressure. Moreover, the slimtube displacement process simulation shows that the miscible zone is developed in the flooding edge, namely first contact evaporative miscible flooding.4)The long-core flooding experiments indicate that the top gas injection and short soaking time flooding is preferred. The recovery is88.45%, including exhaustion accounted for5.41%, matrix32.12%, and cracks50.92%.5)Xinggu reservoir should be researched matrix inspiratory conditions, seepage relationship between matrix and fracture,microfracture and main fracture, the relative permeability, displacement efficiency and recovery contribution of matrix and fracture in vertical gas displacement, by long core physical simulation and numerical simulation.