An Analysis of Horizontal Wells Intercepted by Multiple Fractures
- Rajagopal S. Raghavan | Chih-Cheng Chen | Bijan Agarwal
- Document ID
- Society of Petroleum Engineers
- SPE Journal
- Publication Date
- September 1997
- Document Type
- Journal Paper
- 235 - 245
- 1997. Society of Petroleum Engineers
- 2 Well Completion, 3.3.1 Production Logging, 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 5.5 Reservoir Simulation, 5.8.7 Carbonate Reservoir, 2.2.2 Perforating, 5.6.4 Drillstem/Well Testing
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A mathematical model is developed and used to discern the characteristic responses of a multiply-fractured horizontal-well. A systematic discussion of pressure behaviors is given. New interpretations and conclusions are provided. A simple, screening guide to evaluate the efficacy of this completion scheme is presented. The consequences of perforating selective sections after fracturing are examined. The pressure behaviors that are discussed in this work are used to analyze responses of a field test. This test was conducted on a medium-radius horizontal-well completed in a dolomite/anhydrite formation with a 1900' horizontal section. Four distinct intervals were perforated and individually stimulated. Results from the analysis of the commingled test are presented in this work. The methodology outlined here should be useful to others. Practical guidelines are provided.
This paper presents results based on the following premise: The purpose of fracturing horizontal wells is to create a system such that the long-time performance of the horizontal well will be equivalent to that of a fractured well with a specific conductivity (preferably infinite-conductivity) and fracture length equal to distance between the two outermost fractures. This perspective is an important departure from studies presented in the literature. We begin by presenting new correlations to determine the long-time performance of a multiply-fractured, horizontal-well system. This phase of our work should be suitable for screening and designing purposes and for predicting long-time performance either by analytical models or by numerical simulation. As a consequence of the availability of this correlation, exercises similar to those given in Refs. 1 and 2 may be performed more conveniently and comprehensively. The second part of this study presents analytical procedures to evaluate pressure measurements in a multiply-fractured horizontal-well. A comprehensive and complete evaluation is provided. The third part of this work examines a field example that permits the use of the theoretical developments noted in this work, highlights the measurements that can be helpful and the improvements that need to be made in our abilities to analyze pressure responses.
The mathematical model assumes that distinct fractures are created in a horizontal well. Each fracture is assumed to have distinct properties (conductivity, kfw, fracture half-length, L f, skins, s, etc.). Issues such as flow convergence towards the horizontal well (linear-radial flow1,3), imperfect contact between the fracture and the formation2 are quantified by appropriate skin factors. The fractures are assumed to be produced at a common wellbore pressure. Most results given here assume that the fractures are normal to the horizontal well, and that the sections between the fractures are impervious; however, we do examine the influences of perforated intervals between fractures and of longitudinal fractures. In this model, the production rate from each fracture is determined by computations and is not specified a priori. In general, the flow rates from each fracture are a function of time. Specific details regarding the model are discussed in Appendix A. The development given there is much more general than the solutions considered here.
We shall not examine well performance during the linear-radial flow-regime because this flow period has been examind, thoroughly, by Larsen.3 The analytical procedures discussed here are generic, in the sense that they apply if the linear-radial flow-regime is evident. For convenience, we also assume that wellbore-storage effects are nonexistent.
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