Analysis of Production Data From Hydraulically Fractured Horizontal Wells

Abstract

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 110848, "Analysis of Production Data From Hydraulically Fractured Horizontal Wells in Tight, Heterogeneous Formations," by F. Medeiros, SPE, Petrobras, and B. Kurtoglu, SPE, E. Ozkan, SPE, and H. Kazemi, SPE, Colorado School of Mines, prepared for the 2007 SPE Annual Technical Conference and Exhibition, Anaheim, California, 11–14 November. The paper has not been peer reviewed. The full-length paper discusses the analysis of production data from hydraulically fractured horizontal wells in tight, heterogeneous formations. Horizontal wells with longitudinal and transverse hydraulic fractures that might be surrounded by a region with natural fractures are considered. These well/reservoir configurations are of interest in many unconventional reservoirs, including tight gas sands and shale-oil or -gas formations. A semi-analytical model that incorporates the key features of reservoir heterogeneity and the details of hydraulic-fracture and wellbore flow was used to compute production decline. Introduction In the last decade, interest in developing unconventional oil and gas reservoirs has grown. Most of these unconventional reservoirs have very low permeability, as in the case of tight gas sands and fractured shale formations. Production economics for these reservoirs normally requires large reservoir contact per well. An efficient means of increasing reservoir contact to achieve higher well productivity is to drill horizontal wells and stimulate with hydraulic fractures. Productivity might be improved further if the horizontal well and hydraulic fractures are connected to an active natural-fracture network. This fracture network may be pre-existing in a naturally fractured reservoir (dual-porosity system) or may be generated or reactivated locally by hydraulic fracturing around the well. Production characteristics of wells in globally and locally fractured reservoirs may differ significantly, depending on the contrast between the matrix and natural-fracture properties. The full-length paper discusses the analysis of production data from hydraulically fractured horizontal wells in reservoirs with a global- or localized-natural-fracture network. It explains the characteristics of production decline associated with various transient-flow regimes, describes the procedure to generate production-decline curves, and demonstrates matching field data with the model. The general idea of this work follows from a production-decline-analysis concept. A transient productivity index (PI), J, is used in the analysis of production data for horizontal wells. Material-balance time is incorporated into the analysis to generalize the analysis procedure for all phases and modes of production. There are two important aspects of the approach presented in the full-length paper. The first aspect is the use of a semianalytical model that incorporates the important features of reservoir heterogeneity and hydraulic fractures without elaborate numerical computations. The model was built on the basis of a semianalytical simulation approach. Having a computationally efficient model is important in that the production-decline model needs to be used in an iterative manner in the analysis of the field production data. Moreover, especially in the early development stage, there are not enough data to sufficiently characterize heterogeneous, unconventional reservoirs. Therefore, more-detailed numerical modeling may not be a viable option until more data become available later in the development of the field.