Integration of Production Analysis and Rate/Time Analysis by Use of Parametric Correlations - Theoretical Considerations and Practical Applications
Authors: Denney Dennis 
Published: February 2015

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 140556, ’Integration of Production Analysis and Rate/ Time Analysis by Use of Parametric Correlations - Theoretical Considerations and Practical Applications,’ by D. Ilk, SPE, Texas A&M University/DeGolyer and MacNaughton; J.A. Rushing, SPE, Apache Corporation; and T.A. Blasingame, SPE, Texas A&M University, prepared for the 2011 SPE Hydraulic Fracturing Technology Conference and Exhibition, The Woodlands, Texas, 24-26 January. The paper has not been peer reviewed.

Well-performance analysis in unconventional reservoirs is a challenging task because of the nonuniqueness associated with estimating well and formation properties. Also, estimating of reserves can be uncertain because of the very long transient-flow periods. Recent semiempirical rate/time relations have been shown to model the rate/time behavior properly for wells in unconventional reservoirs. This study focused on finding theoretical and empirical relationships of rate/time-model parameters with well and formation properties.   

Introduction

Unconventional-reservoir systems (e.g., tight-gas-sand, shale-gas, tight/shale-oil, and coalbed-methane reservoirs) have become a significant source of hydrocarbon production, and they offer high potential for reserves growth and future production. Complex geological and petrophysical systems describe unconventional reservoirs in addition to heterogeneities at all scales similar to conventional-reservoir systems. Because of the low-to-ultralow permeability, well-stimulation operations (e.g., single or multistage hydraulic fracturing) are required to establish production at commercial rates.

Analytical and semianalytical modeling of horizontal wells connected to multiple transverse fractures is important in terms of diagnosing well-performance behavior. At early time, the dominant flow is linear (perpendicular to the fracture face) until pressure transients of the individual fractures begin to interfere, leading to a compound-linear-flow regime. A semianalytical solution can model the entire range of flow regimes surrounding a horizontal well with multiple fractures. The solution includes a dual-permeability region near fracture faces to represent the complex fractured region surrounding the primary planar hydraulic fractures.

Reserves estimation for unconventional-reservoir systems has been performed primarily by use of conventional Arps’ decline-curve relations. Application of Arps’ relations (specifically the hyperbolic relation) for reserves estimates yields significant overestimates of reserves because Arps’ relations are applicable only during a boundary-dominated-flow regime, whereas unconventional-reservoir systems exhibit extremely long transient-flow periods. Recently, two rate/time relations were introduced to estimate reserves in unconventional reservoirs in the form of the “stretched exponential function.” These relations have proved to be successful in modeling the rate/time behavior properly, and these relations provide consistent and more-realistic reserves estimates compared with Arps’ decline relations.