Pressure-Transient Analysis for a Well With Multiple Horizontal Sections

Abstract

ABSTRACT Available pressure transient solutions assume that the entire horizontal well section is contributing to flow. Analysis of transient tests using these models result in unrealistic values for permeabilities and skin. Production logging of such wells also indicates that only certain intervals are productive. This is probably the result of heterogeneity (e.g. the presence of fracture swarms) or damage. To solve this problem, engineers use an effective horizontal well length which is shorter than the actual horizontal well section. This however, does not reflect the actual flow configuration, since it assumes that the effective length is a contiguous section. In this paper we show the effects of using too long a production interval on the interpretation of test data by analyzing numerically simulated tests from wells that are only partially open to flow in the horizontal section. We show how the values of horizontal permeabilities, vertical permeability, and skin are affected. We then present an analytical solution that allows for a well to consist of a number of segments of arbitrary length, strength, and skin. We use this model to document the effect of neglecting the actual flux distribution and well length on the results of the well test interpretation. A new radial flow regime is identified from the results of the segmented horizontal well model. It results in a flat pressure derivative at a value of 0.5 divided by the number of producing segments. We also use this model to analyze actual cases where pressure transient and production logging are available. This analytical model is also useful in handling dual lateral completions. We show that the use of incorrect horizontal well length or flux distribution can lead to estimating erroneous well and reservoir parameters from pressure transient tests. We show actual production logging data that demonstrate the variation of the contribution from different sections of the horizontal well. The model presented in this paper enables the engineer to combine production logging data, or any other information that indicate the possible distribution of flow in a horizontal well, and pressure transient data to obtain more realistic well and reservoir parameters.