Use of Type Curve Analysis In Predicting the Behaviour of a Water-drive Reservoir

Abstract

Results of a coning simulation study on five wells in the Fenn-Big Valley D-2A pool were extended to predict the performance of other wells in the field by the use of type curves. Reservoir characterization was based on permeability anisotropy in this strong bottom-water-drive carbonate reef system. The study shows that the ultimate oil recovery is insensitive to rate variations. An evaluation of plugbacks in open hole completions and cement squeezes in cased holes, based on performance, is also presented. Introduction The performance of bottom-water-drive reservoirs can be simulated by cross-sectional or three-dimensional models. However, this can be expensive in a reservoir with a large number of wells. Quite often, single well performance is simulated and extrapolated to other wells in the reservoir by correlating a characteristic parameter. A method is outlined in this paper whereby five wells have been simulated in a large reservoir and type curves have been generated with anisotropy as the parameter of characterization. These type curves are then used to match the performance of over a hundred wells and to predict their future behaviour. Water coning behaviour has been studied extensively in the last five years(1–7), with rate sensitivity to oil recovery being the main subject of study. Approaches to solving coning behaviour range from correlations such as those of Bournazel and Jeanson(l) to the sophisticated numerical models of Aziz et al (2). Correlations are usually based on several assumptions, includinghomogeneity with respect to permeability, and incompressible and steady-state flow. Numerical models eliminate these assumptions in that compressible fluid flow and variations in permeability in all three directions can be handled. One correlation that should be mentioned here is that of Chappelear and Hirasaki(4), in which a coning-model equation has been developed and inserted in a two-dimensional areal simulator. This procedure treats the horizontal movement of fluids and also accounts for vertical coning behaviour by using the developed equation near a well. However for a reservoir with a large number of wells areal simulation with the additional calculations of coning equations can be expensive. Type curves have been used in predicting the performance of wells by matching rate decline curves. However the most extensive use of type curves is made in well test analyses, where they can be used for drawdown, build-up interference and constant pressure testing. The curves themselves are generated by the solution of equations describing a specific situation, such as pressure in a closed square system without wellbore storage and skin, and should always be dimensionless. A type curve that approximates the actual problem to be solved in chosen and a match is obtained graphically. By their very nature, the actual data will be incomplete with respect to time, and extrapolation to desired time is obtained by the type curve match. Alternatively if the data are reasonably complete and match a particular type curve, inference can be made on a certain characteristic; for example, shape of the reservoir.

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