Pseudoskin Factor Caused by Partial Penetration
- A.C. Reynolds (U. of Tulsa) | J.C. Chen (U. of Tulsa) | R. Raghavan (U. of Tulsa)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- December 1984
- Document Type
- Journal Paper
- 2,197 - 2,210
- 1984. Society of Petroleum Engineers
- 5.3.2 Multiphase Flow, 5.5 Reservoir Simulation, 4.1.2 Separation and Treating, 5.1.1 Exploration, Development, Structural Geology, 4.1.5 Processing Equipment, 5.6.4 Drillstem/Well Testing, 5.5.2 Core Analysis, 2.2.2 Perforating, 2 Well Completion
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In this study we examine the pseudoskin factor caused by partial penetration in a two-layer reservoir when only partial penetration in a two-layer reservoir when only one layer is open to flow. We show that the pseudoskin factor can be correlated as a unique function of three reservoir parameters and in many cases can be correlated accurately as a function of two reservoir parameters. We present graphs and procedures for estimating the pseudoskin factor. pseudoskin factor. Introduction
Frequently, wells are perforated over only a portion of the productive zone to delay or to prevent water and/or gas coning. This situation is called "partial penetration" or "restricted entry." This type of well completion has received considerable attention in both the petroleum and groundwater hydrology literature. The problem was studied as early as 1949 by Muskat and has subsequently been studied in a plethora of papers including Refs. 2 through 10. Desirable information papers including Refs. 2 through 10. Desirable information on this problem includes procedures for the analysis of well-test data and the evaluation of the productivity loss from partial penetration or restricted entry. This work provides information on the second topic; specifically, it provides information on the second topic; specifically, it provides methods for evaluating the pseudoskin factor caused provides methods for evaluating the pseudoskin factor caused by partial penetration. As shown in Refs. 1 through 6, the pseudoskin factor determines the productivity decrease pseudoskin factor determines the productivity decrease resulting from partial penetration. The results of Refs. 1 through 10 consider only single-phase flow, whereas in reality partial penetration or restricted entry exists to prevent the partial penetration or restricted entry exists to prevent the production of an undesirable fluid under multiphase flow production of an undesirable fluid under multiphase flow conditionsi.e., to prevent or delay water and/or gas coming. Ref. 11, clearly indicates that the single-phase correlations for the pseudoskin factor do not accurately predict the pseudoskin factor caused by partial penetration under multiphase flow conditions. The results of Ref. 11, which are for an oil/ water system, indicate that if horizontal saturation gradients are negligible, then the two-phase flow situation should be analogous to single-phase flow in a layered reservoir with the oil, transition, and water zones each representing a separate layer. If the transition zone is small, the two-phase flow partial penetration situation should resemble single-phase flow partial penetration situation should resemble single-phase flow in a two-layer reservoir. This provides the motivation for the single-phase flow two-layer reservoir problem considered here. Our main objective is to present methods for estimating the pseudoskin factor in a two-layer reservoir with only one layer pseudoskin factor in a two-layer reservoir with only one layer open to flow. If this can be done, the true skin factor can be estimated by subtracting the pseudoskin factor from the total skin factor computed by semilog analysis techniques. The results of Refs. 1 through 6 are restricted to single-layer, single-phase flow problems. It is relevant to point out that a partially penetrating well in a layered reservoir has been studied previously; see Refs. 7 and 9. However, to our knowledge, no one has identified the key parametric groups that uniquely determine the pseudoskin factor caused by partial penetration in a two-layer reservoir or provided methods for computing this pseudoskin factor. The intended contribution of this paper is pseudoskin factor. The intended contribution of this paper is to provide this knowledge.
Pseudoskin Computation Pseudoskin Computation Hereafter we refer to the pseudoskin factor caused by partial penetration as simply the pseudoskin factor. In this major penetration as simply the pseudoskin factor. In this major section, the mathematical model and the procedure used to compute this factor are discussed.
To compute the pseudoskin factor, we consider a single well in the center of a two-layer cylindrical reservoir with impermeable top, bottom, and outer boundaries. The layers are assumed homogeneous and contain a slightly compressible fluid of constant viscosity. The initial pressure is assumed uniform throughout the reservoir. Gravitational and wellbore storage effects are neglected. Each layer can be either isotropic or anisotropic, but the vertical permeabilities of the two layers are nonzero so that crossflow can occur between the two layers. The well is produced at a constant rate. Since the reservoir pressure exhibits radial symmetry, the mathematical model is two-dimensionali.e., an r-z model (Fig. 1). The pseudoskin factor results presented in this work were obtained by generating the pressure response for the model shown in Fig. 1 under the assumption that only Layer 1 is perforated; that is, all production is from Layer 1 and all perforated; that is, all production is from Layer 1 and all of Layer 1 is open to flow.
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