Rate-Transient Analysis in Multifractured Horizontal Wells of Tight Oil Reservoir

Abstract

Summary Multifractured horizontal wells (MFHWs) have become the most commonly used technology for developing unconventional oil and gas reservoirs. Because unconventional reservoirs are currently the focus of exploration and exploitation around the world, a growing number of researchers and scholars are concentrating on production-performance evaluation of unconventional MFHWs to obtain the stimulated reservoir volume (SRV) or hydraulic-fracture properties, which are usually obtained from expensive reservoir tests or production logs. Rate-transient-analysis (RTA) techniques that use continuous-production and flowing-pressure data have proved to be convenient and applicable approaches to estimate the reservoir parameters and hydraulic-fracture properties. Although many cases or work flows of RTA have been previously studied, most of those works were performed for shale-gas or conventional reservoirs. Few studies on RTA have been conducted for MFHWs completed in tight oil reservoirs, particularly for actual field cases in which the usually scattered production data significantly increase the difficulty in analyzing the production performance. In this research, the authors focus on using convenient and economical methods (RTA techniques) to obtain the SRV parameters and hydraulic-fracture properties that characterize the fracturing-treatment effectiveness of an actual MFHW in a tight oil reservoir, which many engineers and technical personnel expect to achieve. A comprehensive work flow [including production-data filtering, flow-regime diagnosis, straight-line analysis, type-curve matching (TCM), analytical-model analysis (AMA), numerical-model analysis (NMA), and uncertainty and nonuniqueness analysis] has been developed to perform a production-performance analysis of an MFHW completed in a tight oil reservoir. In particular, two approaches for calculating the permeability of SRV (kSRV) and effective half-length of hydraulic fracture (Xf) have been introduced. Moreover, the dual permeability parameters, the storativity ratio, and the interporosity coefficient (ω and λ, respectively), have been derived to enter into the AMA model to improve the accuracy of history matching. With the combination of AMA and NMA, the estimated ultimate recovery (EUR) of an actual MFHW completed in a tight oil reservoir can be predicted. Considering the uncertainty and nonuniqueness of the original reservoir parameters or nature of the adopted methods, a probabilistic analysis using Monte Carlo simulation has been performed to address the uncertainty of the analysis results. In addition, a simplified application of the developed method has been introduced. To demonstrate the feasibility and practicability of the developed work flow, two field cases from an actual tight oil reservoir have been analyzed. The consistent analysis results for field cases validate the developed work flow and proposed methods.