Abstract
Fractured vuggy carbonate reservoirs play an important role in the world crude oil resources. The significant reservoir heterogeneity represented by complex distribution of multi-scale fractures and vugs brings challenges to reservoir oil in place (OIP) estimation, which is a fundamental parameter in oil field development. OIP estimation based on production dynamic analysis is regularly carried out in oilfield practice, the result of which is normally adopted as a comparison to volumetric calculation from geological study for mutual verification. This paper introduces a widely used water injection index curve method on OIP estimation of fractured vuggy carbonate reservoir in Tarim oilfield, which is a straight forward plot of bottom-hole pressure versus cumulative water injection. An improved model taking into consideration the compressibility of second gas gap is presented and applied on real well from Tahe carbonate reservoir. The application of the new model demonstrated that conventional method tends to over-estimate the OIP, while the improved model gives a relatively reliable estimation. The improved water injection index curve in this paper is easy to be conducted based on well production and injection dynamic and shows advantages on convenient pressure conversion from well-head to well-bottom and avoiding dealing with the high uncertainty of aquifers in carbonate reservoir.
Highlights
Fractured vuggy carbonate reservoirs contribute a large proportion of world oil resources, characterized by high heterogeneity and complex fracture-vug/cave system
This paper introduces the commonly adopted water injection index curve method in reservoir dynamic analysis and provides an improved model considering the impact of secondary gas cap
From equation (3) it is clear that a plot of injection pressure vs cumulative water injection shows a straight line and the oil in place can be determined from the slope if oil compressibility is given
Summary
Fractured vuggy carbonate reservoirs contribute a large proportion of world oil resources, characterized by high heterogeneity and complex fracture-vug/cave system. Due to the high formation discontinuity and strong stochastic distribution of reservoir parameters, OIP estimation for fractured-vuggy carbonate reservoirs requires exclusive techniques considering the available dynamic performance data. This paper introduces the commonly adopted water injection index curve method in reservoir dynamic analysis and provides an improved model considering the impact of secondary gas cap. From equation (3) it is clear that a plot of injection pressure vs cumulative water injection shows a straight line and the oil in place can be determined from the slope if oil compressibility is given. This is the foundation of conventional water injection index curve. For the curves with same slope in (d) of Figure 2, different intercept refers to the different initial injection pressure
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More From: International Journal of Oil, Gas and Coal Engineering
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