An Account of Decline-Type-Curve Analysis of Vertical, Fractured, and Horizontal Well Production Data

Abstract

Abstract This paper presents an account of decline-type-curve analysis of production data from vertical, fractured, and horizontal wells. It is discussed that the decline-type-curve analysis techniques presented in the literature are based on an approximate deconvolution of the production data and therefore have some limitations. In addition, decline-type-curve analysis inherits the limitations of both conventional pressure-transient and decline-curve analysis techniques. Because of the theoretical and practical limitations, decline-type-curve analysis may need to be supported by pressure transient analysis to yield meaningful and reliable results. In this paper, we also present an alternate approach to construct and analyze the decline type curves and present new decline type curves for horizontal wells. The application of the new horizontal-well decline type curves is demonstrated by examples. Introduction During the last 5 decades, the petroleum engineering literature has been flooded with methods to estimate reserves and reservoir properties based on the production history of wells. Some popular examples of these methods are the liquid production decline equations by Arps,1 liquid decline curves by Fetkovich,2,3 gas type curves by Carter,4 Reciprocal Productivity Index of Crafton,5 liquid equivalent gas curves by Palacio and Blasingame,6 and decline-type-curves of Agarwal et al.7 One of the oldest and most utilized tools of petroleum engineering is the rate-time decline curves. Empirical rate-time equations given by Arps1 are the bases of nearly all conventional decline-curve analysis techniques. Fetkovich2 presented decline curves for oil wells under the influence of water influx in a finite system at a constant pressure. He also presented a composite of transient rate and decline curves, which combined the analytical solutions for constant pressure production and empirical results for exponential, hyperbolic, and harmonic decline.3 Crafton5 presented a composite of the transient production and decline curves by using the reciprocal productivity index; that is, in terms of pressure normalized by rate. The fundamental claim of this method is the generalization of the results for any time dependent or constant mode of production. By constructing the reciprocal productivity index in terms of pseudopotential, this method is applicable to both liquid and gas flow. Later, Huffman8 extended Crafton's ideas to multiphase flow. Palacio and Blasingame6 followed the idea of rate normalization of pressure to develop a decline-curve analysis technique with type-curve matching. Their significant contribution was the definition of new modified time functions. Specifically, they showed that for all production conditions and liquid types, only one decline curve is required provided that the correct time transformations are utilized. This decline curve corresponds to the harmonic decline curve of Fetkovich3 and Carter.4 In this study, we build upon this idea to present decline type curves for horizontal wells. An extension of the ideas presented by Palacio and Blasingame6 was presented in 1999 by Agarwal et al.7 They showed that the combined decline-curve and type-curve matching analysis concept may be extended to vertically fractured gas wells. They presented type curves in terms of cumulative production and derivative functions to aid the matching process and claimed that these curves present a more direct and less ambiguous means of determining gas reserves. They also provided a clear distinction between transient- and boundary-dominated flow periods. Recently, Marhaendrajana and Blasingame9 presented an extension of the combined type-curve matching and decline-curve analysis approach to evaluate well performance in multiwell reservoir systems.