Although production analysis (PA) for reservoir characterization is approaching the popularity of pressure transient analysis (PTA), there are few consistent diagnostic methods in practice for the analysis of production data. Many of the "diagnostic" methods for production data analysis are little more than observation-based approaches --- and some are essentially "rules of thumb."
In this work we provide guidelines for the analysis of production data, as well as identify common pitfalls and challenges. Although pressure transient and production data analyses have the same governing theory (and solutions), we must recognize that pressure transient data are acquired as part of a controlled "experiment," performed as a specific event [e.g., a pressure buildup (or PBU) test]. In contrast, production data are generally considered to be surveillance/monitoring data --- with little control and considerable variance occurring during the acquisition of the production data. This paper attempts to provide a "state-of-the-technology" review of current production data analysis techniques/tools --- particularly tools to diagnose the reservoir model and assess the reservoir condition. This work also identifies the challenges and pitfalls of production analysis --- and we try to provide guidance towards best practices and best tools. To compliment this mission, we use relevant field examples to address specific issues, and we illustrate the value and function of production data analysis for a wide range of reservoir types and properties.
Prologue
A rudimentary assessment might conclude that pressure transient data are "high frequency/high resolution" data --- and production data are "low frequency/low resolution" data. This would be an oversimplified view, but in practice, the fact is that production data rarely approach the quality, quantity, or accuracy of data acquired during a pressure transient test. Another "generalization" that holds considerable truth is that during a pressure transient test, the pressure data are typically measured at extraordinary frequencies (points/second) and accuracies (pressure to 1 part in 100,000 per pressure range of the gauge) --- while the production history is either ignored, or is derived from "back of the envelope" estimates or cursory reviews of the recent production history.
An inverted generalization often occurs for production data --- the rate history is carefully obtained from daily records (or sales sheets), and the pressure history is infrequent, inaccurate, and/or often non-existent. The challenge of creating a coherent analysis from production data remains that of understanding what information the data may or may not be able to convey. For example, as transient flow data are required to estimate reservoir properties, one should not expect to be able to estimate permeability and skin factor with confidence using monthly production rates and pressures from a well in a moderate to high permeability reservoir. These data simply lack the detail (i.e., the transient history) to provide a competent analysis. In contrast, monthly production data may be sufficient for wells in low permeability reservoirs where the transient state may be maintained for months or even years (although we would certainly prefer to have at least a daily record of production rates and pressures). Due Diligence —- Literature
The literature for production analysis (PA) can be distilled into the following categories and elemental references:
???Basic Analysis of Production Data: The Arps work (ref. 1) was the systematic first attempt to correlate production data in the petroleum literature and is considered to be an essential starting point for analysis. Mattar and McNeil2 provide a coupling of material balance and pseudosteady-state flow theory which provides an analysis/interpretation methodology for production data on a per-well basis. Li and Horne3 provide a recent attempt to "legitimize" production analysis by providing a theoretical basis (where possible) for several of the more common production analysis relations.
Blasingame and Rushing4 provide a synopsis of the historical methods used for simplified production analysis and lend some theoretical support for common applications (e.g., the exponential and hyperbolic decline relations, as well as semi-analytical solutions for gas flow). Ref. 5 by Camacho and Raghavan, while not a production data analysis reference by design, provides the theoretical basis for boundary-dominated flow in solution gasdrive reservoirs --- and should be considered to be an essential reference on production analysis.
???Decline Type Curve Analysis: The required reference for production decline curve analysis using type curves is the original work on the subject by Fetkovich.6 The analytical basis and "integral" plotting functions for variable-rate/variable pressure drop production data are provided by Palacio and Blasingame7 (for gas wells) and Doublet and Blasingame8 (for oil wells).
