Production Data Analysis in Unconventional Reservoirs with Rate-Normalized Pressure (RNP): Theory, Methodology, and Applications

Abstract

Unconventional reservoirs, shale gas and oil for instance, have proven to be an important contributor to hydrocarbon production in North America. Horizontal wells with multiple transverse fractures unlocked these unconventional resources by attaining profitable production rates and increasing gas reserves for future years. A critical challenge in these types of reservoirs is characterizing the stimulated reservoir volume (SRV), by estimating the effective productive volume created during stimulation and quantifying the permeability of the formation.Recent approaches for rate and pressure data deconvolution have emphasized the benefits of using buildup responses acquired whenever the well is shut-in, often for operational reasons, to assess significant insights about heterogeneity and compartmentalization in conventional reservoirs. However, deconvolution performs poorly when the initial reservoir pressure is unknown and might generate ambiguous results when pressure data accuracy is questionable.Regular measurements of daily production rates and wellhead flowing pressures can provide important information about well completion, stimulation, and formation parameters. With effective data processing, rate-normalized pressure (RNP) converts variable-rate and variable-pressure data to an equivalent of the drawdown pressure response to constant-rate production. This reveals flow regimes that enable direct estimation of the formation permeability and the productive fracture extent in the SRV. Subsequently, observed field rates and pressures can be matched with a global model to refine the estimates from the flow regime analysis. Although numerical models can be used to match the data, in this study we employed an analytical flow regime equations that provides fast and accurate results that can be easily programmed.The proposed methodology was applied to production data from Barnett shale wells providing excellent results and demonstrating an efficient, fast, and cost effective method to estimate critical well and formation parameters in unconventional reservoirs. The same methodology can be used to diagnose wells from other unconventional resources.

Characterization of Multiple Transverse Fracture Wells Using the Asymptotic Approximation of the Diffusivity Equation

“…Classical hydraulic fracture fluid flow theory looks at fractures as single planar entities, mostly as a simplifying assumption to enable derivation of fluid flow principles (Economides et al 2013;Lee et al 2003). Planar models certainly seem too good (or simple) to be true, but many authors have shown that planar models provide a foundation for useful production analysis in unconventional reservoirs (Bello and Wattenbarger 2010;Chen and Rajagopal 1997;Samandarli et al 2012;Wattenbarger et al 1998). That said, it would be naïve to assume that fractures simply follow a planar bi-wing geometry in the presence of variable stress fields, anisotropic and heterogeneous rock properties, and natural fractures.…”

New type curves for analyzing horizontal well with multiple fractures in shale gas reservoirs

“…One method that has proved to be very powerful is rate-normalized pressure (RNP) and RNP 0 (semilog derivative of RNP with respect to material balance time or pseudo-time) analysis which has been used in recent years for analyzing production data from multi-fractured horizontal wells Samandarli et al, 2012). Analogous to classic well-test analysis, RNP, which is the inverse of PNR, and RNP 0 are used to analyze production data.…”

Fracture Characterization Using Flowback Water Transients from Hydraulically Fractured Shale Gas Wells

“…The most common methods for fracture characterization are rate-transient analysis (RTA), pressure-transient analysis (PTA), micro-seismic analysis, and tracer test. Many researchers used RTA and PTA to characterize the fracture network − because production data are available for almost every well. Micro-seismic monitoring is also broadly used in the field to characterize the fracture network during and after the hydraulic fracturing operations. − Tracer test is another method commonly used to characterize the fracture network. − Each of these three methods has its strengths and limitations.…”