Flow-Regime-Based Inflow-Performance Relationships of Unconventional Fractured Reservoirs
Authors: Al-Rbeawi Salam 
Published: October 2019

The main objective of this paper is to develop a new approach for constructing the inflow-performance relationships (IPRs) of unconventional reservoirs. The proposed approach focuses on using transient- and pseudosteady-state-flow regimes in developing integrated analytical models for wellhead deliverability and wellbore-pressure decline considering the two wellbore conditions, constant-sandface-flow rate and constant wellbore pressure. The motivation is to reduce the uncertainties in predicting current and future performance of unconventional reservoirs.

Three tasks are conducted in this study for achieving the objective of this paper. The first task includes generating the pressure behavior of the reservoirs of interest using a trilinear-flow model. The pressure behavior helps in characterizing the flow regimes that could be developed during the entire life of production and estimating the time interval elapsed by each flow regime. The second task concentrates on developing integrated analytical models for these flow regimes and using these models for predicting the IPR at the end of the time interval of each flow regime. The third task deals with constructing the IPRs at any time and any flow regime, considering different reservoir conditions. For constructing the IPR during bilinear- and linear-flow regimes wherein most of the production is dominated by these two flow regimes, two new functions are developed. The first is the pressure function (P), which represents the change in pressure with time for constant production rate, whereas the second represents the change in flow rate with time for constant wellbore pressure, and is called the flow-rate function (q). The effects of hydraulic-fracture characteristics, reservoir configurations, and the dominant flow pattern—whether it is Darcy or non-Darcy flow—are considered in constructing these IPRs.

The observations of this study can be summarized as the following:

The IPRs for all transient-flow regimes exhibit linear behavior at a specific production time, even in the cases where non-Darcy flow is the dominant flow pattern and the reservoirs are characterized by high skin factor. However, considering the change in the reservoir and reservoir-fluid properties with time and pressure might cause some deviation from this linear behavior. The IPRs obtained by applying a constant-sandface-flow rate are slightly better than the IPRs obtained by applying constant wellbore pressure. The IPRs of bilinear- and linear-flow regimes are more applicable for unconventional reservoirs than the IPRs of the hydraulic-fracture linear-flow regime and pseudosteady-state-flow regime because the former might not be developed for a long production time and the latter might not be reached.

The novel points presented by this study are the following:

Introducing an approach for constructing the IPRs during transient-state flow when the wellbore conditions deteriorate continuously Introducing two new functions for constructing the IPRs during bilinear-flow and linear-flow regimes: pressure function for constant-sandface-flow rate and flow-rate function for constant wellbore pressure.